The Advanced Very High Resolution Radiometer (AVHRR) sensor is carried on NOAA's Polar-orbiting Operational Environmental Satellites (POES) starting with TIROS-N in 1978. Onboard the TIROS-N, NOAA-6, 8 and 10 POES Satellites, the AVHRR Sensor measures in four spectral bands, while on the NOAA-7, 9, 11, 12 and 14 POES Satellites, the sensor measures in five bands. The AVHRR/3 sensor on NOAA-15, 16, 17, 18 and 19 measures in six bands though only five are transmitted to the ground at any time.

The visible data values may be converted into albedos and the IR data into radiances or temperatures using the calibration information which is appended but not applied. Latitudes and longitudes of 51 benchmark data points along each scan are included. Other parameters appended are: time codes, quality indicators, solar zenith angles, and telemetry.

The objective of the AVHRR instrument is to provide radiance data for investigation of clouds, land-water boundaries, snow and ice extent, ice or snow melt inception, day and night cloud distribution, temperatures of radiating surfaces, and sea surface temperature, through passively measured visible, near infrared and thermal infrared spectral radiation bands.

The Advanced Very High Resolution Radiometer for TIROS-N and the follow-on satellites is a scanning radiometer with either four or five channels, which is sensitive to visible/near IR and infrared radiation. The instrument channelization has been chosen to permit multispectral analyses which provide improved determination of hydrologic, oceanographic, and meteorological parameters. The visible (0.5 micron) and visible/near IR (0.9 micron) channels are used to discern clouds, land-water boundaries, snow and ice extent, and, when the data from the two channels are compared, an indication of ice/snow melt inception. The IR window channels are used to measure cloud distribution and to determine the temperature of the radiating surface (cloud or surface). Data from the two IR channels is incorporated into the computation of sea surface temperature. By using these two channels, it is possible to remove an ambiguity introduced when clouds fill a portion of the field-of-view.

On later instruments in the series, a third IR channel was added for the capability of removing radiant contributions from water vapor when determining surface temperatures. Prior to inclusion of this third channel, corrections for water vapor contributions were based on statistical means using climatological estimates of water vapor content.

AVHRR data have been used for many diverse applications. In general, AVHRR applications encompass meteorological, climatological and land use. Obvious meteorological and climatological applications include detection and analysis of: cold fronts; plumes; weather systems; cloud movement; squall lines; boundary clouds; jet stream; cloud climatology; floods and hurricanes. In addition, land use applications of the AVHRR include monitoring of: food crops; volcanic activity; forest fires; deforestation; vegetation; snow cover; sea ice location; desert encroachment; icebergs; oil prospecting and geology applications. Other miscellaneous AVHRR applications include the monitoring of: migratory patterns of various animals; animal habitats; environmental effects of the Gulf War; oil spills; locust infestations; and nuclear accidents such as Chernobyl.

NOAA Polar-orbiting Operational Environmental Satellites obtain global imagery daily. These data are transmitted to the Command and Data Acquisition (CDA) stations. The CDA stations relay the data to the National Environmental Satellite, Data and Information Service (NESDIS), located in Suitland, Maryland, for processing and distribution.

As a result of the design of the AVHRR scanning system, the normal operating mode of the satellite calls for direct transmission to Earth (continuously in real-time) of AVHRR data. This direct transmission is called HRPT (High Resolution Picture Transmission). In addition to the HRPT mode, about 11 minutes of data may be selectively recorded on board the satellite for later playback. These recorded data are referred to as LAC (Local Area Coverage) data. LAC data may be recorded over any portion of the world, as selected by NOAA/NESDIS, and played back on the same orbit as recorded or during a subsequent orbit. LAC and HRPT have identical Level 1b formats.

The full resolution data are also processed on board the satellite into GAC (Global Area Coverage) data which are recorded only for readout by NOAA's CDA stations. GAC data contain only one out of three original AVHRR lines. The data volume and resolution are further reduced by averaging every four adjacent samples and skipping the fifth sample along the scan line.

POES satellites operate in relatively low orbits, ranging from 830 to 870 km above the earth. They circle the earth approximately 14 times per day (with orbital periods of about 102 minutes). The orbits are timed to allow complete global coverage twice per day, per satellite (normally a daytime and a nighttime view of the earth) in swaths of about 2,600 km in width. High resolution (1 kilometer) data are transmitted from the satellite continuously, and can be collected when the satellite is within range of a receiving station. Recorders on board the satellite are used to store data at a 4 kilometer resolution (processed by the on-board computers) continuously, and a limited amount of data at a 1 kilometer resolution on demand. The recorders are dumped when the satellite is within range of a NOAA receiving station.

AVHRR Level 1b data are present as a collection of data sets. Each data set contains data of one type for a discrete time period. Thus, for AVHRR, there are separate HRPT, LAC, and GAC data sets. Time periods are arbitrary subsets of orbits, and may cross orbits (i.e., may contain data along a portion of an orbital track that includes the ascending node, the reference point for counting orbits). Generally, GAC data sets are available for corresponding time periods and usually have a three to five minute overlap between consecutive data sets. Level 1b (following FGGE terminology) is raw data in 10 bit precision that have been quality controlled, assembled into discrete data sets, and to which Earth location and calibration information has been appended, but not applied. Other parameters appended are: time codes, quality indicators, solar zenith angles, and telemetry.

The AVHRR provides a global (pole-to-pole) on-board collection of data from all spectral channels. At an 833 km altitude, the 110.8 degree scan equates to a swath 27.2 degrees in width (at the Equator), or 2,600 km, centered on the subsatellite track. This swath width is greater than the 25.3 degree separation between successive orbital tracks, providing overlapping coverage (side-lap).

For LAC and HRPT, the instantaneous field-of-view (IFOV) of each channel is approximately 1.4 milliradians (mr) leading to a resolution at the satellite subpoint of 1.1 km for a nominal altitude of 833 km. Since GAC data contain only one out of three original AVHRR lines and the data volume and resolution are further reduced by averaging every four adjacent samples and skipping the fifth sample along the scan line, the effective resolution is 1.1 x 4 km with a 3 km gap between pixels across the scan line. This is generally referred to as 4 km resolution.

Each scan of the AVHRR views the Earth for a period of 51.282 milliseconds (msec). The analog data output from the sensors is digitized on-board the satellite at a rate of 39,936 samples per second per channel. Each sample step corresponds to an angle of scanner rotation of 0.95 milliradian (mr). At this sampling rate, there are 1.362 samples per IFOV. A total of 2,048 samples for the LAC/HRPT data are obtained per channel per Earth scan, which spans an angle of +/- 55.4 degrees from the nadir (subpoint view). Successive scans occur at the rate of 6 per second, or at intervals of 167 msec.

For GAC data, successive sets of 4 out of every 5 samples in every third scan line are averaged to obtain an array of data spaced at intervals of 125 msec along the scan and at 500 msec along the satellite track. This leads to a data rate of 49,080 samples-per-minute and 2 scans-per-second. There are a total of 409 samples for the GAC data per channel per Earth scan.

Because the satellite is sun-synchronous, visible data revisit time is daily. Infrared imaging is accomplished twice daily with the second visit occurring during the pass over the dark side of the Earth. Instrument operation is continuous.

The overall coverage of the archived AVHRR data base is shown in the following tables. However, associated with equipment malfunctions, there may be short gaps in the time ranges.

GAC

LAC

HRPT

CLASS offers an on-line digital image browse feature for selected satellite image data sets. This image browse feature is primarily intended to support data set selection for order, by allowing users to visually judge overall image quality, determine the extent of cloud cover, and/or verify geographic coverage. The first satellite image data set to be supported with the browse feature is the AVHRR Level 1B data set. The sample browse images below show Hurricane Andrew and Norway.

