CHIRP from a bottom mapping perspective

Maybe you’ve been hearing about this term in sonar circles called “Chirp” and noticing that most consumer sonar units now come with Chirp capability. Indeed, Chirp is a game changer for more precise definition of acoustic targets suspended from bottom (e.g., fish) and the technology is helping more anglers find fish in a wide range of aquatic environments (Figure 1).  But what does Chirp mean for mapping the bottom of waterbodies?  Does it provide any advantages or disadvantages over traditional 200 kHz frequency broadband sonar that is the foundation of Insight Genesis and BioBase
EcoSound mapping services?  Here we take a brief look at Chirp, explain what it is, and present some findings from preliminary tests in a couple of different lake environments.

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Offset Tool and Public Water Databases to Create Accurate Depth Maps

One of the best features of BioBase EcoSound and its sister technology for anglers, C-MAP Genesis, is the ability to aggregate partial maps created over time into a complete map later.  The recent blog post on Ten Mile Lake in Minnesota, USA, details a notable example of the power of aggregation.  However, changing water levels over the course of time can impact the accuracy of aggregated maps if recorded water depths are not offset against a standard benchmark water elevation.

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Citizen Lake Mapping: Power of Aggregation!

Ten Mile Lake in Hackensack, Minnesota is one of many crown jewel lakes of Minnesota.  It’s no wonder the Ten Mile Lake Association is serious about lake monitoring and conservation.  When BioBase approached TMLA member and hobby Fisheries Biologist Dr. Bruce Carlson in late 2012 demonstrating how members could passively log their sonar data and map habitat while enjoying a pleasure cruise or fishing, Dr. Carlson jumped at the opportunity.

Two hundred and twenty four trips spanning two seasons (2013-2014) and 5,065 acres (2,049 ha) later, Dr. Carlson and colleagues have produced the most accurate and detailed map of Ten Mile Lake on the planet (Figure 1)!

Figure 1. Track lines from 224 Lowrance sonar logs uploaded to BioBase and merged (left) and resultant contour map (right) produced automatically for Ten Mile Lake, Hackensack, MN USA.  Ten Mile Lake is a 208-ft (63-m) deep lake with 16-ft (5-m) clarity.

When comparing the hand-made maps of 1947 from the long-dissolved MN Dept of Conservation one has to wonder if creating this map took a dedicated and highly trained survey crew all summer to create this map (Figures 2-4)?  Now a critical mass of anglers or pleasure boaters with no mapping experience can create a community-sourced contour map that rivals anything produced by the most trained hydrologists using the most expensive “survey-grade” echosounders.

Figure 2. Original map of Ten Mile Lake created in 1947 by the MN Department of Conservation (left) next to the aggregated map produced by TMLA volunteers in 2014 after uploading to BioBase.  Maps created in the mid 20th Century remain the only maps offered to anglers and recreationists by a large number State Natural Resource agencies. Often these old maps are digitized and artfully recontoured and shaded for resale.
Figure 3. Close up of the 10-ft contours displayed in the 1947 Department of Conservation map compared with the 2014 aggregated map created by TMLA volunteer uploads to BioBase.
Figure 4. Tight zoom of 10-ft contours from 1947 MN Department of Conservation map (ink blob on top) compared with 3-ft contours from aggregated map created by TMLA volunteer uploads to BioBase.

Not just an improvement in aesthetics!
The efforts of TMLA and volunteers from other Lake Associations across the US (e.g., Lake Paradise, Honeoye, Prior Lake) are producing not only pretty maps but also updated digital maps for the public and highly detailed fish habitat and aquatic plant data for aquatic researchers and managers.

First, public trips uploaded and aggregated both from BioBase and C-MAP Genesis mapping services from anywhere across the globe go to Social Map where they are available for viewing and downloading for free to Lowrance, Simrad, and B&G chartplotters (Figures 5 and 6).

Figure 5.  Insight Genesis Social Map coverage of Sweden.

 

Figure 6. Example map of Anten (Sweden) as viewed from Insight Genesis social map.  Professionals (BioBase) and Anglers (Insight Genesis) can community-source their mapping efforts to “fill-in” unmapped areas and create up to date digital maps for the public.

Second, Fisheries across the globe are threatened by a range of impacts too long to go into detail here and Aquatic Invasive Species are a global pandemic.  Researchers and managers mourn the decline of native aquatic species and often target habitat degradation or loss as a primary driver.  But rarely does information on habitat match the detail of the information on species declines. Citizen Scientists are now helping Natural Resource Agencies fill in the habitat knowledge gaps.  Returning to our example on Ten Mile Lake, now with updated bathymetry provided by TMLA volunteers and data sharing with MN Department of Natural Resources (DNR), Fisheries researchers have precise knowledge about how much cold, well oxygenated water is available for cisco (an important cold-water forage fish for popular gamefish).  Similarly, thanks to the efforts of the Prior Lake Spring Lake Watershed District and citizen volunteers on Prior and Spring Lakes, the response of invasive aquatic plants to watershed and in-lake management actions can be monitored.

Harnessing the power of technology and citizen science to conserve aquatic resources
“Doing more with less” or “working smarter not harder” are common cliché truths that will continue to limit the reach of publicly funded natural resource management programs into the foreseeable future. Through advances in affordable off-the-shelf consumer technology, automation, and the collective enthusiasm of citizen volunteers, good information on aquatic habitat need’nt suffer from declining public natural resource budgets.  Rather, by enrolling the help of citizens and technology such as described here, aquatic biologists and managers can focus their energies on using the information to make wise aquatic resource management decisions.