Interannual and seasonal changes in the south seasonal polar cap of Mars: Observations from MY 28-31 using MARCI

This data set collects contours for the seasonal cap retreat published in Figure 3 of the associated article in Icarus. There are two zip files, one for text and one for shapefiles.  See the methods for how to convert pixel locations to lat/lon coordinates.

The Mars Color Imager (MARCI) camera on the Mars Reconnaissance Orbiter provides daily synoptic coverage that allows monitoring of seasonal cap retreat and interannual changes that occur between Mars Years (MY) and over the southern summer. We present the first analysis of this data for the southern seasonal cap evolution observed in MY 28, 29, 30 and 31 (2/2007 to 07/2013). Observation over multiple Mars years allows us to compare changes between years as well as longer-term evolution of the high albedo deposits at the poles. Seasonal cap retreat is similar in all years and to retreats observed in other years by both optical and thermal instruments. The cryptic terrain has a fairly consistent boundary in each year, but numerous small-scale variations occur in each MY observed. Additionally, numerous small dark deposits are identified outside the classically identified cyptic region, including Inca City and other locations not previously noted. The large water ice outlier is observed to retain seasonal frost the longest (outside the polar dome) and is also highly variable in each MY. The development of the cryptic/anti-cryptic hemispheres is inferred to occur due to albedo variations that develop after dust venting starts and may be caused by recondensation of CO2 ice on the brightest and coldest regions controlled by topographic winds. Ground ice may play a role in which regions develop cryptic terrain, as there is no elevation control on either cryptic terrain or the late season brightest deposits.

Methods
The data are strored as region of interest (ROI) text or evf shape files saved from the software ENVI.  Each subfolder includes a png image of the contours over MOLA elevation.  For the text files, each ROI is stored sequentially, the header notes the number of points in each ROI and then provides an x, y value for each point in the ROI. There are 12 ROIs for each year, every 10 degrees of Ls from 205 to 315. To convert these to lat lon, the image is a polar stereo projection 720 x 720 pixels.  These reach 60 deg latitude at the edges of the frame, there are lower latitudes in the corners. 0,0 is the upper left by the Argyre impact basin and 720,720 the lower right.  The center of the image (360,360) is the south pole(90S, 0). Use the pixel coordinate to determine the distance from the center of the image, this radial distance in converted to latitude using 30 deg/360 pixels. Longitude is similarly calculated using the angle from center top, which is 0 degrees with E quadrants note in Figure 1 of the associated Icarus article.