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Acquisition Summary Data

The first four values that NASA SkyWatch will display on the Table Tab are the predicted time of Closest Approach, Satellite Rise, Satellite Set, and the Maximum Elevation. Note that all times in the acquisition summary data are expressed in local time of the observer location.

Satellite Rise is when the satellite will cross the observer horizon from negative to positive elevation (Acquisition of Signal). It is at this point that an acquisition is established (either visually or by electronic means). This value is generally to within 20 seconds of the true acquisition of signal. The error is a result of SkyWatch's inability to model terrain masking and its effect on line of sight inconsistencies. Oblate Earth effects are accounted for but the terrain around an observer is not.

Satellite Set is when the satellite will cross the observer horizon from positive to negative elevation. It is at this point where all line of sight acquisition is lost (Loss of Signal). As with Satellite Rise, the Satellite Set times are to within 20 seconds due to terrain masking.

Closest Approach is the time when the satellite is at its maximum elevation above the observer and is generally at the middle of the pass.

Maximum Elevation is the maximum angle (in degrees) above the horizon that the satellite will reach during the pass. Maximum elevation generally occurs at the time of closest approach. 90 degrees is a zenith pass and is straight overhead while a lower elevation pass (< 10 degrees) may be difficult to acquire due to atmospheric effects.

Curator: Kim Dismukes | Responsible NASA Official: Amiko Kauderer | Updated: 09/23/2011
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