Contribution to Sandy Site Characterization: Spectro-Directional Signature, Grain Size Distribution and Mineralogy Extracted from Sand Samples

Viallefont-Robinet Viallefont-Robinet,Grignon Grignon,Rivière Rivière,Idoughi Idoughi,Lemaître Lemaître,Ouhssain Ouhssain,Bouvet Bouvet,Bacour Bacour,Kheireddine Kheireddine,Munesa Munesa

doi:10.3390/rs11202446

Abstract

The characterization of sands detailed in this paper has been performed in order to support the in-flight radiometric performance assessment of space-borne optical sensors over the so-called Pseudo-Invariant Calibration Sites (PICS). Although the physical properties of PICS surface are fairly stable in time, the signal measured from space varies with the illumination and the viewing geometries. Thus, there is a need to characterize the spectro-directional properties of PICS. This could be done on a broad scale, thanks to multi-spectral multi-directional space-borne sensors such as the POLDER instrument (with old data). However, interpolating or extrapolating the spectro-directional reflectance measured from space to spectral bands of another sensor is not straightforward. The hyperspectral characterization of sand samples collected within or nearby PICS could contribute to a solution. In this context, a set of 31 sand samples was compiled. The BiConical Reflectance Factor (BCRF), linked to Bidirectional Reflectance Distribution Function (BRDF), was measured between 0.4 and 2.5 µm, over a half hemisphere when the amount of sand in the sample was large enough and for only a single fixed angular configuration for small samples. These optical measurements were complemented by grain size distribution measurements and mineralogical analysis and compiled together with previously published measurements in the so-called PICSAND database, freely available online.

Highlights

Some sandy desert sites known for their temporal stability and their spatial uniformity have been used for a long time to radiometrically calibrate and monitor optical space-borne sensors [1]
The spectral behavior of BiConical Reflectance Factor (BCRF) measured by the Banc de BRDF Grands Echantillons” (BBGE) is presented for an intermediate source zenithal angle, 40◦, and a nadir viewing
This study presents the sensitivity of reflectance to grain roundness and sphericity in the visible domain, for three sand samples

Summary

Introduction

Some sandy desert sites known for their temporal stability and their spatial uniformity have been used for a long time to radiometrically calibrate and monitor optical space-borne sensors [1]. The characterization of PICS directional signature could be achieved, at a kilometric scale, and in narrow spectral bands thanks to multi-spectral multi-directional space-borne sensors such as the POLDER (POLarization and Directionality of Earth Reflectances) instrument [2] (with old data). This characterization enables, in the first instance, to compare calibration sites in terms of the magnitude of directional effects, considering that the lower, the better for instrument drift assessment [3]. The interpolation/extrapolation of the directional properties found at a limited number of spectral bands (e.g., for POLDER: 490, 565, 670, 765, 865, 1020 nm) to other spectral channels is not straight forward and can be achieved only through hyperspectral sensor measurements or modeling assumptions on the atmosphere and surface optical properties (e.g., [4])

Methods

Results

Discussion

Conclusion