New Diviner South Polar Data Products Released on PDS
New Diviner south polar data products have been released on the Diviner PDS data archive this week. These new data products supplement the existing level 4 Polar Cumulative Products (PCP). Previous PCP products highlighted diurnal (daily) temperatures at the lunar poles by splitting the Diviner Level 1 data into 96 diurnal bins. This data was then separated into winter and summer months defined by whether the sun was north or south of the equator. The new dataset, which focuses on the south polar region, emphasizes the seasonal temperature variations by dividing the data into 6 seasonal bins (rather than just 2). This was done by defining the ecliptic longitude (Ls) for the Earth-Moon system. The values of Ls describe the angular distance, 0° – 360°, of the progression of the Moon through its seasonal cycle where 0° represents for the northern hemisphere the vernal equinox, 90° the summer solstice, 180° the autumnal equinox, and 270° the winter solstice, with the seasons reversed for the southern hemisphere. The annual seasonal cycle, referred to as the draconic year, is 346.62 Earth days, and is less than the Earth’s seasonal cycle of 365.25 days due to a precession of the Moon’s orbit around the Earth. The seasons on the Moon are caused by a small tilt of the Moon’s rotation axis which generally does not have a noticeable effect on the Moon’s surface temperatures. However, within the polar regions, small changes in the Sun’s elevation in the sky can have a large influence on illumination and shadowing. As a result, the amount of shadowing and scattered light that makes its way into shadowed areas, including the permanently shadowed area (PSRs), varies substantially with the seasons.
The new Polar Cumulative Products are formatted as simple ASCII tables with additional raster files and browse images available here. The data was produced by binning Diviner RDR (Level 1b) radiance measurements for each IR channel (channels 3-9) in 240 meter bins of a south polar stereo projected grid and split into 24 subsolar longitude bins (diurnal) and 6 Ls bins (seasonal), to determine the mean bolometric brightness temperatures over a 10 degree latitudinal cap. For more details see: Schorghofer, N., and J.-P. Williams (2020), Mapping of ice storage processes on the Moon with time-dependent temperatures, Planetary Science Journal, 1:54, https://doi.org/10.3847/PSJ/abb6ff.
Figure: (A) Average temperatures for the south polar region to 80°S latitude. (B) The ratio of the diurnal and seasonal temperature amplitudes. Areas with yellow/green colors, including the large PSRs near the pole, are where the seasonal temperature variations are as large, or larger, than the daily variation in temperatures. These are the regions where seasons play a large role in the surface temperatures (Adapted from Schorghofer and Williams, PSJ, 2020).