Viking Imager Processing using ISIS Level Software
Isis 2 Documentation
Viking Imager Processing using ISIS Level Software
Written by Ella Lee June 03, 2005 ---------------------
The Viking Orbiter data processing sequence is designed to create clean, radiometrically corrected, and photometrically normalized mosaics using Viking Orbiter digital data and USGS ISIS software version 2.3.0. In the current version of ISIS, all programs are run under UNIX using the command line mode or within TAE. Some of the program names, and the label keywords information have changed in ISIS2.3.0. ISIS processing is generally broken up into levels. These levels are: Level0 - unprojected raw data; Level1 - unprojected cleaned up calibrated images; Level2 - projected calibrated images; Level3 - photometrically corrected images; Level4 - tonematched mosaics; and Level5 - cutline plots showing image layout. This documentation will cover Level0 and Level1.
The sequence starts with accessing the raw digital data (i.e., the Viking Experiment Data Records, or EDRs) via the Internet or from the NASA Mission to Mars CDROM volumes.
Before processing begins, the user must first determine the image coverage in the area of interest. The first data processing step (cartographically referred to as Level0 processing) involves transferring the raw images to a work disk, and converting them to ISIS format. They can be downloaded via the internet from pdsimage2.wr.usgs.gov (see below) or read in directly from the Viking Orbiter CDROM Volumes VO_1001 through VO_1064, as follows (note that data ranges describe revolution numbers):
Mission to Mars: Images of Mars (Experiment Data Records)
vo_1001 - images in the range 122S01 - 166S24
vo_1002 - images in the range 167S01 - 210S42
vo_1003 - images in the range 149S16 - 251S30
vo_1004 - images in the range 252S01 - 321S72
vo_1005 - images in the range 152S11 - 363S56
vo_1006 - images in the range 365S01 - 405S30
vo_1007 - images in the range 406S11 - 436S36
vo_1008 - images in the range 437S01 - 467S36
vo_1009 - images in the range 286C01 - 485S24
vo_1010 - images in the range 003A01 - 038A32
vo_1011 - images in the range 039A01 - 070A32
vo_1012 - images in the range 071A01 - 105A48
vo_1013 - images in the range 106A01 - 212A64
vo_1014 - images in the range 214A01 - 272A36
vo_1015 - images in the range 273A01 - 322A40
vo_1016 - images in the range 326A01 - 372A50
vo_1017 - images in the range 373A01 - 414A40
vo_1018 - images in the range 416A01 - 443A10
vo_1019 - images in the range 444A01 - 472A60
vo_1020 - images in the range 474A07 - 527A10
vo_1021 - images in the range 529A01 - 572A36
vo_1022 - images in the range 573A01 - 605A96
vo_1023 - images in the range 606A01 - 634A48
vo_1024 - images in the range 635A01 - 663A86
vo_1025 - images in the range 664A01 - 693A48
vo_1026 - images in the range 694A01 - 718A60
vo_1027 - images in the range 719A01 - 743A66
vo_1028 - images in the range 744A41 - 771X00
vo_1029 - images in the range 772A01 - 825A52
vo_1030 - images in the range 826A01 - 888A16
vo_1031 - images in the range 890A01 - 919A62
vo_1032 - images in the range 920A06 - 980A10
vo_1051 - images in the range 004Y01 - 048B53
vo_1052 - images in the range 049B01 - 077B95
vo_1053 - images in the range 078B11 - 140B54
vo_1054 - images in the range 141B01 - 187B52
vo_1055 - images in the range 188B01 - 262B75
vo_1056 - images in the range 264B01 - 308B90
vo_1057 - images in the range 310B31 - 355B60
vo_1058 - images in the range 356B01 - 392B20
vo_1059 - images in the range 393B01 - 434B14
vo_1060 - images in the range 437B01 - 497B96
vo_1061 - images in the range 499B01 - 544B16
vo_1062 - images in the range 545B01 - 576B60
vo_1063 - images in the range 577B01 - 703B72
vo_1064 - images in the range 704B01 - 705B52
Next, the raw EDR images are converted to ISIS format (Level0), and appropriate keywords are placed in the image labels. The geometry information is also added based on the target definition file the user specifies, and on which of these options were selected, east or west longitude direction, ographic or ocentric latitude system, and 180 or 360 longitude system. If the longitude system is 180, then the longitude ranges returned are values between -180 and 180 degrees. For 360, the ranges are from 0 to 360 degrees.
It is recommended to have a rough layout of image placement (how and where the images overlap); this allows the user to eliminate redundant image coverage. The images selected must be visually inspected for data quality (e.g., cloudy, grainy, saturated, etc.) to determine whether or not they are acceptable to use.
