A review of modern optimal and quasi-optimal algorithms for radiometric signal processing, which provide images with a high spatial resolution is given. It is shown that the high resolution is achieved with ultra-wideband or multi-band time or space-time signal processing. Analytical expressions for the limiting error of image estimation, ambiguity functions and potential fluctuation sensitivity of systems designed according to the algorithms are derived.

Review of modern algorithms for high resolution imaging with passive radar

New method of radar imaging from aerospace carriers is proposing. The method allows to obtain the radar images with high spatial resolution of surface area in the angle range of ±25° from normal aircraft axis. This area is traditionally doesn't map due to the lack of the range resolution in this observation sector of angles. Method assumes the irradiation of the underlying surface by the multifrequency signal and a subsequent space-time processing of the reflected signals in the aperture synthesis system. In contrast to the aperture synthesis systems used in radio astronomy and remote sensing, signal processing is performed under parametric a priori uncertainty.

A new method of multi-frequency active aperture synthesis for imaging of SAR blind zone under aerospace vehicle

The new algorithm of signal processing for building of high spatial resolution radar images is developed. A distinctive feature of this algorithm is the ability to form images of the area that is traditionally not viewable from aircraft and aerospace objects. This area approximates usually ±(20°…25°) from the aircraft's normal axis. In this angle sector the horizontal range resolution of radar images is low. The block diagram of complex radio engineering system that combines advantages of active radar and passive aperture synthesis systems is developed for obtaining of images with the acceptable spatial coordinate resolution in the angle sectors of observation.

UWB active aperture synthesis radar the operating principle and development of the radar block diagram

To solve problems of high-precision mapping of spatially extended objects regardless of weather conditions and time of day, radar imaging systems are used. The globality and efficiency of the survey is provided by the placement of radars on aerospace carriers. At the same time, there has been a proliferation of side-scan radars (providing a wide viewing range with a low spatial resolution) and antenna aperture synthesis radars (these provide high resolution in spatial coordinates, which depends on the type of survey). Radars used for imaging are classified according to various characteristics determining their advantages and disadvantages. Among such features, we can also distinguish the radar viewing area, which is currently limited to angles of 15° to 60° to the right and left of the observation in the nadir. The viewing range from -15° to + 15° from the nadir is characterized by a low resolution in range and traditionally is not visible by these radars (the socalled “blind zone”). In this regard, an alternative system for building radar images from aerospace carriers is proposed. It will provide imaging with high angular resolution of the viewing range from -15° to + 15° from the nadir. The main feature of the developed radar lies in the signal processing algorithm that combines methods of active (the presence of probing UWB signal) and passive (aperture synthesis) radiolocation. In addition, the radar implements a new method of “spectral aperture synthesis,” which allows the transition from processing of UWB signals with the continuum spectrum to processing multi-band signal processing.

Active Aperture Synthesis Radar for High Spatial Resolution Imaging

The algorithm of spatio-temporal ultrawideband (UWB) signal processing for radiometric imaging is synthesized and investigated. Analytical expressions for the limiting error of the radiometric image estimate and ambiguity function of system are derived. The possibility of ambiguity function formation with one main lobe in the UWB cross-correlation and compensation system with ultra-sparse antenna array is substantiated. The simulation examples of radiometric imaging are shown.

Algorithm for radiometric imaging by ultrawideband systems of aperture synthesis

The optimal algorithm for forming images using multi-antenna ultra-wideband radiometric complex is synthesized and investigated. Expression for the limiting error of radiometric image is obtained.

http://ieeexplore.ieee.org/iel7/7529352/7537982/07538181.pdf

Optimal structural synthesis of multi-antenna ultra-wideband radiometric complex

New method for the spatio-spectral sensitivity domain filling and radiometric imaging with high resolution in aperture synthesis systems

The methods of filling the domain of spatio-spectral sensitivity (SSS) are considered The spectral method for filling the SSS domain in aperture synthesis systems is proposed It is shown that instead of filling the SSS domain of the serial synthesis using one radio-interferometer with variable base expedient to use fixed antennas and ultra-wideband (UWB) signals processing The criterion for the uniqueness of the main lobe of the ambiguity function of the two-antenna array using UWB signals processing is obtained

Spectral method for the spatio-spectral sensitivity domain filling in aperture synthesis system

Analytical expression for the ambiguity function (AF) of ultra-wideband, multi-band and narrow-band radiometric complexes with a three-element antenna system is derived. Examples of AF simulation for different geometries and input tracts (narrow-band, multi-band, UWB) are shown. It is stated that UWB and multiband signal processing allows to form AF with one main lobe, which excludes ambiguity of radiometric images (RMI) reconstruction in antenna systems with a small number of antennas.

O. M. Tymoshchuk

Papers

Algorithm for radiometric imaging by ultrawideband systems of aperture synthesis

Optimal structural synthesis of multi-antenna ultra-wideband radiometric complex

New method for the spatio-spectral sensitivity domain filling and radiometric imaging with high resolution in aperture synthesis systems

Spectral method for the spatio-spectral sensitivity domain filling in aperture synthesis system

Investigation of ambiguity function of ultra-wideband multi-band and narrow-band radiometric complex with a three-element-antenna system