Color Enhancing your Sonar Log

ciBioBase’s Trip Replay feature that couples bottom depth, aquatic vegetation biovolume, and bottom hardness maps with your actual Sonar Log empowers you with a verification tool that ensures an accurate map in every system you map, every time.  The sonar log also provides users and our Quality Control team helpful information about signal quality and transducer placement that can help both parties diagnose issues.

A little known feature in ciBioBase allows users to reprocess their Lowrance HDS/Elite sonar log at different color and sensitivity settings (Figure 1).

Figure 1. Trip Reprocessing Tab that allows ciBioBase users to reprocess their trips with new edits.  Try reprocessing your sonar log at a higher color (e.g., 240) for “cooling” the colors in your sonar log in ciBioBase and to bring out subtle bottom features.

Sometimes, your Sonar Log may look a little too “hot” making it difficult to distinguish between plants and bottom (Figure 2).

Lowrance, ciBioBase, Sonar Log
Figure 2.  Sonar Log showing colors that may be “too hot” to distinguish between plants and bottom.

Try reprocessing the sonar log at a colorline of 240 (default is 220).  This will bring in “cooler” colors to the sonar log and may help you better distinguish subtle bottom features and gaps in plant beds (Figure 3).

Figure 3.  Sonar Log reprocessed with a colorline of 240.

Alternatively, Lowrance has a powerful free desktop software program called SonarViewer which allows you to replay your Sonar Log with options to dynamically control sensitivity, colorline, zoom, and range (Figure 4).

Figure 4.  SonarViewer is a free download from Lowrance and has a range of tools for enhancing the contrast of bottom features detected by your Lowrance HDS or Elite.

Use SonarViewer to review your files prior to upload to ciBioBase if you suspect possible signal quality issues or are testing different transducer setups for optimal signal quality.  Signal Quality should also be continually monitored by watching your SONAR page on your HDS or Elite while collecting data on the water.  A helpful rule of thumb is that a signal that is clear and crisp to your eyes is most likely clear and crisp to ciBioBase algorithms.

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.