1. An automated method of processing sensor data, the method comprising: (i) using a sensor to measure values of a parameter over a region of interest to produce an image of the region of interest, the image having a plurality of pixels, a sensor electronic transmitter device connected to said sensor and receiving said values of a parameter from said sensor, said sensor electronic transmitter device sending digital values of said parameter for each said pixel of each said image to a memory of one or more processors, said memory storing said digital values of said pixels of said image for processing in real time, said one or more processors performing the steps of: (ii) for each pixel, determining an orientation of a gradient of the parameter, at that pixel, using the measured parameter values; (iii) for each of a plurality of predetermined ranges of gradient orientation values, determining a number of said pixels that have a gradient orientation value within that range; (iv) determining a number of groups of predetermined ranges, wherein each group of predetermined ranges is determined such that it satisfies a criteria that: for each predetermined range in that group, a number of said pixels that have a gradient orientation value within that range is above a threshold value; if that group contains more than one predetermined range, each predetermined range in that group is contiguous with at least one other predetermined range in that group; and for each group, the one or more predetermined ranges in that group are not contiguous with any of the predetermined ranges in a different group; and (v) using the determined the number of groups, discriminating between the presence of a man-made object and clutter in the image; wherein an object in the region of interest is labeled as man-made if the number of groups is greater than or equal to a further threshold, and is otherwise labeled as clutter.