DISTRIBUTION STATEMENT A: Approved for Public Release- Distribution Unlimited Theory Pertaining to Comparison and Calibration in an Experiment to Measure Acoustic Reflection Coefficients

For the purpose of analysing data to determine underwater acoustic reflection coefficients at low megahertz frequencies, relevant theory is developed. For a target that may be in the near field, the three-dimensional point spread function for image points close to the target, is derived for rather general arrays and waveforms. The model of the active system is extended to allow a coded signal, a spherical transmitter, and a transmitter not in the receiver array plane. Here and elsewhere, conditions of validity are carefully obtained. Conditions are derived under which a ball target (used for calibration in the experiment) behaves as a point reflector. The image of a rectangular target, described by an angle-dependent reflection coefficient, is obtained. The preceding results lead to an 'integral relationship, ' or 'energy conservation' relationship, proved for a point target and conjectured to hold generally. It is shown how this result would enable one to analyse the experiment to determine absolute reflection coefficients