As such, we often stress the importance of monitoring your sonar and GPS display while logging sonar making sure you get a clear view of bottom with a continuous digital depth reading (Figure 1). If you can't see a digital depth reading on your screen, add it (here's how). If you're a first timer not familiar with sonar of "fish finders" you should spend some time familiarizing yourself visually interpreting a sonar display prior to mapping "for real."
Areas of waterbodies less than 2 ft (< 0.75 m), are difficult to characterize with acoustics. Target separation between the bottom and the face of the transducer is extremely small and these environments are very acoustically noisy due to wind mixing. Accordingly, by default BioBase requires a minimum depth of 2.4 ft (0.76 m) to create vegetation and bottom hardness outputs. Reading depth alone is not as difficult and you may find your Lowrance unit providing reliable depths as shallow as 1 ft (0.3 m). But, as stated earlier, this is a tricky environment and the acoustic signal can easily be lost and difficult to recover, especially in Auto Range.
Alternative 1: Fix the Range (Shallow Water Only)
Fixing the Sonar Range to 5 ft in very shallow waters can be a tool to establish a known zone where the sonar should search for a bottom signal (Figure 3). This may ensure a more consistent bottom lock. But, Range should be reset to Auto if mapping in variable or deep waters to ensure the 3200 bytes of data are in the optimal range for bottom typing. Never change range during logging or it could corrupt the .sl2/.sl3 file.
Alternative 2: Use a Kayak
|Figure 4. Sit-on-top kayak mounts of HDS. Kayak's are light and will not draw as much water. You may be able to bring your transducer.|
Alternative 3: Use a Jet-ski pulling a Catamaran
|Figure 5. See how EnvirolinkSouth Ltd in New Zealand maps shallow waters with a Jet-ski pulling a Catamaran with a transducer and Point-1 GPS tethered by long cables to the Jet Ski with HDS Display. Ensure cavitation behind the jets do not create noise under the transducer.|
Alternative 4: Use a Robotic Boat (especially if you have to map rivers with Hippos)!
|Figure 6. Autonomous Platypus Lutra boats equipped with Lowrance can help you stay alive if Hippos are in your way or if you want to map waters difficult to access with a boat. Ask a Platypus rep about Boat Rental/BioBase EcoSound Bundles.|