ISSN:0143-1161    

DOI:10.1080/01431169608949071

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This work presents a study of the possibility of estimating forest fire danger by means of the analysis of the temporal evolution of the Normalized Difference Vegetation Index (NDVI) Advanced Very High Resolution Radiometer (AVHRR). Images of Spain corresponding to areas of Valencia and Eastern Andalusia in 1993 have been used. The slope of the evolution curve of the NDVI is an indicator of water stress and it is used to estimate danger. Forested areas are previously selected using the NDVI integral in the period studied. In order to determine the reliability of the index, ground data measured by the Spanish National Forestry Service (ICONA) are available to us

ISSN:0143-1161    

DOI:10.1080/01431169608949072

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Forest ecosystem modelling requires information about canopy chemistry. This is usually obtained through chemical analysis and laboratory spectrometric measurements. The potential of spectrometric remote sensing was investigated with two airborne campaigns organized in 1991 with AVIRIS (Airborne Visible/Infrared Imaging spectrometer) and in 1993 with ISM (Infrared SpectroMeter) over the 'Landes’ forest (south-west France): AVIRIS covers the 400-2500 nm spectral range with 210 bands, whereas the ISM instrument is an airborne profiling spectrometer that operates in the 800-3200 nm spectral range with 128 bands. The study area consists of homogeneous parcels of maritime pines with a wide variety of ages from 2 to 48 years. Simultaneously with the airborne acquisition, foliar samples were collected in the field. These samples were chemically analysed for determining nitrogen, lignin and cellulose contents. Reflectance spectra of dried pine needles were obtained with the help of two laboratory spectrometers: (1) the Technicon lnfraAlyser-450 with 19 spectral bands centred on chemical absorption features; and (2) the NIR-6500 System with l0nm wide 1050 bands from 400 nm to 2500 nm. Predictive relationships of nitrogen, lignin and cellulose concentrations were established by using stepwise regression analysis on the laboratory spectral measurements. These predictive relationships were quite different, depending on the laboratory spectrometers and the year of sampling. Consequently, different correlations (r2) were obtained between predicted and actual chemical concentrations: 66-94 per cent for nitrogen, 37-79 per cent for lignin and 45-85 per cent for cellulose. The stability of predictive relationships from laboratory to remote sensing level was especially analysed. The application of laboratory derived predictive equations to airborne data led to encouraging results: best correlations (r2) were obtained for nitrogen (AVIRIS: 55 per cent -ISM: 66 per cent) and cellulose (AVIRIS: 63 per cent) but lignin could not be predicted. It was attempted to improve these results while talking into account atmospheric effects: whereas AVIRIS-derived correlations were not improved, ISM-derived correlations were improved for nitrogen from 66 per cent to 76 per cent and lignin from 9 per cent to 77 per cent. The better signal-to-noise ratio of ISM may be the reasons for the better results obtained with this instrument

ISSN:0143-1161    

DOI:10.1080/01431169608949073

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Taking forest areas specified according lo information on the National digital land data, the vapour pressure deficit at leaf temperature and the degree of stomatal opening were presumed using the vegetation index of forest areas derived from Landsat TM data. Assuming the principle of Monin-Obukhov similarity is correct, a new method for calculating the latent and sensible heat fluxes of regional forests was proposed taking into account the difference in Leaf Area Index. The relation of the increase of latent heat flux with the vegetation index was obtained, and the plane distribution of latent and sensible heat fluxes in large areas is calculated.

ISSN:0143-1161    

DOI:10.1080/01431169608949074

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The region of Midwestern North America from 80-95° W and 35-55° N is examined in terms of land cover and convective cloud cover during the summers of 1985 and 1989, using a combination of published land use maps and GOES visible and infrared satellite imagery, for the presence of favoured convective cloud cover over large areas (˜ 100 km scale) of homogeneous forest. Days with synoptic flow are eliminated through analysis of 500-mb winds and surface frontal activity. The resulting ‘weak flow’ days’ imagery is organized into 1° × 1° latitude/longitude cells, within which total cumulus cloud cover is manually determined. Three-hourly analysis of convective cloud cover from visible and infrared imagery shows forests in Ontario and the Appalachians to have greater convective cloud cover and the Great Lakes to have less convective cloud cover, on days without frontal activity. This pattern persists throughout the day, for both 1985 and 1989, despite differences in soil moisture (as determined from Crop Moisture and Palmer Drought Indices) and topography. The apparent associated cloud cover increase over forests for the Midwest matches well with similarly predicted patterns of cloud and precipitation from the existence of weak non-classical mesoscale circulations

