Remote Sensing of Snow in the Solar Spectrum: Experiments in the French Alps.

Two experiments were perfonned irliApril and December 1992 in the French Alps using simultaneous relnote sensing and ground truth data. Snow grain site and soot content of samples collected in thefield were measured. The Landsat thematic mapper (TM) sensor was used because it has a good spatial resolution, a middle infrared channel which is sensitive to grain size and a thermal infraredchannel. Firstj the reflectance data were compared with the theoretical results obtained from a bidirectional reflectance model. Then, some remote sehstng-derived snow parameters wbre comparediWith the outpllt ofa snow metamorphism model (CROCUS),viz., lower elevation of the snowcover, lhe surface grl1in size and the surface temperature. A digital elevation model was used to obtain thelocal incidenc:f angles and the elevation of each snow pixel. The pixels were then grouped according to CROCUS classification (range, elevation, slope, and orientation) and the mean snow chart;cheracteristicsfor each class were .compared with the tROCUS results. The lower limit of snow and the surface grain size derived from TM data were compared favourably with the model results. Larger differences werefound for the temperature, because it varies rapidly and is very sensitive to shadowing by the snrrounding mountains and also because its remote measurement is dependent on atmospheric conditions

Preface paper to the Semi-Arid Land-Surface-Atmosphere (SALSA) Program special issue

The Semi-Arid Land-Surface-Atmosphere Program (SALSA) is a multi-agency, multi-national research effort that seeks to evaluate the consequences of natural and human-induced environmental change in semi-arid regions. The ultimate goal of SALSA is to advance scientific understanding of the semi-arid portion of the hydrosphere–biosphere interface in order to provide reliable information for environmental decision making. SALSA approaches this goal through a program of long-term, integrated observations, process research, modeling, assessment, and information management that is sustained by cooperation among scientists and information users. In this preface to the SALSA special issue, general program background information and the critical nature of semi-arid regions is presented. A brief description of the Upper San Pedro River Basin, the initial location for focused SALSA research follows. Several overarching research objectives under which much of the interdisciplinary research contained in the special issue was undertaken are discussed. Principal methods, primary research sites and data collection used by numerous investigators during 1997–1999 are then presented. Scientists from about 20 US, five European (four French and one Dutch), and three Mexican agencies and institutions have collaborated closely to make the research leading to this special issue a reality. The SALSA Program has served as a model of interagency cooperation by breaking new ground in the approach to large scale interdisciplinary science with relatively limited resources

The CPLEAR detector at CERN

The CPLEAR collaboration has constructed a detector at CERN for an extensive programme of CP-, T- and CPT-symmetry studies using ${\rm K}^0$ and $\bar{\rm K}^0$ produced by the annihilation of $\bar{\rm p}$'s in a hydrogen gas target. The ${\rm K}^0$ and $\bar{\rm K}^0$ are identified by their companion products of the annihilation ${\rm K}^{\pm} \pi^{\mp}$ which are tracked with multiwire proportional chambers, drift chambers and streamer tubes. Particle identification is carried out with a liquid Cherenkov detector for fast separation of pions and kaons and with scintillators which allow the measurement of time of flight and energy loss. Photons are measured with a lead/gas sampling electromagnetic calorimeter. The required antiproton annihilation modes are selected by fast online processors using the tracking chamber and particle identification information. All the detectors are mounted in a 0.44 T uniform field of an axial solenoid of diameter 2 m and length 3.6 m to form a magnetic spectrometer capable of full on-line reconstruction and selection of events. The design, operating parameters and performance of the sub-detectors are described.

L'engraissement des bovins

National audienc

Remote sensing of snow cover by SAR sensors : application in the French Alps of a backscaterring model developed in Quebec

The main objective of this study is to analyse the signature of snowcovered high alpine terrain for different snow surface and volume conditions. Two radar experiments were performed in the French Alps at the beginning of the runoff season, in April 1990 and 1992. The aerial E-SAR from DLR was used in april 1990 (X band) and an ERS1 image (C band) was available for april 1992. The study was carried on an experimental drainage bassin, also a sky resort (Les Arcs), with elevation ranging from 1600 to 2400 m. Ground data included snow and underlaying soil characteristics were collected in situ. A DEM was used for the radiometric and geometric corrections, because of the slope effects. A backscattering model was used to estimate the relation between snow parameters (snow water equivalent) and backscattering power issued from the calibrated data. The results of these two experiments show that corrections of slope effects are necessary in mountain aereas and that volume scattering within the snowpack is responsible for most of the backscattering signal in X-band, due to presensce of a wet layer at the bottom. The X band seems more appropriated the C-band to the SWE in those specific conditions. / L'objectif de cette étude est d'analyser la signature radar de couverts de neige alpins pour différentes conditions de surface et de volume de la neige. Deux expériences radar ont été réalisées dans les Alpes françaises au début de la saison de fonte, en avril 90 et 92. Des images aéroportées E-SAR du DLR (avril 90) et ERS spatioportées (avril 92) ont été utilisées. L'étude s'est déroulé sur un bassin-versant expérimental ainsi qu'une station de ski (les Arcs) avec des altitudes allant de 1600 à 2400 m. Les données de terrain disponibles étaient les caractéristiques de la neige et du sol sous-jacent sur des parcelles d'échantillonnage. Un MNT a été utilisé à des fins de corrections géométriques et radiométriques, afin d'éliminer les effets de pente. Un modèle semi-empirique de rétrodiffusion radar par un couvert de neige a été utilisé afin d'aborder la relation entre les paramètres de neige (teneur équivalente en eau) et la rétrodiffusion radar corrigée du relief. Les résultats de ces deux expériences démontrent 1) la nécessité de correction du relief et 2) que la plus grande partie de la rétrodiffusion est due à une diffusion de volume en bande X, à cause de la présence d'une couche humide. La bande X s'est avérée être plus appropriée que la bande C, considérant la fréquence ainsi que la visée différente entre les deux instruments

Espaces, exploitations, développement rural : proposition d'une démarche de diagnostic territorial (Argentine)

National audienceCet article propose une démarche originale de diagnostic régional fondé sur la prise en compte des pratiques et stratégies territoriales des agriculteurs. L'objectif en est de définir des portions de territoire sur lesquelles il est possible de mettre en place des actions de développement communes à une partie importante des exploitations ainsi que des opérations de recherche sur les conditions techniques, économiques et organisationnelles pour un développement durable. Une première étape consiste à définir dans l'espace régional des Unités agro-géographiques. Les auteurs proposent ensuite un détour par les exploitations agricoles afin de caractériser les pratiques et les stratégies territoriales des agriculteurs et de construire une typologie du fonctionnement des exploitations agricoles. La dernière phase consiste à définir les Unités agro-physionomiques à partir de l'analyse du paysage prenant en compte notamment les pratiques et les stratégies territoriales. La méthodologie proposée a été appliquée en Argentine dans le cadre d'un programme de coopération Inra-Inta