Spectral mixture modeling: A new analysis of rock and soil types at the Viking Lander 1 Site

TLDR

At the Viking Lander 1 site, rocks are largely dust‑covered yet unweathered, with rock‑like soil forming lag deposits and trench layers likely derived from wind abrasion, and the dust is spectrally distinct from the rocks but matches global‑scale dust observed telescopically. The study develops a method to model a multispectral image as mixtures of end‑member spectra and to compare the resulting image spectra directly with laboratory reference spectra. The method incorporates shade and secondary illumination as spectral end‑members to isolate or remove topographic and illumination effects, and it is absolutely calibrated from laboratory spectra with close agreement to direct calibrations. Applying the method to a Viking Lander 1 image, the authors modeled the scene as mixtures of palagonite dust, gray andesitelike rock, and coarse rock‑like soil, finding that dust dominates the surface and demonstrating the method’s broad applicability to interpreting multispectral images, including satellite data.

Abstract

A Viking Lander 1 image was modeled as mixtures of reflectance spectra of palagonite dust, gray andesitelike rock, and a coarse rocklike soil. The rocks are covered to varying degrees by dust but otherwise appear unweathered. Rocklike soil occurs as lag deposits in deflation zones around stones and on top of a drift and as a layer in a trench dug by the lander. This soil probably is derived from the rocks by wind abrasion and/or spallation. Dust is the major component of the soil and covers most of the surface. The dust is unrelated spectrally to the rock but is equivalent to the global‐scale dust observed telescopically. A new method was developed to model a multispectral image as mixtures of end‐member spectra and to compare image spectra directly with laboratory reference spectra. The method for the first time uses shade and secondary illumination effects as spectral end‐members; thus the effects of topography and illumination on all scales can be isolated or removed. The image was calibrated absolutely from the laboratory spectra, in close agreement with direct calibrations. The method has broad applications to interpreting multispectral images, including satellite images.