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
------------------------------------------------------------------------