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.
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
------------------------------------------------------------------------
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
------------------------------------------------------------------------
Last updated 26 August 2003