HiRISE Radiometric Calibration |
HiRISE Radiometric Calibration |
Jun 11 2010, 03:23 AM
Post
#1
|
|
Newbie Group: Members Posts: 6 Joined: 13-October 08 Member No.: 4450 |
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 |
|
|
Jun 11 2010, 04:10 PM
Post
#2
|
|
Member Group: Members Posts: 713 Joined: 30-March 05 Member No.: 223 |
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. The real dynamic range is actually only 8 bits. This is because of a fixed on-board lookup-table (LUT) reducing the original 14 bit to 8 bit *before* the data is sent to earth, i.e. it is lost forever. On the other hand, the 10 bit range of the JP2 PDS products is a result of the postprocessing like photometric calibration and map projection that involves, among other things, resampling of the data, thereby kind of "smoothing" the dynamic range from 8 to 10 bit again. But still there is no more of 8 bit "real" dynamic range in a HiRISE image. As far as the I/F conversion is concerned: it should be ok to just use the D/N values of the PDS product JP2 with the "factor" and "offset" parameters from the corresponding label file. EDIT: yes, the low I/F value of 0.2 you reported for clear frost/ice does seem rather low ... it should be higher at least for exactly sun facing slopes... maybe it's the dust attenuation. Hope this helps Bernhard |
|
|
Jun 11 2010, 04:31 PM
Post
#3
|
|
Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
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.
-------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
|
|
|
Jun 11 2010, 04:34 PM
Post
#4
|
|
Member Group: Members Posts: 890 Joined: 18-November 08 Member No.: 4489 |
0.09 to 0.2
that is looking like that tiff is a 32bit float .I get those when i import a isis cub into openev well a 16 bit image values in a 32 bit format for PSP_003386_1080 http://hirise.lpl.arizona.edu/PSP_003386_1080 the jp2 remapped should have the correct values |
|
|
Jun 11 2010, 07:34 PM
Post
#5
|
|
Member Group: Members Posts: 713 Joined: 30-March 05 Member No.: 223 |
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. |
|
|
Lo-Fi Version | Time is now: 25th April 2024 - 05:40 PM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |