Viewing Parameters (INCIDENCE_ANGLE,...) for HRSC images ? Options

[Nirgal]

Hi,

Does anyone know if/where the INCIDENCE_ANGLE & SUB_SOLAR_AZIMUTH parameters are available for a given MEX/HRSC observation ?

For HiRISE those parameters are usually published in the HiRISE Observation Toolbox or as part of the standard RDR product label file like this for example:

CODE

GROUP = VIEWING_PARAMETERS
    INCIDENCE_ANGLE   = 61.388593 <DEG>
    EMISSION_ANGLE    = 4.314944 <DEG>
    PHASE_ANGLE       = 57.393195 <DEG>
    LOCAL_TIME        = 15.59382 <LOCALDAY/24>
    SUB_SOLAR_AZIMUTH = 156.071516 <DEG>
END_GROUP = VIEWING_PARAMETERS

Maybe I overlooked something, but for MEX/HRSC I could not find those parameters among the parameters listed in one of the ( published standard HRSC/PDS products

Calculating those values oneself using ISIS3 (via the "campt" application) would be an option but then the raw intrument data would be needed which does not seem to be straightforwardly available for HRSC observations ...

Thanks for any help with this,
Bernhard

[mwolff]

Hi,

although you may have thought about this, but are interested in a tabular source or something similar. Nevertheless, I will mention it just in case. As long as you know image/pixel latitude, longitude, and UT time, you can obtain that which you seek by calculating the sub-solar latitude and longitude using NAIF (only requires basic solar system kernels, and possibly an SCLK kernel if want to use the MEX SCLK, MICA, or some other ephemerides software. With this info (and the target lat, lng), the incidence angle and azimuth can be computed from spherical trig.

If you are interested, but don't care for spherical trig, I will dig up my derivations (I never remember this stuff and usually have rederive it each time unless I write it down).

regards,

--mike

Hi,

Does anyone know if/where the INCIDENCE_ANGLE & SUB_SOLAR_AZIMUTH parameters are available for a given MEX/HRSC observation ?

[snip]
Calculating those values oneself using ISIS3 (via the "campt" application) would be an option but then the raw intrument data would be needed which does not seem to be straightforwardly available for HRSC observations ...

Thanks for any help with this,
Bernhard

[Nirgal]

Thanks for the suggestion !

If you are interested, but don't care for spherical trig, I will dig up my derivations ...

Yes, this would be great ... Maybe I could then write a small script/program to automate the process to work with a lot of images (somehow extracting the necessary input parameters from the raw EDR files)

Thanks again for your help
- Bernhard

[mwolff]

cos i = cos(bp) cos(bs) cos(delta_lng) + sin(bp) sin(bs)

i = incidence angle at point P
bp = latitude at point P
bs = latitude at subsolar point
delta_lng = difference of longitude between points P and subsolar. given that it is a cosine, it shouldn't matter how you define the difference (i say "should" because I always find cases that I didn't consider after I code the algorithm, but I think that we are safe). The ASSUMPTION is that surface is a sphere, at least for the region that contains the triangle of North Pole, target point, and sub-solar point.

I can scan a figure if that would be helpful, though my drawing skill may obfuscate the matter. Also, if you want to tell me how you want to use solar azimuth (I didn't find the definition of the HiRISE SUB_SOLAR_AZIMUTH to be useful in terms a surface or atmospheric modeling perspective), I will work on that next. If you just want the azimuth angle of the sub-solar point (relative to north) at the target point, this can be determined from the Law of Sines.

--mike

Thanks for the suggestion !



Yes, this would be great ... Maybe I could then write a small script/program to automate the process to work with a lot of images (somehow extracting the necessary input parameters from the raw EDR files)

Thanks again for your help
- Bernhard