ssical Documentation

ssical - Perform Radiometric correction on GALILEO-SSI Imaging
PROGRAMMER: G. Yagi (JP), adapted to PICS by Eric Eliason

"ssical" was derived from the GALSOS program developed by G. Yagi at
MIPL/JPL. This program is a subset of the full capabilites of GALSOS.

"ssical" is used to radiometrically correct flight images using a linear
model of the light-transfer function.  "ssical" 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.


"ssical" will radiometrically correct the input image, converting the
input DN values to some specified radiometric unit.  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.

"ssical" 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 $ISISGALDATA/gll_gain.sav defines the gain file to
use for the given filter, gain state, and frame mode.  The file
$ISISGALDATA/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.

"ssical" 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 and dc is retrieved
    from the Dark-Current File.

 2. The output pixel is scaled to radiometric units R.  The
    user determines the output picture scale by specifying one of the
    following (see IOF and CONV parameters.):

	A1 = number of 'I over F' units per DN, where 1 I/F units
             would be produced by normal incidence of sunlight on a
	     a Lambert disk at the planet's distance from the sun.

 	A2 = number of nanowatts per cm**2 per steradian per nanometer
             wavelength per DN.

    If A1 is specified, then

		           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.
	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 A2 is specified, then

			   S2       K
		r = e * -------- * ---
			A2(t-to)    Ko

    where S2 is the filter-dependent conversion factor from ft-Lamberts
    to units of nanowatts/cm**2/steradian/nanometer.

 5. The default output DN is 16-bit data format, usually in the range,
    0.0 to 1.0.  A negative DN value may occur if the dark-current frame
    has a higher dark-current level than that of the input image.

If the keyword UBWC="YES"  is specified, 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.

PROGRAM HISTORY:
 ISIS conversion by:  Tracie Sucharski
 PICS adaptation by:  Eric Eliason
 Original GALSOS Program by: Gary Yagi

INPUT FILE NAME
(RAW GALILEO SSI IMAGE)

NONE

RADIOMETRICLY CORRECTED
OUTPUT FILE (16-BIT)

NONE

GAIN FILE
(OPTIONAL)

" "

DARK CURRENT FILE
(OPTIONAL)

" "

SHUTTER-OFFSET FILE
(OPTIONAL)

" "

I OVER F UNITS PER DN
(OPTIONAL)

1.0

NUMBER OF NANOWATTS PER
CM**2 PER STERADIAN PER
NANOMETER WAVELENGTH PER DN
(OPTIONAL)

0.0

UNEVEN-BIT-WEIGHTING
CORRECTION.
(YES,NO)

"NO"

Optional exposure time
in seconds
 (Override labels)

--

Output pixel type
 NULL = input type
    1 = 8 bit
    2 = 16 bit
    3 = 32 bit

2

Output min/max data range

0.0,1.0

User comment

" "

ADDITIONAL NOTES:

Parm	Description
FROM	Raw, uncorrected Galileo-SSI image.
TO	Ouput file, radiometrically corrected image, output file is in 16-bit.
CAL	Input Radiometric GAIN File. Use only to over-ride the file name determined by "ssical". The Radiometric File's filter position must match the filter position of the input image.
DC	Input Dark-Current File. Use only to over-ride the file name determined by "ssical". The dark-current must match the input image in Gain-state, frame-rate, PNI, and BPM setting. Also, extended-exposure mode frames require and extended-exposure dark-current.
ABLE OFFSETS	Input Shutter-Offset File. Use only to over-ride the file name determined by "ssical". The Shutter-Offset File is independent of all camera modes, and a single file may be used (for a fixed temperature).
IOF	IOF=r where r specifies the output DN scale in number of 'I over F' units per DN. 1 'I over F' unit would be produced by normal incidence of sunlight on a Lambert disk at Jupiter's distance from the sun (5.2 A.U.). Default is IOF = 1.0.
CONV	CONV=r where r specifies the output DN scale in number of nanowatts per cm**2 per steradian per nanometer wavelength per DN. IF CONV=0.0, Then CONV is calculated internally in "ssical".
ABLE UBWC	If the keyword UBWC="YES" is specified, the input DN values (d) will be corrected for uneven-bit-weighting due to the ADC. The current correction table was supplied by Herb Breneman, 2 Mar 89, and is based on 1975 calibration data.
EXP	Exposure overide value. User can optionally enter the exposure time of the image. "ssical" will normally extract the exposure time from the image labels. This values is in seconds. This is in response to the shuttering time error described by Herb Breneman.
OTYPE	Output pixel data type. Permitted values are: NULL = output type is same as input file pixel type 1 = 8-bit (integer with type conversion parameters) 2 = 16-bit (integer with type conversion parameters) 3 = 32-bit (floating point) When processed data are being written back into the input file, the output pixel type must be the same as the existing pixel type in the input file.
ORANGE	Output pixel data range. If ORANGE is NULL, then the CORE_BASE and CORE_MULTIPLIER in the output file will be set to represent the same range of data as the input file. If OTYPE=1 (8-bit) or OTYPE=2 (16-bit), then the CORE_BASE and CORE_MULTIPLIER in the output file will be set to values that allow representing the specified range of output values. Output values outside this range will be stored as a special "representation saturation" value. The ORANGE parameter is ignored if OTYPE=3 (32-bit) since the CORE_BASE and CORE_MULTIPLIER are not applicable to floating point pixel values. **NOTE** For a more detailed explanation of ORANGE, tutor the orange.pdf.