Methodologies that I have encountered thus far are 1). Ultrasonic sensors, 2) Hi-Res sonar, 3) Optical backscatter arrays (e.g., Sedimeter) and photovoltaic arrays (PEEP sensor), 4) Green-laser altimeters, 5) Load cells.
Do you know of other novel techniques that can measure fine-scale sedimentation in the offshore environment? Any favorite commercially-available instruments?
Thanks!
no, I am not aware of other techniques. At present, the most frequently used is multi-beam ultrasonic sensors
It's very complicated to determine bed elevation of few millimetres, specially if the observed area is under variable streams.
Dear colleagues. In order to measure the thickness of sediment layers so thin like 20-40mm the best tool I know is the subbottom profiler developed by a finish company named Meridata. This SBP deals with frequencis between 20 and 50 kHz and so it can identify a few cm thickness layers. I have good examples if some one would like to see.
The only tool for detecting bed-levelchanges with a resolution of about 1 cm I got to know have been experimental devices. We used them at CRS on intertidal beaches and flats in the 1990s. But they deliver only information for single points.
Acoustic backscatter sensors which ensonify the entire water column. Or the CCP-probe that was recently developed at the University of Delaware. It has a resolution of 1 mm but a range of only 3 cm, see Lanckriet et al 2013, J.Oceanic Eng 38, 55-70.
Before you even start to develop an instrument to measure the bed level you have to ask yourself, "How do I define the bed level?". What is "the bottom"? Sometimes it is very clear, but at other times what visually is the bottom is not what one would define as the bottom if probing with a stick. Fluid mud looks like the bottom but a diver can swim through it. Second, for what purpose do you need to know the bottom level? The SediMeter was developed to detect sediment transport. If the sediment transport takes place through migrating bed forms the resolution does not have to be that high, or if there is net accumulation or net erosion. But if the sediment transport takes place as sheet transport, bedload over a flat bed that does not change level, then the instrument needs to be able to detect very small changes. If it can detect the addition or removal of a single grain of sediment, then it for sure has sufficient resolution. As far as I know, only the SediMeter is capable of doing that, and that was the original purpose of me developing it 31 years ago.
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