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due to side-lobe interference (surface and bottom boundary layer) are handled by interpolation. To understand the full processes of a WEA���s currents, sampling at multiple sites is necessary. Measuring the distribution of wave energy (height, speed, direction and frequency) by surface-buoy-mounted systems (accelerometer or GPS-based sampling) or acoustically from Doppler current meters mounted on the seafoor can also be included in these data sets. Understanding the orbital velocities, among other parameters, within the acoustic energy near the surface allows for wave spectra to be deciphered. High-frequency radar may also be employed if a WEA is within the arc of the radar footprint; the backscatter of radio waves can measure the surface current and wave spectra. Additional measurements and sampling to complete a metocean survey may include: conductivity, turbidity, water quality, dissolved oxygen, fuorescence, pH, nitrates, phosphates and CO2 levels. Further numerical modeling can also help resolve tidal and wave cycles. Biological Measurements Marine Fauna. Biological sound has always been present in the ocean and is critical for cetaceans��� survival. For navigation, migration, searching for prey and determining the presence of other mammals and species, clear hearing is necessary. A side effect of establishing a WEA is artifcial sound. Multiyear assessments will be needed for WEA approval to determine seasonal and annual variability of cetacean and other marine fauna. Aerial and shipboard observations will contribute to these assessments. ���Sound in the sea��� studies Example of a dolphin-call spectrogram. (Credit: Loggerhead Instruments) have already been conducted in the academic, and oil and gas communities worldwide. By mounting hydrophones in a WEA, sample rates can cover the frequency range of all baleen whale sounds, sperm whale clicks and cetacean whistles. Dolphin clicks can also be recorded. Birds and Bats. The Mid-Atlantic coastline of the U.S. plays a major role in the migratory patterns of North America���s bird population. Many species living in this habitat are well-documented and protected. Construction activities both onshore and offshore along with the associated vessel traffc to and from a WEA will have an impact on bird populations. It has been suggested that migratory species will fy higher than deployed buoys or met towers with minimal risk of collision, but experience placing structures on the sea surface (buoys, towers, markers, etc.) has shown that birds tend to take up residence while gathering food and resting. www.sea-technology.com FEBRUARY 2013 / st 27