Voyager ISS Voyager ISS Calibration Memo 1986-01-16


To: Voyager Imaging Team                     Date: 16 jan. 1986 
From: T. V. Johnson, Arithmatic Society 
Subject: Corrections to Danielson et al. Calibration 
 
     The current calibration factors used to correct FICOR output 
to I/F are derived from the Danielson et al. paper.  These 
factors, and their associated omega0 values qualitatively amount 
to the assumption that the VGR camera bench calibrations for the 
Blue filter are correct and that the color of the inflight plaque 
target is the same as that measured by Rennelson for a piece of 
similar material.  This correction brought most VGR I/F values 
for Jupiter targets into resonably good agreement with ground- 
based data both in absolute albedo at Blue (~4800 A) and in 
relative spectral reflectance between filters. 
     Subsequent analysis of VGR spectral data and comparisons 
with ground-based spectral reflectance measurements have shown 
that the Danielson et al. corrections to bench calibration values 
do not completely correct VGR values to the best estimates of 
ground-based spectral albedoes for a number of targets, both at 
Jupiter and Saturn (see Johnson et al. 1982 for a discussion of 
Jupiter satellite comparisons).  The attached figure shows 
several estimates of 'corrected' VGR I/F values divided by 
ground-based 'truth'.  The square points are an average and 
standard deviation of VGR data divided by ground-based data from 
McFadden et al. (appropriately convolved with the NA camera 
system response), for all four Galilean satellites and for both 
the Voyager 1 and 2 cameras.  The circled X's are a similar 
exercise carried out by Bonnie Burratti for several Saturnian 
satellites compared with values from ground-based photometry by 
Noland et al.  The other points are individual comparisons I made 
of Rhea photometry with data from Bell et al.  The ratios are all 
very consistent and the current estimate of the correction to the 
Danielson et al. values has been made from the average of the 
Johnson values for Jupiter and the Burratti estimates for Saturn. 
Scaled to Blue filter correction = 1.0000 these values are: 
 
UV - 0.828 
VI - 0.935 
BL - 1.000 
OR - 1.053 
 
     The values of IPL correction factors and the Omega0 values 
for each planet in the attached table are derived from the above 
by multiplying the existing omega0's by the above values and 
dividing the IPL factors by the same. 
 
     We recommend that the the MIPL FIXVGR program replace the 
existing values for these correction factors with the ones in the 
table and use them for future I/F processing. 
 


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Date:   16-Jan-86 
VOYAGER 2 CALIBRATION FACTORS: NARROW ANGLE CAMERA 
 
------------------------------------------------------------------------ 
Filter            Clear    Violet   Blue     Orange   Green    Ultraviolet 
#                    0,4       1        2        3       5,6       7 
------------------------------------------------------------------------ 
J IPL Corr.factor    0.913    0.884    1.000    0.961    1.013    3.151 
S IPL Corr.factor    3.054    2.957    3.345    3.215    3.388   10.540 
U IPL Corr.factor   12.346   11.954   13.523   12.999   13.698   42.611 
J omega 0(5.2au)  2161.980  669.114  909.510  205.368  475.310   69.292 
S omega 0(9.51au)  646.394  200.053  271.928   61.401  142.109   20.717 
U omega 0(19.122au 159.879   49.481   67.259   15.187   35.149    5.124 
------------------------------------------------------------------------ 
 


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VOYAGER 2 CALIBRATION FACTORS: WIDE ANGLE ANGLE CAMERA 
 
------------------------------------------------------------------------ 
Filter                     Blue     Clear    Violet   Green    Orange 
#                              1        2        3        5        7 
------------------------------------------------------------------------ 
J IPL Corr.factor             1.068    1.022    0.897    1.003    0.989 
S IPL Corr.factor             3.572    3.418    3.000    3.355    3.308 
U IPL Corr.factor            14.442   13.820   12.130   13.563   13.374 
J omega 0(5.2au)            6099.45 11447.76  2569.06   3369.9  963.684 
S omega 0(9.51au)          1823.628 3422.679  768.104 1007.541  288.125 
U omega 0(19.122au)         451.056  846.566  189.983  249.205   71.265 
------------------------------------------------------------------------ 
 


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figure_1986_01_16