The HR mode is meant to be used for a shorter portion of the water column, with smaller cell sizes and higher sampling frequency when compared to typical velocity profiling. High temporal and spatial resolution are at the expense of range. However, the higher accuracy and the pulse coherent method make the HR mode suitable to use on areas with high shear, low energy flows, near boundaries, under breaking waves or rapidly small-scale varying flows. This is made possible by the increased individual ping accuracy and low noise. Variables like Reynolds’ stresses, Turbulence Intensity, Turbulence Kinetic Energy (TKE), Dissipation Rate, coherence, anisotropy, shear stress and other turbulent parameters can be calculated using data from the HR mode.
The Figure below shows the different time and spatial scales of a few oceanographic processes. For example, studying the dynamics of a fringing coral reef, Taebi et al. (2011) deployed an AquaPro 1 MHz with 100.0 cm cell size, averaging currents for 15 minutes and sampling waves at 2 Hz for ~17 minutes every hour to study the forcing mechanism at the reef channel and the water turnover time. To understand the role turbulence plays in resuspending sediment in seagrass meadows, Contti Neto et al. 2017 deployed an AquaPro HR with 4.0 cm cell size in continuous mode (no averaging).
Examples of studies that used the AquaPro HR encompass turbulence in lakes and the surface mixing layer (Kirillin et al., 2015); turbulence and sediment dynamics in coral reefs (Pomeroy et al., 2017), mangroves (Mullarney et al., 2017) and seagrass meadows (Contti Neto et al., 2022); rip currents (Houser et al., 2013); planning design of tidal energy conversion devices and physical loading on structures (Ramírez-Mendoza et al., 2018).
Although the HR mode provides higher accuracy and range resolution when compared to the standard velocity measurements, a few points need to be well thought before deploying or upgrading the firmware:
- Comparatively to the regular measurements, the HR mode:
- Can be prone to phase ambiguity
- Have a shorter profiling range.
- Have a low tolerance for platform motion.
- The deployment of an HR is less forgiving. A considered deployment plan to suit the deployment environment is important to achieve good-quality data.
- The frame or platform where the HR is mounted must be stable and it must follow a few specific rules found on the deployment FAQ.
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The HR mode is not capable of recognizing phase shifts that are larger than +/- 180 degrees. Additionally, fast-flowing water generates a higher phase shift, which in turn means that the pulse separation must be made smaller. In other words, fast-flowing water leads to a shorter profiling range.
References:
Contti Neto, Nery, Andrew Pomeroy, Ryan Lowe, and Marco Ghisalberti. "Seagrass Meadows Reduce Wind-Wave Driven Sediment Resuspension in a Sheltered Environment." Frontiers in Marine Science (2022): 2108.
Cronin, Meghan F., Robert A. Weller, Richard S. Lampitt, and Uwe Send. "Ocean reference stations." Earth Observation (2012): 203-228.
Houser, Chris, Ryan Arnott, Steffen Ulzhöfer, and Gemma Barrett. "Nearshore circulation over transverse bar and rip morphology with oblique wave forcing." Earth surface processes and landforms 38, no. 11 (2013): 1269-1279.
Kirillin, G. B., A. L. Forrest, K. E. Graves, A. Fischer, C. Engelhardt, and B. E. Laval. "Axisymmetric circulation driven by marginal heating in ice‐covered lakes." Geophysical Research Letters 42, no. 8 (2015): 2893-2900.
Mullarney, Julia C., Stephen M. Henderson, Johan AH Reyns, Benjamin K. Norris, and Karin R. Bryan. "Spatially varying drag within a wave-exposed mangrove forest and on the adjacent tidal flat." Continental Shelf Research 147 (2017): 102-113.
Pomeroy, Andrew WM, Ryan J. Lowe, Marco Ghisalberti, Curt Storlazzi, Graham Symonds, and Dano Roelvink. "Sediment transport in the presence of large reef bottom roughness." Journal of Geophysical Research: Oceans 122, no. 2 (2017): 1347-1368.
Ramírez-Mendoza, R., L. O. Amoudry, P. D. Thorne, R. D. Cooke, S. J. McLelland, L. B. Jordan, S. M. Simmons, D. R. Parsons, and L. Murdoch. "Laboratory study on the effects of hydro kinetic turbines on hydrodynamics and sediment dynamics." Renewable energy 129 (2018): 271-284.
Taebi, Soheila, Ryan J. Lowe, Charitha B. Pattiaratchi, Greg N. Ivey, Graham Symonds, and Richard Brinkman. "Nearshore circulation in a tropical fringing reef system." Journal of Geophysical Research: Oceans 116, no. C2 (2011).
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