Interpreting bottom hardness in shallow lakes and ponds: digging deeper into the data

BioBase’s EcoSound bottom composition (hardness) algorithm has become quite popular for researchers and lake/pond managers to determine where sedimentation from the watershed may be occurring.  However, interpreting sonar returns in shallow environments (e.g., less than 7 ft or 2 m) with off-the-shelf sonar is challenging, especially if aquatic vegetation is present.  Each situation is different and the objective of this blog is to inform you of how to interpret your EcoSound map in situations when you encounter counter intuitive bottom hardness results.

Here are some high level points to remember.

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What’s this Kriging Business?!

Thanks to advances in Geographic Information Systems (GIS) computing technology, evaluating changes to lake bottoms over time has gotten much easier!  Prior to GIS, biologists and surveyors would go through great pains to ensure that repeated data collection in study areas of interest would precisely fall on the same area or transect.  If this condition was not met, data would have to be thrown out because biologists could never be sure that the difference seen between two time periods was real, an artifact of sampling a different area, or a product of sampling in a different way.  Consequently, efforts from multiple groups collecting similar data in the same system but in a slightly different way could not be leveraged.  This is an unfortunate missed opportunity that BioBase uniquely handles.

First, BioBase uniformly interprets acoustic signals and the output is the same regardless of the skill level of the individual collecting the data.  Second, BioBase employs kriging to create a statistically robust uniform map output that figuratively turns Survey 1 by Bob Smith from an orange into an apple and Survey 2 by Amy Johnson in the same area from a grapefruit into an apple.  This is unique to kriging which is a geostatistical procedure.  All other standard interpolation methods are simply 3D representations of the input data and each map will look different depending on the precise location of your survey points.  Only kriging turns different fruits into apples.

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