Mapping habitat in navigable streams using low-cost side scan sonar

Natural resource professionals need an inexpensive and rapid technique for mapping and quantifying the habitat of navigable river systems at the landscape scale.  Unlike more expensive side scan sonar devices, the Humminbird^(R) Side Imaging system ($2,000) can be interfaced with GPS devices to capture spatially-referenced imagery in streams that include shallow, rocky areas.  Since first presenting a concept for sonar mapping in 2007, we have refined our techniques for capturing sonar imagery and developed the tools required to produce sonar image maps (SIMs) exclusively within in a GIS environment employing ESRI’s ArcGIS 9.x software.  The resulting SIMs are high resolution (~10 cm) layers representing continuous, bank-to-bank imagery that can be interpreted and analyzed to map features such as substrate types, large woody debris, and relative depth.  To demonstrate the utility of sonar-based maps and to explore the effective boundaries of the technique we conducted a series of mapping studies on small (width 30-50 meters) to medium sized (90-130 m) river systems in Georgia.  Overall, the technique produced accurate (classification accuracies 77-84%), spatially explicit habitat maps of underwater landscapes.  The applications for such detailed maps are widespread and numerous; techniques for map production are now accessible to researchers and managers alike.