AEROGRAPHER'S MATE 3 & 2 



transparent orbital overlay, tracking diagram, 

 APT ephemeris predict message, and a clock. 

 The correct procedures for utilizing this equip- 

 ment and the ephemeris predict message are 

 discussed in chapter 10, Satellite Observations, 



METEOROLOGICAL SATELLITE 

 PLOTTING BOARD 



The APT plotting board is a polar projection 

 diagram of the earth centered at either pole 

 and extending 30 degrees of latitude past the 

 equator into the other hemisphere. The board or 

 diagram has radials from the pole representing 

 one-degree intervals of longitude ; each fifth 

 radial is accentuated. Concentric circles on 

 the projection represent latitudes. Tie equa- 

 torial latitude (zero degrees) is represented by 

 a heavier circle for clarity. (See fig. 6-14.) 



SATELLITE TRACKING 

 DIAGRAM 



If the altitude of the satellite and the distance 

 from the APT ground station antenna to the 

 satellite subpoint (the point on the earth directly 

 below the satellite at any given time during 

 its orbit, figure 6-15) are known, then the 

 elevation angle of the satellite may be com- 

 puted. The tracking diagram (an example is 

 shown as part of figure 6-16) provides a graphi- 

 cal solution of this equation. 



Tie tracking diagram was constructed to 

 show azimuth and distance of the satellite from 

 the APT ground station antenna for a given 

 subpoint position. The concentric curves (near 

 ellipses) are isopleths of great circle arc dis- 

 tance drawn at two-degree intervals. 



Azimuth is used directly in tracking. Arc 

 distance must be converted to elevation angle. 

 Tables are provided for this conversion. 



NOTE: The arc distances on the diagram 

 may be converted and labeled directly as ele- 

 vation angles if a circular orbit is achieved 

 (i.e., no change in satellite altitude through- 

 out the orbit). An elliptical orbit will require 

 frequent conversions through use of the tables 

 provided. 



SATELLITE 



SSP = SUBSATELLITE POINT 

 = ELEVATION ANGLE 

 h = ALTITUDE 



209.103 

 Figure 6-15. — Determining elevation angle of 

 satellite. 



A tracking diagram is available for each 

 5-degree latitude belt. The diagram for the 

 latitude closest to that of the ground station 

 should be used. 



TRANSPARENT ORBITAL 

 OVERLAY 



The transparent orbital overlay is a clear 

 plastic disk centered at the pole on the plot- 

 ting board. Notice the subpoint track plotted 

 in figure 6-17. The overlay is not apparent in 

 the figure due to its transparency; however, 

 the subpoint track of the satellite from which 

 data will be acquired is plotted on the overlay 

 rather than the plotting board. Tils prevents 

 marring the board and allows the plot to be 

 moved as needed. 



CLOCK 



It is necessary to have a station clock read- 

 ily available for the purposes of tracking the 

 satellite and determining the times of the pic- 

 tures. This clock should be accurate to +1 sec- 

 ond and should have an easily read second 

 hand. 



120 



