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Case Study: Hands-On Mobile Surveys Using Hydroacoustic Echo Sounders, Seattle-Style  
Portage Bay, Lake Union, Seattle, WA Hands-On Mobile Surveys Using
Hydroacoustic Echo Sounders, Seattle-Style

Hosts: HTI & University of Washington Student
Chapter of the American Fisheries Society (AFS)
Location: Lake Union, Seattle, WA USA

See Project Pics - Download Pub See Project Pics Download FM Slide-Chirp Pub GoPro with the Divers
Copper Rockfish next to sea star. Image: G.AmptmanResearch Vessel Kittiwake. Image: A.Drake


Every February, students from HTI’s intensive hydroacoustic short course get an opportunity to “get out on the water” on Seattle’s Lake Union to conduct a hands-on hydroacoustic mobile survey instructed by HTI and co-hosted by the University of Washington Student Chapter of the American Fisheries Society (AFS). The 2-day course covers mobile and fixed-location survey techniques. Subjects include basic hydroacoustic theory, deployment logistics, data collection and processing, and typical results. Split-beam, dual-beam, and single-beam techniques are discussed in detail; with examples illustrating what other researchers have accomplished to-date.

In the hands-on mobile survey, students head out on the R/V Kittiwake for an evening of mobile survey hydroacoustic techniques. With a hydroacoustic system sampling with two transducers at a frequency of 200 kHz one at 6 degrees and the other at 15 degrees (other available frequencies are 120 kHz and 420 kHz), HTI instructors share best practices for fisheries assessment. These include hands-on training in system deployment, transect allocations, as well as how to produce real-time results.

Potential Results:

The mobile systems record the complete, unthresholded digital samples allowing the data from our evening survey to be saved and used in the next day’s coursework. The following day, data processing methods for an assortment of results are covered (e.g., horizontal and vertical fish distributions, temporal distribution in diel and seasonal, target strength fish size estimation, velocity, and trajectory).

With summary data available every 6 seconds and a ping rate of up to 50 pings/seconds, high resolution data is produced in real-time with range strata as small as 10 cm. To take it further, students learn how to employ the FM slide-chirp signals to provide up to a 15 dB gain in signal-to-noise ratio, reducing bias and variability in resulting fish target strength and biomass estimates. This increases both resolution and range at the same time.

Of course, this is Seattle, so there is usually coffee onboard, and we’re out to learn and have fun. To see how much productive fun we had at the hands-on mobile survey last February, check out the Survey Photo Album. And to find out what a difference an FM slide/chirp can make for a mobile hydroacoustic survey, check out the Powerpoint Presentation by hydroacoustic expert, Pat Nealson entitled "Improving Signal-to-Noise Performance in Hydroacoustic Monitoring Systems through the use of FM Slide-Chirp Signals".


Preparing to deploy marine hydrophones to listen for tagged rockfish. Image: L.McGarry
Setting software parameters. Image: A.Drake

Diver checking new marine hydrophone mount. Image: J.Nordstrom
How to maximize the resolution and range for real-time mobile survey data. Image: D.Ouellette

Example of tag being moved around to test new marine tag positioning system. Image: S.Johnston
Instructor Steig's mobile introduction. Image: L.Rudolph
Deploying a hydrophone mount from the R/V Centennial. Image: C.Greene.
Deploying a hydrophone mount from the R/V Centennial. Image: A.Drake
A great exercise in practical use of active acoustics…specific instruction provided the best insights into how the acoustic theory we learned earlier in the week works in action.
  - 2015 Short Course Student
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