ISSN:0143-1161    

DOI:10.1080/01431168708954759

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Four groups of severe storms with a total outbreak of 27 tornadoes have been studied by using satellite remote sensing and rawinsonde observations. Geographical distributions of the areas of high moisture concentration at 850 mb height, 7 to 12 hours prior to the formation of the storms, using the best available conventional rawinsonde soundings, and 2 to 3 hours prior to the touchdown of tornadoes, using the three hourly AVE-SESAME soundings, were analysed in conjunction with the ambient pre-storm wind and air mass stability. Using the area of high moisture concentration as a basis, the time-dependent geographical variation of the tropopause height distribution was analysed. It was found that, within the area of a low-level high concentration of moisture, the local tropopause height was lowest at the time of the storm cloud formation and development. The potential energy storage per unit area for the overshooting clouds penetrating above the tropopause is closely related to the intensity of the storms produced, in terms of the Fujita scale of storm damage. To make up the discrepancy of more than 3-hour intervals of available sounding data, numerical cloud modelling is carried out. The results obtained from the cloud modelling are in agreement with the results of satellite remote sensing and rawinsonde observations drawn earlier.

ISSN:0143-1161    

DOI:10.1080/01431168708954760

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

We have tried an adaptation of the radiation model proposed by FAO, applicable in any area, for the estimation of the regional maximum evapotranspiration, ET, from temperature and albedo images obtained from a satellite. This model is based on the relationships

ISSN:0143-1161    

DOI:10.1080/01431168708954761

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Some 10-15 percent of the Seasat altimeter returns over land and inland water, and a larger proportion of sea ice returns, are strongly peaked, in some cases resembling the instrument point target response. Many of these narrow-peaked pulses, from a wide variety of surface types, exhibit well-defined precursors. This paper demonstrates these precursors to be the result of instrument saturation. The response of the altimeter to narrow-peaked pulses is modelled theoretically. The consequences of saturation are shown to be well-defined pre- and post-cursors whose delay depends upon the location of the narrow-peaked component within the altimeter range window, and the clipping of high amplitude events. Seventy-one Seasat pulses exhibiting precursors are examined and their location is shown to coincide with that predicted. It is concluded that, whilst great care must be taken in attempting a quantitative interpretation of narrow-peaked waveforms, their arrival time, and hence measured range, is unaffected by instrument saturation.

ISSN:0143-1161    

DOI:10.1080/01431168708954762

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The technique recently proposed by Barton and Scott to monitor surface pressure using absorption of reflected sunlight in the oxygen A-band is subject to errors due to aerosol scattering. Errors arising from specified uncertainties in the aerosol optical depth are evaluated. It is shown that, for a sea surface over which the optical depth is 0.1 ± 20 per cent, measurements accurate to better than a few millibars can be obtained only by observing towards the maximum of the sunglint region. The method is not feasible under hazy conditions where the optical depth is 0.3 + 20 per cent. Zones of feasibility are presented for typical surface conditions and aerosol parameters. This shows that the region within which an accuracy of 2 mbar is obtained is so small as to render the technique operationally unviable, even if monitoring of the aerosol optical depth to ±0.02 was available. Measurements over land would be feasible where surface albedo is above ∼ 10 per cent provided that the aerosol optical depth uncertainty is below ±0.02. However, obtaining this accuracy over land may be problematic.

ISSN:0143-1161    

DOI:10.1080/01431168708954763

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Various methods are compared for carrying out land cover classifications of South America using multitemporal Advanced Very High Resolution Radiometer data. Fifty-two images of the normalized difference vegetation index (NDVI) from a 1-year period are used to generate multitemporal data sets. Three main approaches to land cover classification are considered, namely the use of the principal components transformed images, the use of a characteristic curves procedure based on N DVI values plotted against time, and finally application of the maximum likelihood rule to multitemporal data sets. Comparison of results from training sites indicates that the last approach yields the most accurate results. Despite the reliance on training site figures for performance assessment, the results are nevertheless extremely encouraging, with accuracies for several cover types exceeding 90 per cent.

ISSN:0143-1161    

DOI:10.1080/01431168708954764

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The aggregate soil reflectance is an important parameter in remote sensing. It was found by one of the authors (A.N. Patel) that soil reflectance initially decreases with an increase in moisture content and subsequently.increases with higher moisture content. The present work embodies an attempt to analyse this effect and explain its physics. A new concept of cut-off thickness is evolved to interpret optical characteristics of sand as a multi-layer process. A statistical phenomenological model is developed to account for the observed dependence of the aggregate reflectance of sand and the cut-off thickness of various fractions of sand. The presence of moisture is found to affect the optical characteristics in two different ways. The model provides a way to estimate aggregate reflectance and particle reflectance from measurements to cut-off thickness.

ISSN:0143-1161    

DOI:10.1080/01431168708954765

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Data compression techniques are frequently discussed for data which are in the form of images. Some forms of geophysical data can be considered as matrices, similar to images. Results are shown of the effectiveness of several compression techniques on data from the plasma wave experiments flown on three scientific satellites. The use of actual data shows that an average telemetry bandwidth saving of a factor of two or three can be achieved without serious degradation. This saving can be used to increase the data quality, usually by way of improved resolution (either spectral or spatial), when regions of scientific interest are encountered.

ISSN:0143-1161    

DOI:10.1080/01431168708954766

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

SPOT HRV imagery acquired in ‘double’ mode displays near vertical striping occurring every seven or eight pixels in the down-track scan direction. Six digital image restoration procedures have been examined for suppressing or removing this noise. Image restoration by filtering in the spatial frequency domain was found to be the most effective procedure. However, although less effective at noise removal, a simple median filtering procedure could be used with greatly reduced computational cost.

ISSN:0143-1161    

DOI:10.1080/01431168708954767

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The reliability of a 1-weck composited normalized difference vegetation index has been evaluated by using a cloud-screening algorithm applied to the visible and near-infrared data from the Advanced Very High Resolution Radiometer on NOAA-9. It is found that in some areas ofthe U.S. Great Plains this satellite sensor product may not be reliable due to the high frequency of cloud occurrence. Using the example of day-to-day variation in (he observed clear-sky radiances for one target, the vegetation index is shown to have maxima at high off-nadir and low solar zenith angles: this behaviour has been examined in detail. Some recommendations to improve the compositing technique are given.

ISSN:0143-1161    

DOI:10.1080/01431168708954768

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor