image  received  from  a  polar-orbiting  satellite.  Once an image has been earth-located, you can then merge appropriate   geographical   boundaries   and   a latitude/longitude   grid   with   the   image.   Without accurate placement of a grid system, even the clearest high-resolution  images  are  nothing  more  than interesting   pictures.   Environmental   applications require the analyst or forecaster to be able to determine where a feature is and how fast it is moving, which is an impossible  task  without  an  accurate  reference  grid. Since geostationary satellites do not move relative to  the  earth,  their  ephemeris  data  does  not  need frequent   updates. However,   they   are   moved periodically and their positions are updated via special bulletins  as  necessary.  These  bulletins  are  posted  on the Internet at the NOAASIS web site. Several software programs are in use in various systems  to  automatically  calculate  polar-orbiting satellite   orbits   and   antenna-aiming   data.   The AN/SMQ-11 system and the SAT MOD both perform these  functions,  but  rather  differently.  TESS,  which may be used to control the AN/SMQ-11, also has a separate   orbital   prediction   function. Software upgrades are in development that will alleviate some of these differences. In this section, we will discuss how to interpret various  elements  of  ephemeris  information  from  the most   common   polar-orbiting   satellite   prediction bulletins.  The  exact  information  required,  as  well  as data entry methods for each system, are discussed in the individual operator’s manuals. Ephemeris data for each polar-orbiting satellite is available from several sources. Information for the NOAA  satellites  is  available  from  the  National Weather Service telecommunications center as NOAA APT Predict bulletins and from NASA as Two-Line Orbital Elements bulletins. Orbital information for the DMSP  satellites  and  all  foreign-operated,  polar- orbiting  satellites  is  available  from  the  Naval  Space Surveillance Center, Dahlgren, Virginia, as C-Element Orbital  Data  and  Satellite  Equator  Crossings bulletins. NOAA APT PREDICT BULLETINS (TBUS) NOAA  APT  Predict  bulletins,  because  of  the message’s data identifier TBUS, are more commonly referred to as TBUS data. These bulletins are routinely provided  over  the  WEFAX  broadcast  and  the automated weather network (AWN). They are also available  on  the  meteorological/oceanographic  data channel of the fleet multichannel communications broadcast, as well as via AUTODIN message. TBUS data can also be obtained from the Internet through the NOAASIS  website. The TBUS bulletins are in a special U.S. national code form. The code form is only used for orbital prediction  information  for  satellites  operated  by  the United  States.  Complete  information  on  this  code  is available in the NOAA KLM User’s Guide. Satellites in the TBUS bulletin are identified in the message header by name, such as NOAA 14, and by the U.S. satellite identification number, such as 37 for NOAA 12, and 38 for NOAA 14. In Part IV of the bulletin, the satellites are identified by an internationally recognized satellite number, such as 1994 089A for NOAA 14. A   separate   NOAA   APT   predict   bulletin   is composed daily for each operational NOAA series satellite. TBUS 1 bulletins are used to indicate north to south  (descending)  daylight  orbits,  and  TBUS  2 bulletins  are  used  to  indicate  south  to  north  (ascending) daylight orbits.  Each bulletin is composed of six parts: Part  I  contains  equator-crossing  reference information. Day  Part  II  contains  satellite  altitude  and subpoint coordinates in 2-minute intervals for reference  orbits  over  the  Northern  Hemisphere in the sunlight portion. Day Part III contains the altitude and subpoint coordinates for the portion of the reference orbits over the Southern Hemisphere in the sunlight portion. Night Part II contains 2-minute coordinates for the  portion  of  the  orbit  over  the  Northern Hemisphere in the dark sector. Night  Part  III  contains  coordinates  for  the portion   of   the   orbit   over   the   Southern Hemisphere in the dark sector. Part   IV   contains   high-precision   orbital calculation  elements,  transmission  frequencies, and  remarks. Parts II and III (day and night) are useful only when satellite orbits must be manually plotted and will not bediscussed further. TESS requires information from both Parts I and IV, while the SAT MOD and AN/SMQ- 11 require only information from Part IV. 1-31