This program is used to radiometrically correct flight images using a linear model of the light-transfer function. This program is specific to the Galileo SSI camera.

References:

1. D-4264 MIPL Software Structural Design for the Instrument Calibration of GLL SSI Science Processing.
2. K. Klaasen, "Reduction in Number of Unique SSI Calibration Files", 29 May 1987.
3. 625-210,"Galileo SSI Calibration Report Part 1", K. Klaasen, H. Breneman, November 1, 1988.
4. JPL VICAR GALSOS application help page.

This program will radiometrically correct the input image, converting the input DN values to some specified radiometric unit (either I/F or radiance). The program requires a radiometric file generated from calibration data acquired at the same filter position as the input image, and a dark-current file acquired at the same camera gain-state, frame-rate, PNI, and BPM settings. Also, extended exposure mode frames require an extended-exposure mode dark-current file.

This program extracts the filter position, exposure time, and frame-rate from the label of the input file to determine the required gain file to use. The file $ISISDATA/galileo/calibration/gll_gain.sav defines the gain file to use for the given filter, gain state, and frame mode. The file $ISISDATA/galileo/calibration/gll_dc.sav defines the DC file to use for the given, gain state, frame mode, frame rate, blemish protection mode, clock mode, and extended exposure mode.

This program performs the following processing steps on each pixel:

1. The radiometric correction is applied:

             e = z(d - dc)
   
             where:
               z is retrieved from the Radiometric File.
               d is the DN.
               dc is retrieved from the Dark-Current File.
           

2. The output pixel is scaled to radiometric units R (units of reflectance or units of radiance). If output units are I/F, the following equation is used:

    
       		     S1       K
             r = e * -------- * --- (D/5.2)2
       		  A1(t-to)    Ko
   
             where:
               S1 = filter-dependent conversion factor from ft-Lamberts to
                    I/F units for a reference distance of 5.2 AU from the Sun.
               A1 = output picture scale factor (see SCALE parameter for more info).
               t  = commanded exposure time of the input image (msec).
               to = line-dependent shutter offset.
               K  = system gain constant for the gain-state of the image.
               Ko = system gain constant for the calibration file gain-state.
               D  = target distance from the Sun (in AU).
           

   If output units are in radiance, the following equation is used:

       		     S2       K
             r = e * -------- * ---
       		  A2(t-to)    Ko
   
             where:
               S2 = filter-dependent conversion factor from ft-Lamberts to
                    units of nanowatts/cm2/steradian/nanometer.
               A2 = output picture scale factor (see SCALE parameter for more info).
               t  = commanded exposure time of the input image (msec).
               to = line-dependent shutter offset.
               K  = system gain constant for the gain-state of the image.
               Ko = system gain constant for the calibration file gain-state.
           

   Note: The original version of this equation (found in GALSOS) was multiplied by 10,000. The Isis 2 version of the program chose to remove this scaling factor, so we do the same here.
3. The output DN is usually in the range of 0.0 to 1.0.

If the uneven bit weighting correction is enabled, the input DN values (d) will be corrected for uneven-bit-weighting due to the ADC. If the input dark-current file is in byte format (i.e. an individual dark-current frame), then the correction will be applied to the dark-current as well. The current correction table was supplied by Herb Breneman, 2 Mar 89, and is based on 1975 calibration data.

Please note that the original Isis 2 version of this app (ssical) included negative I/F values in the output. We will not be supporting this behavior as negative I/F are not useful and do not make sense. Thus, this app outputs LRS for any negative I/F values that are encountered.

If run on a non-spiceinited cube, this program requires access to local mission-specific SPICE kernels, in order to find the distance between the sun and the target body. When run on a spiceinited cube, this can be determined using the camera model. Using a spiceinited cube as input has the advantage of not requiring that local mission-specific kernels be available. (See spiceinit web=true.)