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The paper describes the use of metric techniques in an electronic support measures (ESM) data processing scheme developed at Smith Associates Consulting System Engineers Limited for the UK Ministry of Defence (Procurement Executive). The ESM data processing scheme takes in digital pulse data describing the radar pulses illuminating an ESM receiver. The output from the scheme is a continuously updated emitter table, which lists the emitters present in the environment and specifies the deduced parameters of these emitters. Metric techniques play an important role at two distinct stages of the scheme: firstly in direction-of-arrival (DOA) RF pulse filtering, and secondly in emitter table updating. In DOA RF filtering, the pulses are processed using two-dimensional cluster analysis. The method ensures that pulses from a single emitter are not separated into different batches, but that pulses from distinct emitters are separated, unless their parameters overlap in both DOA and RF. The same result cannot in general, be achieved using one-dimensional filtering. The scheme uses a computationally efficient method, in which the metric technique is applied to groups of pulses following sequential one-dimensional filterings in DOA and then RF. In emitter table updating, a metric technique is used to ensure that the pulses from an emitter already on the emitter table are correctly associated with that emitter table entry, and are not added as a new emitter seen for the first time. This overcomes the problem that, for some emitters, some of the parameters can change discontinuously when the emitter changes mode. The metric technique ensures that, provided some of the parameters remain approximately constant, the correct association is made.