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SHARAD ground intercept points


Jun
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have a question regarding the SHARAD RDR products. I noticed that the rdr.fmt

file describes several geographic parameters in each data record.

 

http://pds-geoscienc...1/label/rdr.fmt

 

Specifically, I see the SUB_SC_PLANETOCENTRIC_LATITUDE and SUB_SC_EAST_LONGITUDE.

 

I realize that this point may not coincide completely with the actual footprint of

SHARAD on the surface. That depends on how far off nadir the instrument aims.

Does SHARAD acquire data sufficiently off nadir such that I need to apply SC_YAW_ANGLE,

SC_PITCH_ANGLE and SC_ROLL_ANGLE to determine the Mars surface intercept points?

 

Are the ground intercept points perhaps described elsewhere in the rdr.fmt?

 

 

Thank you,

Jun

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Hi Jun.

 

the effective spacecraft orientation in space has no effect on the real position of the radar footprint. This is because the antenna of SHARAD has very little directivity, and in effect irradiates in all directions. The real position of the radar footprint is thus the portion of the surface which is closest to the spacecraft, which could or could not be the same as SUB_SC_PLANETOCENTRIC_LATITUDE and SUB_SC_EAST_LONGITUDE.

 

In general, the flatter (i.e. not sloping) and the smoother (i.e. not rough) the surface, the closer the radar footprint is to the computed spacecraft ground track. For sloping terrain (for examples, the flanks of Olympus Mons) the only way to know I can think of is to take the MOLA planetary radii dataset (not topography) and to compute the distance of all points in the vicinity of the ground track (up to a few tens of km, to be sure). The points which result the closest to the spacecraft are those from which the first echo recorded in SHARAD data originates. You can ths consider such area as the footprint of the radar.

 

Hope this helps.

 

Roberto

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Hi Jun.

 

the effective spacecraft orientation in space has no effect on the real position of the radar footprint. This is because the antenna of SHARAD has very little directivity, and in effect irradiates in all directions. The real position of the radar footprint is thus the portion of the surface which is closest to the spacecraft, which could or could not be the same as SUB_SC_PLANETOCENTRIC_LATITUDE and SUB_SC_EAST_LONGITUDE.

 

In general, the flatter (i.e. not sloping) and the smoother (i.e. not rough) the surface, the closer the radar footprint is to the computed spacecraft ground track. For sloping terrain (for examples, the flanks of Olympus Mons) the only way to know I can think of is to take the MOLA planetary radii dataset (not topography) and to compute the distance of all points in the vicinity of the ground track (up to a few tens of km, to be sure). The points which result the closest to the spacecraft are those from which the first echo recorded in SHARAD data originates. You can ths consider such area as the footprint of the radar.

 

Hope this helps.

 

Roberto

 

Thank you very much!

 

Jun

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