Level1_HiRISE
Level1 HiRISE ¶
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).
General Overview of Radiometric Calibration: Overview of Radiometric Calibration
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 the Isis software will be made over time as the calibration sequence matures.
For now, run hical on each Isis cube in the observation.
The following example shows the command line for calibrating the image from channel 0, red filter, CCD 5:
hical from=PSP_002733_1880_RED5_0.cub to=PSP_002733_1880_RED5_0.cal.cub
See the following Isis documentation for information about the applications you will need to use to perform this procedure:
- hical : radiometrically calibrates HiRISE channel images
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.
Recall the HiRISE instrument 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. The channels can be merged using the histitch program as follows:
histitch from1=PSP_00273_1880_RED5_0.cal.cub from2=PSP_00273_1880_RED5_1.cal.cub \
to=PSP_00273_1880_RED5.cal.cub
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.
- histitch : combines two HiRISE channels to form a single CCD image
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.
General Overview: Overview of Noise And Artifacts
Vertical Striping and Channel Tone Differences ¶
This step may be removed 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 (e.g., red 9). Additionally, tone differences caused by the the electronic read-out of the left/right channels may not be fully corrected by the calibration program. The cubenorm application can be used to remove both the striping and left/right normalization problems. The following example shows the command line for removing the noise and tone mismatch from the CCD image using cubenorm:
cubenorm from=PSP_002733_1880_RED5.cal.cub to=PSP_002733_1880_RED5.cal.norm.cub
Before cubenorm: This image depicts problems with both vertical
striping (red arrows) and left/right channel tone problem.
After cubenorm: This image shows the results of the cubenorm
application, which removes both problems.
- cubenorm : normalizes values in a image
Merging_Channel_Images_Example.jpg View (69.6 KB) Ian Humphrey, 2016-05-31 05:43 PM
Cubenorm_Before.png View (196 KB) Ian Humphrey, 2016-05-31 05:43 PM
Cubenorm_After.png View (133 KB) Ian Humphrey, 2016-05-31 05:43 PM