The Diviner Lunar Radiometer Experiment onboard the Lunar Reconnaissance Orbiter (LRO) has been acquiring solar reflectance and mid-infrared radiance measurements nearly continuously since July of 2009. Diviner is providing the most comprehensive view of how regoliths on airless bodies store and exchange thermal energy with the space environment.
Approximately a quarter trillion calibrated radiance measurements of the Moon, acquired over the first 5.5 years of the mission, have been compiled into our Level 4 - Global Cumulative Products (GCP). This data represents a compilation of all Diviner nadir observations from 5-July-2009 to 1-April-2015. They are produced by binning Diviner RDR (Level 1b) radiance measurements for each IR channel (channels 3-9) in 0.5 degree bins in longitude and latitude, and 0.25 hours of local time to determine the average brightness temperatures on a global cylindrical grid. Additionally, the average radiance values for all the channels were used to determine the bolometric brightness temperatures for each bin. From this data, we generated snapshots of the lunar surface temperatures for 24 different locations of the sun to represent global temperatures during an entire lunation.
Maps generated with this dataset provide a global perspective of the surface energy balance of the Moon and reveal the complex and extreme nature of the lunar surface thermal environment. Daytime maximum temperatures are sensitive to the albedo of the surface (surface brightness) and are ∼387–397 K (∼237-255° F) at noon at the equator, dropping to ∼95 K (∼-290° F) just before sunrise. Nighttime temperatures are sensitive to the thermophysical properties of the regolith. Dense materials, such as large rocks, remain warmer during the long lunar night and result in warmer nighttime temperatures. The brightness of the surface is seen in a global map derived from Diviner’s channel 1 of reflected visible sunlight from the local time hours of 9 – 10 (mid-morning) and examples of the average temperatures at noon and midnight are provided.
The variations in maximum and minimum temperatures are highlighted in a series of maps. In addition to the minimum and maximum temperatures, maps with the average temperatures for given latitude subtracted out (zonal average removed) highlight anomalous temperatures due to variations in the regolith properties as well as the ratios and the difference between the minimum and maximum temperatures which highlight the relative differences between the two temperature extremes and the amplitude of the extremes in temperature. The minimum and maximum temperature anomalies, along with the channel 1 visible brightness map, have been combined into an RGB color composite image to provide a broad characterization of the terrains globally.
Variations in temperatures within Diviner’s field of view result in temperature differences between individual channels in the instrument. The difference between Diviner’s channel 6 (∼13-23 μm) and channel 8 (∼50-100 μm) highlight areas where there are mixtures of warmer surface temperatures (such as rocks) at night as the shorter wavelength channel is more sensitive to the warmer temperatures. Differences in daytime temperatures between Diviner’s channels 3 and 7 and channels 4 and 7 highlight differences in emissivity as there is a peak in thermal emission at wavelengths near channels 3 and 4 around 8 μm. Variations in the composition of the regolith cause the peak in the emission to shift to different wavelengths and cause variations in the temperatures in channels 3 and 4 relative to channel 7.
The files may be accessed here.