clemuvviscal

This program performs radiometric corrections to images acquired by the Clementine spacecraft UVVIS camera. It performs dark subtraction, readout correction, non-linearity and flat field corrections and gives the user the option of writing the output image values as radiance values or as reflectance(I/F) values.

PLEASE NOTE: In the ISIS2 Fortran code the method FIXTEMP uses a REAL*4 (6 digits of accuracy) to store the RIMGID (8 digits) which results in the last digits being lost. In the table that references RIMGID the value is a REAL*4 again resulting in the same loss of precision; this makes the lookup table for temperature corrections inaccurate.

ALGORITHM


General algorithm applied to data for radiometric correction is described below:

Step 1. Global Offset Correction

Step1_DN = raw_DN - C4*OffsetModeID - C5
C4 = -8.177
C5 = 15.56

Step 2. Divide by gain

Step2_DN = Step1_DN / g(GainModeID)
g(GainModeID)
g(1) = 1.0
g(2) = 2.907
g(4) = 6.906

Step 3. Dark current correction

Step3_DN = Step2_DN - (DC + C3)
C3 = 7.13

Non-linearity correction

XMUL = ACO + BCO*Step3_DN + CCO*(Step3_DN**2) + DCO*(Step3_DN**3)
CorrectedStep3_DN = Step3_DN * XMUL
ACO = 1.062
BCO = -.1153E-02
CCO = .6245E-05
DCO = -.1216E-07

Step 4. Temperature-Dependent Offset Correction

Step4_DN = CorrectedStep3_DN - C2 * u
C2 = .003737 * exp(.0908*(T-273.15))
T = Corrected FocalPlaneTemperature (The value in the labels is not correct. The value used is taken from an interpolated set of values from ACT)
u = t + readout time
t = ExposureDuration + .0494
readout time = 60.05 + .05*(line # - 1)

Step 5. Frame Transfer Correction

Step5_DN = Step4_DN - ro
ro = column_sum*dt/(t+288*dt)
column_sum = sum of all 288 Step4_DN values
dt = frame transfer time per row = .00068
t = ExposureDuration + .0494

Step 6. Flat-Field and Exposure Time Normalization

Step6_DN = Step5_DN / (FF*t)
FF = Filter-dependent flat-field
t = ExposureDuration + .0494

The units of Step6_DN are now in counts/ms.

Step 7. Normalize to Sun-Moon distance of 1 AU

Step7_DN = Step6_DN * (SolarDistance in AU)**2

Step 8a. Conversion to 1 AU Relative Radiance

L = Step7_DN / C1 ( L = Radiance in mW/sr-cm**2 )

CenterFilterWavelength C1
415 nm 1.39
750 nm 2.57
900 nm 4.35
950 nm 4.76
1000 nm 2.77

Step 8b. Conversion to Reflectance

R = Step7_DN * CR

The following CR values were derived by Eric Eliason on 6/20/96. These are slight improvements over Carle Pieter's values because Eric used the most current flat files and Alfred McEwen's non-linearity correction. For more information, see Eric's memo from 6/20/96.

CenterFilterWavelength CR
415 nm .021406
750 nm .012266
900 nm .010674
950 nm .010831
1000 nm .024271

Note: if the cub has a compression ratio of 1.0 (the cube is uncompressed) it will use difference flat field file.

Description

Specify the input file to be corrected.

Type	cube
File Mode	input
Filter	*.cub

Description

Specify the output file. The result will be the radiometrically corrected image. The output values can either be output as absolute radiance or converted to reflectance (I/F) values.

Type	cube
File Mode	output
Pixel Type	real
Filter	*.cub

Description

This option allows the output values to be written as absolute radiance or converted to reflectance values (I/F).

Type	boolean
Default	true

Description

This option defines whether or not to use temperature correction. If disabled, the focal plane temperature read from the labels is used (if it is not equal to zero, otherwise temperature correction is used anyways). When TCOR is enabled, the temperature read from the labels is disregarded and a table is searched based on the orbit number and mission phasederived from the ProductID stored in the labels.

Type	boolean
Default	true

Description

This option allows the user to input a constant value for the dark current, or alternatively a cube file with dark current values (default).

Type	string
Default	DCFILE
Option List:	Option Brief Description DCFILE Uses a dark current cube The dark current values used in the equations will be taken from a cube. Exclusions DCCONST DCCONST Uses a dark current constant The dark current values used in the equations will be a constant number. Exclusions DCFILE Inclusions DCCONST

Description

This constant will replace the array of dark current coefficients in the derived dark current file. In most cases, the default should be used for this parameter to indicate the derived dark current file is to be used.

Type	double

Description

This parameter allows the user to use an alternate dark current file. In most cases, the default should be used for this parameter to indicate the derived dark current file is to be used. The name of the derived dark current file is $ISIS3DATA/clementine1/calibration/uvvis/dark_5_15_96.cub.

Type	cube
File Mode	input
Internal Default	Automatic
Filter	*.cub

Description

This parameter allows the user to use an alternate flat-field file. In most cases, the default should be used for this parameter to indicate the derived flat-field file is to be used. There is a different version of the flat file for compressed and uncompressed images. The name of the derived flat-field file is $ISIS3DATA/clementine1/calibration/uvvis/lu[filter]_[un]comp_flat_long.cub. An example for a compressed B filter image is $ISIS3DATA/clementine1/calibration/uvvis/lub_comp_flat_long.cub.

Type	cube
File Mode	input
Internal Default	Automatic
Filter	*.cub

Calibrating a cube to I/F values using temperature correction

clemuvviscal clemuvviscal FROM=lua1841h.cub TO=lua1841h.cal.cub TCOR=TRUE

Calibrate lua1841h.cub using temperature correction

Calibrate lua1841h.cub using temperature correction In this example clemuvviscal will calibrate lua1841h.cub using temperature correction.

lua1841h.cub before being corrected

Image before correction Parameter Name: FROM This is the input image lua1841h.cub before being corrected with clemuvviscal.

lua1841h.cub after being corrected

Image after correction Parameter Name: TO This is the input image lua1841h.cub after being corrected with clemuvviscal. The values in this cube are all I/F because CONV was set to true by default.