Search results for "Planet"

Compared regimes of NDVI and Rainfall in semi-arid regions of Africa

2006

International audience; Bi-monthly normalized difference vegetation index (NDVI) at an 8km spatial resolution from the advanced very high resolution radiometers (AVHRR) was used from 1981 to 1995 to analyse the vegetation response to rainfall supply in semi-arid regions of Africa. Within the 200-600 mm annual rainfall belt, for which the apparent NDVI response to rainfall was the strongest, three regions were selected which exhibited different patterns in their NDVI regimes and/or relationships with rainfall. The regions, located in western, southern and eastern Africa, were split into coherent sub-regions in terms of mean regime of photosynthetic activity through a cluster analysis. Overal…

Europa traicionada

2002

Estimating the difference between brightness and surface temperatures for a vegetal canopy

1995

Abstract The difference between the surface temperature T S and the brightness temperature T b , which can be measured with a thermal infrared radiometer, has been calculated for different surface emissivity values and different atmospheric conditions. These calculations show that T s − T b is often significant even for high surface emissivities and that the spectral band in which the measurements are performed is a key factor in the interpretation of T s − T b . In particular, it is not a simple matter to use the characterisation of the whole spectrum atmospheric radiation to derive T s from T b when the measurements are performed in the 8–14 μm atmospheric window.

A numerical simulation scheme for the albedo of city street canyons

1985

A numerical scheme is described for the calculation of effective albedo values of long city street canyons. The method is based on a generalization of the radiation model for inclined surfaces recently presented by Bruhl and Zdunkowski (1983). Calculated albedo values are compared with Aida's (1982) experimentally determined results. It is found that experiment and theory are in reasonable and in some cases in excellent agreement. Additional results obtained by varying the geometry of the street canyon as well as the surface reflectivities are shown to demonstrate the versatility of the calculation scheme.

Adsorption of organic compounds at the surface of Enceladus' ice grains. A grand canonical Monte Carlo simulation study

2021

International audience; In this paper, we characterise the adsorption of ethylene, propanol and hexanal molecules on crystalline ice by grand canonical Monte Carlo simulations performed at 236 K, a temperature which is typical of some Enceladus’ environments. We show that at low coverage of the ice surface, the adsorption of propanol and hexanal is driven by the interaction of these molecules with the ice phase and, as a consequence, the adsorbed molecules lie more or less parallel to the ice surface. On the other hand, upon saturation, the adsorbate–adsorbate interactions become more and more important and the molecules tend to become tilted with respect to the surface, the aliphatic chain…

Interacción de procesos geomórficos y distribución de componentes de la superficie del suelo en relación a la evolución de los abarrancamientos de Ta…

2009

Este artículo se ha desarrollado en el contexto de los proyectos: REN2003-045707GLO(PECOS); CGL2007-63258/BOS(PREVEA) y CGL2006-11619(PROBASE), financiados por la CICYT en el marco del Plan Nacional I+D+I

Wavelet-like efficient analysis of two-dimensional arbitrarily shaped radomes using a surface formulation

2007

[1] Radomes are usually made of lossy dielectric materials, and their accurate analysis is often cumbersome because of their typical large electrical size and geometrical complexity. In real reflector antenna structures, there are always complex interactions between the radome, the reflector surfaces and the directional feeds, which are typically neglected for the sake of simplicity. In this paper we will consider all such interactions in a very accurate way, thus requiring a high number of unknowns for the numerical solution of the problem. To overcome such drawback, an integral equation formulation based on the Equivalence Principle in combination with the wavelet transform has been emplo…

Land surface emissivity retrieval from different VNIR and TIR sensors

2008

This paper discusses the application and adaptation of two existing operational algorithms for land surface emissivity (epsiv) retrieval from different operational satellite/airborne sensors with bands in the visible and near-infrared (VNIR) and thermal IR (TIR) regions: (1) the temperature and emissivity separation algorithm, which retrieves epsiv only from TIR data and (2) the normalized-difference vegetation index thresholds method, in which epsiv is retrieved from VNIR data.

Surface temperature and water vapour retrieval from MODIS data

2003

This paper gives operational algorithms for retrieving sea (SST), land surface temperature (LST) and total atmospheric water vapour content (W) using Moderate Resolution Imaging Spectroradiometer (MODIS) data. To this end, the MODTRAN 3.5 radiative transfer program was used to predict radiances for MODIS channels 31, 32, 2, 17, 18 and 19. To analyse atmospheric effects, a simulation with a set of radiosonde observations was used to cover the variability of surface temperature and water vapour concentration on a worldwide scale. These simulated data were split into two sets (DB1 and DB2), the first one (DB1) was used to fit the coefficients of the algorithms, while the second one (DB2) was u…

Surface emissivity retrieval from Digital Airborne Imaging Spectrometer data

2002

[1] A study has been carried out on the most recent algorithms for the estimation of land surface emissivity (e) using high-resolution data (Digital Airborne Imaging Spectrometer, DAIS) over the Rhine Valley (France) and Castilla La Mancha (Spain). Three published methods have been applied for extracting absolute spectral emissivity information from images recorded during the DAISEX experiment in 1999. They are NDVI Thresholds Method (NDVITHM), Normalized Emissivity Method (NEM) and Temperature/Emissivity Separation (TES). These lather two methods were originally designed to work over geological surfaces. Five methods have been used for extracting relative spectral emissivity. They are temp…