Level1 HiRISE¶
HiRISE Radiometric Calibration¶
About HiRISE Radiometric Calibration
A radiometric calibration product is representative of an ideal image acquired by a camera system with perfect radiometric properties. Values in the resulting image represent the reflectance of the surface (I/F).
The radiometric calibration of HiRISE images has been a challenging work in progress. The camera has 14 CCDs with separate readouts, and many different operating modes such as pixel binning and time delay integration. Understanding and solving the radiometric calibration for HiRISE is like solving for 28 individual cameras. The HiRISE Science Team is continually working on the calibration of their instrument, and updates to ISIS will be made over time as the calibration sequence matures.
Radiometrically calibrating a single HiRise image with hical
See hical ISIS App Documentation for more info.
Do it again!
Run hical on each ISIS cube in the observation.
Channel Stitching¶
A special requirement for HiRISE is the reconstruction of the CCD data. That is, merging the left and right channel data from an individual CCD into a single image.
HiRISE reads the data from one CCD into two separate channels. The next step in level 1 processing is to combine the two channel cubes back into an individual CCD image.
Merge two channels with histitch
histitch from1=PSP_00273_1880_RED5_0.cal.cub from2=PSP_00273_1880_RED5_1.cal.cub \
to=PSP_00273_1880_RED5.cal.cub
The left and right channels (0 and 1) are stitched together to form a single RED5 CCD image.
histitch illustration
Left three images: Data from channels 0 (left) and 1 (center) of a red 5 image stitched together to create the full red 5 CCD image (right). The images shown here are scaled-down full HiRISE channel images.
Right three images: Close-up on a portion of the images shown on the left. Data from channels 0 (left) and 1 (center) of a red 5 image stitched together to create the full red 5 CCD image (right). Note that in the final image, the data from channel 0 appears on the right, and the data channel 1 appears on the left.
Noise Removal¶
For HiRISE, systematic noise appears as vertical striping, referred to as furrows, which occur under certain observing conditions, and tonal mismatches among the data sets collected by adjacent channels in a CCD.
- See Also: General Overview of Noise and Artifacts
Vertical Striping and Channel Tone Differences¶
This step may be removed in the future as the radiometric calibration matures.
The current radiometric calibration of the HiRISE data may reveal vertical striping noise in the CCD images. This is especially true for data collected by CCDs which have shown degradation in data collected over time (like RED9).
Tone differences caused by the the electronic read-out of the left/right channels may not be fully corrected by the calibration program.
cubenorm,
which normalizes values in an image, can be used to remove both the striping and left/right normalization problems.
Removing noise and tone mismatch with cubenorm
cubenorm illustration
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Before cubenorm: Vertical striping (red arrows) and left/right channel tone problem.
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After cubenorm: Vertical striping and tone problem removed.