Steven Dewitte

Lossless integer wavelet transform

Signal compression can be obtained by wavelet transformation of integer input data followed by quantification and coding. As the quantification is usually lossy, the whole compression/decompression scheme is lossy too. We define a critical wavelet coefficient quantification, i.e., the coarsest quantification that allows perfect reconstruction. This is demonstrated for the Haar transform and for arbitrarily smooth wavelet transforms derived from it. The new integer wavelet transform allows implementation of multiresolution subband compression schemes, in which the decompressed data are gradually refined, retaining the option of perfect reconstruction.

In-Flight Performance of the Virgo Solar Irradiance Instruments on Soho

The in-flight performance of the total and spectral irradiance instruments within VIRGO (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (SOlar and Heliospheric Observatory) is in most aspects better than expected. The behaviour during the first year of operation of the two types of radiometers and the sunphotometers together with a description of their data evaluation procedures is presented.

On-Orbit Degradation of Solar Instruments

We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions.

Outgoing longwave flux estimation: improvement of angular modelling using spectral information

A radiance-to-flux conversion is needed to estimate radiative fluxes at the top of the atmosphere from directional measurements made by broadband (BB) radiometers on satellites. Such a conversion is known to be one of the major sources of error in the resulting instantaneous shortwave and longwave fluxes. This paper analyzes the possibility to improve the radiance-to-flux conversion for the longwave radiation when spectral information about the radiation is available through a set of narrow-band (NB) measurements. The study is based on a database of spectral radiance fields at the top of the atmosphere built using radiative transfer computation. The analysis of this database shows that there exists a certain degree of correlation between the angular and the spectral behaviors of the radiation field. According to the type and the accuracy of the spectral information, this correlation allows a 25–55% reduction of the error introduced by the radiance-to-flux conversion with respect to a simple model that uses only broadband information. The method discussed in this paper might be used when broadband radiometer and spectral imager data are available together like the combination of Geostationary Earth Radiation Budget (GERB) and Spinning Enhanced Visible and Infrared Radiometer Imager (SEVIRI) or the combination of CERES and MODIS.

Total solar irradiance observations from DIARAD/VIRGO

The Differential Absolute Radiometer is making measurements of the total solar irradiance as part of the Variability of Irradiance and Gravity Oscillations experiment on the Solar and Heliospheric Observatory. We present the measurements made during its 7.8 years of operation, from 1996 until the present (2003). The aging due to UV exposure of the continuously measuring left channel is determined by comparison with the backup right channel; the loss in sensitivity of the left channel is 0.5 W/m 2 or 364 ppm over 7.8 years. A raise of the total solar irradiance from a level of 1365.5 W/m 2 at the end of the solar minimum in 1996 towards a maximum level of 1368 W/m 2 at the beginning of 2002 has been measured by DIARAD.

SOLAR CONSTANT TEMPORAL AND FREQUENCY CHARACTERISTICS

The Suns total irradiance at the mean Sun-Earth distance decreased from mid-1979 to mid-1987 during the descending part of solar cycle 21. After the minimum had been reached it increased with the onset of cycle 22 and came to a maximum at mid-1991 during the highest solar activity of cycle 22. From the modelized shape of the time signal of the solar constant based on the Space Absolute Radiometric Reference (SARR), temporal, amplitude and behaviour characteristics are derived. It is suggested that the variation observed over a period of more than 14 years is the response of the outer solar layers, the photosphere in particular, to some excitation originating somewhere near the bottom of the solar convection zone also responsible for the solar spots and the correlated photospheric features. Wavelet analysis and periodiograms are shown for the solar constant and the sunspot index. Their non-stationarity is well illustrated as well as strong recurrent periods.

The satellite application facility on climate monitoring

Abstract The Satellite Application Facility on Climate Monitoring is a joint project of the National Meteorological Services and other institutes from Belgium, Finland, Germany, Sweden and The Netherlands. The objective of the project is to set up a system to provide atmospheric and oceanographic data sets from (primarily) operational geostationary and polar orbiting meteorological satellites for climate monitoring, research and applications at regional European scale, for some products on a global scale. Initial operational SAF products are related to clouds, radiation budget, ocean status and water vapour content in the atmosphere. SAF operations are foreseen to start in 2004.

PICARD: Simulataneous measurements of the solar diameter, differential rotation, solar constant and their variations

Abstract PICARD is a CNES micro-satellite mission due for flight by the end of 2002, named after the name of a French astronomer who first observed with consistency the solar diameter changes during the Maunder minimum in the 16th century. It consists of two instruments measuring (i) the solar diameter and differential rotation, and (ii) the total solar irradiance. These quantities are fundamental for the understanding of the solar-Terrestrial relations, e.g. the influence of the Sun on the Earths climate, and of the internal structure of the Sun. The continuous — or nearly continuous — viewing of the Sun from an appropriate orbit, the 5 minutes sampling rate and the very low noise measurements, will allow g-modes detection and precise diameter measurements besides accurately establishing the relationship between irradiance and diameter changes. Providing an absolute measure of the solar diameter to 1 milliarcsecond, PICARD is the first step towards instruments capable of accurate and perennial measurements, for the centuries to come, of the solar-terrestrial influence. The objectives of the mission, instrument capabilities, observing modes and performances are described.

On the optimality of embedded deadzone scalar-quantizers for wavelet-based L-infinite-constrained image coding

In wavelet-based L/sub /spl infin//-constrained embedded coding, the bit-stream is truncated at the bit-rate that corresponds to a guaranteed, user-defined distortion bound. The letter analyzes the optimality of embedded deadzone scalar-quantizers for high-rate L/sub /spl infin//-constrained scalable wavelet-based image coding. A rate-distortion model applicable to the family of embedded deadzone scalar-quantizers is derived and experimentally validated. Conclusions are drawn regarding the optimal subband-quantizer instantiations. The optimal quantizers are employed in a coding algorithm that retains the coding performance and the flexibility options of wavelet-based codecs while allowing for a fully embedded L/sub /spl infin//-oriented bit-stream.

The Space instrument SOVAP of the PICARD mission

PICARD is a Satellite dedicated to the simultaneous measurement of the absolute total and spectral solar irradiance, the diameter and solar shape and the Suns interior probed by helioseismology method. Its objectives are the study of the origin of the solar variability and the study of the relations between the Sun and the Earths climate. PICARD was launched on June 15, 2010. The Satellite was placed into the heliosynchronous orbit of 735 km with inclination of 98.28 degrees. The payload consists in two absolute radiometers measuring the TSI (Total Solar Irradiance) and an imaging telescope to determine the solar diameter, the limb shape and asphericity. SOVAP (SOlar VAriability Picard) is an experiment developed by the Belgian STCE (Solar Terrestrial Center of Excellence) with a contribution of the CNRS (Centre National de la Recherche Scientifique) composed of an absolute radiometer provided by the RMIB (Royal Meteorological Institute of Belgium) to measure the TSI and a bolometer provided by the ROB (Royal Observatory of Belgium). The continuous observation of the solar irradiance at the highest possible precision and accuracy is an important objective of the Earth climate change. This requires: high quality metrology in the space environment. In this article, we describe the SOVAP instrument, its performances and uncertainties on the measurements of the TSI.