Atmospheric Correction Validation of casi Images Acquired over the Boreas Southern Study Area

Abstract

h~x. T. ox-in • r. Zagobki • \1. Bergeron' \. Roycr > .I. R. \Iiller' .I. I· rccmantle RESUME Des procedures de correction atmospherique a haute altitude d'images de teledetection acquises au moyen du capteur casi (Compact Airborne Spectrographic Imager) dans le cadre du projet BOREAS (Boreal EcosystemAtmosphere Study) ont ete testees au-dessus d'une variete de sites de validation. Une analyse de regression appliquee sur des donnees casi multi-altitudes a ete utilisee pour estimer les facteurs de reflectance bidirectionnelle apparente de surface (FRB) qui ont servi comme spectres de realite de terrain pour valider les procedures de correction atmospherique. Des etalonnages de luminance absolue de donnees casi ont permis de determiner des luminances normalisees en tant qu'intrant aun module standard de correction atmospherique (une variante du modele H5S) pour la transformation d'images en FRB apparents de surface. De plus, nous avons calcule independamment les FRB apparents multi-altitudes a partir des etalonnages de FRB relatifs derives, d'une part, de mesures in-situ de panneaux d' etalonnage correspondant aplusieurs pixels et bien caracterises, et d'autre part, de rapports de luminances ascendantes normalisees par L'eclairement descendant casi. Les FRB apparents multialtitudes ont permis de caracteriser les spectres au sol des FRB apparents cons ideres comme realite de terrain. Supposant une connaissance de l' epaisseur optique locale des aerosols et base sur une certaine connaissance a priori du type d'environnement entourant chaque site de validation, les differences absolues moyennes entre les FRB apparents non-corriges et corriges et les FRB apparents consideres comme realite de terrain sont de 1,6% et 0,6% respectivement, dans la region visible du spectre, et de 1,1% dans les deux cas, dans la region du proche infrarouge. On peut reduire les erreurs des FRB corriges en augmentant les specifications des parametres d' entree du modele de correction atmospherique au detriment cependant de la simplicite de la methode. SUMMARY High altitude atmospheric correction procedures for remotely sensed images acquired by the Compact Airborne Spectrographic Imager (casi) during the Boreal EcosystemAtmosphere Study (BOREAS) were tested over a variety of validation sites. Regression analysis on multi-altitude casi data was employed to estimate apparent surface Bidirectional Reflectance Factors (BRFs) which served as ground truth spectrafor validatingthe atmospheric correction procedures. Absolute radiance calibrations of casi data permitted normalized radiances to be input into a standard atmospheric correction package (a variant of the H5S model) for image transformation to apparent surface BRF. In addition, relative BRF calibrations derived from in-situ measurements of well-characterized multi-pixel sized calibration panels and ratios of upwelling casi radiance signals normalized by downwelling casi irradiance signals were employed to independently compute the multi-altitude apparent BRFs used in deducing the ground tr...

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