Additional information on the AVHRR sensor and data for satellites TIROS-N through NOAA-14 can be found at: http://www.ncdc.noaa.gov/oa/pod-guide/ncdc/docs/podug/html/c3/sec3-0.htm

Details of the AVHRR/3 sensor can be found at: http://www.ncdc.noaa.gov/oa/pod-guide/ncdc/docs/klm/html/c3/sec3-1.htm while calibration information for AVHRR/3 is at: http://www.ncdc.noaa.gov/oa/pod-guide/ncdc/docs/klm/html/c7/sec7-1.htm and data format details for AVHRR/3 LAC and HRPT are at: http://www2.ncdc.noaa.gov/docs/klm/html/c8/s831-3.htm and data format details for AVHRR/3 GAC are at: http://www.ncdc.noaa.gov/oa/pod-guide/ncdc/docs/klm/html/c8/sec831-4.htm)

The Geostationary Operational Environmental Satellite (GOES) series of satellites is owned and operated by the National Oceanic and Atmospheric Administration (NOAA). The National Aeronautics and Space Administration (NASA) manages the design, development and launch of the spacecraft. Once the satellite is launched and checked out, NOAA assumes responsibility for the command and control of the satellite, transmission of data, and the archive and dissemination of the data and its derived products to the user community.

The NOAA National Climatic Data Center (NCDC) is responsible for the long term archive of GOES data, while the NOAA National Environmental Satellite, Data, and Information Service (NESDIS) operates the satellites and is responsible for providing real-time data and products.

Where Polar-orbiting Operational Environmental Satellites (POES) provide daily global coverage for analyzing long-term climatic and environmental trends, the GOES satellites' primary goal is to monitor the atmosphere for severe weather development such as tornadoes, flash floods, hail storms and hurricanes. When these conditions develop, the GOES satellites can track storms on a minute to minute basis.

The GOES satellite is positioned 35,790 km (22,240 statute miles) above the equator allowing it to view a major portion of the Western Hemisphere including southern Canada, the contiguous 48 states, major portions of the eastern Pacific Ocean and western Atlantic Ocean and Central and South America. Because the Atlantic and Pacific basins strongly impact the weather over the United States, coverage is typically provided by two GOES spacecraft, one at -75.0 Longitude (GOES East) and the other at -135.0 Longitude (GOES West).

The combined footprint (radiometric coverage and communications range) of the two spacecraft encompasses Earth's full disk about the meridian approximately in the center of the continental United States.

Availability of GOES data in CLASS is shown in the following table. 

Legend
 + SMS-2 operation was intermittent
++ GOES-9 replacement for GMS-5 over western Pacific - limited data in CLASS
Satellites were moved to different orbital positions to fulfill seasonal operational needs during times when there was a single satellite configuration. Click here to view a graphical representation of GOES-5 and later satellite coverages.

The GOES information that follows is specific to the current series of satellites (i.e. from GOES-8 forward). For users needing technical information for the earlier satellites, please go to the Comprehensive Information section for links to technical documents and guides.

The objective of the GOES satellites is to provide continuous, timely and high-quality environmental and atmospheric observations over much of the Western Hemisphere to enable forecasters to more accurately predict weather conditions and monitor and track severe storms. GOES data are used in a number of forecast situations such as estimating heavy rainfall, measuring movement and strengths of tropical storms, tracking volcanic plumes for aviation safety, measuring sea-surface temperatures, and much more. Since the GOES data archive extends well over two decades, its applications in long-term climate studies are being used by scientists around the world.

GOES Data Acquisition Introduction

The GOES Support System includes the Command and Data Acquisition (CDA) Station at Wallops Island, VA, and the Satellite Operations and Control Center (SOCC) at Suitland, MD. At the CDA station, raw instrument data and telemetry are read out from the satellite. Data are processed, calibrated, earth-located and converted to GOES Variable data format (GVAR) and rebroadcast to the satellite along with spacecraft command schedules. The GVAR data are then broadcast to direct readout users. SOCC is responsible for the overall safety of the spacecraft, scheduling of the instruments, data quality and performance. Continuous monitoring and checks are conducted on orbital position, image navigation and registration, and various subsystems including primary imager and sounder instruments. It is also responsible for planning and operating the ground system equipment for GVAR acquisition at NESDIS, the initial stage of product processing.

The GVAR satellite data are received at the Wallops Island, VA CDA station and relayed to SOCC in Suitland, MD for data monitoring at SOCC and product generation at the Office of Satellite Data Processing and Distribution (OSDPD)  Environmental Satellite Processing Center (ESPC). SOCC also forwards its GVAR data via microwave line-of-sight communications to the NOAA Science Center in nearby Camp Springs, MD for product processing.

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GOES System Functions and Instruments

The GOES spacecraft performs three major functions:

• Environmental Sensing: Acquisition, processing and dissemination of imaging and sounding data, independent of imaging data processes and the (in-situ) space environment monitoring data, and measurement of the near-earth space weather�.
• Data Collection: Receive data from earth surface-based Data Collection Platforms (DCPs) and relay to various acquisition stations.
• Data Broadcast: Continuous relay of weather facsimile and other meteorological data to independent users, research and educational institutions; relay of distress signals from aircraft or marine vessels to the search and rescue ground station of the search and rescue satellite-aided tracking system.

Each mission function is supported or performed by components of the GOES payloads:

Environmental Sensing:

• Five-channel Imager
• Nineteen-channel Sounder
• Space Environment Monitor (SEM)
  • Energetic Particles Sensor (EPS)
  • High energy proton and alpha particle detector (HEPAD)
  • X-ray Sensor (XRS)
  • Magnetometers

• Processed Data Relay (PDR) and Weather Facsimile (WEFAX) transponders
• Search And Rescue (SAR)
• Sensor data and Multiuse Data Link (MDL) transmitters

The remote sensing function is carried out by the 5-channel Imager and 19-channel Sounder. The acquisition of sensed data and its handling, processing, and final distribution are performed in real-time to meet observation time and timeliness requirements, including revisit cycles. Remotely sensed data are obtained over a wide range of areas of the western hemisphere, encompassing the earth's disk, selected sectors and small areas. Area coverage also includes the visibility needed to relay signals and data from ground transmitters and platforms to central stations and end users.

Imager Introduction

The Imager instrument is designed to sense radiant and solar-reflected energy from sampled areas of the Earth's surface and atmosphere. The Imager's five spectral channels simultaneously sweep an 8 km north-south (N/S) longitudinal swath along an east-west (E/W) latitudinal path by means of a two-axis gimballed mirror scan system. Beamsplitters separate the spectral channels into the various IR detector sets.

The primary characteristics of the imager are defined in the following tables:

Imager Instrument Characteristics:

Imager Instrument Parameters:

Imaging Channels Allocation:

Imager Performance Summary:

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Imager Scanning Characteristics

The Imager scans pre-determined areas in alternate directions on alternate lines. The imaging area is defined by a coordinate system related to the instrument's orthogonal scan axis. During imaging operations a scan line is generated by rotating the scanning mirror in the east-west direction while concurrently sampling each of the active imaging detectors. At the end of the line, the Imager scan mirror performs a turnaround, which involves stepping the mirror to the next scan line and reversing the direction of the mirror. The next scan is then acquired by rotating the scanning mirror in the opposite, west-east direction, again with concurrent detector sampling. Detector sampling occurs within the context of a repeating data block format. In general, all visible detectors are sampled four times for each data block (four times 1 km wide); while each of the active IR detectors is sampled once per data block (one times 4 km wide).

There are three operational imaging modes which satisfy a number of requirements defined by the NOAA NESDIS/NWS Study Group. The operational modes are designated as Routine, Rapid Scan and Super Rapid Scan. The tables below provide information on coverage, scan duration and scan times for GOES-East and GOES-WEST during Routine operational mode.

GOES-EAST Imager Scan Sectors in Routine Mode

GOES-WEST Imager Scan Sectors in Routine Mode>

During GOES Rapid Scan Operations (RSO), four views of the continental United States (CONUS) are provided at approximately 7.5 minute intervals in a half hour period. A northern hemisphere scan for both GOES East and GOES West satellites is also included in the 30 minute cycle. This yields eight views of the continental U.S. per hour.

