This week I will be discussing the Thermal Emission Spectrometer (TES) Dust Cover Index (DCI) map of Mars.
1. What is the TES DCI?
- The TES DCI is a measure of the relative abundance of the spectrally obscuring dust across the surface of Mars. It is independent of albedo and it is based on the fact that fine grains of silicates show an average emissivity from 1350 to 1400 cm-1, where surfaces with high abundance of silicate particulates (dust-covered surfaces) show lower emissivity and surfaces with an absence of silicates particulates (dust-free surfaces) show high emissivity.
2. What is the value range of the TES DCI?
- The values of the TES DCI range from 0.89 to 1.00, where lower values represent dust-covered surfaces and higher values represent dust-free surfaces.
3. What are the average TES DCI values for dust-covered and dust-free surfaces on Mars?
- Dust-covered surfaces have an average value of 0.931 ± 0.009, and dust-free surfaces have a value of 0.969 ± 0.007 (see Figure 1).
Figure 1: Global map of the TES DCI of Mars on top of the Mars Orbiter Laser Altimeter shade relief base map. Courtesy of NASA/JPL/Goddard
4. What wavelengths the TES DCI uses?
- TES DCI is sensitive to thermal-IR wavelengths (few tens of microns), making it a perfect metric to measure physical characteristics of surfaces.
Here, we identified the TES DCI average values for some volcanic surfaces on Mars and plot them against their RMS slope (see Figure 2), to help us establish how the TES DCI affects our surface roughness values for these surfaces. Note that the TES DCI range for this work is from ~ 0.92 to 0.98. With a range of 0.06, every change is significant; even a difference of 0.01, 0.02, or 0.03. In this plot, we see that duster surfaces have low RMS slope (they are smoother) with some exceptions and vice versa.
Figure 2: RMS slope vs TES DCI for volcanic surfaces of Mars.
Ruff, S. W., and P. R. Christensen, Bright and dark regions on Mars: Particle size and mineralogical characteristics based on Thermal Emission Spectrometer data, J. Geophys. Res., 107(E12), 5127, doi:10.1029/2001JE001580, 2002.
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