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Temporal constraints on linear BRDF model parameters
Linear models of bidirectional reflectance distribution are useful tools for understanding the angular variability of surface reflectance as observed by medium-resolution sensors such as the Moderate Resolution Imaging Spectrometer. These models are operationally used to normalize data to common view and illumination geometries and to calculate integral quantities such as albedo. Currently, to compensate for noise in observed reflectance, these models are inverted against data collected during some temporal window for which the model parameters are assumed to be constant. Despite this, the retrieved parameters are often noisy for regions where sufficient observations are not available. This paper demonstrates the use of Lagrangian multipliers to allow arbitrarily large windows and, at the same time, produce individual parameter sets for each day even for regions where only sparse observations are available
A model to estimate daily albedo from remote sensing data : accuracy assessment of MODIS MCD43 product
L’albedo superficial és un parà metre fÃsic que afecta al clima de la Terra i, a més, suposa una de les majors incerteses radiatives en l’actual modelització climà tica. Aquest parà metre és molt variable tant a nivell espacial com temporal degut als canvis en les propietats de les superfÃcies i als canvis en les condicions d’il•luminació. En conseqüència, es requereix una resolució temporal dià ria de l’albedo per a realitzar estudis climà tics. L’augment de la resolució espacial dels models climà tics fa necessari l’estudi de les seues caracterÃstiques espacials a nivell global. La teledetecció proporciona l’única opció prà ctica de proporcionar dades d’albedo a nivell global amb alta qualitat i alta resolució tant espacial com temporal. El sensor MODerate Resolution Imaging Spectroradiometer (MODIS) a bord dels satèl•lits Terra i Aqua presenta unes caracterÃstiques adequades per a l’estimació d’aquest parà metre. En el present treball realitzem diversos estudis buscant les possibles fonts d’incertesa del producte oficial d’albedo de MODIS (MCD43). A més, presentem un model que millora la resolució temporal d’aquest parà metre.Surface albedo is a critical land physical parameter affecting the earth’s climate and is among the main radiative uncertainties in current climate modelling. This parameter is highly variable in space and time, both as a result of changes in surface properties and as a function of changes in the illumination conditions. Consequently, an albedo daily temporal resolution is required for climate studies. The increasing spatial resolution of modern climate models makes it necessary to examine its spatial features. Satellite remote sensing provides the only practical way of producing high-quality global albedo data sets with high spatial and temporal resolutions. The MODerate Resolution Imaging Spectroradiometer (MODIS) sensor on board the Terra and Aqua satellites presents the required sampling characteristics in order to derive the this parameter. In this PhD we develop several studies looking for the improvement of the official MODIS albedo product (MCD43) accuracy. Moreover, we present a model that improves the temporal resolution of this parameter