ISSN:0143-1161    

DOI:10.1080/01431169608949087

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Today there is a worldwide trend towards protecting the environment and its natural resources. This goal is achieved using different procedures and techniques. Remote sensing and geographical information systems, however, are two of the most suitable techniques for monitoring, analysing, and managing Earth resources. Conserved natural areas for wildlife is one of the most important natural resources that should be explored using GIS and RS technologies

ISSN:0143-1161    

DOI:10.1080/01431169608949088

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The allocation of confidence level to a classification product is considered to be essential. The acquisition of site-specific data to check the classification was discussed. A statistical approach to the determination of an appropriate confidence level from the check data was presented. The test scene was classified using Maximum likelihood classification with various band combinations. These combinations were used as statistical variables. The results are analysed and the best possible combinations selected for accurate classification system. Keeping the percentage overall accuracy in view, these tests demonstrated the complexity of relations between the land cover classes and the data processing variables. Further, they indicated the variables best suited to the classification of certain classes, based on the performance of variable by class. Here, Hyderabad City is taken as a test site.

ISSN:0143-1161    

DOI:10.1080/01431169608949089

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The satellite over-pass time ground surface temperature can be determined using split-window methods. The diurnal ground temperature is derived from the advanced thermal inertia model as a solution of the heat diffusion equation with a constant diffusivity under periodic forcing on the ground surface in terms of temperature. The model was tested by applying it to NOAA AVHRR data for France. The results indicate that the advanced thermal inertia model can be used to predict the diurnal ground surface temperature quasi-operationally with any two sets of over-pass satellite data and it is better to use any two daytime sets of over-pass satellite data than one night-time set and one day time set of over-pass satellite data, especially in vegetated areas. The model can be used to interpolate the surface temperature values between two over-pass time satellite measurements.

ISSN:0143-1161    

DOI:10.1080/01431169608949090

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The array of Normalized Difference Vegetation Index (NDVI) products now being derived from satellite imagery open up new opportunities for the study of short and long-term variability in climate. Using a time series analysis procedure based on the Principal Components transform, and a sequence of monthly Advanced Very High Resolution Radiometer (AVHRR)-derived NDVI imagery from 1986 through 1990, we examine trends in variability of vegetation greenness for Africa for evidence of climatic trends. In addition to the anticipated seasonal trends, we identify signals of interannual variability. The most readily identified is one that periodically affects Southern Africa. It is shown that the temporal loadings for this component exhibit a very strong relationship with the El Nino/Southern Oscillation (ENSO) Index derived from atmospheric pressure patterns in the Pacific, Pacific sea surface temperature (SST) anomalies, and with anomalous Outgoing Longwave Radiation (OLR). However, we have also detected a second interannual variation, affecting most particularly East Africa and the Sahel, that does not exhibit a consistent ENSO relationship. The results show the teleconnection patterns between climatic conditions in the Pacific Ocean basin and vegetation conditions at specific regional locations over Africa. The comprehensive spatial character and high temporal resolution of these data offer exciting prospects for deriving a land surface index of ENSO and mapping the impacts of ENSO activity at continental scale. This study illustrates that vegetation reflectance data derived from polar orbiting satellites can serve as good proxy for the study of interannual climate variability.

ISSN:0143-1161    

DOI:10.1080/01431169608949091

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The most frequently used vegetation index (VI), the Normalized Difference Vegetation Index (NDVI) and its variants introduced recently to correct for atmospheric and soil optical response such as Global Environment Monitoring Index (GEMI) and Modified Soil-Adjusted Vegetation Index (MSAVI) are evaluated over a Sahelian region. The usefulness and limitations of the various vegetation indices are discussed, with special attention to cloud contamination and green vegetation detection from space. The HAPEX Sahel database is used as a test case to compare these indices in arid and semi-arid environments. Selected sites are characterized by sparse vegetation cover and day-to-day variability in atmospheric composition. Simulated indices values behaviour at the surface level shows that these VIs were all sensitive to the presence of green vegetation but were affected differently by changes in soil colour and brightness. We showed that GEMI is less sensitive to atmospheric variations than both NDVI and MSAVI since it exhibits a high atmospheric transmissivity over its entire range for various atmospheric aerosol loadings and water vapour contents. These results were first tested on a vegetation gradient, and secondly evaluated on a transect which encompasses various soils formations. On the vegetation gradient, it was found that GEMI computed from measurements at the top of the atmosphere is invariable from one day to the next. On the bare soils transect, MSAVI calculated at the surface level, has shown a great insensitivity to soil optical responses modifications, while GEMI exhibits from space noticeable variability in this bright soil context. Finally, it was illustrated that GEMI exhibits interesting properties for cloud detection because of the strong decrease of its value on cloudy pixels.

ISSN:0143-1161    

DOI:10.1080/01431169608949092

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Applications of airborne C-band synthetic aperture radar imagery for determining variations in agricultural crop characteristics were investigated at a test site in southern Alberta, Canada. Synthetic aperture radar (SAR) imagery and ground-based crop characteristics data were acquired on 19–20 July 1994 for wheat, canola, beans, peas, and wheat + alfalfa cultivated under a variety of irrigation conditions. The results indicate that the statistically significant relationships that were derived between the ground-based data and SAR imagery are a function of crop type, crop condition parameter, and image processing procedures, and that crop characteristics such as leaf area index and plant height are negatively correlated with radar backscatter.

ISSN:0143-1161    

DOI:10.1080/01431169608949093

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Airborne optical multispectral imagery was acquired in conjunction with contemporaneous ground-based measurements of various crops (leaf area index, canopy temperature, plant height) at a test site in southern Alberta, Canada. Data were acquired on three occasions in July 1994 for a variety of crops and irrigation practices. A large number of crop condition-spectral relations were examined to determine whether the imagery could be used to measure the various crop condition parameters. It was found that a number of statistically significant correlations exist between the imagery and the crop condition parameters and that these correlations vary as a function of crop type, time of year, and crop condition parameter. The results suggest that in many cases, multi-spectral optical imagery can be used to monitor variations in crop condition parameters across the growing season for a variety of crop types.

ISSN:0143-1161    

DOI:10.1080/01431169608949094

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Ice concentration in the Arctic derived from ERS-1 Synthetic Aperture Radar (SAR) and Special Scanning Microwave/Imager (SSM/I) images are compared. The satellite data are compared to video images andin situmeasurements. The data were acquired during the freeze-up period of the ARCTIC'91 expedition. The studied areas were characterized by melting conditions and new ice formation with frost flowers. The ERS-1 SAR images are classified by a local averaging method and a segmentation method. Parameters for the methods are derived from the backscattering distributions. Temporal sequences and meteorological information are used for consistent results. Ice concentration derived from SAR are compared with the SSM/I ice concentration (NASA team algorithm) and ship observations. SSM/I may underestimate the ice concentration by 20 per cent due to thin ice formation and melting conditions while SAR may overestimate. However, by using the SAR estimate of the different ice classes we believe it is possible to increase the accuracy of the NASA team algorithm. We conclude that it is important to compare results from different sensors and methods.

ISSN:0143-1161    

DOI:10.1080/01431169608949095

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Significantly different sea-ice concentrations estimated by the well known Bootstrap and NASA/Team SSM/I algorithms are found to occur when the brightness temperature of horizontally polarized radiation is depressed, possibly as a result of ice layers in the snow cover. Furthermore, discontinuous ice concentrations, which do not reflect real concentration variations, sometimes occur when the Bootstrap algorithm switches between polarization and frequency schemes. The Bristol algorithm is designed to overcome these problems, and is described in this paper. In an initial evaluation against 10 cloud-free Advanced Very High Resolution Radiometer (AVHRR) winter scenes of the Greenland and Barents Seas, the Bristol algorithm, with a correlation coefficient (ccorr) of 0·88 and r.m.s. error (er.m.s.) of 5·2 per cent, outperforms the NASA/Team (ccorr= 0·82,er.m.s.=6·2 per cent), Bootstrap (ccorr= 0·74,er.m.s.= 8·3 per cent) and AES/York (ccorr= 0·82,er.m.s.=6·4 per cent) algorithms, although further work is required to confirm its possible advantages.

ISSN:0143-1161    

DOI:10.1080/01431169608949096

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor