Environmental Measurements Derived from Tactical Mine-Hunting Sonar Data

Confidence in naval operations that search for mine-like objects (mine-hunting) is dependent on knowledge of the operational environment. Historic information in some areas may misrepresent the environmental picture due to sparse measurement or data perishability. As a result, operations in some areas may require real-time environmental measurements to refresh the data sources. This information can be derived from sensors that are dedicated to mine-hunting even though these platforms often do not accommodate traditional environmental sensors. In response to this need, the U.S. Naval Research Laboratory developed "Through-The-Sensor" techniques to extract this information with no impact to tactical functionality. This paper reports on calibration and uncertainty quantification efforts associated with using an AN/AQS-20A mine hunting sonar system to extract multibeam bathymetry and sediment type. For bathymetry, the sensor needs a correction factor for depth offset, determined by comparing the derived data with high-resolution data obtained from a dedicated multibeam system. After calibration, the extracted bathymetry data has a mean error on the order of 0.3 m. For sediment type, calibration of the software uses an iterative approach for tuning the calibration coefficient so that the calculated impedance matches data from grab samples. Once calibrated, the uncertainty for the acoustic impedance agrees well with the estimates for sandy areas.

I. Introduction

The mine countermeasures (MCM) portion of mine warfare (MIW) establishes supremacy in contested littoral waters and security of homeland ports as a deterrence against mine deployment which is critical in the current age of asymmetric warfare and terrorism. Confidence in emerging MCM capabilities, as well as legacy systems, is heavily dependent on the certainty MCM operators have in environmental knowledge. Obtaining superior environmental knowledge is difficult because MCM operations occur in dynamic, shallow water areas where historic knowledge alone may give an inadequate environmental picture since meteorological and oceanographic properties often change within a span ofhours - or be absent [1], [2].