Level1 processing involves using a series of ISIS programs designed to update camera pointing, find and remove reseau marks, change the reseau location, remove random and systematic noise, and radiometrically correct the images. The images can also be geometrically controlled to MDIM2.1(Mars Digital Image Mosaic) or another base map product.
In Level2 processing, the images are projected to an Equirectangular Cylindrical, Sinusoidal Equal-Area, Simple Cylindrical Equal-area, Polar Sterographic, or Orthographic projection using the same map scale and center longitude. The map projections that are available in ISIS 2.1, and the required format are listed in mappars.pdf. The user can type help mappars in TAE to receive help.
In Level3 processing, a photometric correction is applied to the images or the correction is simulated by applying a high pass filter and a low pass filter to the projected images.
In Level4 processing, these images are normalized for tone matching, and mosaicked together to form a seamless product.
For the Geologic Base Maps, a layout of each image in the mosaic (Level 5) called a cutline plot is generated. Each image in the mosaic is assigned a different density value and a border is drawn around each image boundary.
To get help on any ISIS program tutor the program and type help*. After reading the information, type "ex" to return to the main window. Additional information for the available parameters can be obtained by typing help "parameter name" after tutoring the program.
Command line sequence:
tae>t sedrsort tae>help* tae>ex tae>help list (where list is a parameter of "sedrsort") tae>ex
Sort through the Viking Orbiter database using user defined constraints to identify images that are available in the area of interest using "sedrsort". The user must define a combination of parameters: latitude range, longitude range, resolution of images, etc. (within TAE type "t sedrsort" to tutor the program for help on all parameter options that are available). If the TO parameter is not specified, the selected image numbers will only go to the default output print file (print.prt) that is automatically generated by the application. Otherwise, the PRODUCT_IDs will be output to an ASCII file as a single column list. The Viking Orbiter image information is stored as west longitude values, so convert east longitude values to west longitude values first (360 east_longitude), and enter the calculated values for longitude range.
tae>sedrsort to=mars.lis res=(0,.116) lat=(10,15) +
lon=(-15,-10) target=MARS mission=VIKING_ORBITER
The next example runs the program four times so there are four separate output lists for the different Missions and Camera IDs.
tae>sedrsort to=mars_1a.lis res=(0,.116) lat=(10,15) +
lon=(-15,-10) target=MARS mission=VIKING_ORBITER_1 +
inst=A
tae>sedrsort to=mars_1b.lis res=(0,.116) lat=(10,15) +
lon=(-15,-10) target=MARS mission=VIKING_ORBITER_1 +
inst=B
tae>sedrsort to=mars_2a.lis res=(0,.116) lat=(10,15) +
lon=(-15,-10) target=MARS mission=VIKING_ORBITER_2 +
inst=A
tae>sedrsort to=mars_1b.lis res=(0,.116) lat=(10,15) +
lon=(-15,-10) target=MARS mission=VIKING_ORBITER_2 +
inst=B
>ftp pdsimage2.wr.usgs.gov
>Name: anonymous
>Password:email address
>cd /cdroms/viking_orbiter
>cd vo_101
>cd f431axx
>binary
>get f431a56.imq
>bye
>cdmount
>cp /cdrom/f431axx/f431a56.imq .
>cdumount
tae>vikftp fromlist=mars.lis
To download a single image using VIKFTP, enter the PRODUCT_ID in the FROM
parameter.
tae>vikftp from=097a30
The next step is to convert the raw files to ISIS format by running viklev0, or "pds2isis" and levinit. The pds2isis program requires a translation table in order to put the correct keywords in the image labels area. Always use the latest version of vik2isis_translations.def in the directory if working with raw EDRs. Do not use pds2isis_translation.tbl, which is the default file that the program selects if no entry is made for the transtab parameter in pds2isis.
The other program that is run is levinit which puts the geometry information in the labels. The parameter TARGDEF defines the planetary constants that will be used by a variety of lev software (2.1 version). The target definition file /target/mars.def.4 should be used for any map that will be registered to MDIM2.1 mosaic, which was controlled to the MOLA DEM. The file also defines an east longitude direction for Mars. The older version mars.def.3 defines a west longitude direction and contains radii values derived for MDIM2.0 mosaic. There are other definition files for Mars included in /targets directory; these text files can be viewed using any editor.
