Noise immunity of images autofocusing algorithm by entropy minimum at complex background situation

Mathematica modeling, numerical technique and program complexes


Аuthors

Likhachev V. P.*, Sidorenko S. V.**

MESC Air Force “Air Force Academy named after professor N.E. Zhukovskii and Yu.A. Gagarin”, 54a, Starykh bol'shevikov, Voronezh, 394064, Russia

*e-mail: lvp_home@mail.ru
**e-mail: sidor-vire@rambler.ru

Abstract

Modern SAR ensure a longer range, compared to optical systems, a faster (within a few seconds) radar image of a large land area receiving with a sub-meter resolution, as well as independence of the images quality from weather conditions and natural illumination state of the scenery.

Comparatively small weight-size indices of modern SAR allowed install them on unmanned aerial vehicles (UAVs) of small class, which application reduces significantly the operation costs and maintenance of a carrier. However, application of such UAVs as SAR carriers is associated with significant instabilities in the trajectory and flight speed due to atmospheric turbulence.

To form a high-quality radar image with given resolution in time scale close to the real one, it is necessary to obtain accurate information on the carrier motion parameters and, primarily, its flight speed.

Placing a high-precision inertial navigation system on a small class UAV is impossible, and application of navigation receivers under interference conditions does not ensure the required accuracy in estimating the SAR carrier speed while the radar image formation. To compensate the speed estimation error, various radar image autofocusing algorithms are employed, such as the radar image autofocusing with regard to the minimum entropy function. It does not require the presence of powerful point-like reflectors in the field of vision. However, to evaluate the efficiency, for example, in solving the problems of correcting navigation errors by the radar image in conditions of a large noise / signal ratio q, additional investigations are required.

The relevance of the article is determined by the need to form a radar image with a specified resolution in a time scale close to the real one, by a small SAR installed on the UAV, which lacks the capability to compensate for trajectory instabilities from information from the inertial navigation system, etc. In the presence of noise-masking interference and background reflections, it is necessary to determine the boundaries of the stable radar image autofocus algorithm functioning at minimum entropy.

The article deals with the operation of a radar station with digital SAR with the RLI autofocusing for a minimum of the entropy function in conditions of noise-masking interference and complex background situation.

Keywords:

radar with digital synthetic aperture antenna, entropy, radar images, autofocusing, unmanned aerial vehicle

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