Level2_HiRISE
Level2 HiRISE ¶
Overview ¶
In this section, we'll discuss how to create a Level 2 HiRISE image. Following Level0 and Level1, there should be up to 14 CCD images that have had spiceinit successfully applied, are radiometrically calibrated and have had noise removed.
Focal Plane Assembly Each CCD has 2048 pixels in the cross
scan direction The 14 staggered CCDs overlap by 48 pixels
at each end. This provides an effective swath width of
approximately 20,000 pixels for the red images and 4,048
pixels for the blue-green and near infrared images.
Credit: NASA/UA/Ball
Constructing a map projected HiRISE observation image is much more difficult than most instruments. There are 14 Charge-Coupled Devices (CCD) in the camera, ten red, two infrared, and two blue-green. When the camera electronics read out the image data, each CCD is broken in two halves (left and right channels). On the ground, the data for one observation ends up stored in 28 image files (14 CCDs x 2 channels per CCD). The goal of this lesson is to show the necessary steps to combine the CCD images into a single mosaic.
The Level2 process involves the following:
- Geometric transformation of each CCD image from spacecraft camera orientation to a common map coordinate system
- Correction of tonal mismatches among the projected images. Prior to mosaicking the projected CCD images, it is optional to fix tonal mismatches among the projected images. As the radiometric calibration becomes more accurate, this step could be eliminated.
- Creation of a HiRISE observation mosaic of the tone matched CCD images to create a complete HiRISE observation image.
The results of this process will be an uncontrolled observation mosaic, meaning that the output map will only be as accurate as the original SPICE allows. Software and procedures for creating controlled (adjusted SPICE) mosaics are underway. Information and documentation will be released on our site.
For additional information, refer to:
Learning About Map Projections
Overview of Map Projecting Images
Map Projecting HiRISE Images ¶
To assemble our HiRISE observation mosaic from the CCD images, we will use the application cam2map to convert each CCD image to a map projected image. We'll show here how to easily match the projection information among the CCD images. Alternatively, you can define your own map file using the maptemplate application. The first step is to project one of the CCD images, usually red 5 as it is in the center of the observation:
cam2map from=PSP_002733_1880_RED5.norm.cub to=PSP_002733_1880_RED5.sinu.cub
The default projection for cam2map is sinusoidal, so the resulting red 5 CCD image is now in sinusoidal projection. As with many Isis applications, cam2map has several parameters, but the default values for these parameters will result in good projection results.
The output cube contains all the mapping parameters we need for projecting the remaining CCD images so they can be mosaicked. To process the remaining CCD images, use the following command:
cam2map from=PSP_002733_1880_?.norm.cub \
to=PSP_002733_1880_?.sinu.cub \
map=PSP_002733_1880_RED5.sinu.cub pixres=map
- Quick Tip : We use the red 5 sinusoidal cube as our map file. The remaining CCD images will use the same projection parameters as red 5, which is required for mosaicking the CCD images into our final observation image.
See the following Isis documentation for information about the applications you will need to use to perform this procedure:
- maptemplate : generates a map file that can be used to project images
- cam2map : geometrically transforms a raw camera image to a map projected image
Tone Match ¶
Tone matching among the CCD images will be necessary until the radiometric calibration procedure matures. To illustrate the need for tone matching, the example images on the right show a mosaic with and without the CCD image normalization. Here, we will make a mosaic of the red CCD images. The infrared and blue-green CCD images follow a similar process.
In order to tone match the CCD images, we use the equalizer application program to normalize the images.
- Hold the tone of the red 5 CCD image. That is, the pixel values in the red 5 CCD image will not be changed. Create a list containing the filenames of the images that will be held. In this example, the red 0 through 4 and 6 through 9 CCD images will be normalized to the the red 5 image:
ls *RED5.cub > hold.lis
- Create a list containing the filenames of red 5 images to be normalized in preparation for creating the mosaic. The contrast and brightness of these images will be updated so that tones match the red 5 image listed in the hold list. We are effectively normalizing to the red 5 calibration. Note the equalizer program does a statistical analysis among only the pixels in the overlap regions to determine the corrections to the contrast and brightness differences.
ls *RED*.cub > redCCD.lis
- Run the equalizer application using the two lists created above as input. equalizer automatically generates output filenames with the extension .equ.cub. The output results will be ten cubes (red CCD 0 through 9 images) with the extension .equ.cub added to each filename.
equalizer fromlist=redCCD.lis holdlist=hold.lis
Mosaicking ¶
Finally we will construct the mosaic. A new list of the equalized cube
filenames is required as input to
automos
.
Note : Make sure you only add filenames for one observation (or
adjacent observations) to the list file, otherwise all the images in
the list will be mosaicked into a single output image.
ls *RED*.equ.cub > mosaic.lis
automos fromlist=mosaic.lis to=redMosaic.cub
Related Isis Applications ¶
See the following Isis documentation for information about the applications you will need to use to perform this procedure:
- equalizer : tone match overlapping map projected images
- automos : automatically mosaic a list of map projected images
Full view of the red 5 mosaic **without** equalization
Full view of the red 5 mosaic **with** equalization
Close-up of red 5 mosaic **without** equalization
Close-up of red 5 mosaic **with** equalization
Tone_Matching_Close_Up_With_EQ.png View (665 KB) Ian Humphrey, 2016-05-31 05:45 PM
Tone_Matching_Close_Up_Without_EQ.png View (605 KB) Ian Humphrey, 2016-05-31 05:45 PM
Tone_Matching_With_EQ.png View (281 KB) Ian Humphrey, 2016-05-31 05:45 PM
Focalplaneassembly.png View (125 KB) Ian Humphrey, 2016-05-31 05:45 PM
Tone_Matching_Without_EQ.png View (249 KB) Ian Humphrey, 2016-06-01 11:26 AM