Implementation of modified recurrent-search estimation algorithm of correlation-extremal terrain-aided navigation system

The article discusses the recurrent-search algorithm of correlation-extremal terrain-aided navigation system that is able to estimate horizontal coordinates, altitude and vertical velocity from measurements of the inertial navigation system, radio altimeter and reference information. However, in the presence of failures in measurements and ill-conditioned reference information, this algorithm cannot provide reliable and accurate correction. In relation to the above, it is proposed to introduce the reliability condition that prevents wrong solution to be given in case of ill-conditioned reference information or presence of large errors in measurements. This allows us to find the solution in the presence of failures, and also to limit the influence of errors in the determination of horizontal velocity. Overall effect of reliability conditions is to solve a large number of ill-conditioned cases, but minimize the probability of wrong correction. In addition, the article examines features of the above-stated algorithm, aimed at improving an overall performance.