Investigation of the Fetch Effect Using Onshore and Offshore Vertical LiDAR Devices

Susumu Shimada,Yuko Takeyama,Teruo Ohsawa,Satoshi Nakamura,Tetsuya Kogaki

doi:10.3390/rs10091408

Abstract

An offshore wind measurement campaign using vertical light detection and ranging (LiDAR) devices was conducted at the Hazaki Oceanographic Research Station (HORS) as part of an investigation into determining the optimal distance from the coast for a nearshore wind farm from a meteorological perspective. The research platform was a 427 m long pier located on a rectilinear coastline on the Pacific coast of the central Honshu Island in Japan. The relationship between the ratios of the increase of wind speed near the surface and fetch length within 5 km of the coast was analyzed via LiDAR observations taken at heights from 40 to 200 m. The results showed that the speed of the coastal wind blowing from land to sea gradually increased as the fetch length increased, by approximately 15–20% at 50 m above sea level around a fetch length of 2 km. Moreover, empirical equations were derived by applying the power law to the relationship between the increase of wind speed and fetch lengths at 1–5 km, as obtained from the LiDAR measurements. It was also found that the wind speed increase at a 2 km fetch length was equivalent to the effect of a 50–90 m vertical height increase on the coast in this region.

Highlights

In addition to the light detection and ranging (LiDAR) over the sea on the Hazaki Oceanographic Research Station (HORS) research platform, another LiDAR was deployed on land to investigate coastal wind modifications, which is known as the fetch length effect, by comparing the onshore and offshore LiDAR observations
As part of efforts to obtain additional offshore wind observations for the New Energy and Industrial Technology Development Organization, the Offshore Wind Information System (NeoWins) project [1], a coastal wind measurement campaign using light detection and ranging (LiDAR) was conducted from October 2015 to December 2016 at the Hazaki Oceanographic Research Station (HORS) [2] operated by the Port and Airport Research Institute in Japan’s Ibaraki Prefecture
Some previous studies [5,6,7] have shown that offshore winds simulated by Weather Research and Forecasting (WRF) near the coast, where offshore wind farms are likely to be located in Japan in the near future, are less accurate than those simulated over the open ocean

Summary

Introduction

In addition to the LiDAR over the sea on the HORS research platform, another LiDAR was deployed on land to investigate coastal wind modifications, which is known as the fetch length effect, by comparing the onshore and offshore LiDAR observations. The increase in wind speeds around wind directions of 155◦ and 325◦, which might be associated with the fetch length effects, declined to a few points at 207 m height ASL.

Results

Conclusion