Abstract.Wetland biogeochemical transformations are affected by flow and mixing in wetland surface water. We investigate the influence of wind on wetland water flow by simultaneously measuring wind and surface water velocities in an enclosed freshwater wetland during one day of strong-wind conditions. Water velocities are measured using a Volumetric Particle Imager while wind velocities are measured via sonic-anemometer. Our measurements indicate that the wind interacting with the vegetation canopy generates coherent billows and that these billows are the dominant source of momentum into the wetland water column. Spectral analysis of velocity timeseries shows that the spectral peak in water velocity is aligned with the spectral peak of in-canopy wind velocity, and that this peak corresponds with the Kelvin-Helmholtz billow frequency predicted by mixing layer theory. We also observe a strong correlation in the temporal pattern of velocity variance in the air and water, with high variance events having similar timing and duration both above and below the air-water interface. Water-side variance appears coupled with air-side variance at least down to 5 cm, while the theoretical Stokes' solution predicts momentum transfer down to only 2 mm assuming transfer via molecular viscosity alone. This suggests that the winddriven flow contributed to significant mixing in the wetland water column.
We describe the development of a field-deployable Volumetric Particle Imager (VoPI) and the methods that enable it to measure three-dimensional particle tracks in situ. The VoPI has the unique ability to obtain threecomponent particle velocity records in a volume. The device has a slender, single-camera design ideal for optically accessing study sites in the environment, including hard-to-reach places like the inside of coral reefs and marshes. Unlike other underwater measurement techniques, the VoPI implements a defocused imaging method that relies on ambient light in place of laser light for particle illumination. We describe the construction, calibration and validation of this device. We also demonstrate the VoPI's abilities by measuring velocity statistics of passive tracer particles dispersed in a high-Reynolds-number turbulent flow. By measuring velocity variances and integral timescales from these Lagrangian velocity records, we can compute the turbulent diffusivity directly from the VoPI measurements.
Model parameters that represent a photovoltaic (PV) system as built may not align with the original pro forma pa rameters estimated and possibly guaranteed a priori in the pro curement phase of a project. In this paper, the pro forma parame ters of an existing system are revisited via on-site survey, indoor characterization, analytical modeling, and ex-post performance analysis. Moreover, the Photovoltaic System Analysis Toolbox (PVSAT) is introduced, validated, and used to execute a modern performance guarantee to investigate the impact of varying de grees of model true-up on production forecasts. Improvements to the original parameter values are achieved, demonstrating how calibration efforts performed even over a brief data collection in terval can provide valuable insights and mitigate risk.
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