GOES Tech Notes last update 16 February 2007

Table of Contents

• GOES I-M Databook
• GOES N-P Databook
• GOES Project at NASA-GSFC
• SOCC Pages
• Commercial Vendors
• Status Reports
• Assessments
• Schedules
• Technical Details
  • Spacecraft
  • Spectrum
  • Calibration
  • Navigation
  • Acuity
  • Documentation
  • GVAR
  • Paperwork
  • Problems

GOES I-M Databook

GOES N-P Databook

GOES Project at NASA-GSFC

• Project Documents
• GOES Acronyms (PDF)

NESDIS Office of Satellite Operations (OSO), GOES

• Wallops Command and Data Acqusition (WDCA) Facility

Commercial vendors of GOES data reception systems

Status Reports

• Satellite Services Division (SSD)
• GOES subsystems status
• GOES and other geo-satellite news and status reports
• NOAA-NESDIS Satellite Information Service (SIS), weekly operations notes, technical reports and publications
• NOAA Satellite Operations Schedule for GOES-EAST and GOES-WEST
• Brief status report for the geosynchronous weather satellites in the western hemisphere

Assessments

National Weather Service (NWS) Programs

• Initial GOES Assessment Report
• NWS GOES Assessment Plan
• NWS 1998 GOES Assessment Meeting Summary

Schedules

Standard Schedules

• GOES-8 (GOES-EAST) Imager routine operations schedule for the 24 hour day, deduced from springtime operations in 1995. NOAA has 3 operational scan scenarios:

       In the GOES routine schedule scan mode, two views at approximately 15 
       minute intervals of the CONUS (GOES-8) or PACUS (GOES-9) are provided in a 
       half hour period.  A northern hemisphere scan is also included in the 30 
       minute cycle.
       
       During GOES Rapid Scan Operations (RSO), 4 views of the CONUS (GOES-8) or 
       Sub-CONUS (GOES-9) are provided at approximately 7.5 minute intervals in a 
       half hour period.  A northern hemisphere scan for both GOES is also 
       included in the 30 minute cycle. 
       
       During GOES Super Rapid Scan Operations (SRSO), approximately 10 one minute 
       interval scans are provided every half hour using prescribed 1000x1000km 
       sectors.  The remaining time in the half hour cycle is devoted to scans of 
       the northern hemisphere and CONUS (GOES-8) or Sub-CONUS (GOES-9).
       
       When GOES RSO or SRSO is utilized, most of the southern hemisphere is not 
       scanned. 
  

  The corresponding GOES-8 schedules are:
  • Routine
  • Rapid
  • Super-rapid
• GOES-9 (GOES-WEST) Imager routine and rapid-scan operations schedule for the 24 hour day.
  Meanwhile, witness a day of GOES-WEST operations as an MPEG movie.
• The routine schedule is always altered by events described in the GOES operations schedule for this week.
• In a Simulated animation of NOAA's standard 3-hour operational cycle, the progress of GOES-8 images are updated at 5-minute intervals, showing the progress of north-to-south scans. The small CONUS and South American images take just 5 minutes to acquire. About 10 minutes out of every hour is used by GOES-8 for radiance calibration and stellar navigation instead of Earth-imaging. A full earth disk takes almost 30 minutes, and is taken once every 3 hours.
• Compare the ideal cycle to an actual frame-by-frame animation of the 24-hour cycle, constructed from observations on December 27th in the 11 micron channel. There are similar animations in other channels on other days.
• List of the springtime eclipse periods for GOES-7 and GOES-8.
• NOAA's WEFAX page.
  • GOES-EAST (GOES-8) WEFAX schedule
  • GOES-WEST (GOES-9) WEFAX schedule
• NOAA's Special Bulletins about Satellites
• All Operational WEFAX problems should be first addressed to the NOAA QC POC, Sam Patterson.

  Samuel Patterson
  DOC/NOAA/NESDIS
  FB4 Rm. 0312 E/SP11
  Suitland Federal Center
  Suitland, Maryland 20233
  Voice: 301-457-5205  Fax: 301-457-5199
  spatterson@nesdis.noaa.gov
  

• If the GOES data stream seems corrupted, call SOCC
• Chuck's Hobby Home Page. Contains introductory information about WEFAX reception and sample images.
• For completeness, here is a schedule for WEFAX from METEOSAT.
• The full-Earth images are internationally coordinated with the other geo-satellites to make a synoptic cloud analysis of the globe every 3 hours.
• NOAA's science tests of GOES-9 in the first two weeks of September.

Special Schedules

Technical Details

Spacecraft

Spectrum

• GOES spectral response curves are available via anonymous FTP from NASA-GSFC. More up-to-date filter functions are available from NOAA-NESDIS.
• Some spectral response curves are also available via HTTP from NASA-GISS

Calibration

• Imager Calibration coefficients, formulas, and advice direct from NOAA.
  • GOES image calibration is performed using NOAA's calibration coefficients embedded in the broadcast GVAR data stream.
  • NOAA Technical Memorandum NESDIS 44, "Operational Calibration of the Imagers and Sounders on the GOES-8 and -9 Satellites", Mike Weinreb, et al.
  • The trend in decreased throughput for the visible channel on the Imager is several percent per year (7.7% for GOES-8 and 5.0% for GOES-9), based on the apparent brightness of stars. The decrease fits an exponetial curve. It is due to radiation darkening of the coating used on the scan mirror. Unfortunately, the same coating is being used for all the ITT instruments, at least through GOES-O.
  • The time series of the responsivities of the GOES Imagers' visible channels, determined from repeated observations of 40 stars, have been extended to May 2002. Averaging the results from all 40 stars, the yearly losses in responsivity for the visible channels of the Imagers on GOES-8 and GOES-10 were found to be 5.3 +/- 0.11% and 6.9 +/- 0.13%, respectively. Until GOES-9 was deactivated in May 1998, the visible channel on its Imager lost 5.4 +/- 0.28% per year.
• Imager Calibration coefficients, formulas, and advice from here at NASA.
• GOES-8/9 Imager and Sounder Calibration coefficients, copied from NOAA memos in the mid-1990's.
• Sounder Calibration coefficients, formulas, and advice (under construction).
• There are always issues:
  • Calibration-Validation Overview.
  • There is upper/lower detector striping due to independent calibration of the two infrared detectors used to make this high contrast picture using channel 5 (12 microns) to observe the upper east coast of the USA in September 1994.
  • After launch, there was a noticeable east-west calibration error in the apparent brightness of outer space at 11 microns because the scan mirror emissivity and reflectivity changes by a few percent across the scene. A software correction has been installed in the ground system to correct for the effect.
  • Imager calibration was worked in the post-launch tune-up of GOES-8.
  • Sun glare at midnight:
    • Sun glare movies for August 24th, in the GOES-8 visible, with less in the 3.9 micron IR, and not apparent in the 11 micron IR. Glare and glint are unavoidable problems in geosynchronous orbit. GOES-7 and GMS-4 suffer similar glare at their local midnights. Normal sun glint occurs in reflection from the oceans and clouds when the sun is behind and to the side of the satellite.
    • Photo composite of GOES-8 hourly images with significant sun glare near local midnight (06:00 UTC) on July 24th, in the visible, and less so in the 3.9 micron IR, but not apparent in the 11 micron IR.
    • Sun glare will also upset radiometric calibration for 2 hours on either side of midnight during the month before and after the spring and autumn equinoxes, especially in channel 2 every July. By August, scattered sunlight in the face of the GOES-8 Imager near midnight shows up in almost every channel: visible, 3.9 microns, 6.7 microns, 11 microns, 12 microns.
• The infrared detectors in the SN04 Imager on GOES-9 are the most sensitive ones used in the entire GOES-I/M series:

          A preliminary assessment of the performance of the infrared channels 
  of the GOES-9 Imager was made on June 16, after the detector-patch 
  temperature had stabilized at 101K.  GOES-9 performance, in general, beats 
  specification and GOES-8 performance.  The responsivities of all seven IR 
  detectors were within 2% of their prelaunch values.  It is noteworthy that the 
  significant responsivity losses that affected channels 2 and 3 of 
  the GOES-8 Imager were not reproduced on GOES-9.  (The higher responsivity 
  in GOES-9's channel 2 still allows the sensor to observe a maximum scene 
  temperature of approximately 325K.)
  
  Noise in the GOES-9 Imager's IR channels, tabulated below, is far 
  lower than the specified maxima and even below the GOES-8 values.
  
             NOISE (in degrees K @ 300K, unless otherwise noted)
  
      Channel        GOES-9      GOES-8   Specification (max)
  
        2A            0.11        0.20         1.4
        2B            0.11        0.22         1.4
        3              0.14        0.18         1.0  (all values at @ 230K)
        4A            0.09        0.12         0.35
        4B            0.08        0.10         0.35
        5A            0.18        0.22         0.35
        5B            0.19        0.22         0.35
  

• The visible channel on GOES-9 is about 16% (+-2%) more sensitive than GOES-8's, according to a test conducted by Mike Weinreb at NOAA-NESDIS in July 1995.
• Radiance saturation in Channel 2 is a problem for GOES-9 and GOES-10. Because of the strong nonlinear increase in radiance with temperature and reflected sunlight at 4 microns (Imager channel 2), this channel can saturate over sunglint oceans, hot deserts, and large wildfires. This is particularly common with the Imagers on GOES-9 and GOES-10, where the saturation level corresponds to 320 K. On the other Imagers, the saturation level is between 330 K and 340 K, and radiance saturation is rare.

Navigation

• Imager Navigation advice
• NESDIS provides a GOES Earth Location Users Guide (ELUG) and GVAR Users Guide. Here are the March 1998 versions of these documents converted (imperfectly) to PDF format :
  • GOES Earth Location Users Guide, without Appendix C
  • Appendix C to the GOES Earth Location Users Guide
  • GVAR Users Guide
• The GVAR coordinate system, in N-S detector-by-detector scanlines and sample-by-sample (oversampled) pixels, is sketched
  • for GOES at 75W
  • for GOES at 90W
  • for GOES at 135W
  to help the user select regions using satellite coordinates.
• GOES altitude and azimuth with respect to the horizon at Goddard Space Flight Center.
• Excel 4 spreadsheet used for calculating the altitude and azimuth of a GOES satellite from any observer on Earth.
• FORTRAN code to "navigate" GOES-8 Imager pixels, converting line-pixel to/from latitude-longitude. The FORTRAN code was originally developed by ISI Corp. before launch, and modified by NOAA-NESDIS after launch. If usually needs small modifications to run under your local FORTRAN compiler.

Acuity

• Imager acuity is set by NOAA's reqirements on the Modulation Transfer Function (MTF) for resolving high spatial frequencies in each channel.
• Sounder acutiy is set by NOAA's requirements on the encircled energy.

On-line Documentation

• GOES I-M DataBook
• NASA-GSFC GOES Project - on-line technical reports
• NESDIS's list of GOES documentation
• NOAA technical report NESDIS-82: An Introduction to the Goes I-M Imager and Sounder Instruments and the GVAR Retransmission Format
• NOAA technical report NESDIS-40: GOES Data Collection System
• NESDIS-OSO-OSD download site for technical documentation about Earth location and GVAR.
  • Earth Location Users Guide (ELUG), revision 1, March 1998 in MS-WORD format.
  • Earth Location Users Guide (ELUG), appendix C, "Kamel to Keplerian Transformation" in MS-WORD format.
  • Earth Location Users Guide (ELUG), revision 1, March 1998 in MS-WORD format.
  • GVAR Transmission Format in PDF format.
  • GVAR Transmission Format in WordPerfect 6 (DOS) format.
  • GVAR Transmission Format in WordPerfect 4 (Mac) format.
  • We also have a chaotic copy in several file formats of 1995's Revision D of the detailed documentation for NOAA's Operational Ground Equipment (OGE), especially for the demonically complex GVAR format for broadcasting Imager and Sounder data.
• SSEC's 1993 documentation of McIDAS file format for satellite data, and a rough draft of their 1995 MCIDAS documentation.

GVARIngest and image processing

You can order raw broadcast data from the NOAA-NESDIS Satellite Active Archive (SAA), in the GOES format known as GVAR.

NASA copies of GVAR Documentation

• NOAA's GVAR Users Guide (circa 1998)
• SOCC's on-line information about GVAR
• Description of the GOES data ingest and file service system at NASA-GSFC. (PDF format, from the SPIE 96 Conference "GOES-8 and Beyond")
• NASA-developed portable C++ code to read GVAR format and convert it to standard image format, with many user-selectable options.
  • 1998 version of "gvar", for GOES-8/9/10, with some updates for later satellite and portability to linux platforms.
    How to compile?

    Date: Thu, 15 Oct 1998
    From: Craig Mayhew
    Subject: gvar processing
    
    If your compiler does not have the header file stream.h then it is
    probably not designed to compile C++ as we know it.  To get a compatible
    compiler for the SUN you may need to get the GNU C++ compiler.  It is
    free to download from:
    
    ftp://gatekeeper.dec.com/pub/GNU/
    
    You will need the files:
    
    gcc-2.8.1.tar.gz
    libstdc++-2.8.1.tar.gz
    
    These archives should contain instructions for building the compiler. 
    If you do not have any compiler then you can get a binary file for the
    SUN from:
    
    ftp://sunsite.unc.edu/pub/solaris/sparc/
    
    You can get binaries for Solaris 2.4, 2.5, 2.5.1, or 2.6.  You can even
    get the latest version (2.8.1) which should contain all of the files you
    need to build gvar.
    
    The gvar program has had some changes made to work with the GOES-10
    satellite which operates in an inverted mode.  I have placed the most up
    to date source in:
    
    ftp://goes.gsfc.nasa.gov/pub/goes/
    
    The file  gvar.tar.gz  contains all required source code.  It is exactly
    a tar of the gvar directory that you will see there.
    
    -- 
    Craig Mayhew
    Science Systems and Applications, Inc.
    Goddard Space Flight Center
    mayhew@agnes.gsfc.nasa.gov
    

• Notes about the changes in GVAR format anticipated for GOES-M/N/O, as of 2001.

Paperwork

• Order old GOES data from NOAA's archives.
• Standard form for registering a ground receiver with NOAA, such as a WEFAX or GVAR receiver, so they can justify public broadcasts and help you with radio interference problems.
• Another, less technical form for registering a ground receiver with NOAA, such as a WEFAX or GVAR receiver, so they can report you to the WMO. If your browser supports "forms", register on-line with NOAA.
• Or, just register directly with the WMO, which is considering de-allocating the weather satellite frequencies so that the cellular phone people in Brazil can chat on the weather bands.

