The widespread use of ground penetrating radar (GPR) with a mixture of success and failure has Led to a greater understanding of where GPR is likely to work and where it won't. The ability to quantitative/y predict and emulate the response of simple targets has been needed for some time and is now easily achieved with simple PC programs. This paper de scribes some procedures for interactive radar modelling which can be used to define parameters for optimal system configuration prior to field survey work. The procedures for estimating radar range, for generating synthetic radargrams, and for calculating simple ray tracing travel time are outlined; examples of results are presented. The techniques have been developed from the necessity of understanding and explaining field observations and are now used prior to a survey to optimize survey parameters.