Seafloor Sounding in Polar and Remote Regions (SSPARR) Project - Initial Field Trials

The Seafloor Sounding in Polar and Remote Regions (SSPARR) project, under sponsorship of the National Science Foundation, is developing the capability to acquire autonomous bathymetric observations in remote regions, by means of an inexpensive (expendable) depth sounder supported by a GPS navigation receiver and global satellite telemetry capability. The depth sounder component operates at 12 kHz and is packaged in a watertight housing suspended approximately 10 meters below the water surface. A sonar transducer is mounted on the bottom of the cylindrical sounder housing; electronics and batteries for powering the sounder are contained in the housing. A cable carrying data and control signals connects to the surface package, which houses the telemetry and control system, GPS receiver, and batteries. This surface package would include flotation, so the SSPARR system could be deployed as a drifting buoy or installed in suitable ice floes. The depth sounder electronics utilize a Freescale Semiconductor DSP56309 digital signal processor to synthesize the transmitted signal, and to acquire and process the acoustic echoes. The signal processing involves quadrature detection at 12 kHz, matched filtering and decimation; data are acquired for intervals ranging from 125 milliseconds to 8 seconds, depending upon the desired range. At present, the sounder software records data for the entire acquisition interval; this raw data is being used to test bottom detection algorithms. In order to minimize the likelihood that a mid-water scattering layer or ice keel mask the true bottom reflection, the desired algorithm will report multiple reflections to the control and telemetry processor when they are detected. The bottom detection function has been evaluated with field trial data will be incorporated into the final sounder design. A test of the sounder transducer was conducted in May 2004 aboard the R/V Kilo Moana, using electronics from the University of Hawaii's Integrated Mapping Instrument-30 kHz, (IMI-30), programmed for operation at 12 kHz. Electronics designed specifically for SSPARR were fabricated and tested in June 2005 aboard the USCGC Healy in the Arctic Ocean north of Barrow, Alaska; further testing in greater water depths is scheduled for September 2005 in the Hawaiian Islands. Initial results are promising; the sounder should have the capability for measuring depths in excess of 5,000 meters. SSPARR is a collaboration between Robert Anderson of Science Applications International Corporation; Mark Rognstad of the Hawaii Mapping Research Group, University of Hawaii; Dale Chayes of Lamont-Doherty Earth Observatory of Columbia University; and Larry Mayer of the Center for Coastal and Ocean Mapping, University of New Hampshire.