AEROGRAPHER'S MATE 3 & 2 



DMSP. — Within the Navy this satellite sys- 

 tem uses an Air Force satellite in conjunction 

 with the Navy tracking equipment, TMQ-29 

 (ashore) and SMQ-10 installation (shipboard). 

 The DMSP routinely employs two polar orbiting 

 satellites; both have visual and IR scanning 

 radiometers. Direct real-time readout of re- 

 gional data is provided to selected military 

 locations around the world. Data for the entire 

 globe is provided to the Air Force Global 

 Weather Central, Offutt AFB, several times per 

 day. This system was developed with the pri- 

 mary objective of providing maximum respon- 

 siveness to the military decision maker. 



APT Predict Message 



In order for Naval Weather Service person- 

 nel to utilize the facsimile picture for meteoro- 

 logical purposes, certain information must be 

 furnished. Full utilization of the picture data 

 depends upon acquiring a video signal trans- 

 mitted by the satellite, geographically locating 

 the picture center, orienting the picture into 

 the correct geographical aspect, and extracting 

 the meteorologically significant data. 



In order to track the satellite and to locate, 

 orient, and grid the facsimile picture, personnel 

 operating the ground equipment require certain 

 satellite predictive data; the APT daily pre- 

 dict message provides this required information. 



The APT predict messages are provided 

 routinely to Navy users in two different forms. 

 One form is a daily teletype message, the other 

 is the WEFAX message. Both messages contain 

 identical information. The message contains all 

 the necessary information required for tracking 

 the satellite during normal operations. 



The APT predict message contains a head- 

 ing and four parts. For the convenience of 

 the user, daylight and night portions of the 

 message have been separated. 



Part I contains information pertaining to 

 the reference orbit, and to orbits four, eight, 

 and twelve. Information contained in this part 

 includes the time and location of the crossing 

 at the Equator of the reference orbit, nodal 

 period, nodal increment, and the time and place 

 of the crossing of the Equator for the fourth, 

 eighth, and twelfth orbits; these orbits are in 

 relation to the day of the predict message. 



Part II (day) contains the satellite's altitude 

 and subpoint data at 2-minute intervals over the 

 sunlit portion of the orbit north of the Equator. 



Part II (night) contains the satellite's altitude 

 and subpoint data at 2-minute intervals for the 

 portion of the orbit which is in darkness north 

 of the Equator. 



Part in (day) contains the satellite's altitude 

 and subpoint data at 2-minute intervals over 

 the sunlit portion of the orbit south of the 

 Equator. 



Part IE (night) contains the satellite's alti- 

 tude and subpoint data at 2-minute intervals 

 for the portion of the orbit in darkness south 

 of the Equator. 



Parts II and III provide data for plotting the 

 subpoint track. The 2-minute intervals used 

 are based on the ascending node of time and are 

 given as minutes after or before this time. 



Part IV is reserved for any remarks perti- 

 nent to the operation of the system, including 

 the orbital elements of polar orbiting satel- 

 lites. These elements will be updated peri- 

 odically. In addition, messages concerning polar 

 orbiting satellites contain the current scanning 

 radiometer calibration temperatures. 



The symbolic format of the APT predict 

 message is contained in the NOAA direct trans- 

 mission user's manual and other appropriate 

 satellite manuals. 



Tracking and Satellite Location 



The task of keeping the receiver tuned and 

 the antenna pointed at the satellite for receipt 

 of the incoming data Is referred to as "track- 

 ing." 



For proper satellite tracking, the location of 

 the satellite in relation to the ground equipment 

 must be known for the entire period that the 

 satellite is within range of the ground equip- 

 ment. Depending on the satellite, it will first 

 appear as it crosses either the southern or the 

 northern horizon. From the time the satellite 

 comes within the line of sight until it disappears 

 over the opposite horizon, the antenna of the 

 ground equipment must always be pointed at 

 the satellite. In order to train the antenna on 

 the satellite, the proper azimuth and elevation 

 angles must be known. 



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