The LRO Diviner Lunar Radiometer has been mapping the entire Moon on a nearly continuous basis since July, 2009. The Diviner dataset includes excellent spatial and diurnal coverage of the Mare Imbrium region. The Diviner team has produced maps of the thermal behavior and and a range of derived quantities at Chang’e 3 landing site that are described below.
Brightness temperature (TB):
Brightness temperature is the temperature that a black body (a body with emissivity = 1) in thermal equilibrium with its surroundings would have to be to produce the radiance that Diviner observes in a particular wavelength interval.
Bolometric temperature (TBOL):
Bolometric temperature is the wavelength-integrated radiance in all seven thermal Diviner channels expressed as the temperature of an equivalent blackbody (Paige et al., 2010). Using data from the entire Diviner dataset to date (Jul. 2009 - Dec. 2013), we can calculate the maximum and minimum bolometric temperatures that have been observed at the Chang’e 3 landing site.
Regolith Temperature and Rock Abundance
The maps show Lunar surface rock abundance and nighttime rock free regolith temperatures. These data were derived from LRO Diviner channels 6-8 (wavelengths of 12-100 microns) data. The colorized maps are shaded using the LRO Camera derived digital terrain model.
Bandfield, J.L., R.R. Ghent, A.R. Vasavada, D.A. Paige, S.J. Lawrence, M.S. Robinson (2011) Lunar surface rock abundance and regolith fines temperatures derived from LRO Diviner Radiometer data. Journal of Geophysical Research, 116, 010.1029/2011JE003866.
Scholten, F., J. Oberst, K.-D. Matz, T. Roatsch, M. Wählisch, E.J. Speyerer, M.S. Robinson (2012) GLD100: The near-global lunar 100 m raster DTM from LROC WAC stereo image data. Journal of Geophysical Research, 117, 010.1029/2011JE003926.
Taking into account the different nighttime cooling behavior of rocks and regolith, we use Diviner brightness temperatures to produce maps of rock abundance and nighttime regolith temperature (Bandfield et al., 2011). We then fit thermal models to the regolith temperature data to derive a subsurface profile of thermal conductivity and density (Hayne et al., 2013). The steepness of this profile is described by the “H-parameter”, where small values of H indicate more compact regolith, and large values of H are consistent with more fluffy, unconsolidated regolith. This parameter is similar to thermal inertia, a commonly used quantity in planetary science.
Diviner Standard Christiansen Feature (CF) Value
Diviner uses three bands near 8 microns (Ch 3, 4, & 5) to measure the Christiansen Feature (CF) and determine the bulk composition of lunar soils (Greenhagen et al., 2010, Science). The CF is related to silicate polymerization and shifts in a systematic way across lunar compositions (e.g. Conel, 1969, JGR; Logan et al., 1973, JGR; Salisbury and Walter, 1989, JGR). The median CF Value for highlands materials is 8.15 and mare materials is 8.28. Standard CF is sensitive to illumination and viewing geometry, and space weathering.
Diviner Corrected Christiansen Feature (CF) Value
Due to an observed dependence of Standard CF Value with solar illumination and instrument viewing geometry, we attempt to normalize the radiance data to equatorial noon and calculate a “corrected” CF Value (after Greenhagen et al., 2010, Science; Greenhagen et al., 2011, LPSC). Corrected CF Values are useful to comparisons across ranges of latitude and local time and for comparisons to laboratory data. Data artifacts are most noticeable in very dark terrains, which are underrepresented in the photometric database used to compile the correction.
Diviner Concavity Index (CI)
This spectral concavity index was developed to identify compositions that have CFs outside (either short- or long-ward of Diviner’s 8 micron bands (Glotch et al., 2010, Science). The CI is particularly useful for identifying highly silicic materials such as quart and alkali feldspar, which have a strong positive CI (Glotch et al., 2010, Science).
Diviner Ch 4 Brightness Temperature (TB)
The peak of the CF is most consistently near Diviner’s Ch 4 passband; therefore, Ch 4 has a TB with close to unit emissivity.