June 9, 2021
Japan Renewable Energy Corporation

Offshore wind field measurement method using scanning
Doppler lidars established
Outstanding Presentation Award at Japan Wind Energy Association symposium
JRE and Professor Takeshi Ishihara of the University of Tokyo, Graduate School ofEngineering, have conducted a joint study on a new method of wind fieldmeasurement for offshore wind power generation. We were able to establish an
innovative method that enables accurate measurements and is more cost effective
than the conventional method that requires the construction of meteorological masts.
The study findings are anticipated to be of great benefit to offshore wind power
generation in the future.
JRE and Professor Takeshi Ishihara*1, the University of Tokyo, Graduate School ofEngineering, co-wrote a research paper on a study to verify the accuracy of an offshore
wind field measurement method using dual scanning Doppler lidars*2. We demonstrated
that the method offers an effective procedure for obtaining wind data to assess economic
efficiency and safety levels of offshore wind power plants. JRE employee Keiichiro
Watanabe presented the paper at the 42nd Wind Energy Symposium sponsored by theJapan Wind Energy Association (JWEA) in November 2020, and the paper was awarded
an Outstanding Presentation Award in February 2021*3.
When constructing an offshore wind power plant, it is necessary to obtain data on windconditions in the targeted sea area: wind speed, direction and turbulence intensity andvertical profiles of wind speed (i.e., wind speeds at different altitudes). The conventional
method of obtaining such data is to build a marine meteorological mast. However, thestructure requires considerable cost and time to construct, creating a major bottleneckat the early stages of project development.
In the study, we used two scanning Doppler lidars, which are more economical andquicker to install than meteorological masts, to obtain data on offshore wind speed,
direction and turbulence intensity and the vertical profiles of wind speed. The data on
wind speed and direction were then compared with those from an anemometer mounted
on a meteorological mast to ascertain the accuracy of our dual scanning Doppler lidar
method.

The study verified the usefulness of the dual scanning Doppler lidar method and resulted
in the establishment of a new way of obtaining offshore wind field measurements. The
study findings are as follows:
Data on wind speed, direction and turbulence intensity obtained by transmitting laser

beams from two onshore scanning Doppler lidars toward a single spot for fixed-point
observation provides the same degree of accuracy as data from meteorological masts.
It is also possible to obtain vertical profiles of wind speed by switching the angle oflaser beam transmission at short time intervals.
JRE will take advantage of the study findings to contribute to the advance of offshorewind power generation. At the same time, we will continue to work toward the overall
growth of renewable energy and the realization of a carbon free society.
(Click here for more information on the abovementioned paper. Japanese version only)*1

For more information on Professor Takeshi Ishihara:

http://windeng.t.u-tokyo.ac.jp/ishihara/e/*2

A Doppler lidar (DL) works by transmitting laser beams into the atmosphere. Wind

speeds are determined on the basis of the Doppler effect of light energy scattered backby airborne aerosols (solid particles and liquid droplets). A scanning DL is a DL capableof transmitting laser beams 360 degrees laterally and 180 degrees vertically. As two DLunits were used in tandem in the study, the method is referred to as dual scanning
Doppler lidar measurement.
*3

See JWEA website for the award: https://jwea.exblog.jp/30420547/ (Japaneseversion only)
Measurement methodA meteorological mast with an anemometer mounted on the highest boom wasplaced on top of a breakwater. Laser beams were transmitted toward theanemometer, and dual scanning Doppler lidar measurements were made.

Surveying was used to make adjustments so that laser emissions could be expected
to be no more than two meters off target.

For inquiries about this matter, please contact:
Japan Renewable Energy Corporation
Corporate Communications & CSR
tel:+81-3-6455-4905

email:pr@jre.co.jp