Third HSRC Release!, Includes map-projected calibrated images |
Third HSRC Release!, Includes map-projected calibrated images |
Apr 26 2006, 04:21 AM
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#1
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Newbie Group: Validating Posts: 17 Joined: 25-April 05 From: Pilsen, CZ, EU Member No.: 363 |
ESA released new set of HRSC images from orbits 1225 and 1863, which are map projected and radiometrically calibrated. At this moment you have to get them through the PSA interface
A color composite of a stripe of Meridiani Planum (includes Victoria) can be found here (2MB) |
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Jul 20 2006, 08:41 PM
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#2
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Member Group: Admin Posts: 468 Joined: 11-February 04 From: USA Member No.: 21 |
I got a reply from the HRSC data processing manager, Dr. Thomas Roatsch, about some of the map-projected PDS/PSA tag issues, which seemed appropriate to share here.
As to the duplicate RADIANCE_OFFSET and RADIANCE_SCALING_FACTOR tags, the second ones are correct to the map projected images. For anyone particularly interested in the reflectance data, there is a necessary tag which is missing (REFLECTANCE_OFFSET). Dr. Roatsch has suggested to the PDS/PSA that they deliver a new version soon to fix both of these problems. When considering the radiance information recoverable by applying the offset and scaling factors, a third tag becomes important as well. The radiance values are in units of Watts/m^2/sr, and is not spectral radiance (Watts/m^2/sr/nm). This means that the calibrated radiance values in the images are a summation across the whole bandwidth of the filter+ccd. This is important because bandwidths of the HRSC color filters differ significantly. The red filter is 48 nm wide, green is 88 nm wide, and blue is 76 nm wide. In other words, if one didn't take this into consideration, the green filter would appear almost twice as 'bright' as the red filter, since its radiance is considered across a spectrum twice as wide. So, to recover spectral radiance from the HRSC map-projected images, one must apply the offset and scaling factors, then divide that value by the bandwidth of the filter. |
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