ISSN:0143-1161    

DOI:10.1080/01431169108955180

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper presents a Monte Carlo model for radar backscatter from a layer consisting of a mixture of randomly orientated discrete scatterers. The random layer is bounded on top by a Kirchoff rough surface using the scalar approximation, and bounded at the bottom by a plane lossy half-space. The discrete scatterers are modelled as spheroids and ellipsoids. The multiple-scattering processes are considered to be chains of collisions between the photons in the incident beam and the discrete scatterers. An algorithm is developed to track the trajectory of each photon and to collect the intensity of the backscattered photon flux, from which the radar cross-sections are calculated using the ensemble averages of the backscattered power. The technique so developed is used to study the backscatter from wet snow modelled as a three-phase mixture of elliptical scatterers (representing the water inclusions), spherical scatterers (representing the ice particles) and a background of air. A comparison is made with the results from the two-phase radiative transfer theory. It is found that our three-phase Monte Carlo model predicts higher levelsfor both the co- and cross-polarized returns and appears to give better agreement with experimental data. This is apparently due to modelling the water inclusions in the snow as a separate scatterer type, rather than combining the water and air as an average background medium. Comparisons are also made with measured data obtained by Stiles and Ulaby. They show good agreement, both in trends and levels, for co-polarized backscatter. Computations for cross-polarized backscatter are also presented, but no experimental data arc available for comparison.

ISSN:0143-1161    

DOI:10.1080/01431169108955181

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The use of algorithms incorporating radiance information from one or a number of wavelengths is a standard technique for detecting the concentration and distribution of water quality parameters in coastal and open ocean waters. It has become clear, however, that in a turbid dynamic coastal environment there is no one algorithm applicable for all times, seasons or area because the composition of the suspended material variescontinually. Consequently site specific algorithms have been proposed. Results of an eigenvector analysis of radiance spectra and sea-truth data collected as part of airborne remote sensing campaigns in 1984 and 1985 are presented. The eigenvectors of radiance data are shown to be dependent on the type and relative concentrations of material in suspension. The technique is shown to have great potential for the identification of the composition of material in suspension without recourse to sea-truth data. This information could be used as a criterion for selection of an appropriate algorithm.

ISSN:0143-1161    

DOI:10.1080/01431169108955182

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Ground-data quality is an important issue in the analysis of remotely sensed data. Since the results of such an analysis are evaluated against the ground data these ground data must be accurate. Two issues affecting the quality of soil moisture content ground data are investigated in this paper. These are the laboratory procedures employed in its estimation and the effect of cultivation practices on the distribution of surface soil moisture in the field. Laboratory procedures commonly used may not always be appropriate and different approaches are likely to give estimates of variable accuracy. Cultivation practices were found to produce significant variations in soil moisture distribution, with over 10 percent difference in soil moisture content estimates between the top and bottom of a ridged soil. Ground data collectors using different sampling designs and adopting dissimilar laboratory techniques may therefore produce considerably different estimates of the soil moisture content. Consequently ground-data collection programmes should be fully documented, especially if the results obtained by different research groups are to be compared or merged, so that users may be aware of the quality of the data recorded

ISSN:0143-1161    

DOI:10.1080/01431169108955183

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Many remote sensing applications, especially multitemporal approaches, require radiometric corrections of image data in which radiometric normalization to standard conditions and modelistic atmospheric corrections are often considered as alternative solutions. Successful radiometric normalization depends on the availability of suitable reference targets within the scenes under considerations, which may be critical. It is demonstrated that even simplified atmospheric correction modelling can provide a valuable alternative solution. We present an atmospheric correction approach for Thematic Mapper data, which is based solely on the evaluation of scene information and may therefore be considered operational. The method is based on the determination of aerosol optical thickness from histogram minima and clear water targets. Atmospheric conditions are assumed constant over the scene, but their variation with the Sunto-satellite scattering angle is accounted for. The environment effect is approximately corrected for each pixel. The accuracy of the method is analysed with respect to ground measurements, and a between-scene comparison of modelled reflectance factors from invariant targets. These first results indicate a precision of the retrieved reflectance factors which is suitable for a quantitative image analysis and a comparison with radiometric field data.

