An Introduction to GOES WEFAX

Weather Facsimile (WEFAX) is a communications transponder service provided through the GOES I-M satellites. WEFAX involves the retransmission of low resolution geostationary and polar orbiter satellite imagery or other meteorological data through the GOES I-M satellites to relatively low cost receiving units within receiving range of the satellite. WEFAX enables the greatest possible number of individual users to have access to the imagery products, or other data, relayed by the satellite systems. The WEFAX service is a continuation from the previous GOES Satellites. However, the GOES I-M WEFAX transmission is now an independent function and no longer interferes with other spacecraft functions. The GOES WEFAX service is not to be confused with WEFAX, which refers to the radio transmission of weather charts in the High Frequency bands, usually between 3.0 and 30.0 MHz. This service is provided by commercial and government radio stations as an aid to maritime activities, and not related to the NOAA GOES WEFAX.

The low-resolution geostationary and polar satellite images are produced at Central Environmental Satellite Computer System (CEMSCS) located at the NOAA NESDIS facility in Suitland, Maryland. This imagery is produced from the retransmitted GVAR (GOES VARariable data format) data streams received at the facility. The CEMSCS ingests these retransmitted GVAR data streams through a Front End Processor (FEP). Basic functionality provides Level 1A data set processing. Based on an automated schedule, the data are extracted into sub areas, reduced in spatial resolution, if necessary, and enhanced according to predefined look-up tables. The resultant WEFAX products are referred to as sectors. A sector, which is a spatial subset of the full earth disk corresponds to an area of interest to weather forecasters and similar users.

The generated sectors are then transmitted from Suitland as analog facsimile signals via dedicated telephone lines to the Wallops, Virginia Command and Data Acquisition (CDA) station for transmission through the GOES I-M.

WEFAX Historical Background

WEFAX was first introduced as a communications relay experiment on Applications Technology Satellites (ATS) -1, launched in December 1966, later included on ATS-3, and subsequently refined for incorporation on the new generation of satellites carrying a double nomenclature, Synchronous Meteorological Satellite (SMS) / Geostationary Operational Environmental Satellite (GOES). SMS/GOES satellites were developed by Philco-Ford Corporation and the National Aeronautics and Space Administration (NASA) for the National Oceanic and Atmospheric Administration (NOAA). SMS-1, the first prototype of the GOES series, was launched May 17, 1974. NASA's SMS-2 was launched February 6, 1975. The first NOAA funded satellite, GOES-1, was launched October 16, 1975.

The WEFAX dissemination from the SMS/GOES satellites, which began in 1976, was, and still is, on a down-link S-band frequency of 1691.0 MHz. In the early days of SMS/GOES, it was assumed that many potential WEFAX users already had Very High Frequency (VHF) Automatic Picture Transmission (APT) receiving stations operating in the 135 to 137 MHz region. These stations were used for receipt of ATS WEFAX and polar orbiting satellite APT. Technical standards for the SMS/GOES WEFAX dissemination were developed by National Earth Satellite Service (NESS), which allowed most of the existing APT ground receiving components to be used to receive SMS/GOES WEFAX. Although the transmission frequency from the spacecraft would be 1691.0 MHz, the 2400Hz sub-carrier signal characteristics, the type of modulation (AM/FM), and the image format were not changed. Therefore, the users' existing recording equipment could continue to be used. In addition, with a relatively simple S-band to VHF conversion kit, the existing receiver systems could also be used.

A brief explanation of the history and purpose of Coordination on Geostationary Meteorological Satellites (CGMS) is in order relative to the international aspects for positioning of the spacecraft in geostationary orbit. CGMS came into being in September 1972, when representatives of the European Space Agency (ESA), the United States, Japan, and observers of the World Meteorological Organization (WMO) met in Washington, D.C., to discuss questions of compatibility among Geostationary Meteorological Satellites. The meeting identified several areas, particularly for WEFAX dissemination, where both technical and operational coordination would be needed. The Soviet Union, having expressed it's intention to develop and operate a geostationary satellite, joined the small group of satellite operators at the second CGMS meeting in 1973. The WMO turned from its observer role at the first CGMS to full participation in the second CGMS meeting. Thus, since 1973, the WMO, ESA, Japan, the United States, and the USSR have cooperated in developing the technical elements and operational principles for the system of geostationary satellites. India, with planned geostationary satellites, joined the group at the 8th meeting of CGMS in 1978.

