1. A method for detection of at least one target in a background locale surrounding the target and overflown by an aircraft having an on-board detector system including a hyperspectral imaging sensor and a real-time processor, and based on target spectra obtained by said hyperspectral imaging sensor, said method comprising: using said hyperspectral imaging sensor to collect raw data including target spectra and background statistics with respect to the at least one target in said background locale, during at least one overflight; processing the raw data prior to a further overflight to produce a database including preselected data structures, said data structures including a plurality of target signatures T 1 , and a background mean μ 1 and a covariance matrix M 1 associated with the locale surrounding the target; using the real-time processor to generate recursive estimates of background statistics on a continuous basis during a further overflight so as to derive further estimates of the background mean vector, denoted μ 2 , and the covariant matrix, denoted M 2 ; applying a covariance equalization algorithm to each target signature T 1 from the database so as to provide transformation thereof into transformed target signature T 2 wherein 
 T 2 =μ 2 +M 2 1/2 ΛM 1 −1/2 ( T 1 −μ 1 ) wherein the superscript ½ indicates a square root and Λ indicates an orthogonal matrix; and using a detection algorithm that exploits the transformed signature T 2 to derive a detection statistic.