Geostationary Operational Environmental Satellites (GOES)

Information updated on Thu May 26 20:25:44 2005

General Data Description

Geostationary Operational Environmental Satellites (GOES) circle the Earth in a geosynchronous orbit over the equator. This means they observe the Earth from the exact same vantage point all the time. This allows the GOES satellites to continuously monitor a single position on the earth's surface from 35,800 kilometers (22,300 miles) above the earth. Currently, GOES satellites provide half-hourly observations of the Americas and their surrounding environment.

Upper Tropospheric Relative Humidity (UTH) which corresponds roughly to the mean relative humidity between 200-500 hPa is derived from GOES channel 3 (6.7mum) channel 4 (11 mum) and sun zenith angle. UTH is available in two separate data streams: one with the same resolution as the GOES data and another with a 0.5 degree gridded output.

GOES-7 data were originally received from the University of Wisconsin McIDAS system. Since July 1994, GOES data are downlinked to the Sea Space receiving station in San Diego. Images cover the Southern Great Plains.

A set of matching overlay files showing a latitude and longitude grid, state boundaries and the positions of the coastline and selected lakes and rivers are also available. The overlay files consist of an 'image' of value 1 everywhere, except at the positions of the features in which case the pixel value is zero. Thus the overlays can be written into the image by multiplying them together; the image data remain unchanged and the overlain pixels become zero. The images are distributed as short words, rather than bytes, to preserve accuracy. The overlay images are in byte format. The files containing the overlay images are available at the ARM Intensive Operation Period (IOP) Data Browser in the "ref-data" directory.

The GOES files are in hdf (generated in TeraScan by the tdftohdf routine - see "Data User Notes" for more information about these), and the metadata can be listed using the ncdump -h command of the hdf v3.3r3 (or later) release.

Data Stream Names

sgpgoesirX1.b1*
sgpgoesvisX1.b1*
* the two data streams above were eliminated. See BCR-663.

sgpgoes7rad8X1.a1
sgpgoes7radX1.a1
sgpgoes7visX1.a1
sgpgoes7irX1.a1
sgpgoes7ir8X1.a1

sgpgoes8X1.a1
sgpgoes8visX1.a1

sgpgoes12X1.a1
sgpgoes12visX1.a1

sgpgoes8irgridX1.a1
sgpgoes8irlat-longX1.a1
sgpgoes8irriversX1.a1
sgpgoes8irstateX1.a1
sgpgoes8visgridX1.a1
sgpgoes8vislat-longX1.a1
sgpgoes8visriversX1.a1
sgpgoes8visstateX1.a1

sgpgoes7minnisX1.c1
sgpgoes7minnis-acfX1.c1
sgpgoes7minnis-scmX1.c1
sgpgoes8minnisX1.c1
sgpgoes8minnis-acfX1.c1
sgpgoes12minnisX1.c1
sgpgoes12minnis-acfX1.c1

sgpgoes8uthX1.c1
sgpgoes8uthgridX1.c1
sgpgoes12uthX1.c1
sgpgoes12uthgridX1.c1

Measurement Description

GOES-7

The images are taken every half-hour, although there are many gaps in 
the temporal sampling.  The infrared images transmitted on the full 
hour are generally from Channel 7 (12.6 micron), Channel 8 (11.2 
micron) and Channel 10 (6.7 micron) and on the half-hour from Channels 
7, 8 and 12 (3.9 micron).  In some cases the channel 7 data are replaced 
by images from  channel 5 (13.3 micron). Both channels 5 and 7 are in 
the 10-13 micron atmospheric window, and therefore contain very similar 
signals, but of the two channel 5 is more influenced by the atmosphere.

sgpgoes7visX1.a1.yymmdd.hhmmss.hdf

GOES images                     Variable        Type    Units
satellite-solar azimuth angle   rel_azimuth     float   degrees
  satellite zenith angle        sat_zenith      float   degrees 
  solar zenith angle            sun_zenith      float   degrees
  Visible channel               vas_visible     byte

sgpgoes7irX1.a1.yymmdd.hhmmss.hdf

GOES images                     Variable        Type    Units
  satellite-solar azimuth angle rel_azimuth     float   degrees
  satellite zenith angle        sat_zenith      float   degrees 
  solar zenith angle            sun_zenith      float   degrees
  Ch 7 brightness temperatures  vas_ir7         short   temp_deg_c
  Ch 10/12 brightness temps     vas_ir10        short   temp_deg_c
                                vas_ir12        short   temp_deg_c

