Remote Sensing of the Surface Wind Field over the Coastal Ocean via Direct Calibration of HF Radar Backscatter Power

Abstract

The calibration and validation of a novel approach to remotely sense surface winds using land-based highfrequency (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 radarmeasured power to surface winds. HF radar-based extractions of the remote wind speed had accuracies of 1.4 m s 21 for winds less than 7 m s 21, 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.

Wave Height Estimation from First-Order Backscatter of a Dual-Frequency High Frequency Radar

“…Recently, the relationship between the first-order echo power and wave height or wind speed was investigated [9][10][11]. Such a relationship was developed to calculate wave height and wind speed.…”

“…In [11], wave height at single location was estimated from the first-order radar Doppler spectra but no calibration of distance and direction dependency was considered. In [10], the same directional spreading model used in [9] were employed. However, calibration was conducted using wind data collected by a mobile Liquid Robotics Wave Glider autonomous surface vehicle, which operated for a long time in order to obtain data for most of the radar coverage.…”

A Transport Method for Restoring Incomplete Ocean Current Measurements

“…The MVCO is a unique high precision system of HF radars with 400‐m resolution that covers 20 × 20 km area south Martha's Vineyard island. Details on the MVCO HF radar can be found in, for example, Kirincich () and Kirincich et al (). Based on its robust local coverage, we use this data primarily for validation.…”

Some considerations about coastal ocean observing systems

“…The Bragg peaks used to estimate surface velocities are flanked by a weaker "second-order" continuum because of double scattering from two freely propagating waves, as well as scattering from nonlinearly bound waves. This continuum contains contributions from all ocean wave components longer than the Bragg waves, and thus the second-order part of the power spectrum can be inverted to estimate the frequency-direction spectrum of the longer waves (Hasselmann 1971;Weber and Barrick 1977;Wyatt, Ledgard, and Anderson 1997) and near-surface winds via a wind-wave model (Heron andRose 1986, Paduan et al 1999;Shen et al 2012;Kirincich 2016). Although operational wave products are available from PA systems, spatially dependent estimates of winds and waves from DF systems are still under development.…”