Aquatic Mapping Strategies

Producing professional-quality aquatic maps has never been easier with Lowrance and BioBase mapping technologies, but there are several strategies that can help you optimize your time on the water and produce the best possible map output:

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Pond Mapping: Why Wait Until Spring?

At this writing, a “Polar Vortex” is invading the Upper Midwestern US.  Temperatures are peaking in the Twin Cities of Minnesota at -11 F give or take a few degrees.  Although this temperature is a wee-bit extreme for even the hardiest of souls, Momentum Environmental recently explored how they could capitalize on the long winter months in Minnesota to rapidly map municipal stormwater basins.  Local municipalities across the US are looking for cost-effective ways to rapidly inventory their stormwater basin infrastructure to ensure compliance with new State and Federal mandates.

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ciBioBase Vegetation Mapping

We love to show off the accuracy of our submerged vegetation mapping algorithm.  Check out this break in the weeds that was picked up and clearly displayed in the ciBioBase vegetation layer:

The BioBase vegetation layer is automatically generated by powerful cloud computers so you receive an objective output every time.  The white line on the right and red dot on the left show the boat position as a cross section and aerial view of the water column respectively. 

Submerged vegetation is displayed as percent biovolume (BV%) which represents the percent of the water column occupied by plants.  This provides a clear picture of total plant abundance from each trip on the water.  Data can be passively logged because none of our users have to do any of the processing when they get back to the office.  Do what you were already planning to do and our automated system will take care of the rest.

Let us know if you have any questions about how this process works!

Lowrance GPS Accuracy: Seeing is believing!

A quick post to demonstrate the precision of Lowrance’s internal WAAS corrected GPS antennae is in a variety of open water environments.  Docks? Boat lifts? Overhanging trees?  No problem.  WAAS correction in North America is explained here.  Have a look at a couple examples in ciBioBase:

GPS Track from a Lowrance HDS on Newport Bay, California overlain onto a bathymetry map created by automated processing of the Lowrance .sl2 log file by ciBioBase.  This trip was used for water volume calculations, bathymetry, and vegetation mapping

GPS tracks and ciBioBase derived bathymetry map in a 3-acre pond in a wooded valley in a metropolitan area of Minnesota, an example of retention pond volume monitoring.

GPS tracks and ciBioBase derived contour map of a 3-acre pond in Illinois for water
volume and aquatic vegetation analysis

GPS tracks around docks and boat lifts and ciBioBase derived contour map on Grand Lake O the Cherokees near Tulsa  Oklahoma.  The satellite even shows data collection in an area where a boat can be moored next to the dock.  That’s close!

Lake Bottom Depth Precision and Accuracy

In an addendum to an earlier post, we continue to evaluate the accuracy and precision of BioBase depth outputs.  Lowrance has been in the depth sounding business since 1957.  They have tight factory calibration standards whereby depth should never be more than 2% different than the actual depth.  Of course then we expect depths to be spot on on hard bottom surfaces where truth can be easily measured.  But what about in mucky bottoms which are common place in many lakes, ponds, backwaters throughout the US and abroad?  With this in mind, in late May of 2012, we traveled to Pool 8 of the Mississippi River near LaCrosse WI to do some testing in a mucky, moderately dense vegetated backwater (Figure 1).  At some point we have to step back and ask, “what is the bottom of a body of water?”

Figure 1.  Vegetation cover and biovolume (% of water column occupied with vegetation) in Pool 8 of the Mississippi R. in LaCrosse WI on 5/29/2012.  Average biovolume was 30% during the survey.

The most difficult aspect of this testing was to get an objective estimate of the true depth.  In other words, where exactly did the plants end and bottom start?  Typically, investigators use a survey rod like that seen in Figure 2 to estimate actual bottom based on where they feel resistance on the survey rod.  Piece of cake over sand.  Not so easy over flocculant silt and muck or vegetative areas.

Figure 2.  Measuring bottom with a survey rod in a mucky Minnesota Lake.  Typically, the survey rod will sink several inches into the bottom before the surveyor feels resistance and judges the depth to the bottom

Many experienced surveyors will tell you that the rod will sink into the muck some distance before you feel resistance.  There is a positive correlation in the distance it sinks and how mucky the bottom is.  So, we went into this investigation expecting deeper rod depths measured than ciBioBase outputs. 

Accurate and precise results in mucky, vegetated bottoms

After 30 points measured with the survey rod, we compared the results with the ciBioBase depths measured in the same location.  We were pleased to see very high precision with a Coefficient of Determination (R^2) of 0.94 and a systematic difference in depth of only 4.9″ (Figure 3).  The depth of 4.9″ was quite possibly the average depth where we first felt resistance of the survey rod.  The upshot here is that ciBioBase depth outputs are highly precise, consistent and accurate even in mucky vegetated bottoms.

Figure 3. Accuracy and precision of ciBioBase depths measured against depths collected with a survey rod in the mucky, vegetated backwaters of Pool 8 of the Mississippi River near LaCrosse, WI.

Verification of ciBioBase Depth Output

At Contour Innovations we are our own skeptics and constantly perform verification investigations of BioBase output for accuracy. 

As Chief Aquatic Biologist, I’ve been comparing bottom depths sampled with a survey rod with its corresponding depth derived from the automated depth outputs from the BioBase System.  In the figure below depths from Elk Lake (Clearwater Co. MN) are color coded from 1 – 50 ft with blue becoming more intense as depth increases.  The circles are depths recorded with a survey rod while the squares are ciBioBase depths.  Below is one visual representation of the high agreement between true depths and BioBase depths. This visual shows the symbol color agreement demonstrating accuracy in the output! 

True depth data come courtesy of Minnesota Dept. Natural Resources Fisheries Research Biologist Donna Dustin and are copyright of Minnesota DNR.