Estimation of target density functions in time-varying environments

Abstract

In this article, two different solutions are presented to the problem of estimation of time-varying range-angle in nonstationary environments. The first one utilizes a wideband signal with a certain bandlimitedness condition on the time variation of the target density function at each point in space. By choosing small successive processing time intervals, bandlimitedness of the time variation becomes much more realistic than assuming no time time variation or a specific time variation. The second one does not have this assumption and utilizes a narrowband signal with a continuous spectral content. Both provide a general methodology for imaging of nonstationary environments. In addition to nonstationarity, time-varying target density functions can also describe nonlinearity of a medium where each point distorts the transmitted wave by multiplying it with a time-varying function during reflection.