HiRISE Radiometric Calibration Options

[manishm1020]

Dear HiRISE experts,

I have obtained .tiff files of HiRISE images taken from PDS. They are all 10-bit data. I would just like to obtain the I/F for each of these images. I basically calculate the I/F from equation: I/F = (gain*DN) + offset. I use the gain and offset provided in the .LBL within PDS for each image. Now the question is - can I use the 10-bit data in the I/F calibration equation? Do I need to convert this 10-bit data to 14-bit data? If I do that, can I basically multiply each DN value by 2^4? If this is not possible, how can I obtain the original 14-bit data? If it is 10-bit data, the dynamic range of I/F for my images in the southern polar dunes (PSP_003386_1080) only spans from 0.09 to 0.2. I have read that frost/ice can approach much higher reflectance values. There must be something that I am missing. If it is 14-bit data, the dynamic range would span 0.09 to 1.5.

Any advice that you could provide, would signficantly help. This has been a bit confusing for me.

Thank you so very much.

-manish mehta

[elakdawalla]

Would the low I/F values you are getting result from the low angle of the Sun? The HiRISE web page for that image says the sun's only 24 degrees above the horizon.

[Nirgal]

Would the low I/F values you are getting result from the low angle of the Sun? The HiRISE web page for that image says the sun's only 24 degrees above the horizon.

yes, with 66 degrees incident angle, a slope would have to be as steep as 66 degrees (!) in order to directly facing the sun for maximum reflectance.
whereas in reality the slopes on mars in this kind of dune landscapes rarely exceed, say 20-30 degrees so its quite plausible to see far less than maximum reflectance even in high-albedo regions when there are both shallow slopes and low sun incidence angles.