ISSN:0143-1161    

DOI:10.1080/01431169108929649

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In this paper we present a general analysis of frequency domain SAR processing based on the relationship between the phase of the two-dimensional Fourier transform of a point response to its range-time history. The paper demonstrates how this provides an appropriate basis for the design of a coherent strip-mode processor, free of geometric or phase distortion and artefacts and without excessive computational cost. In consequence the paper is highly relevant to the real-time, precision, processing of SAR data. The paper comments on the relevance of the analysis to ambiguity estimation and the processing of very long integration time SAR data.

ISSN:0143-1161    

DOI:10.1080/01431169108929650

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Conventional motion compensation schemes correct for unwanted synthetic aperture radar (SAR) platform motions using information from an inertial measurement unit (IMU). Autofocus techniques, which focus SAR images, produce an ‘autofocus parameter’ which is related to the platform motion. In this paper, strong evidence is presented to support the assumption that the contrast optimization autofocus algorithm behaves as a least-squares quadratic fitting to the SAR platform trajectory. Using this assumption, the relationship between the autofocus parameter and across-track accelerations of the SAR platform is derived. This allows the SAR platform motion to be estimated from the autofocus parameter measurements and incorporated in a motion compensation instead of IMU measurements. Three implementations of motion compensation using autofocus are compared and the achievable image quality is quantified.

ISSN:0143-1161    

DOI:10.1080/01431169108929651

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The AgriSAR '86 data set for the Feltwell, U.K. test site is assessed for its ability to provide information on the spatial and temporal variation of backscatter from growing crops. The image data is shown to contain several sources of radiometric distortion which affect any attempt at image calibration. Of these, the simplest to correct is that caused by range interpolation in the amplitude data. All interpolated pixels should be discarded from the amplitude data supplied by CNES. Correction from slant range to ground range is comparatively straightforward. Effects due to variations in antenna pattern, in the range and azimuth direction, require assumptions about the angular variation of the backscatter of crops and statistical homogeneity of ground cover before they can be removed. The properties of system noise appear complicated and are not yet properly characterized, but interfere with corrections for the antenna pattern. Offsets in the two channels of the complex data also interfere adversely with antenna pattern corrections. The size of these offsets cannot be estimated reliably from the AgriSAR amplitude data and complex data should be supplied as a standard product. No sound basis for inter-image comparison has been found.

ISSN:0143-1161    

DOI:10.1080/01431169108929652

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We review some theoretical work on super-resolution of coherent images from a Bayesian point of view. The well known singular value decomposition super-resolution method emerges as a special case and it is extended in order to derive a practical iterative super-resolution algorithm.

ISSN:0143-1161    

DOI:10.1080/01431169108929653

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper presents a detailed theory on the statistical properties of non-Gaussian speckle in the synthetic aperture radar (SAR) images of dynamic sea surfaces, where breaking or near-breaking waves are present. The backscattered complex field is modelled as the sum of two independent fields: one arises from breaking waves which occur discretely and therefore the amplitude fluctuations are also discrete and the other represents the weak background field of a uniform amplitude due to non-breaking sea waves and/or system noise. The elementary scatterers are considered to be either in random or uniform motions and the magnitude of the motion is considered to be much greater for breaking waves than the background non-breaking waves. This compound backscattered field is then imaged by a SAR, resulting in a non-Gaussian speckle pattern which appears as the pronounced azimuth streaks. A general and simple expression is derived for the autocorrelation function (ACF) of the speckle intensity in terms of the statistical properties of the spatial backscattered field and the impulse response degraded by the scatterers' motions. The ACF is evaluated and discussed for a Gaussian impulse response and for different scatters' motions.

ISSN:0143-1161    

DOI:10.1080/01431169108929654

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Many examples of clutter textures in coherent imaging exhibit K-distributed statistics which result from a gamma-distributed surface cross-section. Such a surface can be completely described in terms of the average two-point statistics (for example, the autocorrelation function) of the process. We compare simulation methods based on such a noise model with a direct model in which we attempt to represent the underlying properties of the surface for a particular example of random woodland clutter. We demonstrate that this model has the potential to predict processes (such as shadowing) directly, unlike the noise models which combine all factors into a global description.

ISSN:0143-1161    

DOI:10.1080/01431169108929655

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The two major difficulties associated with SAR image change detection are addressed. These are the removal of speckle noise and the registration of information between images. The problem of image registration is severe in airborne SAR imagery due to the unpredictable nature of the aircraft track. Although inertial navigation systems may be employed to measure this motion, the accuracy obtained is insufficient to allow the creation of large rectilinear images. However, autofocus techniques are used here to measure residual aircraft motions thus allowing the production of large geometrically accurate images. The second problem of speckle reduction has been approached in two ways. The first technique applies an intensity segmentation algorithm to each image and the regions generated by this segmentation are then compared using the change detection algorithm. An alternative approach to the problem of speckle removal is to use neural network methods to learn the speckle removal and region generation task. To reduce this problem to a manageable size a factorization method for the multi-layer-perceptron has been invented.

ISSN:0143-1161    

DOI:10.1080/01431169108929656

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor