What is the minimum deployment depth for an AWAC?Follow
There should be no problem using the AWAC in 5 meters or less, provided it is configured appropriately. The AST measurement operates to ranges as little as 0.7 meters. Below this depth the pressure sensor can be used for non directional wave measurements. Depths that are less than 2 meters may present challenges for directional wave measurements, since the velocity cells will get interference with the surface. Current profile measurements should not be a problem as long as the cells sizes are maintained small. Again depths that are very shallow will have challenges for current measurements.
Potential problems when measuring in shallow water:
- At >4 m depth with High power (especially for 600kHz): AST saturation
- At <4 m depth with high sediments: amplitude returns may look like the surface (try increasing the amplitude threshold)
- For 600kHz in shallow water: determining direction can be difficult due to unreasonably small orbital velocities
The optimal settings for the AWACs are as the ranges in the deployment software (Estimated depth selection):
1 MHz: 2 m
600 kHz: 5 m
400 kHz: 20 m
Shallow water environments are difficult, but you could get useable AST data more shallow than the values listed above. The higher frequency AWACs engage "shallow water mode" and "super shallow water mode" at certain depths (these distances are based on the start of the AST cell):
|AWAC frequency||Shallow water mode||Super shallow water mode||AST ceases to function, switches to pressure|
|1 MHz||4 m||2 m||0.7 m|
|600 kHz||4 m||2 m||0.95 m|
|400 kHz||n/a||n/a||2 m|
Shallow water mode: power level is set to Low- to prevent saturation of the AST ping.
Super shallow water mode: power level is set to Low-, and a fixed AST window is set. The surface is detected when an amplitude threshold is exceeded (by default is 80 counts but can be set by user).
You can consult the Principles of Operation manual to better understand the measurement cell positions and position relative to the surface.
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