The invention is a detection system that provides for background removal from a field of view (FOV) of spectra. A panoramic field of regard may be partitioned into a large number of FOV's. An FOV may include spectra including that of a target substance. Such detection may require removing the spectra other than that of the target. This may amount to removal of the background with an estimated background developed from spectra of one or more FOV's which may be similar to the background of the FOV with the target. An estimation of the background may be a sum of a number of FOV spectra where each spectrum is assigned a weight, the total amount of the weights being one.