During GOES Super Rapid Scan Operations (SRSO), approximately 10 one-minute interval scans are provided every half hour using prescribed 1000 x 1000 km sectors. The remaining time in the half hour cycle is devoted to scans of the northern hemisphere and CONUS (or sub-CONUS for GOES-WEST).

When GOES RSO or SRSO is utilized, most of the southern hemisphere is not scanned.

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Imager Data Characteristics

GOES data transmitted from the satellites and received by users with ground receiving equipment is called GVAR data. This format is primarily used to transmit meteorological data measured by the Imager and Sounder instruments and is archived in this format but rarely provided in this format to users of retrospective data due to its complex nature.

The GVAR format has its origins in the Operational VAS Mode AAA format, which featured a fixed length format composed of 12 equal size blocks of data. These blocks were transmitted synchronously with the spin of the earlier GOES (i.e. one complete 12 block sequence occurred for each rotation of the satellite.

With the launch of GOES-8 in April 1994, the spin-scan satellites were replaced by three-axis stabilized GOES. The continued use of the old transmission format would have been detrimental to the operational capabilities of these satellites. Therefore, the GVAR format was developed. GVAR maintained as much commonality with the Mode AAA reception equipment that many users had invested in and permitted full use of the advanced data transmission technology.

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Imager Calibration

The raw data in the visible channel are relativized and normalized at the CDA, but no calibration is applied. The raw data in the IR channels are calibrated using spacelooks and a heated internal blackbody. The spacelook calibration positions the scanning mirror at an extreme E-W coordinate permitting a view of space. The frequency of these spacelooks depends on the activity of the instrument. The rates vary from once every second to once every 36.6 seconds. A Blackbody calibration sequence is initiated every 30 minutes. During the sequence, the scanning mirror is rotated in the N-S direction through an angle of approximately 180 degrees to present a view of the Blackbody surface to the imaging detectors. The Blackbody surface temperature is maintained at a nominal 290Ëš K. For more information on GOES calibration see http://www.oso.noaa.gov/goes/goes-calibration/index.htm.

Sounder Introduction

The Sounder operates independently of the Imager and is designed to measure atmospheric temperature and moisture across large regions of the western hemisphere. The instrument contains 18 IR channels and one visible channel. There are four detectors for each band. Each detector's Field of View (FOV) is 8 km at nadir. The scan swath width is 40 km wide (N-S). The infrared spectral definition is provided by a rotating filter wheel that brings selected filters into the optical path of the detector assembly. Filters in three spectral ranges, longwave (12µm to 14.7µm), midwave (6.5µm to 11µm), and shortwave (3.7µm to 4.6µm), are arranged on the wheel for efficient use of sample time and optimal channel co-registration. The rotation of the filter wheel is synchronized with the stepping motion scan mirror. The visible channel (0.67µm) is not part of the filter wheel but is a separate set of uncooled silicon detectors having the same field of view size and spacing. These detectors are sampled at the same time as IR channels 3, 11, and 18, providing registration of all sounding data.

The primary characteristics of the sounder are defined in the following tables:

Sounder Instrument Characteristics:

Sounder Instrument Parameters:

Sounder Detectors Channel Allocation:

Sounder Performance Summary:

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Sounder Scanning Characteristics

Like the Imager, the Sounder scans the selected image area in alternate directions on alternate lines. This area is defined by scan coordinates which relate to the latitude and longitude for the northwest corner and southeast corner. The Sounder, however, provides additional scanning features that are not employed on the Imager. This instrument provides the capability to dwell on a particular location for a pre-programmed time period. These dwell times are 0.1, 0.2, or 0.4 seconds for one, two, or four data blocks. The Sounder also employs two N/S scanning modes referred to as the single and double-step modes. When in the single-step mode, the scan mirror steps the equivalent of one output scan line in the N-S direction each time an E-W or W-E scan completes. In the double-step mode, the scan mirror steps two output scan lines in the N-S direction for each E-W or W-E scan. This mode is also referred to as the skip-line mode and will only scan an image area with a dwell of 0.1 second. The single-step mode of operation is considered the normal mode for the Sounder and can scan an image area at any of the three dwell selections.

The tables below show the sounder scan areas, their boundaries, duration and scan times. The scan durations do not include star looks or blackbody calibration operations.

GOES-EAST Sounder Scan Sectors in Routine Mode

GOES-WEST Sounder Scan Sectors in Routine Mode

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Sounder Data Characteristics

The raw Sounder data is also part of the GVAR transmission, which consists of twelve distinct blocks numbered 0 through 11. Blocks 0 through 10 are transmitted as a contiguous set for each Imager scan. Block 10 will be followed by a variable number of Block 11's, which are always at fixed lengths. All sounder data will be included in Block 11, but not all Block 11's will contain sounder data. As the GVAR data are received by NOAA, the sounder blocks are stripped out and converted into McIDAS AREA format for final archive.

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Sounder Calibration

The Sounder performs a spacelook calibration sequence at a fixed nominal rate every 2 minutes. During a Sounder spacelook calibration, 40 raw Sounder data blocks are acquired at the spacelook coordinates. Unlike the Imager, the Sounder has no defined preclamp or clamp activity. A data analyses is also performed for the Sounder spacelook data. The resulting statistics are packaged in the Sounder Block 11. The Sounder performs a Blackbody sequence every 20 minutes. During the sequence, the scanning mirror is rotated in the N-S direction through an angle of approximately 180 degrees to present a view of the Blackbody surface to the imaging detectors. Like the Imager, the Blackbody surface temperature is maintained at a nominal 290˚ K.. For more information on GOES calibration see http://www.oso.noaa.gov/goes/goes-calibration/index.htm.

Detailed technical information on the GOES spacecraft and instruments is found in a paperback publication called GOES I-M DataBook. A copy is available in PDF format and can be downloaded in its entirety or in sections at http://rsd.gsfc.nasa.gov/goes/text/goes.databook.html.

A full description of the GVAR transmission format is located at http://www.osd.noaa.gov/gvar/gvardownload.htm.

Additional information on GOES operations can be found at the NOAA Satellite Information Services web site at http://noaasis.noaa.gov/NOAASIS/ml/gateway.html

GOES Products & Services Catalog: http://www.orbit.nesdis.noaa.gov/smcd/opdb/goescat_v4/.

The GOES Data Users Guide can be found on the NCDC Dataset Documentation web site at http://www4.ncdc.noaa.gov/ol/documentlibrary/datasets.html (document #3701 - Geostationary Operational Environmental Satellites).

For details on the GOES Mode formats, please click on the appropriate links below (caution: intended for GOES data experts)

http://www.ncdc.noaa.gov/oa/documentlibrary.Mode_A.pdf
http://www.ncdc.noaa.gov/oa/documentlibrary/Mode_A_Update_100182.pdf
http://www.ncdc.noaa.gov/oa/documentlibrary/Mode_AA_RevB.pdf
http://www.ncdc.noaa.gov/oa/documentlibrary/Mode_AA_RevC.pdf
http://www.ncdc.noaa.gov/oa/documentlibrary/Mode_AAA.pdf

For helpful information to read, calibrate, or navigate GOES data please click on the link below.

http://www.ncdc.noaa.gov/oa/rsad/satfaq/satfaq.html

The RADARSAT section of the CLASS web interface allows access to SAR data for authorized U.S. Government users only. It permits the users to search the CLASS inventory of RADARSAT data based on data set type as well as geographic locations and acquisition date and time. The user may then order selected data sets from the inventory for electronic delivery.

Access to RADARSAT data through CLASS is available to U.S. Government or Government-sponsored users who have agreed to the terms and conditions in the RADARSAT Affiliated User Agreement.

