ISSN:0143-1161    

DOI:10.1080/014311698215577

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This review article gives an overview of how satellite observations are used to feed or tune crop models and improve their capability to predict crop yields in a region. Relations between crop characteristics which correspond to models state variables and satellite observations are briefly analysed, together with the various types of crop models commonly used. Various strategies for introducing short wavelength radiometric information into specific crop models are described, from direct update of model state variables to optimization of model parameter values, and some of them are exemplified. Methods to unmix crop-specific information from mixed pixels in coarse resolution-high frequency imagery are analysed. The conditions of use of the various methods and types of information are discussed.

ISSN:0143-1161    

DOI:10.1080/014311698215586

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A methodology is developed here to model evapotranspiration (λEc) from the canopy layer over large areas by combining satellite and ground measurements of biophysical and meteorological variables. The model developed here follows the energy balance approach, where λEcis estimated as a residual when the net radiation (Rn), sensible heat flux (H) and ground flux (G) are known. Multi-spectral measurements from the NOAA Advanced Very High Resolution Radiometer (AVHRR) were used along with routine meteorological measurements made on the ground to estimate components of the energy balance. The upwelling long wave radiation, andHfrom the canopy layer were modelled using the canopy temperature, obtained from a linear relation between the Normalized Difference Vegetation Index (NDVI) and surface temperature. This method separates flux measurements from the canopy and bare soil without the need for a complex two layer model. From theoretical analysis of canopy reflectance, leaf area, and canopy resistance, a model is developed to scale the transpiration estimates from the full canopy to give an area averaged estimate from the mean NDVI of the study area. The model was tested using data collected from the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), and the results show that the modelled values of total surface evapotranspiration from the soil and canopy layers vary from the ground measurements by less than 9 per cent.

ISSN:0143-1161    

DOI:10.1080/014311698215595

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Previous studies have shown that the 37 GHz microwave polarization difference index (MPDI) has an inverse nonlinear relationship to the normalized difference vegetation index (NDVI) with the MPDI (NDVI) being more sensitive to vegetation density under sparse (moderate) vegetation conditions. It has also been noted that soil moisture can have a significant influence on the MPDI. This study quantifies the effect of soil moisture on the MPDI using the RADTRAN model and comparison with measurements from a few geographically restricted (eastern USA) study sites. Model results show the MPDI increases with soil moisture but its sensitivity approaches zero when soil moisture values or vegetation densities are large. Results based on special sensor microwave/imager (SSM/I) measured values of MPDI, using the NDVI as a surrogate for vegetation density and an antecedent precipitation index (API) as a surrogate for soil moisture, were consistent with those based on the model. Linear equations, one for each of three categories of vegetation density, expressing MPDI as a function of API were derived based on SSM/I measurements. These equations demonstrate that soil moisture information can be extracted from the MPDI when the NDVI is used to account for the effect of vegetation and that the effect of soil moisture on the MPDI should be taken into account if it is to be used as a vegetation index. The potential to normalize MPDI values for variations in soil moisture is discussed.

ISSN:0143-1161    

DOI:10.1080/014311698215603

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This article presents a new unsupervised method (AutoChange) for change detection and identification. It uses, as an input, two images, acquired on different dates, and a parameter list given by the user. Change detection and identification are performed in separate procedures, and the output is a five channel image estimating the change magnitude and characterizing the changed and unchanged areas. The method carries out the change analysis using homogeneous units selected from the images and only in the ultimate phase the whole image is classified. Changes are detected and identified using clustering in two phases. First, clustering is performed on the earlier and later images to form the so called 'primary clusters'. Second, clustering is performed within the primary clusters of the later image to produce the 'secondary clusters'. Then the change magnitude and change type are obtained by comparing the primary clusters in the earlier image to the secondary clusters in the later image. The method, which was tested in southern Finnish Boreal forest using Landsat Thematic Mapper data, could reliably detect and identify clearcuts. In addition, the method provided information on forest damage since the type of the spectral change was consistent on damaged areas despite a minor magnitude of the change.

ISSN:0143-1161    

DOI:10.1080/014311698215612

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Lineament extraction and analysis is one of the routines in mapping large areas using remotely-sensed data, most of which is the satellite images. In this study, we aimed to test different lineament extraction techniques including single band, multiband enhancements and spatial domain filtering techniques. A fast algorithm has been developed for time and cost limited surveys in an area with known dominant and/or any selected orientation of lineaments. During the study for single band analysis, histogram equalization and stretching, for multiband, Principal Components Analysis (PCA) and for spatial domain filtering Prewitt and Sobel filters are utilized. Furthermore, we have developed a new algorithm which consists of a combination of large smoothing filters and gradient filters, in order to get rid of the artificial lineaments which are out of interest and to determine discontinuous and/or closely spaced regional lineaments. The results are as follows; the number of lineaments and their total lengths are 218 285.3 km using the single band; 255 343.9 km in multiband enhancements, and 347644.9 km in the combination of spatial domain filtering including our algorithm. The 59.17 per cent increase in the number of lineaments and the 126.04 per cent increase in the total lengths indicate that a combination of spatial domain filters is the most cost-time efficient algorithm in lineament analyses.

ISSN:0143-1161    

DOI:10.1080/014311698215621

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Our research in Mauritania focused mainly on the study of phenomena that partially or entirely masked surficial formations overlying bedrock. The analysis of ERS radar images compared to that of optical SPOT data identified geomorphological and geological objects for which the SAR provides complementary information at a regional scale; interpretation difficulties caused by, for example, shadow and lay-over phenomena; and mapping potential using geocoded ERS 1 images, notably for regional geomorphology, the sedimentology of sand bodies, and the structure of bedrock, where possible below windblown cover. The non-geocoded image must be interpreted with care to avoid the phenomenon of dip-direction inversion. The 'unwrapping of slopes' by geocoding gives a picture of the global layout of units, particularly those of the substratum in areas with medium to high topographic relief. Main faults are clearly seen on radar images at small scale and show up under conditions similar to those of optical data, but fractures that are (sub)parallel to the direction of the incident signal can be invisible on the radar data. Occasionally, the 'transparency' phenomenon enables us to 'see' below thin sand cover.

ISSN:0143-1161    

DOI:10.1080/014311698215630

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Repeat-pass Synthetic Aperture Radar (SAR) imagery is useful for change detection. A disadvantage of SAR is the system-inherent speckle noise. This can be reduced by filtering. Various filter types and methods are described in the literature, but not one fits the speckle noise in change detection imagery. A new method is therefore developed in this paper. The new method is based on filtering the logarithmic-scaled ratio of SAR images. Logarithmic scaling changes the multiplicative speckle noise in the ratio-image into additive noise and alters the distribution, which simplifies and optimizes the subsequent filter process. The filter in the new method consists of an additive LLMMSE filter (Kuan et al. 1985), preceded by a structure detection stage for a better contour preserving performance. Testing the new method on a repeat-pass satellite SAR image-set gave an accurate overview of changes compared to a colour-composite of both images, other optical remote sensing images and maps of the same area.

ISSN:0143-1161    

DOI:10.1080/014311698215649

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Using interferometric techniques, a complex coherence image was generated from a pair of complex SAR data. Amplitude images were computed from the SAR and coherence images and subjected to Principal Components Analysis. The first channel of this analysis is an image of remarkable clarity and detail, suitable for various applications. A good lithologic interpretation was realized from this single image channel alone.

ISSN:0143-1161    

DOI:10.1080/014311698215658

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We use a sequence of synthetic aperture radar (SAR) images to map differences in the flood and ebb tidal currents in a cove along the coast of Nova Scotia, Canada. The asymmetry in the tidal flow determines the flushing rate of the cove which, in turn, has a significant effect on biological production within the cove and its potential for aquaculture. We find significant differences in the SAR images collected on flood and ebb tides. Specifically there are well-defined lines on the flood images and large whorls on the ebb. A three-dimensional hydrodynamic model of the tidal currents is used to interpret the SAR images. In particular we use the model flow fields to wind back the SAR images to an earlier stage of the tide in an attempt to determine the physical origin of the features in the images. We conclude that the most likely explanation for the ebb-tide whorls is the advection of surface slicks.

ISSN:0143-1161    

DOI:10.1080/014311698215667

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor