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relative humidity, barometric preson land alongside met towers to sure and radiation. Sea surface provide assessment of perfortemperature completes the meamance and reliability. Offshore surement loop. Sample rate varies deployments of lidar buoys and depending on the sensor but usufxed mounted structures are now ally averages minutes over each underway, showing excellent rehour and is sent to a logger and sults in data analysis. then to a receiving station. These The U.S. plans to deploy lidar data contribute to understanding in WEAs in the near future. It may near-surface fux (air-sea heat exnot be uncommon for each WEA change), extrapolation functions to employ at least two surface and atmospheric stability on locametocean buoys and one foating tion. or fxed lidar system before, durLidar. In parallel to using suring and after site construction. face-buoy applications, met tow- Example of a whale-call spectrogram. (Credit: West Inc.) ers and numerical models, lidar Ocean Currents and Waves technology is now being tested offshore on fxed and movTo get deep into the physics of an offshore region, the ing platforms. Lidar is an optical instrument used in atmomovement of water at the surface and at depth must be unspheric research and meteorology that remotely measures derstood. Wave feld information is also critical, considering 3D horizontal wind velocity and direction within a volume turbines and mounting structures will be under constant atof air. tack by nature. This form of wind profling has been very successful on The standard in the physical oceanographic feld is the land and is used by the U.S. military and NASA regularly. use of acoustic Doppler current proflers (ADCP), which Profles above hub height are being reported by manufaccan be mounted at the surface on buoys or fxed structures turers, allowing for hard measurements to be made at and looking down, or hard-mounted on the seafoor in bottombeyond turbine energy-source levels. mounted applications (looking up). There are other methods, In Europe, lidar technology is run through considerable such as single-point and non-Doppler, but for collecting data testing and calibrated against proven cup-vane-propeller within the full water column, surface to depth, Doppler is and sonic anemometers mounted on tall masts. A permathe best approach. nent reference lidar is used to evaluate consistency between In the shallows of the OCS, it is possible to cover the enunits. Successful system comparisons have been conducted tire depth range of a WEA with one profler. Any gaps in data www.sea-technology.com FEBRUARY 2013 / st 25