New Mars Exploration Rover Panoramic Camera (Pancam) Version 2 
Radiance-Factor (IOF) Calibrated RDRs.
Jim Bell (ASU), Jonathan Joseph (Cornell), 
Kjartan Kinch (Univ. Copenhagen)
25 June 2020

This is a brief summary of how new Version 2 radiance-factor calibrated
("IOF"; an estimate of reflectance) RDRs for the Mars Exploration Rover
Pancam investigation (Bell et al., 2003) have been updated relative to the
existing Version 1 IOF calibrated RDRs previously archived in the PDS.
Specifically, these modified processing steps below were applied to the
original Pancam EDRs, compared to the steps used to create the original
Version 1 IOF calibrated RDRs (documented in Bell et al., 2006):

(A) Raw EDRs were first recalibrated to absolute radiance (“RAD”) units
(W/m^2/nm/sr) using the new Ver-sion 2 RAD calibration process (updated bias,
dark current, and flatfield corrections plus corrections to the ELEVATION
label keyword) described in the pancam_rad_v2_summary document associated
with the new Ver-sion 2 release of the Pancam calibrated RAD files (see:
https://pds-geosciences.wustl.edu/mer/mer2-m-pancam-3-radcal-sci-
v2/mer2pc_1002/calib/pancam_rad_v2_summary.txt).

(B) The standard procedure for calibration of Pancam images to IOF (an
acronym for the quantity I/F, where I = the measured scene radiance from the
RAD files and F = the solar irradiance at the top of the Martian atmosphere)
relies on the fact that the Pancam calibration target has seven different
Regions of Interest (ROIs) with known laboratory-derived reflectance
properties; extracting the observed radiances from these ROIs in the RAD
calibrated images and performing a linear fit between radiances and lab ROI
reflectances at each wavelength re-sults in coefficients that convert the RAD
data to estimated IOF (Bell et al., 2006). In the Version 2 Pancam IOF
calibration process, the calibration target ROIs have been modified across
the entire duration of both rover mis-sions to avoid the use of areas of the
calibration target with abnormal levels of windblown dust during various
phases of the missions. This resulted in a new set of refined radiance to
reflectance (IOF) coefficients.

(C) The calibration targets accumulated low levels of airfall dust
continuously throughout both rover mis-sions. For most of the missions the
dust covering was transparent enough that a straightforward two-stream radia-
tive transfer model was used to correct for the dust cover and “remove” its
influence on the RAD to IOF coeffi-cients derived in Step (B) above. In the
Version 2 Pancam IOF calibration process, the initial Version 1 calibration
target dust model correction was replaced with a much more rigorous and
refined dust model correction (Kinch et al., 2015).

(D) Most calibration target observations were taken, by design, very close in
time to the images they were intended to calibrate. In some cases, however,
the calibration target sequence failed to be properly acquired or downlinked,
or time or power or other concerns did not allow an accompanying calibration
target sequence to be run. In the Version 1 Pancam IOF calibration process,
the calibration pipeline did not optimize the choice of which calibration
target to use for the best IOF calibration of each Pancam sequence, and
simply chose the one that was closest in time. The result was that the
calibration target used may have been acquired at a completely different time
of day and viewing geometry than the sequence that it ultimately calibrated.
In the Version 2 Pan-cam IOF calibration process, the pipeline was modified
to use the best choice of calibration target by balancing the difference in
time and viewing geometry between calibration target sequence and the
sequence that it ultimate-ly calibrated.
 
New Version 2 Pancam calibrated IOF RDRs were created using these calibration
improvements for all MER-A (Spirit) and MER-B (Opportunity) Pancam RDRs.

References cited:

Bell III, J.F., J. Joseph, J.N. Sohl-Dickstein, H.M. Arneson, M.J. Johnson,
M.T. Lemmon, and D. Savransky, In-flight calibration and performance of the
Mars Exploration Rover Panoramic Camera (Pancam) Instruments, J. Geophys.
Res., 111, E02S03, doi:10.1029/2005JE002444, 2006.

Bell III, J.F., S.W. Squyres, K.E. Herkenhoff, J.N. Maki, H.M. Arneson, D.
Brown, S.A. Collins, A. Dingizian, S.T. Elliot, E.C. Hagerott, A.G. Hayes,
M.J. Johnson, J.R. Johnson, J. Joseph, K. Kinch, M.T. Lemmon, R.V. Morris, L
Scherr, M. Schwochert, M.K. Shepard, G.H. Smith, J.N. Sohl-Dickstein, R.
Sullivan, W.T. Sullivan, and M. Wadsworth, The Mars Exploration Rover Athena
Panoramic Camera (Pancam) Investigation, J. Ge-ophys. Res., 108 (E12),
doi:10.1029/2003JE002070, 2003.

Kinch, K.M., J.F. Bell III, W. Goetz, J.R. Johnson, J. Joseph, M.B. Madsen,
and J. Sohl-Dickstein, Dust deposition on the decks of the Mars Exploration
Rovers: 10 years of dust dynamics on the Panoramic Camera calibration
targets, Earth & Space Sci., doi:10.1002/2014EA000073, 2015.