ISSN:0143-1161    

DOI:10.1080/01431169608949116

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We compare wind speeds derived from analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) from 1986 to 1992 with wind speeds retrieved from three space borne instruments: the Geosat altimeter, the Special Sensor Microwave/Imager (SSM/I) microwave radiometer and the European Remote Sensing (ERS-I) scatterometer. The comparison reveals imperfections in both ECMWF and SSM/I wind speeds.

ISSN:0143-1161    

DOI:10.1080/01431169608949117

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Change detection algorithms have been applied to MSS data for monitoring changes inside and outside the Lake Brullus environment. Analysis of the results reveals occurrence of erosion and accretion along both sides of the lake inlet. During the study period (1983 to 1991), the lake area decreased by an average rate of 8·6 km2per year mainly due to drying for land reclamation. Comparison between standardized and unstandardized principal components showed that the standardized PCs are more capable of identifying occurring changes. A simple technique, such as image differencing and ratioing, comprises a powerful method to emphasize changes, especially when we use thresholding.

ISSN:0143-1161    

DOI:10.1080/01431169608949118

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The weighted moving average technique is used to analyse lineament azimuths counted by number and length. The technique enhances peak/noise ratio. The quality of distribution is measured by the χ2-test and the degree of correlation between lineament number and length. Moreover, segmenting lineaments improves the enhancement and makes the counting only by number.

ISSN:0143-1161    

DOI:10.1080/01431169608949119

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The visual analysis of digitally-enhanced Landsat Multispectral Scanner (MSS) imagery, covering the western portion of the Central Zone of the Damara Orogen, Namibia, provides an effective and low-cost means of mapping a north-northeast-trending regional dyke swarm. K.-Ar dating indicates that these dolerite dykes are Lower Cretaceous (∼ 135 Ma) in age, and represent an intermediate phase of Karoo volcanic activity. The synoptic view afforded by the Landsat imagery allows the spatial outcrop of the dykes to be mapped across a large area, and the dykes prove to be easily reconciled from the spatial component of the imagery because they form dark, positive topographic lineaments, with associated areas of shadowing, set against a lighter-coloured, flatter, sandy background. A digitally processed dyke-lineament map reveals a strong north-northeast trend, which is broadly parallel to the contemporaneous Southern Atlantic rift, originally located immediately to the west. The dykes were erupted immediately prior to the splitting of Western Gondwana and the formation of the Southern Atlantic Ocean, and are associated with the initial continental rifting processes. Many dykes may have acted as feeders to the flood basalts which were subsequently erupted over much of the area. It is suggested that the emplacement of this regional dyke swarm may represent the latest activity along an earlier crustal weakness.

ISSN:0143-1161    

DOI:10.1080/01431169608949120

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Large datasets, such as the Global Land 1-km Advanced Very High Resolution Radiometer (AVHRR) Data Set (Eidenshink and Faundeen 1994), require compression methods that provide efficient storage and quick access to portions of the data. A method of lossless compression is described that provides multiresolution decompression within geographic subwindows of multi-spectral, global, 1-km, AVHRR images. The compression algorithm segments each image into blocks and compresses each block in a hierarchical format. Users can access the data by specifying either a geographic subwindow or the whole image and a resolution (1,2,4, 8, or 16 km). The Global Land 1-km AVHRR data are presented in the Interrupted Goode's Homolosine map projection. These images contain masked regions for non-land areas which comprise 80 per cent of the image. A quadtree algorithm is used to compress the masked regions. The compressed region data are stored separately from the compressed land data. Results show that the masked regions compress to 0·143 per cent of the bytes they occupy in the test image and the land areas are compressed to 33·2 per cent of their original size. The entire image is compressed hierarchically to 6·72 per cent of the original image size, reducing the data from 9·05 gigabytes to 623 megabytes. These results are compared to the first order entropy of the residual image produced with lossless Joint Photographic Experts Group predictors. Compression results are also given for Lempel-Ziv-Welch (LZW) and LZ77, the algorithms used by UNIXcompressand GZIP respectively. In addition to providing multiresolution decompression of geographic subwindows of the data, the hierarchical approach and the use of quadtrees for storing the masked regions gives a marked improvement over these popular methods.

ISSN:0143-1161    

DOI:10.1080/01431169608949121

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A method is proposed to estimate the spatial degradation of geometrically rectified AVHRR data resulting from misregistration and off-nadir viewing, and to infer the cumulative effect of these degradations over time. Misregistrations are measured using high resolution imagery as a geometric reference, and pixel sizes are computed directly from satellite zenith angles. The influence or neighbouring features on a nominal 1 km by 1 km pixel over a given site is estimated from the above information, and expressed as a spatial distribution whose spatial frequency response is used to define an effective field-of-view (EFOV) for a time series. In a demonstration of the technique applied to images from the Conterminous U.S. AVHRR data set, an EFOV of 3·1km in the east-west dimension and 19 km in the north-south dimension was estimated for a time series accumulated over a grasslands test site.

ISSN:0143-1161    

DOI:10.1080/01431169608949122

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The effects of atmospheric optical depth and water vapour content on the bidirectional surface reflectance in channel 1 (visible) and channel 2 (near-infrared) of NOAA AVHRR have been analysed using a coupled surface atmosphere reflectance model. Two different cases of surface: (i) bare soil, and (ii) vegetation cover have been considered. In the case of bare soil, both the amplitude and angular distribution of the bidirectional reflectance of the surface are modified at satellite altitude due to scattering caused by atmospheric molecules and aerosols in the two channels and thereby, the directional properties of the surface are smoothed. Whereas, in the case of lawn, in channel 1, the angular variation of surface reflectance is enlarged together with a large augmentation in reflectance amplitude, and in channel 2, a small reduction in amplitude as well as a variation in angular distribution of reflectances are caused due to scattering particularly over large viewing angles and thereby, the directional variations are smoothed. In channel 1, atmospheric scattering reduces the contrast between the soil and vegetation and is very much significant for medium to high aerosol loadings. Atmospheric water vapour reduces the amplitude of the surface bidirectional reflectance without introducing any significant changes in angular distribution of the surface reflectance for both bare soil and vegetation canopy in channel 2.

ISSN:0143-1161    

DOI:10.1080/01431169608949123

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Landsat, SPOT and IRS data, black and white and false colour composite (FCC) imagery of the summer (April, May), rainfed crop season (October) and winter irrigated crop season (January, February) of Indian Arid Zone were interpreted for recognition or three types of salt affected soils, viz. (1) natural salt affected; slight, moderate and severe, (2) saline soils due to saline water irrigation, (3) sodic soils due to high residual sodium carbonate (RSC) water irrigation. These were field checked and supported by analytical data. The Landsat-MSS band 4 could only provide the overall extent of salinity. The moderate and severe natural salt affected soils were identified by Landsat-MSS band 2, Landsat-MSS and TM, IRS LISS-I and LISS-II and SPOT HRV2 data for April and January. But the differentiation between the saline and sodic soils was possible only by the use of multi-date imagery (October and January) and the clue provided by the cropping pattern. The potentiality of remote sensing data products for identification of the types and degree of salt affected soils is discussed.

ISSN:0143-1161    

DOI:10.1080/01431169608949124

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Spectral Mixture Analysis (SMA) was used to distinguish the fractional abundance of green foliage, dry grass, and soil in Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data. Three maximum likelihood classifications were performed using topographic data only, SMA fractions only, and both topographic and SMA fractions. The predictions were compared to a field based vegetation map and to an aerial photograph of the scene. The combined data set produced the highest correspondence with the vegetation map for an overall correlation of 57 per cent for five classes. Part of the difference was attributed to misclassification in the field-based map.

ISSN:0143-1161    

DOI:10.1080/01431169608949125

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor