ISSN:0143-1161    

DOI:10.1080/01431169408954234

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Sometimes in the lower atmospheric boundary layer, depending upon the prevailing micro-/meso-scale meteorological condition, ‘dot’ (also known as ‘lump’) type echo structures appear generally during night-time with light wind and stable stratifications. They are associated often with disturbed atmospheric boundary layer conditions like the occurrence of thunderstorms and/or of precipitation. Digitization and scanning of individual dot/lump echo structure can indicate a cluster of points with varying echo intensity levels. In the coastal region of Calcutta they are found to be spreading vertically and the size of the cluster depends on the vertical height of occurrence. Using image processing technique fine structures of these echoes have been processed, their statisticalnature has been analysed and reported in this paper.

ISSN:0143-1161    

DOI:10.1080/01431169408954235

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Following the assertion of Westwater, on the consideration of the radiometer operating frequency around 22GHz for remote sensing of water vapour distribution in the atmosphere, a comprehensive study has been made to re-examine the validity of considering frequency away from resonant frequency for both dry locations, like Antarctica and for tropical region, Calcutta. Radiosonde data have been utilized to calculate line shape functions and weightingfunctions at different operating frequencies. Results indicate that water vapour sensitive 22·235 GHz is still better for dry climatic regions like Antarctica, whereas, for wet air locations, choice of frequency will be different from the resonance peak.

ISSN:0143-1161    

DOI:10.1080/01431169408954236

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Despite its geological importance, the Earth's volcanic activity has only recently been studied as a global system, with the advent of sophisticated airborne and spaceborne remote sensing systems that safely and economically provide global access at will. Particularly relevant to this approach are global studies of the effects on weather and climate caused by volcanic solid/gaseous products and thermal flux into the environment. To study such time-varying phenomena, observations of volcanic emissions spectral response, acquired simultaneously at a variety of wavelengths from ultra-violet to infra-red, could yield relevant information on the compositions and concentrations of environmentally important components, such as volcanically generated sulphur compounds (e.g., SO2H2SO4), and on volcanoes thermal behaviour. For this purpose, a multi-band imaging spectrometer, dedicated to volcanological observations (VEXUVIO, Visible EXplorer Ultra Violet Infra-red Observer) has been designed to be flown on-board EURECA (EUropean REtrievable CArrier) spacecraft, to be launched by the European Space Agency on the NASA Space Shuttle in 1996. In order to analyse potential observation scenarios with this sensor, volcanoes active during 1991 were studied using a computer code to simulate VEXUVIO capabilities on-board EURECA. Some parameters, representative of the sensor viewing geometry and of the volcanoes observation conditions, are exploited, and several plots are reported, shown their values during the six-months nominal EURECA mission. Despite the limited science objectives of EURECA program and a tightly constrained operational environment, our simulation demonstrates that a reasonable program of volcanologically interesting time-series observations can be carried out during the planned sixmonths lifetime of the EURECA mission.

ISSN:0143-1161    

DOI:10.1080/01431169408954237

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

High spectral resolution images (AVIRIS) providing detailed information on the surfaced mineralogy have been used to evaluate a new indicator kriging based absorption feature extraction technique for mineral mapping exploiting the spectral characteristics of image pixel spectra in comparison with laboratory spectra of minerals. Raw radiance image data from the 1989 Cuprite Mining data set were corrected for atmospheric influence and solar irradiance drop off reducing the data to reflectance using the Empirical Line method. A new technique for mineral mapping is presented based on ordinary indicator kriging. The approach directly uses mineral spectra by defining key bands on shoulders and centres of absorption features which are automatically detected from image spectra using statistical zonation techniques. The image data of selected spectral bands are transformed into binary (0,1) images: the pixel value becoming I if the pixel DN value falls within upper and lower limits characterizing the mineral absorption feature in the spectral band. Performing ordinary kriging and integrating the estimates for the selected bands yields the probability that a mineral absorption feature is present or absent for each pixel (or subpixeJ area) in the scene. Furthermore, kriging provides an estimate for the reliability of this probability.

ISSN:0143-1161    

DOI:10.1080/01431169408954238

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Global Area Coverage (GAC) data from the Advanced Very High Resolution Radiometer (AVHRR) are available on a daily basis, dating back to July 1981. The AVHRR's 3·55–3·93 μm channel is suitable for detection of terrestrial hot spots, such as bushfires. The long-term archives and global cover make the GAC a potentially valuable data source for large scale fire studies. However, these data are sampled spatially through a combination of line skipping and averaging. This study shows that the sampling affects the sensitivity of GAC for fire detection in relation to ecosystem and season. The GAC are found to provide a reasonable measure of fire activity in grassland and open b'ush savannah, but to perform poorly in the forest margins. Overall at least 79 per cent of fires detected with non-sampled AVHRR data are missed by the GAC. This severely limits the use of GAC data for quantitative fire studies. The GAC does appear to provide a reasonable measure of fire calendar (i.e., variations in fire activity with time) and on a continental scale successfully identifies the main regions of fire activity. The potential of these data for continental scale fire studies is illustrated through the preliminary analysis of 277 GAC mosaics of Africa for the period September 1988 to August 1989.

ISSN:0143-1161    

DOI:10.1080/01431169408954239

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Data from the Advanced Very High Resolution Radiometer (AVHRR) have been used for the detection of fires in various ecosystems throughout the world. In this study the most commonlyused methods have been applied to a time-series of 63 AVHRR day time images for the whole of West Africa for the 1991–1992 dry season. The West African region includes ecosystems ranging from dry Sahelian grasslands to moist tropical forests. Furthermore, these ecosystems show considerable seasonal variability. Existing methods were found to be inadequate for fire detection for the whole region becauseof the spatial and temporal heterogeneity of the region's environments. A number of changes were made to the established methods and the new fire detection procedure was applied to the time-series. Field verification and interpretation of the results in the context of the main ecological divisionsof the regionshowed the new method to give good results for all ecosystems throughout the season. Finally, interpretation of fire counts using a Geographical Information System illustrates how such data can improve our knowledge of fire activity at national and sub-continental scales.

ISSN:0143-1161    

DOI:10.1080/01431169408954240

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Since the launch of its first pre-operational model, the Meteosat system has evolved as one of the most well-known Earth observation satellite projects. In particular through its imagery mission it has become an indispensable tool for a large user community. Both the quality of the images produced by Meteosat satellites and their processing onground have been continuously improved in recent years. This paper is a short review of the present capabilities and applications of the Meteosat image processing at the European Space Operations Centre (ESOC, Darmstadt). It starts with a brief overview on available hardware tools for real-time and offline processing of Meteosat images. Geometrical image restoration and radiometric quality control are the main tasks in this area. But in addition a number of dedicated (software) tools and test setups had to be developed for special testing of the satellite performance, for instance during the commissioning of a new spacecraft. Finally, a short summary on current studies and new developments related to the Meteosat imagery mission concludes this review.

ISSN:0143-1161    

DOI:10.1080/01431169408954241

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Texture is an important property of the images. Its inclusion in digital classification is known to improve the classification accuracy. In the present study, the texture features angular second moment, entropy and inverse difference moment were used to differentiate and classify forests affected by jhum (shifting cultivation) in north-eastern India. Large increases (11·1 per cent) in the classification accuracy were observed when texture and tone were used simultaneously. In general, the inverse difference moment was found to be more useful than the entropy. The angular second moment was not useful. The most accurate classification was achieved with a combination of the tone, the entropy and the inverse difference moment.

ISSN:0143-1161    

DOI:10.1080/01431169408954242

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Since the launch of its first pre-operational model, the Meteosat system has evolved as one of the most well-known Earth observation satellite projects. In particular through its imagery mission it has become an indispensable tool for a large user community. Both the quality of the images produced by Meteosat satellites and their processing onground have been continuously improved in recent years. This paper is a short review of the present capabilities and applications of the Meteosat image processing at the European Space Operations Centre (ESOC, Darmstadt). It starts with a brief overview on available hardware tools for real-time and offline processing of Meteosat images. Geometrical image restoration and radiometric quality control are the main tasks in this area. But in addition a number of dedicated (software) tools and test setups had to be developed for special testing of the satellite performance, for instance during the commissioning of a new spacecraft. Finally, a short summary on current studies and new developments related to the Meteosat imagery mission concludes this review.

ISSN:0143-1161    

DOI:10.1080/01431169408954243

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor