imagery, like the APT direct-broadcast imagery, is received  unprocessed  and  ungridded.  Many  user- operated  satellite  receiver  systems  are  unable  to receive and process I-IRPT imagery. The IMOSS satellite module cannot receive or process HRPT, while the AN/SMQ-11 is able to receive and process the signal. High-resolution  imagery  may  also  be  stored aboard the satellite, downloaded to a Command Data Acquisition (CDA) station on command, and sent to NESDIS  in  Suitland,  Maryland.  NESDIS  processes the  imagery,  adds  gridding,  and  forwards  the processed signal to other imagery services. NESDIS operates  two  CDA  stations  for  both  the  NOAA  and GOES  satellites: Wallops  Island,  Virginia,  and Fairbanks,  Alaska. The  Department  of  Defense operates its own CDA stations for the DMSP satellites. WEFAX SERVICE Another  method  for  receiving  satellite  imagery  at your ship or station is to copy a WEFAX (weather facsimile) broadcast from a geostationary satellite. WEFAX  is  the  retransmission  of  low-resolution infrared and visible satellite imagery from U.S. GOES satellites to any receiver capable of copying the signal. WEFAX   transmissions   are   also   available   via METEOSAT,  GMS,  and  other  foreign  satellites. The U.S. GOES WEFAX service provides visual and infrared sectors as well as full disk imagery. The service  also  includes  selected  meteorological  and oceanographic   charts,   TBUS   bulletins,   and operational messages. You can check the NOAASIS web site for information on active WEFAX broadcasts, broadcast   content,   and   frequencies.   Information concerning GOES schedules is also available via the Internet.  Detailed  information  on  WEFAX  services  is provided  in  the  WEFAX  User’s  Guide  issued  by NOAA/NESDIS. Each  GOES  satellite  provides  high-resolution imagery that is transmitted on a high-frequency signal to the CDAs and processed at NESDIS. NEDSIS processes t h e    s i g n a l    t o add   gridding (latitude/longitude),  geographical  boundaries,  borders for land and water masses, and enhancement. The CDAs then retransmit the processed signal back to the satellite for WEFAX transmission. In turn, the satellite retransmits the WEFAX signal back to earth on a lower frequency  signal  for  reception  by  user-operated satellite receivers. The service is generally provided at frequencies near 1691 MHz. The WEFAX signal is much weaker than the APT or   HRPT   signal   from   polar-orbiting   satellites. Normally, a directional antenna with antenna polarity control circuits is necessary to copy the WEFAX signal. The AN/SMQ-11 is fully capable of capturing the WEFAX signal. The IMOSS satellite module can also receive and process the WEFAX signal by using a special  directional  antenna  specifically  designed  to copy the broadcast. Directional  antennas  should  be  aimed  at  the broadcasting  geostationary  satellite  for  the  best WEFAX  reception. Instructions  for  aiming  the IMOSS WEFAX antenna are available in the  Interim Mobile  Oceanography  Support  System  (IMOSS) User’s  Guide.  Appendix C of the guide contains diagrams for calculating elevation and azimuth angles for  different  geostationary  satellites. Be aware that although international agreements call  for  five  operational  geostationary  satellites, problems occasionally arise that require satellites to be moved temporarily to slightly different locations. WEFAX   may   also   be   broadcast   from   older geostationary  satellites  that  have  been  moved  out  of the  primary  position. Figure  1-23  is  a  diagram frequently used to calculate the azimuth (degrees true) and elevation angles needed to find any geostationary satellite located over the equator. To   use   the   diagram,   the   user   subtracts   the longitude of the receiver location (site longitude) from the longitude of the satellite to find delta (D), (ignore the sign). Using the value of D (scale on the left side of the  diagram  with  80  degrees  at  the  bottom  and 3 degrees at the top), follow parallel to the drawn lines sloping downward toward the right. Using the receiver station latitude (site latitude) on the G scale (right side of the diagram), follow parallel to the lines sloping downward toward the left to the intersection of the D value. The antenna elevation angle (look elevation) is found by drawing a horizontal line toward the left to the look elevation scale. The antenna azimuth is found by  drawing  a  vertical  line  downward  to  the  look azimuth scale. The four azimuth scales are used as follows: SW - When receiver is south of the equator and west of the satellite’s position SE - When the receiver is south of the equator and east of the satellite’s position NE - When the receiver is north of the equator and east of the satellite’s position 1-25