Exploring the moon in the thermal infrared: the space environment goniometer

Thesis

Measurements of the light scattering behaviour of the regolith of airless bodies in the Solar System, across wavelengths from the visible to the far infrared are essential to understanding their physical properties. This thesis describes the design, build and calibration of a novel instrument to measure the angular directionality of thermal infrared emission from surfaces (direction emissivity, DE). This work was originally motivated by the need for new DE measurements to support analysis of data collected by the thermal and far infrared Diviner Lunar Radiometer instrument (8 – 400 μm) currently in orbit around the Moon.

To fully interpret the brightness temperatures measured by the Diviner instrument a three dimensional thermal physical model is required. These models typically assume that infrared radiation is scattered isotropically from the lunar surface. Although generally the models are in very good agreement with Diviners measured brightness temperatures, there are some discrepancies particularly in permanently shadowed regions near the lunar poles. One possible reason for these discrepancies is that the thermal infrared DE of the lunar surface is not isotropic as is typically assumed by many of these models. The "Oxford Space Environment Goniometer" (OSEG) was developed to measure the DE of surface across wavelengths from the visible to the thermal and far infrared.

Analysis and modelling of initial DE measurements made with the OSEG show that the DE is dependent on the optical properties and roughness of the surface. DE measurements of the lunar regolith analogue material JSC-1AF have been incorporated into a three dimensional thermal physical model to show that the predicted surface temperatures of a polar lunar-like permanently shadowed region can differ by 10 K compared to assuming an isotropic DE.

Authors: Warren, T

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford