clemuvviscal
Radiometric correction of Clementine UV/VIS camera images
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.
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.
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.
Categories
Related Objects and Documents
Applications
History
| Tracie Sucharski | 1994-11-18 | Original Version (uvviscal.F) |
| Steven Lambright & Steven Koechle | 2007-05-16 | Converted to Isis 3.0 |
| Steven Lambright & Steven Koechle | 2007-06-07 | Beautified and forcing output pixel type to real. |
| Steven Lambright | 2007-06-14 | Cleaned up XML, added an example and added Radiometry group to labels of output cube. |
| Steven Lambright & Steven Koechle | 2007-06-18 | Fixed problem with solar distance calculation |
| Steven Lambright | 2008-02-08 | Changed TCOR paramter's default to TRUE |
| Christopher Austin | 2008-02-20 | Altered the output cube's BandBin group, changing the Keyword "Name" back to "FilterName". |
| Steven Lambright | 2008-05-13 | Removed references to CubeInfo |
| Christopher Austin | 2009-06-11 | Fixed a segmentation fault. |
Parameters
Files
Specify the input file to be corrected.
| Type | cube |
|---|---|
| File Mode | input |
| Filter | *.cub |
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 |
Settings
This option allows the output values to be written as
absolute radiance or converted to reflectance values (I/F).
| Type | boolean |
|---|---|
| Default | true |
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 |
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: |
|
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 |
|---|
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
$ISISDATA/clementine1/calibration/uvvis/dark_5_15_96.cub.
| Type | cube |
|---|---|
| File Mode | input |
| Internal Default | Automatic |
| Filter | *.cub |
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
$ISISDATA/clementine1/calibration/uvvis/lu[filter]_[un]comp_flat_long.cub.
An example for a compressed B filter image is
$ISISDATA/clementine1/calibration/uvvis/lub_comp_flat_long.cub.
| Type | cube |
|---|---|
| File Mode | input |
| Internal Default | Automatic |
| Filter | *.cub |
Example 1
Calibrating a cube to I/F values using temperature correction
Calibrating a cube to I/F values using temperature correction
Command Line
In this example clemuvviscal will calibrate lua1841h.cub using temperature correction.
clemuvviscal
clemuvviscal FROM=lua1841h.cub TO=lua1841h.cal.cub TCOR=TRUE
GUI Screenshot
Calibrate lua1841h.cub using temperature correction
Calibrate lua1841h.cub using temperature correctionIn this example clemuvviscal will calibrate lua1841h.cub using temperature correction.
Input Image
Image before correction
lua1841h.cub before being corrected
Parameter Name:
FROM
This is the input image lua1841h.cub before being corrected with clemuvviscal.
Output Image
Image after correction
lua1841h.cub after being corrected
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.