摘要:

The composite surface model is compared with the Kirchoff method and shown to be equivalent for radar backscatter at moderate incidence angles in most commonly occurring sea states. Based on this comparison, limits are determined for the validity of the composite surface model. The model is then utilized to study the modulation of the radar cross-section of the ocean surface by long surface waves and internal waves. It is shown that apart from the well understood tilt modulation and the direct hydrodynamic modulation of the short waves, there is also an additional indirect modulation of the radar cross-section due to the hydrodynamic modulation of the intermediate waves by the long waves. Computer simulations are used to investigae these modulation mechanisms for different sea states, incidence angles and radar frequencies. It is shown that this modulation is strongest at small incidence angles and high radar frequencies. The simulations show that internal waves may be observed by X-band and Ka-band radars due to the indirect modulation through the intermediate waves. It is also shown that, contrary to previous predictions, the indirect modulation process results in modulation of radar backscatter by surface waves that travel normal to the radar look direction.

ISSN:0143-1161    

DOI:10.1080/01431169208904255

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Techniques arc presented for transforming measured frequency domain radar cross-section (RCS) data into its corresponding time domain representation, and for performing the time gating operation on measured frequency domain data. These two techniques correlate with the time domain features of the Hewlett-Packard (HP) 8510 network analyser. Since both techniques are implemented in software on a digital computer, the major restrictions imposed by the HP 8510 are removed. These restrictions include a limited number of data points and the requirement that all processing be done on-line while the measured data is still in the memory of the HP 8510. Emphasis is placed on applications of the above techniques to RCS measurements, and the benefits of performing the processing off-line from the HP 8510.

ISSN:0143-1161    

DOI:10.1080/01431169208904256

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A primary stage in the analysis of Synthetic Aperture Radar (and other) images, is to produce a segmentation of the image; that is, a division into sub-regions each, hopefully, representing a single object: a field, hedge, wood etc. Producing such a segmentation is made difficult by the high level of speckle inherent in SAR images, and a number of segmentation techniques have been developed. We describe here a methodology for providing objective tests of segmentation algorithms and give representative resulls for one such algorithm.

ISSN:0143-1161    

DOI:10.1080/01431169208904257

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The cumulative effects of salinity and sediment concentration variation on the spectral reflectance measurement from a sediment-laden saline water was studied in the laboratory using a spectroradiometer. Reflectance is observed to be dependent on salinity concentration in addition to sediment type and concentration. It is also observed that, in general, the spectral response (i.e. per cent reflectance at different wavelengths) has a negative correlation with salinity, but a positive correlation with sediment concentration. A model for predicting the suspended sediment concentration from reflectance measurements with due involvement of the salinity variation is developed. The predicted and observed values of the sediment concentration by the presented model show good agreement.

ISSN:0143-1161    

DOI:10.1080/01431169208904258

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor