ISSN:0143-1161    

DOI:10.1080/014311698215856

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Spatial and temporal multi-layered information is required to assess landslide hazard susceptibility. The manual method of data integration for targeting potential zones susceptible to landslide hazard is time consuming. The present study highlights the utility of temporal remotely-sensed data and knowledgebased Geographical Information Systems for collection, integration and analysis of spatially-oriented data, as well as in finding out the inherent relation between separate entities in parts of West ghat in India.

ISSN:0143-1161    

DOI:10.1080/014311698215865

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effectiveness of spectral and textural information in the identification of surface rock types in an arid region, the Red Sea Hills of Sudan, is evaluated using spectral information from the six Landsat TM optical bands and textural features derived from Shuttle Imaging Radar-C (SIR-C) C-band HH polarization data. An initial classification is derived from Landsat TM data alone using three classification algorithms, Gaussian maximum likelihood, a multi-layer feed-forward neural network and a Kohonen self-organizing feature map (SOM), to generate lithological maps, with classification accuracy being measured using a confusion matrix approach. The feed-forward neural net produced the highest overall classification accuracy of 57 per cent and was, therefore, selected for the second experiment, in which texture measures from SIR-C C-band HH-polarized synthetic aperture radar (SAR) data are added to selected TM spectral features. Four methods of measuring texture are employed, based on the Fourier power spectrum, grey level co-occurrence matrix (GLCM), multi-fractal measures, and the multiplicative autoregressive random field (MAR) model. The use of textural information together with a subset of the TM spectral features leads to an increase in classification accuracy to almost 70 per cent. Both the MAR model and the GLCM matrix approach perform better than Fourier and multi-fractal based methods of texture characterization.

ISSN:0143-1161    

DOI:10.1080/014311698215874

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Principal components analysis (PCA), ratioing, image differencing and intensity-hue-saturation (IHS) transformation have been widely used in monitoring various natural resources and environmental hazards. In our study, the temporal behaviour of salt-affected soils in the Indo-Gangetic alluvial plains of Uttar Pradesh has been studied using Landsat MSS data for 1975 and 1992. Apart from routine digital classification of temporal MSS data using Guassian maximum likelihood algorithm, PCA, image differencing, and ratioing were also evaluated for their potential in bringing out temporal changes in salt-affected soils, if any. The results indicate that the third principle component, image differencing, and ratioing of the first two MSS bands for two periods have brought out substantial information associated with the temporal behaviour of saltaffected soils.

ISSN:0143-1161    

DOI:10.1080/014311698215883

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The monitoring of vegetation in Southern Africa with satellite data has become increasingly important over the past decade because it is linked to variation in agricultural production and climate change with implications for wildlife management and tourism. This study shows how maps of vegetation status were produced in near real time from NOAA images acquired from the local receiving stations in Etosha National Park, Namibia and in Zambia. Map products based on the NDVI were put into historical context and stratified to remove effects of the main vegetation types in order to assess vegetation status. The historical data were extracted from the FAO ARTEMIS NDVI archive and processed to obtain a statistical distribution of the NDVI for each 10-day period of the year and vegetation type by applying techniques commonly used in hydrology for the prediction of extreme events. The quintile probability ranges were used to define five classes of a Vegetation Productivity Indicator (VPI). LAC NDVI images obtained in real-time from the receiving station were processed to derive a VPI map for each 10-day period. In Etosha National Park and in Zambia, the VPI was strongly related to the rainfall and the VPI maps provided improved information on the spatial variations. The weighted average VPI for the main agricultural region of Zambia was significantly correlated with maize production.

ISSN:0143-1161    

DOI:10.1080/014311698215892

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An inversion method using a simple bidirectional reflectance model and data on optical reflectances remotely-sensed from satellites has been improved to derive surface properties such as the leaf area index (LAI). Such properties are important in deriving the resistance of the vegetative canopy to uptake of gaseous trace chemicals from the atmosphere and in the study of radiation transfer processes. We found that a multi-pass retrieval technique can greatly improve a model's ability to retrieve surface properties. Because the sensitivity of the model inversion to initial values is an important issue that depends on (1) the partial derivative of reflectance with respect to each parameters to be retrieved ( R / x ) and (2) the degree of independence among model parameters, we investigated the issue with synthetic data constructed by a bidirectional reflectance model. The results revealed that, although the surface optical properties are mostly independent of each other, their initial values did have some effect on the retrieved value of the LAI, with the worse case caused by leaf angle distribution index, n, at close-to-nadir solar and view zenith angles of the reflectance data. At nearnadir angles, n and LAI were strongly correlated, and their retrieval was not unique. When applied to satellite remote sensing data obtained with the advanced very-high-resolution radiometer (AVHRR), the model-retrieved seasonal variation of surface properties agreed reasonably well with independent ground measurements made in the First International Satellite Land-Surface Climatology Project (ISLSCP) Field Experiment (FIFE) campaign. Application to Landsat data to retrieve spatial variation was less successful, largely because of the close-to-nadir solar and view zenith angles in the data.

ISSN:0143-1161    

DOI:10.1080/014311698215900

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The possibility of estimating the concentration of individual photosynthetic pigments within vegetation from reflectance spectra offers great promise for the use of remote sensing to assess physiological status, species type and productivity. This study evaluates a number of spectral indices for estimating pigment concentrations at the leaf scale, using samples from deciduous trees at various stages of senescence. Two new indices (PSSR and PSND) are developed which have advantages over previous techniques. The optimal individual wavebands for pigment estimation are identified empirically as 680nm for chlorophyll a, 635nm for chlorophyll b and 470nm for the carotenoids. These wavebands are justified theoretically and are shown to improve the performance of many of the spectral indices tested. Strong predictive models are demonstrated for chlorophyll a and b, but not for the carotenoids and the paper explores the reasons for this.

ISSN:0143-1161    

DOI:10.1080/014311698215919

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The high spatial resolution of digitized aerial photographs may offer an accurate and effective means of mapping, inventorying, and monitoring forests. Due to the presence of bi-directional reflectance, however, the pixel values are affected by their location within the photo. Two similar sample plots or vegetation types in different parts of the photo may thus have quite dissimilar pixel values and texture features. It is consequently necessary to correct, or calibrate, pixel values when they are used in numerical interpretation. The effect of location of a window of pixels on various colour-infrared (CIR) aerial photographs corresponding to the field sample plots was analysed. Two calibration methods, regression calibration and ratioing, were derived and tested. Linear regression calibration to the principal-point level of the photos was shown to be the most effective, in which the mean pixel value of the window was modelled as a function of solar and sensor direction at the time of exposure. The results indicated that the effect of location on the window mean values was considerable. Calibration also increased the spectral separability of forest stand-classes.

ISSN:0143-1161    

DOI:10.1080/014311698215928

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Using a single layer radiative transfer approach, this paper studies the effects of Mount Pinatubo's perturbations to atmospheric aerosol characteristics, as deduced from long-term ground based observations at a tropical station, on atmospheric radiances, as would be seen by a nadir-looking remote sensor in the visible and near infrared spectral range. We reveal that during the first one-year period after the eruption, direct radiance has been depleted by 30 to 40% while the path radiance increased up to 400%, (more at the near infrared wavelengths). The total radiance is found to decrease, significantly at the longer wavelengths, whereas at the shorter wavelengths the effect is much smaller.

ISSN:0143-1161    

DOI:10.1080/014311698215937

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The results of the investigation of lidar sounding to measure the spacetime distribution of the optical characteristics in oceanic light scattering layers are presented. The shipborne lidar used in the experiments excluded sea-state influences on the sounding results. Such an approach allowed the investigation of dynamic processes in the upper ocean layer. Experimental data for internal wave registration are also given.

ISSN:0143-1161    

DOI:10.1080/014311698215946

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor