Laurent Polidori

Spatial resolution improvement by merging MERIS-ETM images for coastal water monitoring

The Medium Resolution Imaging Spectrometer (MERIS) launched in March 2002 and has been providing images since June 2002. Before its launch, we had implemented a method to improve its resolution by merging its images with Landsat Enhanced Thematic Mapper images in order to preserve the best characteristics of the two images (spatial, spectral, temporal). We now present the results of this method for real MERIS images (level 1b and 2) in a coastal area. The robustness of the method is studied as well as the influence of the delay between the acquisitions of the two images.

Spatial resolution improvement of MeRIS images by fusion with TM images

The medium resolution imaging spectrometer (MeRIS) is ready to be launched. Considering its spatial resolution (240 m), potential users will have to face the mixed pixel problem. The authors propose to improve its resolution by merging MeRIS images with Landsat TM images. The best characteristics of the two images (spatial, spectral, temporal) are then preserved.

Bathymetric Estimation Using MERIS Images in Coastal Sea Waters

Bathymetric estimation using remote sensing images has previously been applied to high spatial resolution imagery such as CASI, Ikonos, or SPOT but not on medium spatial resolution images (i.e., MERIS). This choice can be justified when there is a need to map the bathymetry on large areas. In this letter, we present the results of the bathymetry estimation over a large known area, the Gulf of Lion (France), expanding over 270times180 km

Satellite survey of seasonal trophic status and occasional anoxic 'malaigue' crises in the Thau lagoon using MERIS images

The Thau lagoon, located in southern France, suffers episodically from anoxic crises locally known as ‘malaïgue’. Such crises mostly occur under warm conditions, low winds leading to a strong eutrophication of the lagoon. The development of a sulphur bacterium sometimes gives locally to the waters a ‘milky turquoise’ appearance and leads to shellfish mortality. One of the indicators of the eutrophication status of the lagoon can be surveyed by the chlorophyll product provided by remote sensing images such as Medium Resolution Imaging Spectrometer (MERIS). In this paper we compare chl2 (or algal2) estimations provided by MERIS level 2 products and the ground measurements of chlorophyll a concentrations in water and we propose a linear correction of the chl2 MERIS product. The corrected chl2 estimations obtained over four years are analysed to understand the seasonal evolution of the trophic status of the Thau lagoon. We also study the influence of the anoxic crises of summers 2003 and 2006 on the chl2 estimations and we find a strong correlation between chl2 and the oxygen percentage at 1 m depth (0.70 for measurements in summers 2003 and 2006).

Digital elevation model validation with no ground control: application to the topodata dem in Brazil

Digital Elevation Model (DEM) validation is often carried out by comparing the data with a set of ground control points. However, the quality of a DEM can also be considered in terms of shape realism. Beyond visual analysis, it can be verified that physical and statistical properties of the terrestrial relief are fulfilled. This approach is applied to an extract of Topodata, a DEM obtained by resampling the SRTM DEM over the Brazilian territory with a geostatistical approach. Several statistical indicators are computed, and they show that the quality of Topodata in terms of shape rendering is improved with regards to SRTM.

An estimate of the influence of loading effects on tectonic velocities in the Pyrenees

Surface displacements due to temporal changes in environmental mass redistributions are observable in the coordinate time series of many Global Navigation Satellite System (GNSS) sites. In this study, we investigated the effect of loading on estimates of tectonic velocity computed from campaign-style GNSS observations. The study region is in the Pyrenees mountain range between France and Spain (ResPyr campaigns). In this area, seismic activity is continuous and moderate and the expected amplitude of the horizontal tectonic velocity is less than 0.5 mm/yr. In order to determine the velocity, 4 sparse GNSS campaigns were carried out from 1995 to 2010. Considering this small rate of deformation, loading phenomena can contribute a non-negligible artifact to the velocity computation that could affect our geodynamical interpretation. In this investigation, we specifically considered the atmospheric, hydrological, and non-tidal ocean loading phenomena. The computed loading deformations for this region show the horizontal displacements are dominated by the non-tidal ocean loading (maximum 4 mm for the North and 3.1 mm for the East components); the main vertical contributions are due to the atmospheric and continental water storage loading (maximum 14.3 for the atmosphere and 8.1 mm for the hydrology, respectively). We have found that the dominant loading effect on the horizontal velocity is the non-tidal ocean loading (mean of 0.11 mm/yr), whereas the vertical component is dominated by the hydrological loading (mean of 0.21 mm/yr). Since the study area is in a mountainous region, we also analyzed the difference between the atmospheric and the topography dependent atmospheric loading models at our GNSS campaign sites. We did not find any significant difference between the two atmospheric loading models in terms of horizontal velocity. Finally, we performed simulations to identify the optimum timing and frequency of future GNSS campaigns in this area that would minimize the loading effects on tectonic velocity estimates.

Fusion of MeRIS and ETM images for coastal water monitoring

Ocean colour monitoring is usually based on optical remote sensing with spatial resolutions around 1 km. This spatial scale is available with such sensors as NOAA-AVHRR,POLDER or SeaWiFS, which cover one to several thousand kilometers in a single swath and providing very short revisit periods. The MeRIS sensor, launched on board ENVISAT in 2002, was designed for sea colour observation, with a 300 meter spatial resolution, 15 programmable spectral bands and a 3 day revisit period. Tree hundred meter is a high resolution for an oceanographic sensors, but it is still too rough for coastal water monitoring, where physical and biological phenomena require better spatial resolution [1]. On the opposite, multispectral Landsat ETM images offer a suitable spatial resolution, but have only 4 spectral bands in the visible and near infrared spectrum, allowing poor spectral characterization. A few years ago, in order to combine the spectral resolution of MeRIS and the spatial resolution of Landsat ETM,we had implemented a merging method proposed by Zhukov et al. [2]. Before the launch of ENVISAT, we applied this method to simulated MeRIS images [3]. MeRIS was launched in March 2002 and has been providing images since June 2002. This method is now applied to real MeRIS images. Two product levels are considered. Level 1b contains radiance measurements at the top of the atmosphere for the calibrated and geocoded fifteen (15) MeRIS bands. Level 2 contains normalized surface reflectance and several geophysical and biophysical parameters such as algal pigment index, suspended sediment,Rayleigh-corrected vegetation indices, aerosol type, cloud albedo. The method was tested for radiance (level lb) and reflectance (level 2) over a coastal area of approximately 30times30 km2 located around the Thau lagoon (southern France).

A AULA INAUGURAL DO CURSO DE GEOMETRIA APLICADA ÀS ARTES NO CONSERVATÓRIO IMPERIAL DE ARTES E OFÍCIOS

Nesta comunicacao, apresenta-se a traducao do texto integral da aula inaugural do Coronel Aime Laussedat (1819-1907), professor suplente no Conservatoire Imperial des Arts et Metiers (antigo nome do CNAM), comentado pelo autor na versao original, publicado pela Associacao Francesa de Topografia (revista XYZ vol. 133 4° trimestre 2012, pag. 57-64), traduzido por Laurent Polidori e Antonio M. G. Tommaselli.

MeRis and ETM image fusion for spatial resolution improvement

MeRIS was launched in March 2002 and has been providing images since June 2002. Before its launch, we had implemented a method to improve its resolution by merging its images with Landsat ETM images in order to preserve the best characteristics of the two images (spatial, spectral, temporal). We now present the results of this method for real MeRIS images (level 1b and 2) in a coastal area. The robustness of the method is studied as well as the influence of the delay between the acquisitions of the two images.