Identifying traffic through monitored zone - analysing geophone signals corresp. to sound waves triggered by traffic and propagated underground

The method involves receiving sound waves, at a geophone (10), stimulated by traffic, coupled into the ground and propagated underground. Corresp. geophone output signals are generated. The categories of the different traffic elements, e.g. pedestrians, light motor vehicles, heavy vehicles are associated with frequency ranges, each defined by an upper frequency. The upper frequencies are staggered and measurement signals are derived by envelope curve detection. The measurement signals levels are compared continuously with the level of a reference signal also derived by envelope curve detection in the background noise frequency region. Measurement signals in a frequency range with levels exceeding the reference signal level are preliminarily categorised as associated with that frequency range. Further test criteria are then applied to confirm final categorisation. USE/ADVANTAGE - Identifying various types of traffic passing through monitored zone. Simple detection and classification.