limitations on Signature 1000 HR

Hi,

I've never used a signature 1000 before, and I'm trying to set it up to measure currents, waves, and turbulence in 15 m of water. I'll deploy it near the bed, upward looking, for about 3 weeks; I expect currents at that site will reach 1.5 m/s.

I *think* that the way I want to set it up is in the "waves and burst using 5 beams" single plan, with the HR mode enabled. I plan to get turbulence using the Stacey method (that 1999 JGR paper) from the along-beam velocities, and waves from the vertical beam.

So, will the HR mode add additional turbulence information? What are the limitations on that mode? I understand what you've posted:

Velocity range	3 cm/s - 1.4 m/s
Cell size	2-25 cm
Profiling range	10 cm - 8 m
Range velocity limitations	Product of profiling range and velocity should not exceed 3.0 m2/s.

But, I've heard that noise is high when the cell size is small, and it can only reach 1/2 of the way to the surface. Could you offer some tips as to how to get good turbulence data from this part of the instrument? And is there any guidance on comparing the stacey method using 4 beams, and the HR beam method?

Thank you!

Rachel

Atle Lohrmann

April 10, 2020 19:44

Hi Rachel, thank you for posting.

The HR mode is susceptible to something called "decorrelation" as currents increase. When this happens, the measurement process falls apart and the HR data will not give you any sensible information. When does this happen? Well, this is where we have a problem giving sound advice other than gently progressing toward the limit. So my suggestion, as a first test, would be to run 10 cm cell over a range of 2 m and then simply see what happens. Alternatively, you could ask some of the people who have already done this with the Sig1000 to chime in. Alternatively, take a look at the papers that are out there and see what people say.

Best regards, Atle

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limitations on Signature 1000 HR

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