It was proposed at the second CGMS that five Geostationary Meteorological Satellites be placed in space. One important result in positioning the five proposed geostationary satellites was to achieve some overlap in the fields of view. This principle was sometimes contradictory to national or regional interests, and the geographical location of data reception stations and ranging stations also had influence. The resulting positioning compromise was as follows:

METEOSAT at 0 degrees - ESA, presently referred to as the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT)

GOES-East 75 degrees West - NOAA

GOES-West 135 degrees West - NOAA

Geostationary Meteorological Satellite (GMS) at 140 degrees East - Japan Meteorological Agency (JMA)

FY-2B at 105 degrees East - China Meteorological Agency (CMA). While not part of the original agreement, the CMA is transmitting WEFAX on 1691 MHz.

Geostationary Operational Meteorological Satellite (GOMS) at 70 degrees East - HYDRO MET, USSR, presently referred to as the Russian Committee for Hydro meteorology and Environmental Monitoring, ROSHYDROMET. GOMS is not operating.

In the early days of CGMS, the United States agreed to position GOES-East so as to make it visible from Lannion, France. Thus, in the METEOSAT WEFAX transmission schedule, provisions were made for receipt of WEFAX data from GOES-East to be relayed from Lannion, via METEOSAT, to users in the METEOSAT field of reception. For this reason, WEFAX transmissions from GOES East have been of first priority. Another important factor for locating GOES-East in view of Lannion was the plan for Lannion to receive stored sounding data from the TIROS series satellites and to relay the data to the NOAA computer complex using the GOES-East Data Collection System (DCS). In 1975, the satellite operators agreed to provide WMO with WEFAX schedules. These are still published by WMO, and updating the schedules is a continuing activity. (Current NOAA GOES WEFAX transmission schedules)

Geostationary environmental satellites launched by these nations as part of the First GARP (Global Atmospheric Research Programme) Global Experiment (FGGE) also provided WEFAX services. Compatibility exists among the WEFAX communications subsystems on all spacecraft which permits ships or fixed ground stations the option of selecting WEFAX broadcasts from whichever spacecraft best meets their data requirements.

On October 11, 1979, GOES-2 (after an earlier VISSR failure) was reactivated for WEFAX broadcasts and began operation as GOES-Central at 105 degrees West. The position was later changed to 107 degrees West to minimize the possibility of in-space collision of the spacecraft with space debris.

GOES-4 and GOES-5, the sixth and seventh spacecraft in this series, were launched on September 9, 1980 and May 22, 1981, respectively. The GOES-4 and GOES-5, spacecraft developed by the Hughes Aircraft Corporation, are significantly different from the earlier SMS/GOES spacecraft. Onboard were a visible and infrared spin scan radiometer (VISSR) atmospheric sounder (VAS). This instrument is a more sophisticated version of the VISSR on board the earlier GOES spacecraft. The VAS had a new capability, atmospheric temperature sounding for gathering infrared (IR) radiation data which can be used, with known atmospheric properties, to calculate atmospheric temperature profiles over a selected geographic area. With the positioning of GOES-4 as the GOES-West satellite, and the positioning of GOES-5 as the GOES-East operational satellite, the users receiving the WEFAX broadcasts from either of these satellites were required to change the polarity of their antennas. While the S-band antennas on SMS/GOES spacecraft through GOES-3 had linear horizontal polarization (polarization parallel to the place of the Equator), the GOES-4 and -5 spacecraft have parabolic antennas which have linear vertical polarization (perpendicular to the plane of the Equator). During the time of three simultaneous WEFAX transmissions, this difference required a user switching reception of broadcasts from either the GOES-East or -West to the GOES-Central, to change the polarity of the user's antenna.

With the failure of GOES-7, the VAS instrument concluded its usefulness in the GOES series of satellites. The newest series (GOES I - M) have a multi spectral imager that scans west to east and returns while stepping from north to south. While the earlier GOES were stabilized by having the satellite spin (at approximately 100 rpm), GOES I - M is 3-axis stabilized, or fixed in space. This provides a continuous view or "stare" on the weather across the western hemisphere. GOES-8, the first of the I - M series, was launched in April 1994.

The current analog WEFAX transmission will be replaced with a digital service, Low Rate Information Transmission (LRIT). Testing of LRIT will be carried out during 2003 and 2004, with alternating WEFAX and LRIT transmissions. By 2005, it is expected the NOAA GOES satellites will transmit only digital LRIT. The transmission frequency for LRIT will remain 1691 MHz, but will require changes to present receivers and the decoding and display software to accomodate a digital data stream. The advantage of a digital signal will be improved resolution or visual quality of the images and the addition of additional data to the transmission.

More information about the NOAA geostationary GOES and polar orbiting POES satellites.

The "User's Guide for Building and Operating Environmental Satellite Receiving Stations" discusses the WEFAX (and polar APT) transmission service in greater detail, and is available without charge by sending a request to the Email address below with your name, postal address, orginization and a brief statement of how you plan to use the guide. The National Technical Information Service (NTIS) has a limited number publications on issues pertaining to the GOES program, for sale.