sgpgoes7radX1.a1.yymmdd.hhmmss.hdf

GOES images                     Variable        Type    Units
  satellite-solar azimuth angle rel_azimuth     float   degrees
  satellite zenith angle        sat_zenith      float   degrees 
  solar zenith angle            sun_zenith      float   degrees
  Ch 7 calibrated radiances     vas_ir7         short   radiance
  Ch 10/12 calibrated radiance  vas_ir10        short   radiance
                                vas_ir12        short   radiance

sgpgoes7ir8X1.a1.yymmdd.hhmmss.hdf

GOES images                     Variable        Type    Units
  satellite-solar azimuth angle rel_azimuth     float   degrees
  satellite zenith angle        sat_zenith      float   degrees 
  solar zenith angle            sun_zenith      float   degrees
  Ch 8 brightness temperatures  vas_ir8         short   temp_deg_c

sgpgoes7rad8X1.a1.yymmdd.hhmmss.hdf

GOES images                     Variable        Type    Units
  satellite-solar azimuth angle rel_azimuth     float   degrees
  satellite zenith angle        sat_zenith      float   degrees 
  solar zenith angle            sun_zenith      float   degrees
  Ch 8 calibrated radiances     vas_ir8         short   radiance

GOES-8

For each time there are two output files - one contains the 1km visible channel data, and ancillary fields, and the second contains all five channels at 4km resolution, together with the ancillary fields. The ancillary fields are the solar and satellite zenith angles, and sun-satellite azimuth angles.

Prior to February 10, 1995, the input files were only available with a resolution of 8 km in all channels. This was simply the result of temporary limitations on disk capacity.

Nearest neighbor sampling is used in the re-mapping.

The visible channel (ch1) image is in albedo units and is calculated using the prelaunch channel characteristics, and are stored as short integers in units of albedo(%)*100. The infrared channels are given as brightness temperatures, which are stored as short integers in units of ^oC; and angles are stored as floating-point numbers.

The scheduling of GOES images is controlled by NOAA and responds to the needs of the weather forecasting community. Our GOES data is collected and pre-processed by SeaSpace. The selection algorithm they use was intended to pick the GOES image that falls closes in start time to 15 and 45 minutes after the hour. That algorithm did not always work properly, but we do get for most days > 40 files per day. Visible channel data are processed only for the portions of the day when the Central Facility is sunlit.

sgpgoes8visX1.a1.yymmdd.hhmmss.hdf

GOES 8 images			Variable	Type	Units
  Visible channel 'albedo' 	gvar_ch1	 short	albedo*100%
  satellite-solar azimuth angle rel_azimuth     float   degrees
  satellite zenith angle        sat_zenith      float   degrees 
  solar zenith angle            sun_zenith      float   degrees

sgpgoes8X1.a1.yymmdd.hhmmss.hdf

GOES 8 images Variable Type Units Ch 1 'albedo' gvar_ch1 short albedo*100% Ch 2 brightness temperature gvar_ch2 short temp_deg_c Ch 3 brightness temperature gvar_ch3 short temp_deg_c Ch 4 brightness temperature gvar_ch4 short temp_deg_c Ch 5 brightness temperature gvar_ch5 short temp_deg_c satellite-solar azimuth angle rel_azimuth float degrees satellite zenith angle sat_zenith float degrees solar zenith angle sun_zenith float degrees time * time float minutes in the day

^* This is the time at which the pixel measurement was made. It appears beginning September 24, 1998. Note that several pixels will appear to have the same time. In the along-scan direction this is a consequence of the finite time increment used in the calculation of the pixel time, and can be improved upon, if necessary, by least-squares fitting a curve to the the pixels times to obtain times unique to each pixel. In the across-scan direction, the replication of pixel times is correct and results from the multiple detectors used in each channel. These detectors are aligned in a 'north-south' configuration, but away from the sub-satellite point and the Equator, the curvature of the earth causes inclination of the detector array when projected onto the Earth's surface away from the local meridians.

sgpgoes8uthX1.c1 and sgpgoes8uthgridX1.c1

sgpgoes12uthX1.c1 and sgpgoes12uthgridX1.c1

latitude and longitude (degrees)
Ch 3 brightness temperature (degrees K)
Ch 4 brightness temperature (degrees K)
satellite zenith angle (degrees)
upper tropospheric relative humidity (percent)

In addition for sgpgoes8uthgridX1.c1 and sgpgoes12uthgridX1.c1

number of valid channel 3 observations in grid cell average
number of valid channel 4 observations in grid cell average
number of valid UTH samples in grid cell average

GOES-12

GOES-12 data files are similar to GOES-8. The changes from GOES-8 are: 
The 6.7 micron water vapor channel (number 3) has a 4 km footprint 
instead of 8 km.
The 11.5-12.5 micron water vapor channel (number 5) was moved to 
12.9-13.8 microns (called channel number 6) and given a 8 km footprint 
instead of 4 km to determine cloud cover instead of volcanic ash and sea 
surface temperature.
The TeraScan routine fastreg uses bi-linear interpolation to 4km x4km 
output fields, so the changes in resolution of the input fields should be 
transparent to the user of these data.
The overlay files that were created for the GOES-8 data files can also
be used to overlay the GOES-12 data files.

Temporal Coverage

McIDAS GOES-7 files are available from January 17, 1994 - June 1, 1994.

GOES-7 files from SeaSpace are available from July 17, 1994 - April 6, 1995.

GOES-8 files are available from December 15, 1994 - March 31, 2003.

UTH files are processed for all available GOES-8 and GOES-12 files.

GOES-12 files are available beginning April 1, 2003.

GOES-12 files are available at the ARM Archive two days after the date generated. If files are missed in this "near real-time" processing, they may be filled in from tapes provided by SeaSpace approximately one month later.

The files provided by Pat Minnis' group are available a few months later.

Area Covered

For the GOES-7, GOES-8 and GOES-12 data received from SeaSpace, images are rectified to a Mercator projection, centered at the SGP Central Facility (36.605^o N, 97.485 ^oW).

Each image consists of 640 lines of 350 pixels. The pixel size is 1km for the visible channel images and 4km for the infrared channels.

The areas covered are 33.68 to 39.42^oN, 95.43 to 99.43^o W for the visible channel images, and 24.33 to 47.26^oN to 89.65 to 105.31^o W for the infrared channel images.

Data Stream Inputs

GOES-8

sgpgoes8X1.00
sgpgoes8visX1.00

GOES-12

sgpgoes12X1.00
sgpgoes12visX1.00

UTH

sgpgoes8X1.a1
sgpgoes12X1.a1
sgpgoesirlat-longX1.00.hdf

Notification Form Link

GOES-8 and GOES-12

Minnis GOES Products

GOES Diagnostic Files

Upper Tropospheric relative Humidity (UTH)

Contacts

ARM Mentor

Peter Minnett
Richard Wagener
For UTH algorithm Brian Soden

ARM Software Developer

Laurie Gregory for GOES-7 and 8 files

Li Hong Ma for GOES-12 files

Alice Cialella for UTH files

Data Source

Institution

McIDAS for early GOES-7 data

SeaSpace Corporation for GOES7, GOES8 and GOES12

Pat Minnis group at NASA Langley for Minnis Products

Processing History

October 1, 2002 - Processing of the UTH data streams began. Backprocessing will eventually create UTH data streams back to beginning of GOES-8 data stream.

Reprocessing History

Reprocessing Date

This information is currently unavailable.

Start End Reprocessing

This information is currently unavailable.

Reason Reprocessing

This information is currently unavailable.

FAQ

Question:
The SGP projection is listed as mercator with center lat 36.605N and center lon 97.485 W-- does this mean a traditional north south mercator with coordinate origins at these center values, or is it an oblique mercator?

Answer:
The HDF files at the archive are using regular (equatorial) Mercator projection:
line=scale*ln(tan(pi/4+lat/(2*radeg)))+offset,
where radeg=180/pi, and
where the arbitrary scale and offset are chosen such that (for example in the sgpgoes8X1.a1 datastream, see corresponding sgpgoes8irlat-longX1.00.hdf file):
line=0 for lat=47.21 and
line=639 for lat=24.32

Question:
How do you convert albedo units (for visible channels) and brightness temperatures (for IR channels) to sensor radiance? Answer:
For the IR channels you can recover the radiances from the Brightness temperatures by inverting the Planck Function. Depending on your accuracy requirements, you could use a central wavenumber or wavelength for each channel, or use the full spectral response functions. Either way, the most efficient method would be to build a Look-Up Table. The visible channels are converted to radiance and albedo using the pre-launch calibration. This is described at: http://www.oso.noaa.gov/goes/goes-calibration/goes-vis-ch-calibration.htm

Data User Notes

Short integer type bug

There is a known bug in earlier versions of tdftohdf which gives the incorrect data type code, 23, unsigned short integers, instead of 22, for signed short integers. If you use this information in converting the values read from the files to geophysical units, the answer may be wrong as the sign bit is misinterpreted. This affects most of the data currently available through the ARM Archive. Use of the information given in the HDF file header (metadata) gives the correct values.

Check for Data Quality Reports about these data at the DQR Browse Web Page

Information on reading hdf formatted files can be found at: Reading netCDF, HDF, and GRIB Files

Longitude/Latitude interpolations during map projection

The reason why the longitude, latitude variables in the sgpgoes8irlat-longX1.00.hdf are not constant along the perpendicular directions is because of the way they are derived. The latitudes and longitudes are derived first on the sensor scan coordinates. When those are projected onto the mercator projection the program does "nearest neighbor" interpolation, and it also does this on the latitude and longitude variables. So they make little jumps when the nearest neighbor jumps from one line to another because of the "curvature" of the longitude/latitude lines as seen from the sensor. This is more apparent in the AVHRR data where the sensor scan lines are significantly tilted from the E-W direction.

Another factor to consider is that there are inaccuracies in the spacecraft pointing caused by imperfections in the three-axis stability control. If the user is concerned about very accurate image navigation, the user should examine each image individually and adjust the geolocation by comparison with 'ground control points' - these are few and far between for the SGP, but the overlay file containing the position of rivers (sgpgoes8irriversX1.a1 and sgpgoes8visriversX1.a1) are intended for this purpose.

Time stamp on filename NOT time of first data sample

The start_time header attribute provided by NOAA refers to the beginning of the full disk scan, it is used in the time field of the HDF output file names. Since the area of interest is much smaller than the full disk, the time of first sample in the file is many minutes later than this start_time. This deviates from the standard ARM convention of naming the files with the time of the first data sample in the file.

Example Data

sgpgoes8irgridX1 image Overlay of latitude-longitude lines
sgpgoes8irlat-longX1 image Contains the latitude-longitude of each pixel
sgpgoes8irriversX1 image Overlay of rivers
sgpgoes8irstateX1 image Overlay of state lines
sgpgoes8visgridX1 image Overlay of latitude-longitude lines
sgpgoes8vislat-longX1 image Contains the latitude-longitude of each pixel
sgpgoes8visriversX1 image Overlay of rivers
sgpgoes8visstateX1 image Overlay of state lines

Note: overlay files contain an image that can be overlayed on a goes8 image by multiplying the overlay file and the image file.

The overlay files can be found at: The ARM Archive IOP Web page
in the ref_data directory.

Quicklook Links

SGP GOES 8 Satellite quick looks
SGP GOES Satellite Hovmuller Diagrams

Glossary

This information is currently unavailable.

Acronyms

GOES	Geostationary  Operational Environmental Satellites 
HDF	Hierarchical Data Format
McIDAS	Man computer Interactive Data Access System),
SGP	Southern Great Plains
TDF	Terascan Data Format
UTH	Upper Tropospheric relative Humidity

Citable References

Soden, BJ, RA Ferrare, WL Smith, JEM Goldsmith, D Tobin, DD Turner, and DN Whiteman. 2002. "A Satellite-Based Assessment of Upper Tropospheric Water Vapor Measurements During AFWEX." In Proceedings of the Twelfth ARM Science Team Meeting, Ed. by D. Carrothers, U.S. Department of Energy, Richland, WA.

Soden, B, S Tjemkes, J Schmetz, R Saunders, J Bates, R Ellingson, R Engelen, L Garand, D Jackson, D Jedlovec, T Kleespies, D Randel, P Rayer, E Salathe, D Schwarzkopf, N Scott, B Sohn, S de Souza-Machado, L Strow, D Tobin, D Turner, P van Delst, and T Wehr. 2000. "An Intercomparison of Radiation Codes for Retrieving Upper-Tropospheric Humidity in the 6.3-mm Band: A Report from the First GVaP Workshop." Bulletin of the American Meteorological Society 81: 797-808.

Spangenberg, DA, GG Mace, TP Ackerman, NL Seaman, and BJ Soden. 1997. "Evaluation of Model Simulated Upper-Tropospheric Humidity Using 7.8 Micron Satellite Observations." J. Geophys. Res. Vol. 102 , No. D22 : 25,737.

Soden, BJ and FP Bretherton, 1993. "Upper tropospheric humidity from the GOES 6.7 micron channel: Method and Climatology for July 1987." J. Geophys. Res. Vol. 98, 16669-16688.

Table of Contents

Geostationary Operational Environmental Satellites (GOES)

Information updated on Thu May 26 20:25:44 2005

General Data Description

Data Stream Names

Measurement Description

Temporal Coverage

Area Covered

Data Stream Inputs

Notification Form Link

Related Links

Contacts

ARM Mentor

ARM Software Developer

Data Source

Institution

Processing History

Reprocessing History

Reprocessing Date

Start End Reprocessing

Reason Reprocessing

FAQ

Data User Notes

Example Data

Quicklook Links

Glossary

Acronyms

Citable References