摘要:

In June and July 1988, the European Space Agency organized in five European countries the Agriscatt '88 campaign. For this campaign two airborne scatterometers were used, including the French dual-frequency (CandXband) dual-polarization (HHandW) forward-looking radar ERASME. For the French site, the Orgeval hydrological basin, one of the aims of the experiment was to develop a soil moisture retrieval algorithm from radar data. It is shown, from comparison with the ground-truth data, that the use of a multiconfiguration radar improves the capacity of imaging radar for soil moisture mapping. In particular, an algorithm based on a vegetation absorption index and a soil moisture one is tested over wheat fields.

ISSN:0143-1161    

DOI:10.1080/01431169408954102

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

AC-band (5·35GHz) empirical model of the normalized radar cross-section σ°of the sea surface is combined with an electromagnetic model relating the two-dimensional spectral properties of a randomly rough surface to σ°. This is used to document the anisotropy of the sea surface over the wavenumber range 0·2≤k≤2rad cm−1(wavelengths 3 ≤ λ 30 cm). Over that spectral range, the anisotropy of the two-dimensional spectrum is thus found to exhibit a strong increase with wavenumberk, as well as a moderate increase with wind speed. Those features are compared with the behaviour of models of the sea surface which have been proposed previously, based upon quite different approaches. Although some differences exist among them, those various descriptions tend to converge towards a picture involving a transition from nearly isotropic spectra at lowkto highly anisotropic spectra at highkaround the spectral region 0·2≤k≤2rad cm−1.

ISSN:0143-1161    

DOI:10.1080/01431169408954103

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431169408954104

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the semi-arid region of eastern Australia quantitative field surveys showed that microphytic crusts (lichens, mosses and blue-green algae) contributed up to 27 per cent of the ground cover. Spectral reflectance at wavelengths between 0·4 μm and 2·5 μm were recorded from crusts on two soil types and under a number of different moisture conditions. Results showed that the presence of microphytic crusts on both soil types decreased reflectance throughout the spectrum. When crusts were actively photosynthesising chlorophyll absorption features were observed. A strong photosynthetic response occurred within ten minutes of wetting. This work highlights the importance of microphytic crusts as a ground component in the semi-arid region of Australia and also the importance of a knowledge of soil moisture regimes and their effect on the biotic soil crusts when interpreting remotely sensed imagery of the region.

ISSN:0143-1161    

DOI:10.1080/01431169408954106

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This study examined spatial subsets derived from one flightline of Geophysical Environmental Research (GER) 63 channel scanner data from Makhtesh Ramon, Israel, to determine the relationship between the size of spatial subsets and the quality of the Internal Average Relative Reflectance (IARR) atmospheric correction technique. The IARR procedure was run separately on spatial subsets containing 100, 53, 24, 9, 3, 0·16 and 0·02 per cent of the original data set. The correction quality was determined by comparing the reflectance spectra derived from each subset for a site containing the mineral kaolinite. Signal-to-noise ratio (SNR) calculations illustrate that the raw data quality does not vary significantly from one subset to another. The quality of the correction was affected only by changes in the ‘average reference spectrum’ (ARS) associated with the selected subsets. The short-wave infrared (SWIR) region (1·440−2·443 μm) was found to be less sensitive to ARS changes than the visible (VIS) region (0·477−0·848 μm). It was concluded that the IARR correction technique should be applied to the whole (100 per cent) data set prior to any data subsetting. Three parameters, the ‘target area ratio’ (TAR), the subset size relative to the original data set (SSR), and the correction quality ratio (CQR) are proposed as indicators of IARR correction quality.

ISSN:0143-1161    

DOI:10.1080/01431169408954107

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A relation between wet tropospheric range correction and precipitable water has been proposed for correcting satellite-borne radar altimeter data over the Indian Ocean region for south-west monsoon months (May-July). The proposed regional relation, which used data from May-July 1979, gave an rms error of 1·53 mm as compared to rms error of 4·54mm for Liu and Mock's relation using global data. The precipitable water values ranged from 30 mm to 75 mm with larger concentration of data points between 40 to 65 mm. The wet tropospheric range correction could be useful for analysing ERS-1 radar altimeter data over Indian oceans whose dual angle split thermal IR channels and/or microwave channels could be used for estimating total precipitable water with an accuracy of 2 to 4 mm.

ISSN:0143-1161    

DOI:10.1080/01431169408954108

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Ratios of leaf reflectances that were measured within narrow wavebands (2nm) were evaluated as indicators of plant stress. Wavebands used in ratio computation were based on earlier studies that determined the wavelength regions in which reflectance was most affected by 8 stress agents among 6 plant species. Several ratios, such as reflectance at 695 nm divided by reflectance at 670 nm (R695/R670), were affected by some but not all stress agents. However, R695/R420, R605/R760, R695/R760 and R710/R760 were significantly greater (p≤0·05) in stressed compared with non-stressed leaves for all stress agents. The ratios that most strongly indicated plant stress were reflectance at 695 nm divided by reflectance at 420 nm or 760 nm.

ISSN:0143-1161    

DOI:10.1080/01431169408954109

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The concentration of chlorophyll in a crop can be related to both the position of the red edge in a reflectance spectrum and the yield of that crop. The use of a remotely-sensed red edge to estimate yield is dependent upon a well-understood relationship between chlorophyll concentration and yield and a poorly understood relationship between red edge and chlorophyll concentration.

ISSN:0143-1161    

DOI:10.1080/01431169408954110

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Evidence from a very strong and rare case of sunglint in a NOAA-11 AVHRR image is used to show that a problem exists in the on-board signal processing of channel 3. This problem, associated only with targets of high reflectivity and/or temperature, causes erroneous indication of digital counts (DN) and calculated brightness temperatures for near-saturation ranges in channel 3 images. The explanation proposed, a spurious conversion of the sensor signal to DNs, fits observations of sunglint and fire detection data in AVHRR images of the NOAA-series satellites which could not otherwise be explained.

ISSN:0143-1161    

DOI:10.1080/01431169408954111

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The effectiveness of an algorithm which removes sun-glitter from Thematic Mapper imagery of the sea has been demonstrated by computation and tested on Landsat Thematic Mapper data of the Gulf of Naples.

ISSN:0143-1161    

DOI:10.1080/01431169408954112

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor