Dr. John E. Hughes Clarke
Research Professor
Center for Coastal and Ocean Mapping
University of New Hampshire
Friday, February 13, 2025, 3:10pm
Chase 105
Abstract
The stability and longevity of continental shelf infrastructure depend in part on tide (and wave) driven movement of sediments. Investigations of these phenomena have traditionally been undertaken using separate campaigns for current measurements (static and underway ADCP), and repetitive bathymetric surveys. Such programs adequately address long-term bank and dune migration and mean depth-averaged tidal streams.
There is increasing interest, however, in shorter time scale bedform activity, addressing the transport associated with daily reversing flows that directly impact seabed infrastructure. Such investigations require simultaneous, co-located current and bedform migration monitoring across large areas. It also places much higher demand on shorter wavelength bedform resolution and positioning. To address this, survey vessels increasingly are being equipped with all the sensors to make these observations (most recently the four new NOAA platforms). Simultaneous operations, however, have significantly more issues related to inter-sensor interference.
To better understand the impact of inter-sensor operability, over the past two years, a dedicated 10m vessel has been equipped with 8 different acoustic current, seabed and water column imaging sensors. As a practical case study, the instrumentation has been used to try to monitor short temporal and spatial scale seabed change across active headland-associated sand banks. The associated current fields and estuarine oceanography is fortunately well modeled at the kilometer scale, providing a regional insight into the expected current patterns.
Examples of inter-sensor interference, coping strategies and resulting seabed insights and compromises will be presented.
Bio
With degrees in Geology and Oceanography from Oxford, Southampton, and Dalhousie, John has always had an underlying interest in seabed sediment transport. For the past 40 years, however, he has been working primarily with assessing and improving the performance of underway acoustic seabed and water column survey instrumentation (multibeams, sub-bottoms, ADCPs and fisheries sonars). These tools of course are one of the prime means of monitoring the seabed and oceanography.
He is in the process of winding down his full-time commitments at CCOM but continues to be interested in those field programs that (perhaps incidentally) study beautiful bedform fields.
