ISSN:0143-1161    

DOI:10.1080/01431169608949050

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Previous attempts to map land cover at broad scales were based on single year time series and usually on the Normalized Difference Vegetation Index ( NDVI) Single years of data lack statistical representativity and the NDVI is partially driven by short-term climatic characteristics. We investigate two approaches to produce land-cover classifications that are not excessively influenced by short-term climatic variability: (i) averaging a climate-driven variable over several years, and (ii) measuring a more climate-independent variable. We test, compare and combine these two approaches for the African continent using 8 years of AVHRR Global Area Coverage (GAC) data. Our results demonstrate that times series of the ratio between surface temperature and NDVI are less influenced by interannual variations in climatic conditions than NDVI time series and thus produce more stable land-cover classifications. This finding is consistent with the biophysical interpretations of these two variables. When data are averaged over longer periods, NDVI- or Ts/ NDVI-based land-cover classifications display few differences.

ISSN:0143-1161    

DOI:10.1080/01431169608949051

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

HRV-XS of SPOT imagery and MNT (Modè le Numè rique de Terrain) are used to compare, in dè sert areas, gè ological mapping from the visual interpretation of à stereoscopic pair ofHRV scenes and the combined classifications using the texture of HRV images and MNT. This comparison enables us to evaluate belter information from HRV imagery and to choose how to process information depending on the kind of ground studied and the means utilized. Combined classifications may be useful, however they do not have to be systematically undertaken, they may only support visual analysis which is a priority.

ISSN:0143-1161    

DOI:10.1080/01431169608949052

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The current orientation of remote sensing applied research favours the use of both multisource and multidate data which are not always available to developing countries. The exploitation of the data available must therefore be optimized. This paper shows that we can improve the thematical supply of a simple picture by using some methods that bring together PCA ( principal component analysis) image restoration and segmentation.

ISSN:0143-1161    

DOI:10.1080/01431169608949053

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Investigation of spectral and textural classification of high resolution ATM image of a semi-natural scene is presented. Pure spectral classification using bands 5, 7, 9 and the maximum likelihood classifier yielded 56, 63 and 64 per cent overall classification accuracies with 1-25m, 2-5m, and 50m spatial resolution data respectively. Application of combined spectral and textural classification using bands 5, 7, 9 and various texture features from seven texture algorithms ( spatial grey level dependence matrices-SGLDM, grey level run length matrices-GLRLM, busyness, neighbouring grey level dependence matrices-NGLDM, sum and difference histograms-SADH, and fractal analysis), yielded overall classification accuracies from 58-65 per cent at 1-25 m resolution. It is concluded that texturally-based classifications improve overall classification although improvements are not dramatic. The first-order texture measures from algorithms like GLDH and SADH have shown more promise than second-order algorithms, like SGLDM and NGLDM. The energy feature from most of the texture algorithms shows considerable classification potential. A selection of distance metric corresponding to the size of the spatial unit for a given cover type improves the classification of that class. With degradation of spatial resolution the overall accuracy of textural classification improves up to 69 per cent for 5-0 m resolution data.

ISSN:0143-1161    

DOI:10.1080/01431169608949054

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Dracunculiasis has been shown to be a major cause of agricultural work loss in many parts of West Africa. Monitoring the magnitude of agricultural loss caused by this parasite has been a problem due to the non-market nature of the agricultural output, which is often used for subsistence or barter. To test the hypothesis that ‘ Optimization of water and sanitation interventions in areas with high Dracunculiasis prevalence have a measurable socio-economic impact’ a temporal analysis of Landsat Thematic Mapper (TM) satellite data was conducted. A region in which intervention had not taken place (the control) and a region in which it had were compared to determine the change in agricultural activity. Paired comparisons were made of the difference between two Landsat TM data sets, a 31 January 1986 scene ( pre-intervention) and a 5 January 1991 scene (post-intervention) using the digital number ( DN) values in bands 5, and 7, and the Normalized Difference Vegetation Index (NDVI) calculated from bands 3 and 4. The results of the paired comparison indicated that agricultural activity increased in regions where intervention had taken place. The analysis also indicated that the Harmattan winds may have effected the utility of the NDVI because of its differential effect on atmospheric scattering in the visible and infrared parts of the spectrum.

ISSN:0143-1161    

DOI:10.1080/01431169608949055

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The phenomena of land use/ change were evaluated by using a remote sensing approach in a case study in Yogyakarta, Indonesia. The index of changes, which was calculated by the superimposition of land use/ images of 1972, 1984, and land use maps of 1990, were introduced to analyse the pattern of change in the area. The results demonstrated that the pattern of land use/ change in the study area was that of paddy coverage to open/ land to settlement. The annual growth ratios of new settlements to absorb paddy coverage, mixed vegetation, and open/ land were 16 per cent, 20 per cent, and 64 per cent respectively. The larger the percentage of the paddy coverage, the higher the tendency for settlement growth to absorb the paddy coverage, and the larger the percentage of open/ land, the higher the tendency for settlement growth to absorb open/ land. Settlement growth had a high correlation with road accessibility. The highest settlement growth was distributed mostly in suburban areas between 200 and 400 m from secondary roads. Without intelligent intervention by the government and public awareness, the loss of these agricultural land cannot be stopped and will jeopardize the local and regional economy.

ISSN:0143-1161    

DOI:10.1080/01431169608949056

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The existing procedures for crop yield estimation involve Crop Cutting Experiments ( CCEs) conducted during harvesting time in the plots selected based on a pre-designed sampling scheme using available ground data. These ground sampling designs do not consider the crop condition which is directly related to the yield during the season, for stratification and subsequent sample selection leading to biased distribution of plots. Moreover these experiments are capable of providing estimates only at larger areal units such as the total command area. Hence there is a need to improve the sampling design to achieve more accurate estimates. An alternate methodology exploiting the information on crop area and crop condition, derived from satellite remote sensing data on near real-time basis, for improving the ground sampling design has been proposed in this paper. The methodology is demonstrated in the Davangere and Malebennur divisions of the Bhadra project command area to estimate the average yield of paddy during Rabi 1992-93. The results obtained from conventional methodology and the improved procedure showed that the latter has increased the accuracy of estimates. The yield values obtained from CCE plots have been regressed with corresponding Normalized Difference Vegetation Index (NDVI) statistics and thus the derived paddy yield model is capable of providing the yield estimates at smaller area 1 units, such as within distributary command.

ISSN:0143-1161    

DOI:10.1080/01431169608949057

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This project explores an iterative classification process as an alternative to two-stage classifications. In the iterative classification approach cover types are classified, one or two at a time, and the band selection process is repeated in each iteration, so that the combination of bands that provides the best separability among the classes that remain to be classified is selected. The optimum number of bands to perform the classification is also determined for each iteration, so that the classification of the area that is masked in each iteration achieves the highest possible accuracy. Spectral Pattern Analysis, and Spectral Separability Indices are used in the band selection process. GIS analysis is used to obtain prior probabilities, and to determine if variables such as elevation, slope, and aspect can result in a source of information for segmentation of the study area into more homogeneous strata. The results of this study show that: (1) The proposed iterative classification approach is superior to traditional single-step supervised and unsupervised approaches with a 99 per cent confidence level, and (2) Prior probabilities improve band selection process only when the TD separability index is used, but do not improve the classification process itself. GIS analysis of the study area may serve as a very useful tool for segmenting the study area into more homogeneous strata, but due to the large size of the study area, and the large number of classes (21 classes) being discriminated it did not help in the classification performed in this study.

ISSN:0143-1161    

DOI:10.1080/01431169608949058

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Vegetation maps were produced by applying a region-growing segmentation algorithm to Landsat Thematic Mapper (TM) data, and labelling the resulting segments or map polygons by overlay of a per-pixel classification and applying a plurality rule. Thus, each segment was assigned a vegetation class label based on the most frequently occurring pixels in the segment. The segmentation improved overall map accuracies by an average of 10 per cent relative to the underlying per-pixel classification for three subimages within a southern California montane watershed based on a comparison with photointerpreted maps. While it was hypothesized that including transformed slope aspect and image texture as input to the segmentation would improve map accuracy by creating segments corresponding more closely to vegetation stands, our results did not support these hypotheses. Further, performing the segmentation on principal components bands, or a vegetation index, did not improve results over the segmentation based on TM bands 2, 3, and 4.

ISSN:0143-1161    

DOI:10.1080/01431169608949059

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor