45 research outputs found
Assimilation of passive microwave AMSR-2 satellite observations in a snowpack evolution model over northeastern Canada
Over northeastern Canada, the amount of water stored in a
snowpack, estimated by its snow water equivalent (SWE) amount, is a key
variable for hydrological applications. The limited number of weather
stations driving snowpack models over large and remote northern areas
generates great uncertainty in SWE evolution. A data assimilation (DA) scheme
was developed to improve SWE estimates by updating meteorological forcing
data and snowpack states with passive microwave (PMW) satellite observations
and without using any surface-based data. In this DA experiment, a particle
filter with a Sequential Importance
Resampling algorithm (SIR) was applied and an
inflation technique of the observation error matrix was developed to avoid
ensemble degeneracy. Advanced Microwave Scanning Radiometer 2 (AMSR-2)
brightness temperature (TB) observations were assimilated into a
chain of models composed of the Crocus multilayer snowpack model and
radiative transfer models. The microwave snow emission model (Dense Media
Radiative Transfer – Multi-Layer model, DMRT-ML), the vegetation transmissivity
model (ω-τopt), and atmospheric and soil radiative
transfer models were calibrated to simulate the contributions from the
snowpack, the vegetation, and the soil, respectively, at the top of the
atmosphere. DA experiments were performed for 12 stations where daily
continuous SWE measurements were acquired over 4 winters (2012–2016). Best
SWE estimates are obtained with the assimilation of the TBs at
11, 19, and 37 GHz in vertical polarizations. The overall SWE bias is reduced
by 68 % compared to the original SWE simulations, from 23.7 kg m−2
without assimilation to 7.5 kg m−2 with the assimilation of the three
frequencies. The overall SWE relative percentage of error (RPE) is 14.1 %
(19 % without assimilation) for sites with a fraction of forest cover
below 75 %, which is in the range of accuracy needed for hydrological
applications. This research opens the way for global applications to improve
SWE estimates over large and remote areas, even when vegetation contributions
are up to 50 % of the PMW signal.</p
Acquisition Et Reproduction D'images Couleur : Approches Colorimétrique Et Multispectrale
The goal of the work reported in this dissertation is to develop methods for the acquisition and reproduction of high quality digital colour images. To reach this goal it is necessary to understand and control the way in which the different devices involved in the entire colour imaging chain treat colours. Therefore we addressed the problem of colorimetric characterisation of scanners and printers, providing efficient and colorimetrically accurate means of conversion between a device-independent colour space such as the CIELAB space, and the device-dependent colour spaces of a scanner and a printer
Nascimento de outra ruralidade The birth of another rurality
ESTE ARTIGO procura mostrar que Lefebvre (1970) e Kayser (1972, 1990) estavam errados sobre o destino da ruralidade. Evidências empÃricas sobre o caso da Itália não confirmam as conjeturas extremas sobre "completa urbanização" ou "renascimento rural". E uma espécie de hermenêutica dessas duas hipóteses ajuda a fundamentar a terceira, que pretende superá-las.<br>THIS ARTICLE argues that Lefebvre (1970) and Kayser (1972, 1990) were both mistaken about the destiny of rurality. Empirical evidences from Italy do not confirm extreme conjectures on "complete urbanization" or "rural renaissance". And a kind of hermeneutics of these two hypothesis helps to build upon a third which intends to surpass them