ISSN:0143-1161    

DOI:10.1080/01431168808954880

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Satellite-borne radar altimetry offers a unique opportunity for measuring the form and mass balance of the polar ice sheets. Changes in ice-sheet mass balance are intimately linked to climatic change and variations in the global mean sea level. However, previous altimeter measurements of ice-sheet topography have been made without the use of a well-validated model of the altimeter return. Here, we present a theoretical model of the return which, supported by both observational and experimental evidence, suggests that over vast areas of the higher altitude regions of the ice-sheets, significant radar penetration of the firn occurs at frequencies commonly used for space altimetry. This implies the need for a previously-neglected correction to height measurements which can be as much as 3-3 m, depending on the retracking method and location. Since the degree of radar penetration may exhibit variability over a range of time-scales, failure to account for the effect could lead to erroneous estimates of surface elevation change. The detection of variability in the degree of penetration is of considerable interest from the point of view of monitoring the processes of accumulation and ablation of snow over the ice-sheet surface, as the return is particularly sensitive to conditions within a few centimetres of the surface. The model has wider applications as it may be used in modified form to simulate altimeter return from all smooth surfaces which exhibit a combination of surface and volume scattering, including deserts and the surfaces of the terrestrial planets and their satellites.

ISSN:0143-1161    

DOI:10.1080/01431168808954881

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Radar backscatter from bare sandstones, shales and limestones was measured in May 1982 in the Monument Upwarp region of south-eastern Utah using a helicopter-borne 4·4-17·6 GHz multipolarization radar scatterometer. Rock samples for laboratory analysis were collected and surface conditions described. The purpose of the experiment was to observe the backscatter from selected rock formations as a function of incidence angle, frequency and polarization to determine the degree of correlation with the permittivity and roughness of the rocks. An additional goal was to measure the permittivity of the rock samples using free space, waveguide andin situmethods. The permittivity of the sandstone ranged from 3·0 to 3·75, the shales from 4·2 to 5·0, and the limestones from 7·5 to 8·5, Multiple linear regression analysis of the data indicated a high (greater than 90 per cent) correlation between the radar backscatter and the permittivity of the rocks.

ISSN:0143-1161    

DOI:10.1080/01431168808954882

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This paper presents some experimental results on the properties of image speckle along with two adaptive filters that are useful for speckle reduction. An investigation of available SIR-B digital image data over Australia shows that speckle is non-while Gaussian noise and fits a multiplicative noise model in which the noise, uncorrelated with signal, has a mean of 1 and a constant standard deviation. The non-uniform spectrum can be represented by an empirical formula. Based on these results, two adaptive filters have been designed, a moving average filter and a combined moving median filter. In both of these, variance ratios are used to govern the filter parameters. The filters have been applied to some SIR-B image segments, showing good results in both smoothing speckle and maintaining edges.

ISSN:0143-1161    

DOI:10.1080/01431168808954883

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The ability of radar systems to record useful data independently of the prevailing weather conditions and the future increase in radar data availability is likely to result in their increased utilization for crop classification. However, a variety of factors relating to the quantity and quality of the data will influence the accuracy with which these data can be classified. This paper aims to illustrate the effect of some of these factors on crop classification accuracy from a multi-feature synthetic aperture radar data base. The results show that in addition to the number of data channels available for a classification, the method of radiometric correction applied to the data and the use of data from different look directions can have significant effects on the classification accuracy. The use of a multi-feature data base however, was found to enable accurate discrimination of a variety of crop types.

ISSN:0143-1161    

DOI:10.1080/01431168808954884

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This paper describes the complementary use of digital terrain information and SPOT-1 HRV multispectral imagery for the study and mapping of semi-natural upland vegetation. A digital terrain model was derived for a 10 by 10 km study area in southern Snowdonia, Wales, and was used to generate slope and aspect images. A model was developed as a first-order approximation of changes in radiance with local topography, assuming Lambertian behaviour of vegetation canopies. The model was implemented for the study area to assess its use in suppressing the effects of relief on scene radiance. Subsequently the model was refined to describe non-Lambertian reflectance.

ISSN:0143-1161    

DOI:10.1080/01431168808954885

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This study-examines the use of multitemporal Landsat satellite radiance values to classify the potato crop. Using this data, the distribution and area of the crop within the Kincardine and Deeside District of Grampian Region is presented. The area and individual locations identified are found to be comparable to Department of Agriculture and Fisheries for Scotland statistical returns. The study also integrates the spatial distribution database with soil and potential water deficit data to generate statistical information on the proportion of the potato crop growing on drought susceptible soils.

ISSN:0143-1161    

DOI:10.1080/01431168808954886

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A simplified model that accounts for diurnal solar zenith and azimuth angle illumination changes and plant geometry effects on photosynthetically active radiation (PAR) was developed, h was tested using diurnal absorbed PAR (APAR) measurements acquired for cotton (Gossvpium hirsuiumL.) grown at Weslaco, Texas, during the 1984 and 1986 growing seasons. Diurnal canopy reflectance and transmittance measurements were automatically collected at 3-minute intervals from about 9.00 to 14.50 local standard time (LST) using radiometers mounted 3·7m above the soil surface and PAR light bar sensors located beneath the crop canopy perpendicular to the crop rows. Plant growth measurements estimated by the model were significantly correlated with observed measurements during crop development. Model-estimated heliotropic leaf elevation trends agreed with published results for cotton canopies. APAR, relative to incident PAR, was generally lower for east-west rows than for north-south rows during crop development. The APAR response of cotton canopies for both east-west and north-south rows were found to be essentially flat when solar azimuth was between 90° and 270° so one observation close to noon would probably be representative of the diurnal APAR measurements.

ISSN:0143-1161    

DOI:10.1080/01431168808954887

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In this work we use Becker's model for the determination of the effective temperature and emissivity under vertical observation of a citrus orchard. We apply this model to the particular case of a typically radiative night cooling (completely clear sky and calm wind) condition under which radiation frosts are normally produced which are damaging to the fruit and, consequently, to the Valencian economy. An attempt is made to establish a safety limit over which a frost cannot be produced. Ground and orange tree emissivity measurements were carried out by means of the box method. We were able to construct a hand-driven scanning system for the temperature measurement of the ground-orange tree system. We determined that a citrus orchard, under normal observation, can in practice be considered as a homogeneous system as far as the emissivity is concerned and that the orange tree's influence on the effective temperature is approximately three times that of the ground.

ISSN:0143-1161    

DOI:10.1080/01431168808954888

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Raw radiance data measured by a Landsat satellite includes undesirable atmospheric and topographic effects. The correction to allow for these effects is important in order to increase the accuracy of classification. In this paper we show how these effects on the Landsat MSS data are estimated, allowing for the transfer theory of radiation in the atmosphere-ground system. First, we present the theoretical basis of the atmospheric effect correction system (AECS) which corrects for atmospheric effects on the Landsat MSS data over a flat terrain. Then we propose a simple radiometric correction method which can remove both the atmospheric and topographic effects from the Landsat MSS data over a rugged terrain. We have applied it to a mountainous test area with known digital terrain data and obtained satisfactory results. In our analyses, the values of relevant atmospheric parameters such as the optical thickness, the single scattering albedo and the turbidily factor of the atmosphere were adopted from either an Elterman's model atmosphere or a model atmosphere given by Lowtran 5 code in the evaluation of scattering and transmission functions. Lambert's law was assumed as a bidirectional reflection at the ground surface.

ISSN:0143-1161    

DOI:10.1080/01431168808954889

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor