摘要:

Most attempts at predicting soil moisture from C-band microwave backscattering coefficients for bare soil are made by fitting experimental calibration relations obtained for limited ranges of incidence angle and soil surface roughness. In this paper, a more general approach is discussed using an inversion procedure to extend the use of a single experimental calibration relation to a wider range of incidence angle and surface roughness. A correcting function is proposed to normalize the backscattering coefficients to the conditions (incidence angle and surface roughness) of the calibration relation. This correcting function was derived from simulated data using the physical optics or KirchhofTs scatter model using the scalar approximation. Before discussing the inversion procedure, the backscattering coefficients calculated by the model have been compared with experimental data measured in the C-band, HH polarization and three incidence angles (Θ= 15°, 23°, 50°) under a wide range of surface soil moisture conditions (0.02⩾Hv⩾ 0.35cm3cm-3) and for a single quite smooth soil surface roughness (0–011⩾s⩾ OOI4/n)m. The model was found to be experimentally validated from 15° to 23° of incidence and for surface soil moistures higher than 0-I0cm3cm-3. For the inversion procedure, it is assumed to have a wider range of validity (15° ⩾ Θ 35° ) for ihc incidence angle. A sensitivity analysis of the model to errors on roughness parameter and incidence angle was performed in order to assess the feasability and suitability of the described inversion procedure.

ISSN:0143-1161    

DOI:10.1080/01431169208904070

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The use of satellite data for determining daily evapotranspiration over completely vegetated areas has been analysed by different authors. However, if the soil surface is partially covered by vegetation the problem becomes more complicated, because in this case the value of the temperature measured by the satellite varies with the viewing geometry. In this work we have studied the influence of the satellite observation angle for crops with different cover degree, field geometry and ground emissivity. For this purpose we have used the simplified relation proposed by Jacksonet al.LETd=Rnd−B(T3−Ta)iwhereET4andRndare the daily values of evapotranspiration and net radiation respectively, (T3−Ta)iis the difference between crop surface and air temperatures measured at midday,Bis a semi-empirical parameter, andLis the latent heat of vaporization of water. And we have concluded that the imposition of a single value ofBis unacceptable and specific values must be chosen according to certain broad categories of the viewing geometry, whose number will depend on the geometry of each crop.

ISSN:0143-1161    

DOI:10.1080/01431169208904071

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The purpose of this paper is to determine the optimal space-time resolution which is suitable for the estimation of cumulative precipitation by a simple rainfall-radiance relation. The correlations between precipitation ground measurements and convective clouds derived from Meteosat infrared brightness temperatures are computed for different spatial and temporal scales, over the tropical Sahelian region and over a validation site near Niamey (Republic of Niger). It is shown that monthly precipitations display a higher spatial variability than the monthly cold cloud field, causing a low correlation between them. The data set obtained during August 1988 from the dense network of recording raingauges of theEPSAT-NIGERexperiment is used for a study at short time scale. Several infrared cloud indices are compared and it is found that the mean precipitation estimated on a large surface (> 100 by 100km2) is well enough correlated to the satellite infrared index cumulated on daily or even shorter time periods, so that about 70 per cent of the variance of rainfall estimated from these radiances is explained by a linear function of the fraction of surface covered by cold clouds.

ISSN:0143-1161    

DOI:10.1080/01431169208904072

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

One of the uses of remotely-sensed data is to classify a land area into different land cover types. In this paper our aim is to present a systematic study of the ability of two classification procedures to produce accurate classifications. The procedures considered are smoothed maximum likelihood, that is a maximum likelihood classification smoothed using a simple majority filter, and a penalised maximum likelihood approach in which spectral and contextual information are used simultaneously to make a classification. The methods are tested on images of simulated spectral responses for which the true land cover map is known. A technique is presented for simulating spectral responses, which are autocorrelated, and therefore a better model of reality, for any given land cover map. Two variations of the technique are considered, the second giving rise to a higher level of autocorrelation than the first, over a larger neighbourhood.

ISSN:0143-1161    

DOI:10.1080/01431169208904073

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

To determine the optimum tank depth for the assessment of spectral reflectance from suspended inorganic matter (SIM), a 1·10 m × 0.90 m × 0·67 m black-coated tank was used. A plate with the same coating was constructed to simulate various depths. Different concentrations of bentonite and red silt suspensions were produced and radiometric measurements were performed in the 400-900 nm spectral range. The results showed close relationships between optimum depth and suspension characteristics, e.g., at 5mg/l of bentonite the optimum depth was around 0·63 m and at 140 mg/l it was 0·41 m. For red sill, at 140 mg/1 the optimum tank depth was greater than 0·41 m too. Before each experiment the optimum tank depth must be assessed to produce spectral reflectance of SIM.

ISSN:0143-1161    

DOI:10.1080/01431169208904074

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

An optimal estimation (OE) technique has been used to increase the accuracy of crop acreage and yield estimates by combining results from remotely sensed (RS) data and conventional models. For crop acreage estimation the OE increased the accuracy of wheat acreage estimation when the first forecasts of the Directorate of Economics and Statistics (DES) were combined with state level RS estimates over the states of Haryana and Punjab in India.

ISSN:0143-1161    

DOI:10.1080/01431169208904075

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Several studies have shown that the NDVI calculated from NOAA-AVHRR data is related to annual rainfall and primary productivity in Sahelian areas. Such correlations, however, are affected by several environmental factors and have been tested only with data accumulated during rainy seasons, which is not ideal for the prediction of crop yield. In the present study a methodology of NOAA AVHRR data processing is presented which utilizes NDVI computed only in the first part of some rainy seasons and statistically takes into account the geographical variability in land resources and atmospheric conditions. From the first results of the application of the methodology in Niger, its potential has been shown both for environmental monitoring, and, more specifically, for crop yield assessment and forecasting.

ISSN:0143-1161    

DOI:10.1080/01431169208904076

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The specular reflectance of a leaf is unrelated to wavelength or leaf content. However, a vegetation canopy is not a large leaf and specular reflectance is likely to be related to wavelength and vegetation amount because of the correlation between canopy geometry and vegetation amount. It was hypothesised that if the specular component were removed from the total (specular and diffuse) reflectance of a canopy then the strength of the correlation between diffuse reflectance and vegetation amount would decrease in near-infrared wavelengths and increase in visible wavelengths.

ISSN:0143-1161    

DOI:10.1080/01431169208904077

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor