The joint European project “UUV Covert Acoustic Communications” aims at the design of an acoustic communication system between an unmanned underwater vehicle and a support mother ship. To achieve the objective of covert communication over long ranges in littoral waters, knowledge is required on the influence of the environment. The first sea trials of the project therefore focused on the acquisition of noise and channel data for the explicit purpose of building an acoustic channel simulator. The present paper describes the initial design of such a filter model. Measured channel parameters are captured in mathematical models on the assumption of wide-sense stationary uncorrelated scattering. Spreading in time is analysed using the Bellhop acoustic toolbox based on ray tracing; spreading in frequency is investigated with due allowance for platform kinematics and sea surface behaviour. Comparisons between measured and simulated data are presented for different scenarios.