ISSN:0143-1161    

DOI:10.1080/01431169608949075

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The successive operational Meteosat solar (VIS) sensors have shown significant variations of their spectral band which affected their relative sensitivities to the light scattering by aerosols, molecules and Earth surface. This paper provides a calibration of the various Meteosat VIS sensors used between June 1983, the beginning of data archiving for the International Satellite Cloud Climatology Project (ISCCP), and December 1994, taking into account the characteristics of their individual spectral band thanks to an atmospheric radiative transfer model. The method is based on a monitoring of the reflectance of desert and ocean targets free of clouds and aerosols, and relies on the absolute vicarious calibration of Meteosat-2 performed in late 1981. We find different sensitivities and temporal evolutions for Meteosat-2, -3, -4, and -5, and our results compare well with other more limited calibration studies

ISSN:0143-1161    

DOI:10.1080/01431169608949076

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An atmospheric correction algorithm for high spatial resolution satellite sensors like Landsat Thematic Mapper (TM) has been developed. The algorithm works with a catalogue of atmospheric correction functions stored in look-up tables. The catalogue consists of a broad range of atmospheric conditions (different altitude profiles of pressure, air temperature, and humidity; several aerosol types; ground elevations from 0-1 km above sea level; solar zenith angles ranging from 0°-70°). The catalogue covers visibilities (surface meteorological range) from 5-40 km, values can be extrapolated down to 4 km and up to 80km. The 1994 edition of the catalogue was compiled using the MODTRAN-2 and the SENSAT-5 codes.

ISSN:0143-1161    

DOI:10.1080/01431169608949077

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Geophysical Environmental Research (GER) 63 channel scanner data acquired over Makhtesh Ramon, Negev, Israel, were investigated to retrieve information about atmospheric gases. Converting the data into apparent reflectance units via radiometric calibration, solar curve utilization and an offset factor revealed spectral features that matched modelled atmospheric gas spectra. The modelled spectra were generated using Lowtran-7 code and flight conditions. Most of the absorption features in the GER-reflectance spectra matched modelled features. Inconsistencies between the peak intensity at the oxygen bands (# 18 and #24) in the modelled and GER-reflectance spectra suggest error in the GER radiometric calibration for those bands. The modelled gas spectra indicate approximately 1-6cm precipitable water vapour for the flight and show thai the local topographic relief of 500 m can be detected from the spectral slope between 1·680-2·005/mi region (1·68/1·90 and 1·80/2·005) and from the normalized depth of the water vapour and carbon dioxide features at I-800/<m and 2005/im respectively. The correlation with the elevation is best shown by ln[A(λ)/R(λ)] at λ=l·800μm and λ — 2·005fim where A stands for the reflectance at the gas absorption wavelength A, and R for the reflectance at this wavelength if no gases occur. Both parameters (slope and \n[A(λ)/R(λ)] at around λ = 1·680-2·005μm) were calculated on a pixel-by-pixel basis and revealed good correlation with the topography. We conclude that these relations best describe the water vapour and carbon dioxide gas content as viewed by the GER sensor through the optical path length. Surface reflectance features such as clay minerals were found to enhance the slope parameter and to result in overestimation of the water vapour and the carbon dioxide contents by about 10 per cent. Although the calculations described here do not provide absolute water vapour or carbon dioxide values, these results show that quantitative detection of atmospheric gases from GER data may be possible.

ISSN:0143-1161    

DOI:10.1080/01431169608949078

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A new image classification technique for analysis of remotely-sensed data based on geostatistical indicator kriging is introduced. Conventional classification techniques require ground truth information, use only the spectral characteristics of an unknown pixel in comparison, rely on a Gaussian probability distribution for the spectral signature of the training data, and work on a pixel support or spatial resolution without allowing classification on larger or smaller volumes. The indicator kriging classifier overcomes such problems because: (1) it relies on spectral information from laboratory studies rather than on ground truth data, (2) through the kriging estimation variances an estimate of uncertainly is derived, (3) it incorporates spatial aspects because it uses local estimation techniques, (4) it is distribution-free, (5) and may be applied on different supports if the data are corrected for support changes. Comparison of classification results applied to the problem of mapping calcite and dolomite from GER imaging spectrometry data shows that indicator kriging performs better than the conventional classification algorithms and gives insight in the accuracy of the results without prior field knowledge

ISSN:0143-1161    

DOI:10.1080/01431169608949079

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431169608949081

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor