Abstract
Understanding how the surfaces of airless planetary bodies-such as the Moon-scatter visible light enables constraints to be placed on their surface properties and top boundary layer inputs to be set within thermal models. Remote sensing instruments-such as Diviner onboard the Lunar Reconnaissance Orbiter-measure thermal emission and visible light scattering functions across visible (∼0.38-0.7 µm) to thermal infrared (TIR) wavelengths (∼0.7-350 μm). To provide ground support measurements for such instruments, the Oxford Space Environment Goniometer (OSEG) was built. Initially, the OSEG focused on measuring TIR directional emissivity functions for regolith and regolith simulant samples in a simulated space environment, but it has recently been modified to measure visible wavelength Bidirectional Reflectance Distribution Functions (BRDFs) of samples in ambient conditions. Laboratory-measured BRDFs can be used (1) to test and to help interpret models-such as the Hapke photometric model-and (2) as visible scattering function inputs for thermal models. This paper describes the modifications to and initial calibration measurements taken by the Visible Oxford Space Environment Goniometer with a 532nm laser, and details how this setup can be used to measure BRDFs of regolith and regolith simulant samples of airless planetary bodies.
Highlights
Introduction and MotivationMeasuring Bidirectional Reflectance Distribution Functions (BRDFs) for planetary regolith and regolith simulant samples is useful in planetary science for the following reasons: 1) Testing and Interpreting the Hapke Model: The Hapke model is a commonly used photometric model in planetary reflectance data analysis because it is based on solutions to the radiative transfer equation, and because it has nine free parameters which relate to the composition and surface properties of a particulate surface[1,2,3,4,5]
This paper describes the modifications to, and initial calibration measurements taken by the Visible Oxford Space Environment Goniometer (VOSEG), with a 532nm laser, and details how this setup can be used to measure BRDFs of regolith and regolith simulant samples of airless planetary bodies
VOSEG’s BRDF measurements of Spectralon are in agreement with those taken by Bloomsburg University Goniometer (BUG), within standard error
Summary
Measuring Bidirectional Reflectance Distribution Functions (BRDFs) for planetary regolith and regolith simulant samples is useful in planetary science for the following reasons: 1) Testing and Interpreting the Hapke Model: The Hapke model is a commonly used photometric model in planetary reflectance data analysis because it is based on solutions to the radiative transfer equation, and because it has nine free parameters which relate to the composition and surface properties (such as porosity and surface roughness) of a particulate surface[1,2,3,4,5]. Visible reflectance/albedo measurements taken by remote sensing instruments such as the Diviner Radiometer (onboard the Lunar Reconnaissance Orbiter (LRO)) can be interpreted by comparing them with Hapke modelled BRDFs6,7. This provides a method by which compositional/physical property variations can be determined across varying regions of an airless bodies’ surface[6]. Any deductions made using this method rely on the physicality of the free parameters of the model These parameters have been updated over time, as further remote sensing and laboratory BRDF measurements have become available[3,8,9,10]. How the requirements of the VOSEG instrument are derived from these two motivations is described in parts A, and B
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