Improved detection of the first-order region for direction-finding HF radars using image processing techniques

Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 34 (2017): 1679-1691, doi:10.1175/JTECH-D-16-0162.1.For direction-finding high-frequency (HF) radar systems, the correct separation of backscattered spectral energy due to Bragg resonant waves from that due to more complex double-scattering represents a critical first step toward attaining accurate estimates of surface currents from the range-dependent radar backscatter. Existing methods to identify this “first order” region of the spectra, generally sufficient for lower-frequency radars and low-velocity or low-surface gravity wave conditions, are more likely to fail in higher-frequency systems or locations with more variable current, wave, or noise regimes, leading to elevated velocity errors. An alternative methodology is presented that uses a single and globally relevant smoothing length scale, careful pretreatment of the spectra, and marker-controlled watershed segmentation, an image processing technique, to separate areas of spectral energy due to surface currents from areas of spectral energy due to more complex scattering by the wave field or background noise present. Applied to a number of HF radar datasets with a range of operating frequencies and characteristic issues, the new methodology attains a higher percentage of successful first-order identification, particularly during complex current and wave conditions. As operational radar systems continue to expand to more systematically cover areas of high marine traffic, close approaches to ports and harbors, or offshore energy installations, use of this type of updated methodology will become increasingly important to attain accurate current estimates that serve both research and operational interests.This analysis was supported by internal funds from the Woods Hole Oceanographic Institution.2018-02-1

Commissioning form: Windcube V2 WLS7-436 WHOI ASIT Tower

Lidar is deployed on the Air Sea Interaction Tower (ASIT) offshore structure owned and operated by Woods Hole Oceanographic Institution (WHOI); Tower is approximately 2 miles south of Martha’s Vineyard, MA. Station has a walking platform at approximately 11 m MSL, with a section of lattice mast that extends from the platform to approximately 21 m MSL. The walking platform has a “diving board” extension oriented southwest, on which the lidar is deployed. The lidar sits upon a work bench mounted outboard of the southeast side of the diving board. Figure 1 illustrates the site configuration Aside from the immediate structure, the closest obstruction is Martha’s vineyard. Open ocean fetch for the southern half of the compass; Site access controlled by WHOI; additional site details attached separately

Wind resource site commissioning form

The WHOI ASIT Tower station located approximately 2 miles southeast of Martha’s Vineyard. The met tower platform sits approximately 11m above the water line, depending on tide level. Site is accessed using a vessel provided by WHOI (Woods Hole Oceanographic Institution). Tower is maintained by WHOI and WHOI personnel are needed to access tower

Long-term observations of turbulent Reynolds sresses over the inner continental shelf

Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 2752–2771, doi:10.1175/JPO-D-12-0153.1.In situ observations of turbulent momentum flux, or Reynolds stresses, were estimated from a 10-yr acoustic Doppler current profiler (ADCP) record of inner-shelf velocities at the Martha’s Vineyard Coastal Observatory (MVCO) using recently developed analysis techniques that account for wave-induced biases. These observations were used to examine the vertical structure of stress and turbulent mixing in the coastal ocean during tidal-, wave-, and wind-driven circulation by conditionally averaging the dataset by the level of forcing or stratification present. Bottom-intensified stresses were found during tidally driven flow, having estimated eddy viscosities as high as 1 × 10−2 m−2 s−1 during slack water. An assessment of the mean, low-wave, low-wind stress results quantified the magnitude of an unmeasured body force responsible for the mean circulation present in the absence of wind and wave forcing. During weak stratification and isolated wind forcing, downwind stresses matched the observed wind stress near the surface and generally decreased with depth linearly for both along- and across-shelf wind forcing. While consistent with simple models of circulation during across-shelf wind forcing, the linear slope of the stress profile present during along-shelf wind forcing requires the existence of an along-shelf pressure gradient that scales with the wind forcing. At increased levels of stratification, the observed downwind stresses generally weakened and shifted to the across-wind direction during across-shelf and mixed-direction (i.e., onshore and along shelf) wind forcing consistent with Ekman spiral modification, but were more variable during along-shelf wind forcing. No measurable stresses were found due to wave-forced conditions, confirming previous theoretical results.The analysis was funded by the National Science Foundation under Grant OCE#1129348.2014-06-0

Remote sensing of the surface wind field over the coastal ocean via direct calibration of HF radar backscatter power

Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 33 (2016): 1377-1392, doi:10.1175/JTECH-D-15-0242.1.The calibration and validation of a novel approach to remotely sense surface winds using land-based high-frequency (HF) radar systems are described. Potentially available on time scales of tens of minutes and spatial scales of 2–3 km for wide swaths of the coastal ocean, HF radar–based surface wind observations would greatly aid coastal ocean planners, researchers, and operational stakeholders by providing detailed real-time estimates and climatologies of coastal winds, as well as enabling higher-quality short-term forecasts of the spatially dependent wind field. Such observations are particularly critical for the developing offshore wind energy community. An autonomous surface vehicle was deployed within the Massachusetts Wind Energy Area, located south of Martha’s Vineyard, Massachusetts, for one month, collecting wind observations that were used to test models of wind-wave spreading and HF radar energy loss, thereby empirically relating radar-measured power to surface winds. HF radar–based extractions of the remote wind speed had accuracies of 1.4 m s−1 for winds less than 7 m s−1, within the optimal range of the radar frequency used. Accuracies degraded at higher winds due to low signal-to-noise ratios in the returned power and poor resolution of the model. Pairing radar systems with a range of transmit frequencies with adjustments of the extraction model for additional power and environmental factors would resolve many of the errors observed.This analysis was supported by the Massachusetts Clean Energy Center. The HF radar data used were obtained during projects supported by the National Science Foundation, the NOAA Integrated Ocean Observing System (IOOS), and internal funds from the Woods Hole Oceanographic Institution.2016-12-2

Calibration Report of LiDAR unit “WLS7-436”

Following an order of Massachusetts Clean Energy Center a calibration of a LiDAR of the type WindCube V2 by Leosphere (WLS7-436) against a met mast has been performed at a test site in the US. In this report the measurement results of the LiDAR device are compared to those from calibrated cup anemometers mounted on a met mast. The aim of this comparative assessment is to convey traceability to international standards of this particular LiDAR unit. The evaluation process is based on the IEC 61400-12-1 Ed. 2 Annex L [2]. This standard describes the calibration procedure of remote sensing devices in the frame of power curve measurements on wind turbines. However, this approach generally also applies in the field of wind resource assessment, under the recommendations of MEASNET [4]. The data of the LiDAR measurement (130 m, 125 m, 95 m and 60 m) have been compared with the measured met mast data at 4 different heights (130 m, 125 m, 94 m and 58 m) during a period of 36 days (2019.08.20 – 2019.09.25) for wind speed bins between 4 – 16 m/s and for the wind direction sector 67 – 354°. In addition, measurement results of the met mast and LiDAR unit have been compared in terms of turbulence intensity, wind direction and wind shear. UL was not involved in the installation of the instruments on the mast but has gathered all relevant information. However, UL was responsible for the installation of the LiDAR unit close to the mast. It is ensured that the results presented in this report have been measured in an unbiased manner, following the best practices and to the best knowledge of the participating persons

MetOcean monitoring plan

AWS Truepower (AWST) has been engaged by the Massachusetts Clean Energy Center (MassCEC) to develop monitoring campaign guidance in support of MassCEC’s “Metocean Initiative”. The goal of the Initiative is to “advance planning and permitting and reduce the costs of offshore wind energy in the Bureau of Ocean Energy Management’s (BOEM) designated Massachusetts Wind Energy Area (MAWEA) and the Rhode Island/Massachusetts (RI/MA) Wind Energy Area (together, the ‘WEAs’).”[1] The data collected and developed during this campaign are planned to support characterization of the WEAs’ long-term wind resource and metocean design conditions. The body of this report presents a recommended monitoring campaign framework.. The content of this document is based upon the information presented in the MassCEC Metocean Data Needs Assessment report [1], the MassCEC Metocean Initiative RFP [2], and subsequent discussions with the campaign team. The metocean campaign described here is expected to form the cornerstone of new observed public data sets developed specifically to support regional offshore wind energy development

Some considerations about coastal ocean observing systems

Author Posting. © The Authors, 2017. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 75 (2017): 161-188, doi:10.1357/002224017821836743.Coastal ocean observing capabilities are evolving rapidly, both in terms of sensors and in terms of the volume of information available. We discuss the aspects of the coastal ocean that make it a unique environment, both in terms of physical processes and measurement techniques. Although many global-level systems are relevant to the coastal ocean, we concentrate on treating systems that are unique to the continental shelf environment. Further, we briefly discuss examples of measurement systems that would be useful for developing and driving ocean prediction systems.KB gratefully acknowledges support from the U.S. National Science Foundation, Physical Oceanography (grant OCE-1433953) and Ocean Biology (grant OCE-1258667) programs. AK gratefully acknowledges support from the U.S. National Science Foundation, Physical Oceanography (grant OCE-1332646)

Drivers of spring and summer variability in the coastal ocean offshore of Cape Cod, MA

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 1789–1805, doi:10.1002/2015JC011252.The drivers of spring and summer variability within the coastal ocean east of Cape Cod, Massachusetts, a critical link between the Gulf of Maine and Mid-Atlantic Bight, are investigated using 2 years of shipboard and moored hydrographic and velocity observations from 2010 and 2011. The observations reveal sharp differences in the spring transition and along-shelf circulation due to variable freshwater and meteorological forcing, along with along-shelf pressure gradients. The role of the along-shelf pressure gradient is inferred using in situ observations of turbulent momentum flux, or Reynolds stresses, estimated from the ADCP-based velocities using recently developed methods and an inversion of the along-shelf momentum balance. During spring, the locally relevant along-shelf pressure gradient contains a sizable component that is not coupled to the along-shelf winds and often opposes the regional sea level gradient. Together with the winds, local pressure gradients dominate along-shelf transport variability during spring, while density-driven geostrophic flows appear to match the contribution of the local winds during summer. These results suggest that local effects along the Outer Cape have the potential to cause significant changes in exchange between the basins.NOAA. Grant Number: NA10OAR4170083; Woods Hole Oceanographic Institution2016-09-1

High-resolution observations of subsurface fronts and alongshore bottom temperature variability over the inner shelf

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 53(3), (2019): 1639-1649, doi:10.1029/2018JC014454.Circulation patterns over the inner continental shelf can be spatially complex and highly variable in time. However, few studies have examined alongshore variability over short scales of kilometers or less. To observe inner‐shelf bottom temperatures with high (5‐m) horizontal resolution, a fiber‐optic distributed temperature sensing system was deployed along a 5‐km‐long portion of the 15‐m isobath within a larger‐scale mooring array south of Martha's Vineyard, MA. Over the span of 4 months, variability at a range of scales was observed along the cable over time periods of less than a day. Notably, rapid cooling events propagated down the cable away from a tidal mixing front, showing that propagating fronts on the inner shelf can be generated locally near shallow bathymetric features in addition to remote offshore locations. Propagation velocities of observed fronts were influenced by background tidal currents in the alongshore component and show a weak correlation with theoretical gravity current speeds in the cross‐shore component. These events provide a source of cold, dense water into the inner shelf. However, differences in the magnitude and frequency of cooling events at sites separated by a few kilometers in the alongshore direction suggest that the characteristics of small‐scale variability can vary dramatically and can result in differential fluxes of water, heat, and other tracers. Thus, under stratified conditions, prolonged subsurface observations with high spatial and temporal resolution are needed to characterize the implications of three‐dimensional circulation patterns on exchange, especially in regions where the coastline and isobaths are not straight.Deployment of the DTS system was made possible by the Center for Transformative Environmental Monitoring Programs (CTEMPS), with input, assistance, and software provided by John Selker, Scott Tyler, Paul Wetzel, Mark Hausner, and Scott Kobs. The authors thank Hugh Popenoe, Jared Schwartz, and Brian Guest for their technical expertise and effort with setup, deployment, and recovery of the DTS system, as well as the captains and crew of the R/V Discovery and R/V Tioga. Janet Fredericks assisted with integrating the DTS measurements with Martha's Vineyard Coastal Observatory infrastructure. Steve Lentz was instrumental in the design and deployment of the ISLE mooring array. Craig Marquette provided invaluable expertise and effort in the deployment of the ISLE mooring array. The authors thank Greg Gerbi for providing velocity data at site H and Malcolm Scully for providing velocity and near‐bottom temperature data at site E. Kenneth Brink and two anonymous reviewers provided valuable comments on the manuscript. DTS measurements were supported by the Woods Hole Oceanographic Institution. The ISLE project is supported by NSF (OCE‐83264600). T. Connolly acknowledges support from NSF (OCE‐1433716) and a WHOI postdoctoral scholarship funded by the U.S. Geological Survey and the WHOI Coastal Ocean Institute. DTS data are available on Zenodo (Connolly & Kirincich, 2018, https://doi.org/10.5281/zenodo.1136113). ISLE mooring data are available on the WHOI Open Access Data Server (Kirincich & Lentz, 2017b, https://doi.org/10.1575/1912/8740).2019-06-2