Abstract: A method of assessing radar pulses in a passive, i.e. receive-only, radar system to distinguish pulses due to a particular target from pulses due to other targets from noise, interference, etc. Received pulses are assessed, without reference to pulse transmission information, in respect of a number of characteristics by comparing each characteristic of a pulse with the mean value of the respective characteristic for pulses previously received. Using a probability process, confidence values for the pulse can be calculated. By combining the confidence values for each characteristic, an overall confidence value is obtained for the pulse so that it can be determined whether it arises from the particular target.