If you qualify for access to RADARSAT data and would like to be set up as an authorized user of CLASS, please send an email to info@class.noaa.gov providing the following information:

Name of point of contact
U.S. Government affiliation
Mailing address
Phone number
Email address
A brief description of intended use of RADARSAT data obtained through CLASS

Once this information is received, you will be contacted regarding setting up a user account in CLASS. Please note that your U.S. Government line office will be required to submit a signed RADARSAT Affiliated User Agreement if it has not already done so.

NOAA's allocation of RADARSAT data is limited to a percentage of the U.S. Government's investment in the RADARSAT program. As such, CLASS receives only limited amounts of RADARSAT data. These data include those acquired by the U.S. National Ice Center (NIC) for operational sea ice analysis and charting.

All RADARSAT files received and ingested at CLASS since October 1997 are accessible through the web interface. In addition, certain approved RADARSAT users can also access ERS-2 data received in CLASS through the RADARSAT web interface.

All RADARSAT data sets available through CLASS are in the Committee for Earth Observing Systems (CEOS) SAR format. Each data set has one data file and one or two metadata files (depending on the processing site). These files contain variable length records of mixed ASCII and binary values. Each record contains a binary record descriptor in its first 12 bytes that gives information about the record, including the record type and length.

Data sets from the Alaska SAR Facility (ASF) have a slightly different implementation of the CEOS format than data sets from other processing sites available through CLASS. Detailed information about the ASF data set format, including a byte-by-byte breakdown of each record, can be found at the ASF Home Page at http://www.asf.alaska.edu/reference/reference_docs.html

A document containing detailed information about the data set format for other processing sites (Gatineau, Tromso, West Freugh) may be downloaded from the RSI FTP site at ftp://ftp.rsi.ca/CEOS_DFN

Please note that all RADARSAT data sets available through CLASS are distributed with the data file compressed using gzip. To uncompress these data files, you will need to use the gunzip program. The gzip and gunzip programs are free software, and can be downloaded from ftp://ftp.gnu.org/pub/gnu

RADARSAT data sets available through CLASS vary considerably in size. They range from 20 to over 100 MB, with most being between 40 and 70 MB.

Data sets from each of the processing sites received at CLASS are renamed using the following convention:

NSS. < sat_id > . < rec_loc > .D < date > .T < time > . < loc1 > . < loc2 > . < unique_qual > . < file_ty pe >

where:

sat_id = satellite ID
E1 = ERS-1
E2 = ERS-2
R1 = Radarsat-1

rec_loc = receiving location

AF = Alaska SAR Facility (Fairbanks)
GT = Gatineau (Canada)
TR = Tromso (Norway)
WF = West Freugh (UK)

date = data start date in format YYJJJ, where YY is the year and JJJ is the day of year

time = data start time in format hhmmss for hours, minutes and seconds

loc1 = lat and lon of image upper left corner in format xxxyyyy, where xxx is latitude and yyy is longitude (nearest integer number), "N" indicates negative and "P" indicates positive

loc2 = lat and lon of image lower right corner (same format as loc1)

unique_qual - used to distinguish between different data sets that map to the same name (see information above), = A on first occurrence, B on second occurrence, C on third, etc.

file_type
L = leader file
T = trailer file
D = data file

example- NSS.R1.AF.D96338.T195326.P80N173.P74P175.A.D

Commercial software for RADARSAT processing and image display is available from a number of sources. The RADARSAT International (RSI) Home Page lists a number of RSI-endorsed image processing software products.

In addition, the Naval Research Laboratory (NRL) at the Stennis Space Center in Mississippi has developed the Naval Satellite Image Processing System (NSIPS), a PV-Wave based application on workstation platforms which allows SAR imagery ingest, display, and image processing, mainly for ice applications. This system has been made available at no cost to U.S. Government users; however, you still must purchase your own license for PV-Wave. For more information on NSIPS, please contact Nita Sandidge at sandidge@nrlssc.navy.mil, or at (228)688-4812.

Start Date

Refers to the date of the start of the data

Start Time

Refers to the time of the start of the data

Orbit Number

Refers to the satellite's relative orbit number, i.e. the revolution number at which the data were taken

Duration in Seconds

Refers to the total number of seconds elapsed between the start of the data and the end of the data

Satellite ID

Refers to the satellite from which the data were taken

Processing Site

Refers to the facility at which the data were acquired and processed

Min latitude

Refers to the latitude at the northernmost extent of the data

Min longitude

Refers to the longitude at the westernmost extent of the data

Max latitude

Refers to the latitude at the southernmost extent of the data

Max longitude

Refers to the longitude at the easternmost extent of the data

Size in KB

Refers to the size in KB of the data set (including image file and any metadata files)

Beam Mode/Position

Beam mode refers to the size of the image. RADARSAT has seven beam modes, ranging from 50 x 50 km to 500 x 500 km. Beam position refers to the incidence angle at which the data were acquired.

Product Type

Refers to either georeferenced or geocoded. Georeferenced data sets contain information about the geographical location of the image. Geocoded data sets contain data that has been geometrically transformed to an image according to a given map projection.

Ascending/Descending

Refers to the satellite's direction at the time the data were taken

Data Set Name

Refers to the CLASS data set name for the image.

Inventory ID

Refers to a unique numerical ID assigned to the data set for CLASS inventory purposes

Pixel Spacing

Refers to the area each image pixel covers (in meters)

More information about RADARSAT can be found at:

Canadian Space Agency's (CSA) has information about RADARSAT at http://www.space.gc.ca/asc/eng/default.asp

RadarSat International (RSI) Home Page at http://www.rsi.ca

The Defense Meteorological Satellite Program (DMSP) is the Department of Defense program responsible for designing, building, launching and operating polar orbiting meteorological satellites. The satellites can broadcast visual, infrared and microwave imagery directly to transportable tactical sites around the world. The data are also stored for transmission to the Navy's Fleet Numerical Meteorology and Oceanography Center (FNMOC) and to the Air Force Global Weather Central (AFGWC).

In December 1972, DMSP data were declassified allowing access by the civil/scientific community. As a result, both AFGWC and FNMOC relay the Special Sensor Microwave/Imager (SSM/I), the Special Sensor Microwave Temperature Sounder (SSM/T-1) and the Special Sensor Microwave Water Vapor Profiler (SSM/T-2) data to the National Environmental Satellite, Data, and Information System (NESDIS).

In May 1994, the President directed the Departments of Commerce (DoC) and Defense to converge their separate polar orbiting environmental satellite programs. DMSP is now operated by the two departments and NASA. In June 1998, DoC took over the primary responsibility for flying both satellite systems until the converged systems are ready for launch in the 2007-2010 timeframe.

Each of the DMSP satellites flies in a sun-synchronous, low altitude, near-polar orbit. For a satellite in sun synchronous orbit, the ascending equatorial crossing time remains relatively constant with respect to the local time throughout the lifetime of the satellite. The orbital period is 101 minutes and the nominal altitude is 833 km.

The Comprehensive Large Array-data Stewardship System (CLASS) distributes data from three DMSP instruments: 1) the SSM/T-1; 2) the SSM/T-2; and 3) the SSM/I from which antenna temperatures (Temperature Data Records - TDR), brightness temperatures (Sensor Data Records - SDR) and derived geophysical parameters (Environmental Data Records -EDR) are derived.

Each instrument has different characteristics, resolutions, scan properties, etc. which are described below. CLASS archives data beginning with satellite F10.

Data are transmitted in real time to tactical terminals worldwide. Data are also stored using on-board recorders for transmission to and processing by the Air Force Global Weather Central (AFGWC), Offutt AFB, Nebraska and the Fleet Numerical Meteorology and Oceanography Center (FNMOC), Monterey, California. Both AFGWC and FNMOC relay the SSM/I, SSM/T-1 and SSM/T-2 data to the National Environmental Satellite, Data, and Information System (NESDIS). AFGWC also sends the entire data stream to the National Geophysical Data Center (NGDC).

Note that the orbit file names are generated by NESDIS using the information found in the file header. The file header is created by FNMOC and does not always accurately reflect the start and end times of the data in the file.

