Surface Changes Observed at Greeley Haven during Opportunity's Fifth Martian Winter

A series of images acquired by the Pancam imaging system on the Mars Exploration Rover Opportunity between Sols 2825 and 2946 (January to May, 2012) documented changes in surface dust and soils at Cape York (Meridiani Planum) while the rover was parked at its winter location (Greeley Haven) on the rim of Endeavour Crater. Observations included five 360° "albedo pans" acquired using the L1 filter (739 ± 338 nm) and seven multispectral image sets (754 nm, 535 nm, 432 nm) of a single scene near the rover disturbed by the wheels (Fig. 1). The albedo pan images were acquired using 2x2 pixel downsampling and 1 bit/pixel lossy wavelet-based compression, and were all acquired within 1 minute of 12:04 local true solar time (LTST) on each of the five sols (Martian day). The near-field images were acquired using lossless compression, and were all acquired within 1 minute of 12:23 LTST on each sol. All images were calibrated to relative reflectance using established algorithms and observations of the onboard calibration target. Because of minor pointing misregistration and/or slight rover motion (owing to the 15° slope on which the rover was parked), images required alignment using sub-pixel coregistration. Ratios between the earliest and later images documented changes in the scene. Several types of changes were observed over the 121-sol interval, likely caused by winds along the crater rim. These included: (1) albedo changes of the dark aeolian bedforms in the interior of Endeavour Crater; (2) brightening and darkening of ripples on dune faces associated with redistribution of dust; (3) darkening of some compressed rover tracks; and (4) brightening of disturbed areas near the rover tracks related to reappearance of high albedo granules as darker disturbed soil was winnowed away and loose spherules were removed. Changes in the solar azimuth and elevation (and hence phase angle) for the same LTST over 121 sols were only ~5°, so it is unlikely that the observed changes are due to lighting variations with time. Further, several of these events compare favorably to minor dust cleaning episodes documented by the changes in power from the rover's solar cells. This is additional evidence for the influence of winds at both the surface boundary layer and the 70 cm elevation of the rover deck. Fig. 1. False-color scene of wheel tracks in front of rover (Sol 2882, P2551).