Humminbird and Lowrance have recently tried to join the custom lake mapping business in the last 18 months – creating custom bathymetry and bottom hardness maps while you travel through the water collecting data. Although the aesthetics of their maps are enticing, the data behind the pretty-looking maps is lacking for professional purposes. Two main reasons: sonar and GPS accuracy is not accurate enough. Coincidentally, these are the two biggest factors in making accurate maps because it involves all three of the axis that are required to make accurate maps. Your GPS records the X and Y coordinates while your sonar is collecting the Z coordinate.
Recreational sonar (left) like Humminbird and Lowrance create averages due to wide cone angles. Recreational sonar loses accuracy and detail in its data because of its excessive averaging. Survey-grade sonar (right) has a much narrower cone angle and can gather much more accurate data resulting in more accurate sonar data.
Recreational GPS as found on Humminbird and Lowrance units are within the blue and yellow circles. Survey-grade GPS is a speck within the red dot.
Humminbird and Lowrance are in recreational market – their equipment is used by recreational boaters and fishermen. As a result, their equipment caters to their market. If you’re needing a professional, survey-grade map, you wouldn’t look to recreational-grade equipment. In the same way a surveyor would not use an automobile GPS to survey a new highway.
For accuracy and quality, recreational equipment cannot be substituted for survey-grade equipment such as narrow-cone sonar and RTK GPS.
If your project depends on accuracy and quality, depend on PondMedics to deliver survey-grade quality lake maps for things such as bathymetry, sub-bottom profiling (sediment thickness), sediment coring (sediment types) capacity curves, strapping tables, volumetric calculations, dredging planning, dredging verification, hydraulic cross sections, hydrographic and hydraulic modeling and professional lake planning.
Recreational lake maps generalize outputs (left) because they do not have the capacity to produce accurate data like survey-grade maps (right).
Cross-section for engineering project using survey-grade GPS and sonar.
Using survey-grade sonar and GPS, a pre-dredge and post-dredge map was created within 10 cm accuracy, giving the client confidence in a project well done.