ISSN:0143-1161    

DOI:10.1080/01431169108955184

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The capability of SPOT combined with specifically designed classifiers was investigated for computer-assisted land cover/use mapping in Indonesia. Atmospheric conditions and the small size, complexity and dynamic nature of agro-forest systems confuse spectral analyses. In this context, conventional spectral classifiers are inadequate. This led to the development of two classifiers adapted to the large number of spectral classes that are apparent with highresolution satellite data; i.e. an interactive box classifier and a layered textural/contextual classifier. These were tested on two study areas in Java. Preliminary results suggest that in Indonesia SPOT has the potential of a major data source for land cover mapping down to 1:50000/100000 scale.

ISSN:0143-1161    

DOI:10.1080/01431169108955185

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Leaves from ten tree species, including three conifers from a woodlot in southern Ontario were sampled at weekly intervals for a period of 150 days spanning the phenological events in deciduous trees of leaf development and expansion (flushing), leaf maturity and leaf senescence. The highly diverse seasonal red-edge reflection patterns were studied collectively and individually both from the perspective of long-term trends and relatively short-term or oscillating trends. The phenological events characteristic of deciduous trees were most effectively described using the red-edge position (λpg) and the chlorophyll-well position (λog) derived from the inverted Gaussian model. Moreover, these parameters appeared consistent with what is known about the seasonal turnover of leaf chlorophyll and with other parameters R550or Rogwhich more specifically quantify leaf chlorophyll. By these terms of reference chlorophyll declines considerably earlier in the season than the onset of other physiological or structural changes normally associated with senescence. Both parameters λPRand λogand the real red-edge position (λpr) conjointly provide specific information about each species and differentiate clearly deciduous from coniferous growth forms. Individual species variation in these and other variables was more ‘short term’ than ‘long term’, providing support for the perception that the long-term trends as visualized by λpgand λogare species-specific and can probably be correlated with ecological parameters such as tolerance.

ISSN:0143-1161    

DOI:10.1080/01431169108955186

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The lack of accurate, extensive geometric data on tree canopies has retarded development and validation of radiative transfer models. Wc have devised a stratified sampling method to measure the three-dimensional geometry of 16 walnut trees which had received irrigation treatments of either 100 or 33 per cent of evapotranspirational (ET) demand for the previous two years. Graphic reconstructions of the three-dimensional geometry were verified by 58 independent measurements. The distributions of stem- and leaf-size classes, lengths. and angle classes were determined and used to calculate leaf area index (LAI), stem area, and biomass. Reduced irrigation trees have lower biomass of stems, leaves and fruit, lower LAI, steeper leaf angles and altered biomass allocation to large stems. These data can be used in ecological models that link canopy processes with remotely sensed measurements.

ISSN:0143-1161    

DOI:10.1080/01431169108955187

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Landsat images have been analysed visually to assess their utility in delineating cones/ventsin one of the Cenozoic volcanic fields, Harrat Kishb, in the western region of Saudi Arabia. Volcanic cones identified from six sets of Landsat data (one Return Boom Vidicon, two Thematic Mapper and three Multispectral Scanner images) were checked in the field and then compared with those extracted from aerial photographs as shown on the existing geological maps. The result shows that the accuracy of the visual identification varies greatly from 51 per cent for the Multispectral Scanner to 93 per cent for the Thematic Mapper. A new measure of mapping accuracy which incorporates both the commission and omission errors was computed to range between 63 and 88 per cent, respectively, for these two images. To demonstrate further the usefulness of the Landsat images in geological investigations on volcano-tectonics, geometrical properties associated with those delineated cones were also estimated. The cone density is 2·66 cones 100km−2with an average (geometric mean) spacing of 2·29km. The alignment of cones identified on the Thematic Mapper image covering the study area has a mean orientation of N 8°W.

ISSN:0143-1161    

DOI:10.1080/01431169108955188

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Airborne Thermal Infrared Multispectral Scanner (TIMS) data and laboratory thermal infrared reflectance spectra were collected from sites of hydrothermally altered andesitic volcanic rocks near Virginia City, Nevada. Alunitic, kaolinitic, illitic, and propylitic alteration types have distinct laboratory spectral curves, although the individual spectra are difficult to interpret mineralogically. TIMS emittance spectra show a general shift in the wavelength of the silicate emittance minima to shorter wavelengths with increasing intensity of alteration, owing to the increasing abundance of secondary framework and sheet silicate minerals. Strongly altered volcanic rocksare identifiable on TIMS radiance and emittance imagery.

ISSN:0143-1161    

DOI:10.1080/01431169108955189

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor