It is well known that sea clutter in a radar with high range resolution is nongaussian, of pulse type. Sea surface monitoring at small grazing angles and at horizontal signal polarization when pulse nature of sea clutter becomes strongly apparent is considered in this article. It is also known that at nongaussian one-dimensional probability distribution of clutter optimization of signal processing in a radar receiver is possible. At that at the input of matched filter it is necessary to install inertialless converter with amplitude response coordinated with one-dimensional clutter probability distribution. Sea clutter has pulse nature (positive coefficient of excess). For suppression of pulse clutter it is necessary to use limiter of maximum values in the capacity of nonlinear element. Amplitude response of the limiter can be optimized, however, in any case the receiver is one of the modification of «broadband amplifier - limiter - narrowband amplifier» device. In literature we consider the possibilities of suppression of sea clutter using nonlinear converter. At that evaluation of suppression efficiency is performed using digital simulation method. However for such evaluation it is necessary to use adequate clutter model. Efficiency of suppression of pulse clutter in nonlinear converter increases when its coefficient of excess, which can be used as measure of distinction clutter from Gaussian noise, grows. In the article we consider the peculiarities of clutter model, important for optimization of nonlinear converter amplitude response and for evaluation of its operating efficiency. Basing on the data known from literature we present the list of elements of sea surface which generate sea clutter. The most important elements are unshaded wave crests, which form sea spikes and nongaussian probability distribution of sea clutter. It is shown that for all moments of time, included sea spikes, conditions of application of the Central limit theorem are met. It means that clutter probability distribution in each moment is Gaussian. Sea spikes generate of power-time dependency, that determines of sea clutter realizations nonstationarity. Experimental estimate of sea clutter dispersion and excess coefficient for radar with coherent pulse package has perform. It is shown that (provided typical duration of pulse package sampling) sea clutter has Gauss probability distribution. The power of long-time sea clutter realization can change over wide limits depending on presence of unshaded wave crests in a permitted element of surface. For long-time sampling we introduced multiplicative model of nonstationary Gaussian noise realization. The dependence of its variance from time can be estimated and used while signal processing in a receiver. Method of suppression of nongaussian noise using nonlinear converter is asymptotically optimal. It means that in its practical application sea clutter probability distribution should become apparent in full for each realization at the length of the sample which is processed for target detection. As typical duration of pulse package of coherent radar is not more than 200 ms, probability distribution of sea clutter realization is Gaussian. Basing on it we conclude that application of nonlinear converter for suppression of sea clutter is not rational, because at Gauss probability distribution of clutter an optimal receiver is linear.
|Título traduzido da contribuição||About the model interference from the sea surface in coherent radar when non-linear processing of received signa|
|Número de páginas||7|
|Número de emissão||9|
|Estado da publicação||Published - 2018|
Level of Research Output
- VAK List