The example below is for f431a56.imq, which was downloaded from VO_1018 CDROM.
tae>pds2isis from=f431a56.imq to=f431a56.lev0.cub +
trans=/vik2isis_translation.def.1
tae>levinit from=f431a56.lev0.cub latsys=ocentric
The example below runs viklev0 to process a single image or a list containing raw image filenames
tae>viklev0 from=f431a56.imq
or
tae>ls *.imq > raw.lis
tae>viklev0 froml=raw.lis
Note: The extension ".lev0.cub" is automatically appended to the name. The user can also provide a list of raw filenames for the FROML parameter to process all images that have been downloaded.
After the images are download and converted to ISIS cubes they are visually inspected for image quality. The images that are too noisy, too grainy, or that have too much cloud cover are rejected. The program "qview" is used to view the images. After displaying the first image, the browse option can be used to quickly view each image. Click the browse button, and a file selection menu will appear, select the next file and click okay, or double click on the filename. Continue working down the list of filenames until all images have been viewed. Delete all poor quality images.
tae>qview f431a56.lev0.cub
For the LEVEL1 sequence, the images are processed through a series of programs that remove random noise appearing on the images, the reseau marks are found and removed, and the images are radiometrically corrected. The program "viklev1" runs through the following programs to create the level1 files:
trim - set the first row, and the left and right column of pixels to null to remove bad data
lev_findrx - find and store reseau locations in the image labels
remrx - remove the reseau marks by assigning these pixel locations to 'null' and then applying a low pass filter to replace these pixel with an average of surrounding valid pixels. An alternative option is to apply a bilinear interpolation algorithm.
boxfilter - the 'salt and pepper' type noise are removed by applying a series of standard deviation filters to the image, and null pixel values are filled in by applying a low pass filter and replacing them with an average of surrounding pixels
vikcal - radiometrically calibrates the image
The example below creates a level1 file. The user has the option of processing a single image or a list of level0 filenames. The reseau marks are replaced with DN values calculated through a bilinear interpolation.
tae>viklev1 from=f431a56.lev0.cub
or
tae>ls *lev0.cub > lev0.lis
tae>viklev1 froml=lev0.lis
Note: The ".lev1.cub" extension is automatically appended to the file
The next step is to remove the systematic noise patterns by running the program "slosin". The values listed below for STAL, ENDL and WAVE parameters are used the majority of the time for the different spacecrafts, and camera ids. SLOSIN works better if you use the default value for wave.
Viking Orbiter 1 - Camera A (odd),Camera B (even)
revAodd (e.g., 421A01) stal=(26,940) endl=(50,1020)
wave=(103,93)
revAeven (e.g., 421A02) stal=(26,940) endl=(50,995)
wave=(103,103)
revSodd (e.g., 079S01) stal=26 endl=100 wave=93
revSeven (e.g., 079S02) stal=(26,940) endl=(95,995)
wave=103
Viking Orbiter 2 - Camera A (odd), Camera B (even)
revBodd (e.g., 199B01) stal=26 endl=200 wave=127
revBeven (e.g., 199B02) stal=(26,940) endl=(400,1020)
wave=(41,93)
for example (single noise pattern):
tae>slosin from=f431a56.lev1.cub to=f431a56.lev1slo.cub stal=26 endl=50 +
filt=101
(two noise pattern one at top and one at bottom part of image)
tae>slosin from=f431a56.lev1.cub to=f431a56.lev1slo.cub stal=(26,940) +
endl=(50,995) filt=101
After running slosin, inspect the images by displaying them with qview. If the result is unacceptable, determine the starting and ending lines and samples of the noise pattern, and also measure the number of pixels between the dark diagonal or crest-to-crest pattern. The crest-to-crest measurement can be used for the filt parameter or wave parameter. Enter the values of the measurement in slosin and run the program again. This step is an iterative process that requires the user to evaluate the result interactively after each attempt. It is best to keep all the different versions, until the best output image is selected.
The output file at this point is a cleaned up, radiometrically calibrated 32 bit image. The level1 image will need to be trimmed before being used to create a mosaic. The top 25 pixels, bottom 20 pixels, left 30 pixels, and right 30 pixels are trimmed by setting those pixels to null.
tae>trim from=f431a56.lev1slo.cub to=f431a56.lev1slotr.cub top=25 bot=20 +
righ=30 lef=30
The remaining processing steps are: 1) to geometrically control the images, and 2) create a controlled mosaic. The software needed to accomplish these steps is currently being tested and will be available in a future release along with the processing instructions.
In the mean time, to generate an uncontrolled mosaic use the following programs:
lev1tolev2 - creates a transformation file to project the images to a user defined map projection
geom - actually performs the geometry transformation to create a projected level2 file
mosaic - compiles the level2 projected images into a single mosaic
Contact us online at the Isis Support Center: http://isisdist.wr.usgs.gov