Evaluation of the Klein HydroChart 3500 interferometric bathymetry sonar for NOAA sea floor mapping

Abstract

The National Oceanic and Atmospheric Administration (NOAA) follows a specific procedure in the operation of shallow water sea floor mapping. Recently, side scan sonar bathymetric technology (phase measuring interferometry) has been gaining acceptance and is being evaluated for NOAA's charting applications [1]. NOAA standard charting procedure includes the use and calibration of approved sensor technologies and procedures to generate or update published chart products [2]. This process is considered to be efficient and practical by NOAA. Currently, multibeam echo sounder systems (MBES) are used as the primary bathymetry sonar units due to the measurement accuracies that these systems have achieved. However, given the limited 4 to 6 times altitude ground coverage from a MBES and the increasing need for low cost, high quality data from both bathymetry and sidescan, NOAA has long been evaluating interferometric sonar for use in shallow water charting. The Klein HydroChart 3500 interferometric sonar provides 10 to 12 times altitude coverage without a gap in the nadir region of the bathymetry data. When combined with approved motion and navigation units, the HydroChart 3500 offers accurate bathymetry for survey and charting applications from 1.5m to 50m water depths. This paper presents common evaluation data to demonstrate the capability of the HydroChart 3500 in the critical mission of shallow water charting. In parallel, we address two questions raised by NOAA in assessing the use of this system. First, is the HydroChart 3500 compatible with the NOAA standard survey procedures? Second, does the quality of the bathymetric data meet the IHO standard throughout the full swath covering 10 to 12 times altitude without a nadir gap? To accomplish this evaluation, sea test data were collected from Portsmouth Harbor, Piscataqua River Estuary, New Hampshire with guidance from the Center for Coastal and Ocean Mapping (CCOM) at the University of New Hampshire. Patch tests were conducted based upon NOAA's procedure and the calibrated motion biases were checked by using the sonar-integrated Klein KMS-02 motion sensor. Surveys were conducted over two reference areas. The data quality was quantified by calculating the one sigma grid surface over an area of 400 by 1000 meters, against depth and coverage. The results demonstrate that the Klein HydroChart 3500 is capable of meeting the IHO Special Order standards with 10 to 12 times altitude coverage, based on a signal to noise ratio over 8 dB.