SSM/I Introduction

The Special Sensor Microwave/Imager (SSM/I) is part of the instrument suite flown onboard the DMSP series of satellites. The SSM/I is a seven-channel, four-frequency, linearly-polarized, passive microwave radiometric system. The SSM/I measures atmospheric, ocean, and terrestrial microwave brightness temperatures at 19.35, 22.235, 37.0, and 85.5 Ghz.

The SSM/I continuously rotates about an axis parallel to the local spacecraft vertical at 31.6 rpm. The SSM/I measures upwelling scene brightness temperatures over an angular section of 102.4 degrees about the sub-satellite track. When looking in the forward direction of the spacecraft, the scan is directed from left to right with active scene measurements lying 51.2 degree about the forward direction. A conical scan with a swath width of 1,400 km results. Global coverage is obtained in 24 hours. The spacecraft sub-satellite point travels 12.5 km during the 1.9 second period.

For each scan, 128 uniformly spaced 85.5 Ghz scene measurements are taken over a 102.4 degree scan region. The sampling interval is 4.22 msec and equals the time for the beam to travel 12.5 km in the cross track direction. Radiometric data at the remaining frequencies are sampled every other scan with 64 uniformly spaced samples being taken. The sampling interval for these remaining frequencies is 8.44 msec. The start and stop times of the integrate and dump filters at 19.35, 22.235, and 37.0 GHz are selected to maximize the radiometer integration time to achieve concentric beams for all sampled data. The effect of the radiometer integration times is to increase the effective along scan beam diameter to make the beams at 37 and 85 GHz nearly circular.

SSM/I's output voltages are converted into antenna temperatures (Temperature Data Records - TDR), brightness temperatures (Sensor Data Records - SDR) and derived geophysical parameters (Environmental Data Records -EDR). The EDRs contain geophysical parameters derived from the TDRs and SDRs. CLASS archives TDR, SDR and EDR data beginning with satellite F10.

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SSM/I Applications

SSM/I data are available as antenna temperatures (TDRs), brightness temperatures (SDRs) and derived geophysical parameters (EDRs). EDRs measure various parameters over the ocean, ice and land surfaces. There are five oceanic parameters: surface wind speed, cloud water content, water vapor content, rainfall intensity and liquid water content. There are four ice parameters: ice concentration, ice age, ice edge and cloud water content over ice. There are eight land parameters: rain intensity, liquid water content, surface moisture, cloud water content, snow water content, surface character, surface temperature and cloud amount. Not all parameters are simultaneously possible.

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SSM/I Data Acquisition

SSM/I's output voltages are transmitted to the Fleet Numerical Meteorology and Oceanography Center (FNMOC) in Monterey, California, where they are converted to sensor counts. FNMOC then converts the sensor counts into antenna temperatures (Temperature Data Records - TDR), brightness temperatures (Sensor Data Records - SDR) and derived geophysical parameters (Environmental Data Records -EDR). The TDRs, SDRs, and EDRs are sent to NESDIS for archival.

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SSM/I Data Description

SSM/I data from CLASS consist of 12-bit precision antenna temperatures for TDRs, brightness temperatures for SDRs, or derived geophysical parameters for EDRs, along with satellite ephemeris, earth surface positions for each pixel, and instrument calibration.

No subsetting of data is performed on any DMSP data at CLASS.

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SSM/I Spatial Coverage

The 1,400 km wide conical scan of the SSM/I obtains global coverage every 24 hours. The channel footprint varies with channel energy, position in the scan, along scan or along track direction and altitude of the satellite. The 85 GHz footprint is the smallest at 13 x 15 km and the 19 Ghz footprint is the largest at 43 x 69 km.

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SSM/I Temporal Coverage

The scanning period for the SSM/I is 1.9 seconds during which the spacecraft sub-satellite point travels 12.5 km. For 540 msec of that period, 128 uniformly spaced 85.5 Ghz scene measurements are taken over the 102.4 degree scan region. The sampling interval is 4.22 msec and equals the time for the beam to travel 12.5 km in the cross track direction. Radiometric data at the remaining frequencies are sampled every other scan with 64 uniformly spaced samples being taken. The sampling interval for these remaining frequencies is 8.44 msec. The remaining portion of the sampling period allows the SSM/I to rotate through the remaining 257.6 degrees to once again be positioned to start acquiring scene measurements.

The overall coverage of the SSM/I data archived at CLASS is shown in the following tables. However, associated with equipment malfunctions, there may be short gaps in the time ranges.

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TDR

SDR

EDR

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SSM/I Calibration

A small mirror and a hot reference absorber are positioned off axis such that they pass between the feed horn and the parabolic reflector, occulting the feed once each scan. The mirror reflects cold sky radiation into the feed, thus serving, along with the hot reference absorber, as calibration references for the SSM/I. This scheme provides an overall absolute calibration which includes the feed horn every 1.9 seconds. Corrections for spillover and antenna pattern effects from the parabolic reflector are incorporated in the data processing algorithms.

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SSM/I TDR Data Processing Software

To obtain DMSP SSM/I TDR data processing software files, click on the appropriate links below. You will be presented with the source code. To save the source code, go to your file menu and select "Save As."

C language program ssmitdrta.c reads the SSM/I TDR data set file and writes the antenna temperatures, satellite ID, time, revolution number, latitudes, and longitudes to an output file. This output file is read by FORTRAN program ssmitdrtb.f which converts the antenna temperatures to brightness temperatures.

C language program ssmitdrlatlon.c reads the TDR data set and creates a new TDR file containing scans within specified latitude-longitude boundaries.

DMSP/README.tdr
DMSP/ssmitdrta.c
DMSP/ssmitdrtb.f
DMSP/ssmitdrlatlon.c
DMSP/read_ssmi_netcdf.pro <new>

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SSM/I Comprehensive Information

Details of the SSM/I TDR data sets can be found at: http://www.osdpd.noaa.gov/PSB/SHARED_PROCESSING/TDR.HTML.
F-16 - TDR data formats.

Details of the SSM/I SDR data sets can be found at: http://www.osdpd.noaa.gov/PSB/SHARED_PROCESSING/SDR.HTML.
F-16 - SDR data formats.

Details of the SSM/I EDR data sets can be found at: http://www.osdpd.noaa.gov/PSB/SHARED_PROCESSING/EDR.HTML.
F-16 - EDR data formats.

SSM/T-1 Introduction

The Special Sensor Microwave Temperature (SSM/T-1) sounder is part of the instrument suite flown onboard the DMSP series of satellites. The SSM/T-1 is a seven channel microwave sounder, designed to provide global, synoptic scale soundings of temperature throughout the troposphere and lower stratosphere. All seven channels are within the 50 - 60 Ghz oxygen band, with one channel acting as a surface window channel. A single cross-track reflecting antenna is used to direct the upwelling atmospheric radiation through a fixed circular horn which is coupled to the Dicke radiometers. The incoming broad band signal is first split into two bands having orthogonal polarization, and then filtered into the seven discrete channels whose center frequencies and bandwidths are listed below.

Temperature soundings are obtained operationally using a minimum variance approach whose covariance matrices are constructed from a fixed set of simulated SSM/T data and corresponding temperature profiles.

In processing SSM/T-1 data, special attention is placed on the utilization of the two lowest frequency channels. The 50.5 GHz channel receives nearly 70 percent of its energy from the surface and is considered a "window" channel. Since the measurements are strongly dependent on precipitation and surface emissivity variations, the channel is not used as a temperature predictor. However, based on a minimum threshold brightness temperature of about 245 K, the window channel is used to edit the data for precipitation over the oceans. Furthermore, the 50.5 GHz channel also provides surface emissivity corrections for the lowest sounding channel.

