ISSN:0143-1161    

DOI:10.1080/01431168808954832

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Radiometric characteristics of the sensors on board MOS-1 were assessed using pre-launch data and simulations taking into account sea surface conditions, influences due to Sun glitter, atmospheric effects, etc. Consequently, it was found that the following are noticeable: (1) MIN/MAX radiances and signal-to-noise ratios at the radiances of MESSR are almost the same as those of Landsat MSS. (2) A 7 per cent influence caused by Sun glitter, in terms of the equivalent glitter reflectivity, is estimated for the worst case. This would occur at the summer solstice, at 11 00 hours Local Mean Time and with an ocean wind speed of 7 m/s, (3) The percentage ratios of reflectance radiance to path radiance for MESSR-1 to -4 are, respectively, 60·08, 95·29, 130·70 and 267·63 per cent. These ratios would result from a ground cover target with minimum albedo in the summer under hazy atmospheric conditions. (4) A 9 per cent influence caused by Sun glitter, in terms of the equivalent glitter reflectivity, is estimated for VTIR-1 in the worst case. This would occur at the summer solstice, at 11 00 hours Local Mean Time and an ocean wind speed of 7 m/s. The influences due to Sun glitter for VTIR-2 to 4 are negligible. (5) A 38 per cent of influence caused by rim darkening is estimated for VTIR in the worst case. This would occur at the maximum viewing angle, in the summer, under a hazy atmospheric condition. (6) A 2·8 per cent influence on brightness temperature, caused by polarization change due to antenna rotation for the MSR, is estimated. (7) A 12·8 per cent influence on brightness temperature, caused by the side lobe effect for the MSR, is estimated for the case in which a land-ocean boundary coincides with the trough between the main and the first side lobe on the antenna pattern.

ISSN:0143-1161    

DOI:10.1080/01431168808954833

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Portions of the Savannah River floodplain swamp were evaluated for vegetation change using high resolution (5·6 m) aircraft multispectral scanner (MSS) data. Image distortion from aircraft movement prevented precise image-to-image registration in some areas. However, when small scenes were used (200–250 ha), a first-order linear transformation provided registration accuracies of less than or equal to one pixel. A larger area was registered using a piecewise linear method. Five major wetland classes were identified and evaluated for change. Phenological differences and the variable distribution of vegetation limited wetland type discrimination. Using unsupervised methods and ground-collected vegetation data, overall classification accuracies ranged from 84 per cent to 87 per cent for each scene. Results suggest that high-resolution aircraft MSS data can be precisely registered, if small areas are used, and that wetland vegetation change can be accurately detected and monitored.

ISSN:0143-1161    

DOI:10.1080/01431168808954834

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Soil salinity and waterlogging are two of the main soil limitations of irrigated agricultural lands. Full use of these resources requires up-to-date data on their areal extent and geographic distribution. This paper uses Landsat MSS data in imagery form of 1:250 000 scale for these purposes. The study area, forming a part of the Indo-Gangetic alluvial plain, is located in the Mathura district of Uttar Pradesh, India. Large-scale seepage from canals and irrigation channels and obstruction in natural drainage have caused waterlogging and salinity hazards. A collative approach comprising the use of Landsat imagery, Survey of India topomaps and limited field checks was followed for mapping purposes. The wet land soils appeared in bluish tones whereas both the saline and sandy soils appeared in white tones on the false colour composite imagery. Distinction between saline and sandy soils was made after carefully studying the unique patterns of shape and geomorphic setting. The study area covers 381 100 ha, out of which 14 035 ha are saline soils and 14 355 ha are waterlogged soils. Two maps showing areas under soil salinity and wet lands were also made.

ISSN:0143-1161    

DOI:10.1080/01431168808954835

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We compare satellite imagery obtained by an optical sensor and by synthetic aperture radar for a shallow ocean area showing submarine relief features. A Skylab photograph and a Seasat radar image of the North American cast coast (Nantucket Shoals) taken at different dates, but at the same tidal phase and under comparable weather conditions, are analysed. It is shown that the radar imaging as well as the optical imaging is caused by roughness variations of the water surface due to tidal flow over submarine relief. It is investigated whether optical imaging is affected by backscattering by suspended sediment in the water column, by reflection from the sea floor or by variations of the surface roughness associated with wind and tidal flow over underwater bottom topography. We conclude from the analysis of the densities in the blue, green and red layers of the Skylab colour film that specularly reflected sunlight at the rough ocean surface is the dominant imaging mechanism. In cases where the underwater bottom topography has an influence on surface water waves, the slope distribution of these waves cannot be explained by the Cox-Munk model alone because it only describes the relation between windspeed and slopes of the water waves. Therefore we suggest here that perturbation of the mean square slope spectrum caused by current gradients can explain the brightness modulation in the optical imagery.

ISSN:0143-1161    

DOI:10.1080/01431168808954836

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A model for forecasting large-scale patterns of soil erosion and deposition from Landsat MSS data in arid grazing lands is presented. The model is based on the erosion cell mosaic approach and exploits the high degree of temporal and spatial autocorrelation in the erosion process on flat alluvial plains. Erosion and deposition are first mapped using Pickup and Nelson's soil stability index. As a landscape degrades, the variance and autocorrelation function of this index change. These trends represent changes in the physical behaviour of the system and can be explained by it. The model used for forecasting change is a first-order simultaneous autoregressive (s.a.r.) process which can reproduce changes in mean, variance and spatial autocorrelation. This model expresses each pixel value as a function of those of its neighbours plus a noise term. The forecasting procedure involves fitting a s.a.r. model to an area, obtaining the values of the underlying pattern (noise) series by inverse filtering and then obtaining a forecast by filtering the underlying pattern series using a prototype s.a.r. model for a more (or less) degraded state. The prototype s.a.r. model is obtained by fitting to a similar area in a different erosional condition. Testing of the model against observed change indicates that it is reasonably accurate as long as the underlying pattern series is obtained from imagery in which there is sufficient vegetation cover for the soil stability index to be a sensitive indicator of the state of the landscape.

ISSN:0143-1161    

DOI:10.1080/01431168808954837

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Landsat MSS and SIR-A data have been used in the geological study of the Central Baluchistan mountains in Pakistan. The two show both significant similarities and differences. In terms of interpretable images the SIR-A imagery allows better delineation of various rock units. High radiometric radar backscatter enhances surface textures, relief, moisture conditions, land use patterns and abandoned channels in favourable conditions. A number of geological structures including faults, folds and major and minor lineaments were identified on both images. However, structural lineaments were well expressed on radar with the exception of those parallel or sub-parallel to the direction of illumination. Drainage networks in mountainous terrains have been accurately delineated on Landsat but not on radar imagery, whereas more information on drainage in flat areas was extractable from the radar data. Moisture content variations in the surficial deposits were delineated better on SIR-A than on Landsat data.

ISSN:0143-1161    

DOI:10.1080/01431168808954838

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Over large areas in the tropics satellite imagery is the principal source of data on the area, current stature, and extent of disturbance of the forests. The information from imagery that covers large areas at low resolution is greatly enhanced when different types of imagery can be compared. We have made a comparison of data from Landsat MSS and from the Shuttle Imaging Radar (SIR-A) L band HH polarization data for sites in the Amazon Basin. Results indicate that SIR-A backscatter from the undisturbed forest was lower than that from some disturbed areas and from flooded forests and that SIR-A brightness increases nonlinearly with the Landsat normalized difference vegetation index (NDVI). We hypothesize that the brightest radar returns in southern Amazonia are from newly cleared forests that are littered with standing and fallen tree boles that function as corner reflectors; and that backscatter will diminish from disturbed areas over time as fields are burned repeatedly.

ISSN:0143-1161    

DOI:10.1080/01431168808954839

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A method for estimating sea surface temperature (SST) from a single infrared (I R) channel together with an atmospheric model is investigated. Based on a simulated atmospheric height profile, the precipitable water and transmittance can be calculated as a function of height from the known atmospheric pressure, temperature and relative humidity on the ground. An effective transmittance (which is the ratio of the radiance at the satellite to that on the surface) is used to correct the effect of off-nadir scanner angle. Various data from the Heat Capacity Mapping Mission (HCMM), the Advanced Very High Resolution Radiometer (AVHRR) and other sources are used to evaluate the accuracy of the method. The SST derived agrees with available ground truth with a root mean square (r.m.s.) error of about 1 deg K. The apparent surface temperature varies with the scanner angle to produce differences as large as 8degK at 10·5–12·5μm in a moist summer climate at an off-nadir angle of 60°.

ISSN:0143-1161    

DOI:10.1080/01431168808954840

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

To obtain accurate estimates of surface and cloud parameters from satellite radiance data a scheme has to be devised which identifies cloud-free and cloud-filled pixels (i.e. fields of view). Such a scheme has been developed for application to high resolution (1·1 km pixel) images recorded over Western Europe and the North Atlantic by the AVHRR on the TIROS-N/NOAA polar orbiters. The scheme consists of five daytime or five night-time tests applied to each individual pixel to determine whether that pixel is cloud-free, partly cloudy or cloud-filled. The pixel is only identified as cloud-free or cloud-filled if it passes all the tests to identify that condition; otherwise it is assumed to be partly cloudy. Surface parameters (e.g. skin temperature, reflectance, vegetation index, snow cover) can then be inferred from the cloud-free radiances, and cloud parameters (e.g. cloud top temperature, optical depth and liquid water content) from the cloud-filled radiances. Only fractional cloud cover is derived from the partly cloudy pixels which, together with the number of cloud-filled pixels, gives total cloud cover over a given area. The scheme has been successfully applied to data for all seasons, including images with unusually cold or warm surface temperatures. To assess the method both daytime and night-time NOAA-9 passes over the U.K. were obtained for a week in April 1985 and some results from this data set are presented here.

ISSN:0143-1161    

DOI:10.1080/01431168808954841

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor