Abstract: Method and apparatus for obtaining the doppler transform of a one-dimensional linear signal by re-arranging the signal into a two-dimensional raster form image pattern and then obtaining an optical linear transformation of the two-dimensional image. An optical circuit is provided for carrying out the transformation and is designed to process the signal for a large number of doppler levels in rapid succession without it being necessary to rescan the initial signal each time as in the prior art. Accordingly, a substantial reduction in processing time is achieved.The invention has been developed primarily for use in locating the position of underwater objects through the use of sonar, but has application in a variety of other data processing fields.