The lowest sounding channel (53.20 GHz) responds to changes in atmospheric temperature around 700 mb where the weighting functions peaks. However, it receives about 20 percent of its energy from the surface and therefore requires corrections for the effects of surface emissivity and high elevation (greater than 1 km) on the brightness temperature. The window channel provides an emissivity correction while elevation adjustments are based on terrain height information. The next highest peaking channel (54.35 GHz) lies within the more opaque region of the oxygen band where the surface contribution is only 2 percent. As a result, this channel and the remaining channels are generally found to have negligible surface effects.

The SSM/T-1 completes one scan of seven Earth view measurements and two calibration measurements every 32 seconds. Each scan of the instrument covers a swath of roughly 1,500 km perpendicular to the orbital track. Each orbit covers a different area of the earth, except poleward of 57 degrees latitude, where successive orbits begin to overlap. For each of the seven channels, there are 18,900 earth view measurements collected per day.

The SSM/T-1 instrument data, also known as the SSM/T-1 raw data, are received and processed to the 1b level by the NOAA/NESDIS/IPD.

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SSM/T-1 Applications

The SSM/T-1 is a seven channel microwave sounder, designed to provide global, synoptic scale soundings of temperature throughout the troposphere and lower stratosphere. The measurements are within 1K (rms) of the brightness temperatures computed from radiosonde data. The retrievals are generally within 2.5K (rms) of radiosonde temperatures for pressures less than 850 mb. These results are independent of cloud cover and more accurate than the retrievals obtained from the TIROS Operational Vertical Sounder (TOVS), particularly for cloudy atmospheres.

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SSM/T-1 Data Description

DMSP SSM/T-1 files are stored at CLASS under the following naming convention:

NSS.SSMT.Sn.Dyyjjj.Shhmm.Ehhmm.Axxxxxxx.NS

where the upper case characters remain fixed and the lower case characters vary from spacecraft to spacecraft and from orbit to orbit.

The lower case characters correspond to the following variables:

n = Spacecraft identification (e.g. 6 for satellite F-12)
yy = Year of the century
jjj = day of the year
hhmm = Time in hours and minutes
xxxxxxx = Orbit Number

The upper case characters represent the following:

NSS.SSMT = NESDIS SSM/T-1
D = Day
S = Start Time
E = End Time

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SSM/T-1 Header Record Format

Each SSM/T-1 level 1b file contains a header record in the following format:

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SSM/T-1 Data Record Format

Each subsequent data record contains one scan of SSM/T-1 data in the following format:

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SSM/T-1 Spatial Coverage

The radiometer has a field of view (FOV) of 14.4 degrees. At the nominal 833 km altitude, the spatial resolution at nadir is an approximate circle with a 174 km diameter. At the far end of each scan, the footprint degrades to an ellipse 213 x 304 km in size. The seven cross-track scan positions are separated by 12 degrees with a maximum cross-track scan angle of 36 degrees. The SSM/T-1 swath width is 1,528 km. Each orbit covers a different area of the earth, except poleward of 57 degrees latitude, where successive orbits begin to overlap. Elsewhere, there is a data coverage gap between successive orbits.

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SSM/T-1 Temporal Coverage

The overall coverage of the SSM/T-1 data archived at CLASS is shown in the following tables. However, associated with equipment malfunctions, there may be short gaps in the time ranges.

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SSM/T-1 Calibration

The calibration of the SSM/T-1 instrument is provided by two additional scan steps. One position views cold space (~2.7 K) and the second an ambient temperature target (~300K) attached to the scan structure. Ground-based data processing results in individually calibrated brightness temperatures for the seven channels by linearly relating the output channel response to the monitored target temperature and 2.7K cold space temperature. The total scan period is 32 seconds with an integration time of 2.7 seconds for each of the Earth viewing and calibration positions.

The in-flight calibration system is a well-matched, closed-path configuration with very low dissipative wall losses. A shroud on the reflector allows direct coupling to both the cold path and warm load. The cold path is an oversized circular transmission line that is used to restrict the radiometer field of view so that extraneous input signals due to both the surrounding spacecraft and the earth's atmosphere are minimized. Due to the location of the sensor on the spacecraft it is not possible for the sensor antenna to view the sky directly. Therefore, it is necessary to utilize a reflecting miter bend in the cold path to direct the antenna pattern in the proper direction. The warm load is an extended microwave radiator made up of a large number of tapered absorbing sections and is designed to provide a stable blackbody temperature source at approximately 300 K. An accurate measurement of the surface temperature of the load is provided as a result of the warm load thermal design. A shroud allows direct coupling to the antenna and a sun shield located on the antenna reflector prevents the warm load from viewing the sun, thereby enhancing the thermal stability of this load.

The electrical performance requirements of the SSM/T-1 sensor system are a maximum calibration uncertainty of 1 K and maximum NETD for the various channels of 0.4 to 0.6 K.

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SSM/T-1 Data Processing Software

To obtain DMSP SSM/T-1 data processing software files, click on the appropriate link below. You will be presented with the source code. To save the source code, go to your file menu and select `Save As'.

The C language program, ssmt1rdc.c, reads the SSM/T-1 data set file and generates an intermediate file with all the necessary data from the data set. FORTRAN program ssmt1rdf.f reads this intermediate file into arrays.

DMSP/README.ssmt1
DMSP/ssmt1rdc.c
DMSP/ssmt1rdf.f

SSM/T-2 Introduction

The Special Sensor Microwave Water Vapor Profiler (SSM/T-2) is part of the instrument suite flown onboard the DMSP series of satellites. The SSM/T-2 is a cross-track scanning, five channel, passive, total power, microwave radiometer. Of the five channels, three are water vapor channels centered around the 183.31 GHz water vapor line. The other two are window channels at 91.655 GHz and 150.0 GHz. The SSM/T-2 is designed to provide global monitoring of the concentration of water vapor in the atmosphere under all sky conditions by taking advantage of the reduced sensitivity of the microwave region to cloud attenuation.

The SSM/T-2 observation rate is 7.5 scans per minute. The instrument utilizes a step-scan motion in the cross-track direction of +/- 40.5 degrees. The SSM/T-2 scan mechanism is synchronized with the SSM/T-1 so that the beam cell patterns of the two sensors coincide. There are 28 observations (beam positions) per scan for each of the five channels. All five channels have coincident centers. The total swath width for the SSM/T-2 is approximately 1,500 km.

The channel characteristics for the SSM/T-2 are listed below:

The SSM/T-2 employs a single offset parabolic reflector with a 2.6 inch diameter projected aperture. The reflector is shrouded to eliminate the possibility of rays from the sun striking either of the calibration paths and causing unwanted thermal gradients. The feedhorn is a corrugated pyramidal horn with a flare designed to minimize phase center separation over the bandwidth (91 to 183.3 GHz), while providing a spherical wave illumination of the reflector. A 3.3 degree beamwidth is achieved for the 183.3 GHz channels and larger beamwidths of approximately 3.7 degrees and 6.0 degrees for 150 and 91.665 GHz, respectively. These correspond to the Field-of-View (FOV) parameters given in the table above.

To achieve the cross-track scanning, the reflector alone rotates. The rotation of the reflector produces a rotation of the plane of polarization of the upwelling scene Brightness Temperatures which is permitted provided that the polarization remains identical for the two window channels and the 183.3 +/- 7 Ghz channel. These channels must have the same polarization characteristics because they measure contributions from both the atmosphere and the surface. Note that all SSM/T-2 channels possess the same polarization.

The SSM/T-2 observed raw data are processed into the SSM/T-2 Level 1b data set by NOAA/NESDIS Information Processing Division (IPD) and are made available by CLASS. The 1b data set contains earth located and calibrated SSM/T-2 data. Each data set contains one orbit's worth of data and is allowed to accumulate up to 120 minutes of data. Approximately 14 level 1b orbital data sets are generated per day.

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SSM/T-2 Applications

The SSM/T-2 is designed to provide global monitoring of the concentration of water vapor in the atmosphere under all sky conditions by taking advantage of the reduced sensitivity of the microwave region to cloud attenuation.