Problem Areas

• "Lessons Learned From the GOES Experience" - OTA, 1993, a review of the difficulties with getting GOES-I on-line.
• Some examples affecting image quality
  • Image shear due to errors in the assembly of east-west scans.
  • Image jogs due to attitude adjustments.
  • North-south scanline misplacement, due to erroneous scanline labeling.
• Approximately 5% of the Imager's landmark location errors are larger than 4 km (the goal is 1%), with slow drifts and occasional bumps and jumps. Spacecraft motions were minimized early in 1995. The larger "bumps" in time-series animations are caused by imperfections in the earth sensor, in navigation software, and in operating procedures. Pointing quality improved noticeably during May and June 1995, when software and procedures were tuned-up.
• There are significant jiggles due to sunglint near midnight (0400 to 0600 UTC) in the earth-sensor. Software is being used as "shock absorbers" during this jiggle, reducing point errors from 80 km to 8 km. Image navigation jumps whenever NOAA updates the orbital parameters during one of the four "housekeeping" events (currently at 0300 UTC). Near equinox (mid September and mid-March), the shadow of the magnetometer on the anti-earth side of the satellite falls on the north-pointing boom in the afternoon of every day, tipping the satellite for less than an hour.
• There are two earth sensors which scan an east-west chord back-and-forth at 45N and 45S latitude, centering the satellite between the limbs of the earth. When the sun or moon intrudes on the limb of the earth, the north or south sensor is ignored ("single chord" mode). Unfortunately, the single chord mode introduces a north-south tip in the satellite attitude that affects the images just after switching in and out of the single chord mode.
• In winter, the Sun shines from below the satellite, and the magnetometer boom casts a shadow onto the north-pointing ballance boom around local noontime. The boom suddenly cools and snaps, wobbling the spacecraft. For GOES-EAST, the snap occurs in the winter afternoons around 1915 UTC.
• The secondary mirror overheats when the Sun is within 8.5 degrees of the optical axis, leading to a "keep out" zone around the Sun which is the angular diameter of the Earth. During the spring eclipse season, the total downtime for GOES-8 is at least an hour longer than for GOES-7 to deal with the keep out-zones and the more complex shut-down/wake-up procedures.
• GOES-8 Imager calibration has a few percent residuals to be removed by the end of 1995. Software corrections for the mirror emissivity in the Imager were installed early in May 95, and are successful. The GOES-8 Sounder corrections for mirror emissivity, originally scheduled for June 95, were postponed until December 95, and then again until March 96.
• Contamination-induced decreases in the responsivities of the GOES-8 Sounder's infrared channels have been kept to a minimum by weekly heating of the sounder's vacuum housing. The heating, which do not interrupt normal operations, are carried out every Thursday between September and April and last for 24 hours. Despite this, the responsivities did decrease slightly over the long term. For example, in 1995, channel 9 (9.6 micron) lost approximately 4%. On January 24-26, 1996, SOCC will carry out a one-time 72-hour heating of the vacuum housing in an attempt to restore the lost responsivity. Normal sounder operations should not be affected during these 72 hours.
• NOAA is smoothing day-to-day infrared calibration coefficients one the Imager to minimize detector-to-detector striping and sun glare effects near midnight. Detector-to-detector differences vary from scanline-to-scanline, giving highly amplified scenes a faintly striped appearance that is noticeable on cold cloudtops and uniform sea surfaces.
• The responsivity in channel 4 of the GOES-9 Imager has been decreasing steadily by approximately 1.9% per month since October 30, 1995, the date the most recent outgassing of the imager was completed. So far, the responsivity loss has not caused any significant degradation in data quality, so our only action has been to monitor the trend. If this trend continues, at some point in the next year or so we will have to consider outgassing the instrument again. This will interrupt the acquisition of data in the infrared channels for at least a day.
• RF interference at the GVAR broadcast frequency, 1685 MHz, from the first harmonic of cellular telephone tower broadcasts in the 840-850 MHz band. This is a problem for many GOES receivers in urban areas.
• The GOES-8 Imager's visible channel suffers from "salt-and-pepper" noise. The problem is correlated with the intensity of energetic particles at the satellite. Radiation-induced spikes are suspected in the sensitive front-end amplifier, which is not as well shielded on GOES-8 as on the following satellites.
• The NWS radiosonde broadcasts (1675-1685 MHz) sometimes interfere with the GVAR broadcast frequency at 1685.7 MHz. This shows up as hour-long flurries of line drops at 0000-0100 UTC and 1200-1300 UTC every day. If you are having trouble like this, contact:

  Dave McGinnis,  NESDIS Frequency Manager
  Office of Systems Development
  National Environmental Satellite, Data. and Information Service/NOAA
  U.S. Department of Commerce
  Room 3301, Federal Building #4
  Washington, D.C. 20233
  Voice:  301-457-5125
  Fax:  301-420-0932
  E-mail:  dmcginnis@nesdis.noaa.gov