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 NOAA Satellite Operations Facility (NSOF)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. NSOF 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 Office of Satellite Data Processing and Distribution (OSDPD) manages and directs the operation of the central ground facilities which ingest, process, and distribute environmental satellite data and derived products to domestic and foreign users.

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:

Imager Scanning Characteristics

The Imager scans predetermined 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.

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.

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:

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

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.

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 two publications:
GOES I-M DataBook for GOES-8 through GOES-12 and GOES N Series DataBook for GOES-13/14/15. These copies are availabe in PDF format and can be donwloaded in its entirety or in sections at:
http://goes.gsfc.nasa.gov/text/goes.databook.html (GOES-8 to 12)
http://goes.gsfc.nasa.gov/text/goes.databooknop.html (GOES-13 to 15)

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 at http://www1.ncdc.noaa.gov/pub/data/documentlibrary/tddoc/td3701.pdf.

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

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