Major mid-latitude weather phenomena such as fronts and extratropical cyclones have excellent signatures in SSM/T-2 data, including three-dimensional structure. Other phenomena such as tropical cyclones, tropical plumes, subtropical anticyclones and surface states such as sea ice and snow cover may be identified.

Applications other than profiling are also possible with the SSM/T-2. The retrieval of vertically integrated water vapor is possible due to the strong sensitivity of the 183.31 GHz water vapor absorption line.

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SSM/T-2 Data Description

DMSP SSM/T-2 files are stored at CLASS under the following naming convention:

NSS.SSMT.Sn.Dyyjjj.Shhmm.Ehhmm.Axxxxxxx.NS

where the upper case characters remain fixed and the lower case characters vary from spacecraft to spacecraft and from orbit to orbit.

The lower case characters correspond to the following variables:

n = Spacecraft identification (e.g. 6 for satellite F-12)
yy = Year of the century
jjj = day of the year
hhmm = Time in hours and minutes
xxxxxxx = Orbit Number

The upper case characters represent the following:

NSS.SMT2 = NESDIS SSM/T-2
D = Day
S = Start Time
E = End Time

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SSM/T-2 Header Record Format

Each SSM/T-2 level 1b data set contains a header record in the following format:

The header record can be broken down by the following data groups which are described below.

Identification Block

The identification block is contained in Bytes 1 - 48 in the header record. This data group contains the data set name, the number of scans and the number of gaps in the data. The data set name provides the spacecraft identification, the orbit start day, orbit start and end times, and the processing block identification.

The spacecraft identification is a numerical ID assigned to a spacecraft (e.g. ID=6 corresponds to spacecraft F-12). The start and end times of the level 1b orbit are rounded off to the nearest five minutes. Therefore, the first scan may not necessarily be at the start time and the last scan may not necessarily be at the end time. The processing block identification contains a letter code followed by a five digit starting rev number and a two digit ending orbit number. The ending orbit number is obtained by incrementing the last two digits of the starting orbit number by one. The total number of scan records in the data set is given by the number of scans parameter. The number of data gaps parameter corresponds to missing data. If the scene data block is empty or missing, then it is considered as a data gap. If a data gap covers one or more consecutive scans, then it is counted as one data gap. The data gap parameter can be used to determine the completeness of the data.

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Preflight Calibration Data Group

The preflight calibration data group is contained in bytes 49 - 156 in the header record. This data group includes the coefficients used to convert warm load calibration counts to the corresponding temperatures, as well as the correction terms used to compute the slope and intercepts. To compute the temperatures, a set of eleven counts and the corresponding temperatures are provided for each thermistor. Included in the correction terms are a cold path temperature correction term and a warm path temperature correction term for each channel. The preflight calibration data are retrieved from the SSM/T-2 constants file.

Note: Preflight calibration data have no utility to the user. These data are intended for troubleshooting calibration related problems.

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Antenna Pattern Correction Data Group

The antenna pattern correction data group is contained in bytes 157 - 436 in the header record. This data group provides the coefficients required to perform antenna pattern correction. No correction to the antenna pattern is performed by the Level 1b software. Therefore, the coefficients to perform this correction as a post-processing step are supplied in this data group. The correction coefficients are stored in the following order:

Quality Control Summary Group

The quality control (QC) summary data group is contained in bytes 437 - 450 in the header record. This data group provides a summary of the quality of the earth locations, scene data and calibration data at the orbital level. The overall quality of the level 1b data can be determined from the QC summary. The QC summary is reported as a percentage of the total number of samples upon which the quality control is performed. The criteria used to assess the quality of a scan or channel are as follows.

While computing earth locations, the two ephemeris minute vectors are verified for valid data. The scan time is verified to determine if it lies between the ephemeris times. The earth locations are not computed if the ephemeris data are deemed invalid, or if the scan time is not bounded by the ephemeris times and a filler value of 0 is used for the earth locations.

If a scene data block is empty or missing, the corresponding scan is treated as bad as far as the scene data are concerned. No filler values are provided as substitutes for missing data.

The calibration algorithm uses the averages of calibration data taken from 8 scans (four preceding scans, the scan being calibrated, and three succeeding scans). A scan or channel is treated as bad, as far as the calibration data are concerned, when one of the following conditions is satisfied:

1) Warm load counts failed the limit check, or the difference of warm load temperatures computed from the two thermistors exceeded the pre-defined limit, or less than four good scans were obtained to perform the averages.
2) All cold view or warm view counts from a given channel failed the limit check.
3) The averages of cold view and warm view counts were identical in a given channel.
4) Slope or intercept failed the limit check in a given channel.

When the first condition is satisfied, the entire scan is not calibrated and the individual channels are treated as bad. When conditions 2, 3 or 4 are satisfied, the corresponding channel is treated as bad.

In all other instances, the quality of earth location, scene data and calibration counts is validated to be good and identified as such. The level 1b software compiles the data accumulated over the entire orbit, computes statistics and stores the results in the header record in terms of percentages.

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SSM/T-2 Data Record Format

Each SSM/T-2 level 1b data set contains up to 900 data records. Each data record contains one scan of SSM/T-2 data in the following format:

Each data record can be broken down by the following data groups which are described below.

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Scan Information Group

The scan information data group is contained in bytes 1 - 20 in the data record. This data group includes the orbit number, scan number, scan index and scan time. The orbit number corresponds to the rev number provided in the readout header of the raw data. The scan number is a sequential number assigned to a scan. It also coincides with the data record number, i.e. the scan number in the first data record is 1, the scan number in the second data record is 2, and so on. The scan index is used for collocation with SSM/T-1 data. The index is a composite of the scan group and scan sequence number. The scan group is a sequential number assigned to a set of 4 SSM/T-2 scans and the scan sequence number is a number which identifies individual scans within that group. The scan index is stored as the scan group times 10 plus the scan sequence number. For example, if the scan number is 75, the corresponding index is 193 (scan numbers 73-76 becomes group 19; scan number 75 is the third scan in that group, i.e. 19*10+3).

The scan time contains the year of the century and the day, OLS time in seconds, and TS in milliseconds. The OLS time is the time extracted from the first subframe (data ident = 0, 8, 16 or 24) of 8 subframes which make up the SSM/T-2 scan. TS is the time between beam position 1 and the following readout enable. TS is used as an additive term in the earth location algorithm and has no utility to the user. The scan time is stored in the following format:

Note: The day parameter is not reset for orbits which are on a day boundary.

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Earth Location Data Group

The earth location data group is contained in bytes 21-132 of the data record. This data group includes the earth locations for each of the 28 beam positions. The earth locations (latitude-longitude pairs) appear in the following order:

and so on.

The earth locations are specified in degrees and the following convention is used for latitude-longitudes:

Latitudes: North > 0 and South < 0; (-90 <= lat <= 90)
Longitudes: East > 0 and West < 0; (-180 <= long <= 180).

Note: The earth locations provided in the data record must be descaled to determine the appropriate latitudes and longitudes. If the earth locations of all beam positions are identically equal to zero, it indicates missing earth locations and these locations must not be used.

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Scene Data Group

The scene data group is contained in bytes 133-468 of the data record. This data group provides the time at each beam position followed by raw counts of all channels. Scene data appear in the following order:

The raw counts range from 0 to 4,095. These counts are used to compute channel brightness temperatures using the following relationship:

BTn = Bn * Cn + An

where n is the SSM/T-2 channel number (1-5), and BT, B, C and A are the brightness temperatures, slopes, raw counts and offsets, respectively.

The time given at each beam position is the time measured relative to the OLS time. The beam position time is stored in milliseconds and can be converted to an absolute time by adding these milliseconds to the OLS time (byte 13-16). Since the beam position times are derived as a function of ephemeris time, occasionally, the beam position times could lag behind the OLS time by a few seconds. This is a normal condition.

