Interferometric measurements using redundant phase centers of synthetic aperture sonars

Interferometric sonars with multiple horizontal rows of elements have been used routinely to produce swath bathymetry. However, interferometric sonars are larger more complex, and consume more power than arrays with a single row of elements. Synthetic aperture sonar (SAS) systems often require the use of redundant phase centers (RPC), where the aft sonar element positions overlap in space with the forward element positions of the previous ping. Considering that a vehicle carrying a SAS array would likely have non-zero pitch, the use of RPC provides sonar data from receivers at the same along-track position with some vertical displacement. This data is similar to that of interferometric systems with the exception that the distance between receiver pairs can vary with vehicle motion and the received signals are not collected concurrently. This paper evaluates the possibility that an interferometric capability could be achieved using RPC data collected from a SAS system consisting of a single horizontal row of elements. An error analysis was conducted to determine the effect of errors in relative receiver position on swath bathymetry. Results show that errors in receiver vertical displacement result in similar percent errors in elevation. Therefore, errors in swath bathymetry can be reduced by designing the array to increase vertical displacement between RPC pairs. Results also show that increasing vertical displacement between RPC pairs can also reduce the impact of data phase measurement errors on swath bathymetry. Swath bathymetry measurements are very sensitive to errors in across-track displacements, but the predictable nature and scale of the error may indicate that accurate across-track displacements could be calculated from phase measurements. Swath bathymetry images produced from data acquired by an existing SAS consisting of a single horizontal row of elements are shown and illustrate viability of the technique depending on the required resolution of the syst- em.