1. A method for detecting a target in a space-time adaptive processing system, comprising the steps of: receiving M signals, by N antennas, reflected from the target; passing the signals received by each antenna through a delay line with N taps associated with the antenna to generate MN pulses in a receive signal vector x(k); arranging the pulses in a three-dimensional MNK matrix with K range cells; compressing the MNK matrix to produce a compressed matrix, wherein the compressing is achieved at a low computational complexity that is linearly proportional to MN; applying a progressive singular valued decomposition to the compressed matrix to produce an inverse of a clutter covariance matrix C(k) from the inverse of the clutter covariance matrix obtained in a previous time instant, and wherein the clutter covariance matrix obtained within a current time instant, wherein the PSVD provides a low complexity way to compute the inverse of the clutter covariance matrix of the current time instant filtering the received signal vector x(k) according to 
 z ( k ) =C ( k ) −1 x ( k ); and detecting the target using z(k).