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Calibration Data Group

The calibration data group is contained in bytes 469-660 of the data record. Calibration data consists of the following parameters:

Note: Only the channel slope and offset values have utility to the user. The other parameters provided under the calibration data group are intended for troubleshooting calibration related problems.

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Quality Control Data Group

The quality control data group is contained in bytes 661-674 of the data record. This data group indicates the quality of earth locations, scene data and calibration at the scan level. The criteria used for quality control are outlined in the header record Quality Control Summary section above.

The QC information appears in the following order:

If the earth locations QC flag contains a non-zero value, the earth locations from that scan must not be used. If the scene data QC flag contains a non-zero value, it indicates missing scene data and the scene data from that scan should be used with caution. If a calibration QC flag contains a non-zero value, the slopes and intercepts computed for that channel are probably erroneous and are not usable.

Note: The QC data provided in this data group are only applicable to the data record in which they are reported.

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SSM/T-2 Spatial Coverage

At the nominal 833 km altitude, SSM/T-2 observations are made at a spatial resolution of approximately 45 km. Each of the approximately 14 orbits per day covers a different area of the earth, except poleward of 57 degrees latitude, where successive orbits begin to overlap. Elsewhere, there is a data coverage gap between successive orbits. Each orbit is comprised of ascending and descending passes. All five channels have coincident centers. The total swath width for the SSM/T-2 is approximately 1,500 km.

A 3.3 degree beamwidth is achieved for the 183.3 GHz channels while larger beamwidths of approximately 3.7 degrees and 6.0 degrees are achieved for the 150.0 and 91.665 Ghz channels, respectively. These correspond to nadir Field-of-Views of approximately 48, 54 and 84 km, respectively.

The SSM/T-2 scan mechanism is synchronized with the SSM/T-1 so that the beam cell patterns of the two sensors coincide.

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SSM/T-2 Temporal Coverage

The SSM/T-2 makes observations at a rate of 7.5 scans/minute with each scan producing 28 observations or Beam Positions. Each data set contains one orbit's worth of data and is allowed to accumulate up to 120 minutes of data. Approximately 14 level 1b orbital data sets are generated per day per satellite.

The overall coverage of the SSM/T-2 data archived at CLASS is shown in the following tables. However, associated with equipment malfunctions, there may be short gaps in the time ranges.

SSM/T-2 Calibration

The SSM/T-2 employs a calibration period of 8 seconds in which four samples are taken of a warm-load calibration target (~300K) along with four samples of the cosmic background (~3K). The warm load is shrouded to improve radio frequency (RF) coupling of energy to the reflector/feedhorn antenna. This minimizes potential calibration errors arising from the reception of extraneous energy due to scattering of earth or solar radiation off of the spacecraft. The cold path is a cylindrical oversized waveguide tube which permits a direct view of the cosmic background by the antenna reflector during calibration.

The periodic calibration data are modeled by a linear transfer function to characterize the state of the total power radiometer and to remove time variations of the receiver gain and offset for frequencies less than half the reciprocal of the calibration period. As a consequence, relatively large temperature-related receiver gain drifts are taken into account in the periodic construction of the transfer function.

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SSM/T-2 Data Processing Software

To obtain the DMSP SSM/T-2 data processing software file, click on the link below. You will be presented with the source code. To save the source code, go to your file menu and select `Save As'.

C language program ssmt2list.c reads and lists the SSM/T-2 file contents.

DMSP/README.ssmt2
DMSP/ssmt2list.c

SSM/I TDR Data Processing Software

To obtain DMSP SSM/I TDR data processing software files, click on the appropriate links below. You will be presented with the source code. To save the source code, go to your file menu and select "Save As."

C language program ssmitdrta.c reads the SSM/I TDR data set file and writes the antenna temperatures, satellite ID, time, revolution number, latitudes, and longitudes to an output file. This output file is read by FORTRAN program ssmitdrtb.f which converts the antenna temperatures to brightness temperatures.

C language program ssmitdrlatlon.c reads the TDR data set and creates a new TDR file containing scans within specified latitude-longitude boundaries.

DMSP/README.tdr
DMSP/ssmitdrta.c
DMSP/ssmitdrtb.f
DMSP/ssmitdrlatlon.c
DMSP/read_ssmi_netcdf.pro <new>

To obtain DMSP SSM/T-1 data processing software files, click on the appropriate link below. You will be presented with the source code. To save the source code, go to your file menu and select `Save As'.

The C language program, ssmt1rdc.c, reads the SSM/T-1 data set file and generates an intermediate file with all the necessary data from the data set. FORTRAN program ssmt1rdf.f reads this intermediate file into arrays.

DMSP/README.ssmt1
DMSP/ssmt1rdc.c
DMSP/ssmt1rdf.f

SSM/T-2 Data Processing Software

To obtain the DMSP SSM/T-2 data processing software file, click on the link below. You will be presented with the source code. To save the source code, go to your file menu and select `Save As'.

C language program ssmt2list.c reads and lists the SSM/T-2 file contents.

DMSP/README.ssmt2
DMSP/ssmt2list.c

The Solar Backscatter Ultraviolet Radiometer-2 (SBUV/2) is an operational remote sensor designed to map, on a global scale, total ozone concentrations and the vertical distribution of ozone in the earth's atmosphere. The 1b Capture Data Set contains (1) all SBUV/2 sensor data and support data necessary for the derivation of atmospheric ozone and solar flux; (2) instrument in-flight calibration data and housekeeping functions for monitoring post-launch instrument changes; and (3) prelaunch calibration factors, and computed current-day instrument calibration and albedo correction factors to adjust the ozone algorithm for actual instrument performance. The Product Master File (PMF) contains ozone information located in space and time, other meteorological information developed in support of the ozone computation, parameters indicating the validity of the individual ozone retrievals, and the radiance information derived from the SBUV/2 measurements.

The SBUV/2 instruments on the TIROS-N satellites are designed to measure the total ozone in a vertical column beneath the satellite and its distribution with height in the atmosphere. The SBUV/2 contains a scanning double monochromator and a cloud cover radiometer (CCR) designed to measure ultraviolet (UV) spectral intensities. In its primary mode of operation, the monochromator measures solar radiation backscatter by the atmosphere in 12 discrete wavelength bands in the near-UV, ranging from 252.0 to 339.8 nm, each with a bandpass of 1.1 nm. The total-ozone algorithm uses the four longest wavelength bands (312.5, 317.5, 331.1, and 339.8 nm), whereas the profiling algorithm uses the shorter wavelengths. The cloud cover radiometer operates at 379 nm (i.e. outside the ozone absorption band) with a 3.0-nm bandpass and was designed to measure the reflectivity of the surface in the instantaneous field of view (IFOV). The SBUV/2 also makes periodic measurements of the solar flux by deploying a diffuser plate into the field of view (FOV) to reflect sunlight into the instrument.

The monochromator and the cloud cover radiometer are mounted so that they look in the nadir direction with coincident nominal FOV =s of 11.3 by 11.3 degrees. As the satellite moves in a Sun-synchronous orbit, the FOV traces 160-km wide paths on the ground. The earth rotates approximately 26 o degrees during each orbit. The satellite footprint moves at a speed of about 6 km/sec. In discrete mode a set of 12 measurements, 1 for each discrete wavelength band, is taken every 32 seconds. The order of measurements is 252.0 to 339.8 and the integration time is 1.25 seconds per measurement. For each monochromator measurement there is a cloud cover radiometer measurement.

The SBUV/2 instrument can also measure the solar irradiance or the atmospheric radiance with a continuous spectral scan from 160 to 400 nm in increments of nominally 0.148nm.

Collection will include 1B and PMF products in monthly data formats for the entire length of the SBUV/2 life-cycle, beginning with NOAA-9 data in Dec 1984 and continuing through NOAA-N' data (launch estimated Dec 2007). Data will be held in the archive for perpetuity.

1B File Naming Convention

ozone.sbuv.YYYYMM.op1b.n SS

Where YYYY = year
MM = month
SS = satellite ID

PMF File Naming Convention