All HR instruments measure water velocity by detecting Doppler shifts from particles in the water (refer to Principles of Operation: Currents for a detailed explanation on the Doppler principle). However, their sampling geometry can vary from having an divergent (profiler) or convergent beam (velocimeter) configuration:
- Signature 1 MHz & Aquadopp 1/2 MHz (Profiler): These instruments use slanted, monostatic acoustic beams to generate vertical profiles of water velocity. Each beam captures multiple velocity measurements at different depths along its path, enabling detailed, depth-resolved flow data. When operating in HR mode, the profiling range is reduced, but vertical resolution is significantly enhanced - often down to the centimeter scale - making it ideal for capturing fine-scale flow structures.
- Vector (Velocimeter): This instrument features a bistatic acoustic geometry (a configuration where the acoustic transmitter and receivers are in separate locations, reducing flow disturbance and enhancing velocity measurement accuracy), with a central transmitter and three angled receivers arranged symmetrically around it. The beams converge on a fixed point located just a few centimeters above the sensor, enabling high-precision, single-point measurements of all three velocity components. This configuration provides exceptionally fine spatial resolution, ideal for capturing rapid fluctuations and turbulence at a specific location.
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