Performance analysis of Mitsubishi Electric's wind lidar in the measurement campaign at European test sites

Introduction

The efficient wind resource assessment needs (a)cost-effective measurement, (b)many wind information(ex. vertical profiles) (c)stable data obtaining, and so on. Recently, for realizing above needs, the wind lidar is expected to apply to the wind resource assessment. However, conventional wind lidar systems have an issue in the instability of performance, since signal-to-noise ratio (SNR) related to measurable range depends on the atmospheric condition such as the aerosol density, turbulence, and so forth. To overcome this issue, we developed the wind lidar system, DIABREZZA(TM) in 2013 with the adapting parameters function, which automatically realize the best performance under the given atmospheric condition for obtaining high data availability. In this presentation, we demonstrate advantageous of the above mentioned functions with the results of measurement campaign in European test sites.

Approach

In the previous wind lidar system, the constant parameters, for example, (1) laser beam focusing distance and (2) number of accumulation of received signal that can contribute improving the measurable range, are used for each observation. Therefore, the data availability of lidar is severely influenced by the atmospheric condition, for example, in the case of low aerosol density (low backscatter coefficient). On the other hand, the signal processor of this lidar derives the best parameters of above mentioned (1) and (2) automatically, using obtained range profile of SNR upon user’s request. This improves the performance of lidar, especially for the data availability which offers an advantage to the wind resource assessment.

Main body of abstract

To realize this concept, we newly developed (1) the optics of which the laser beam focusing distance can be optimized automatically, and (2) the signal processor which optimizes the measurement time interval by changing the number of accumulation. The laser beam focusing distance can be tuned from a few tens of meters to infinity. The signal processor analyzes the range (height) dependence of SNR and automatically tunes these parameters. We performed the evaluation of this lidar in the actual wind sensing, and compared the height dependence of data availability "before" and "after" the automatic adapting parameters.
Using developed new vertical wind profiling lidar (velocity azimuth display (VAD) lidar) which has the concept of the automatic adapting parameters function, we have carried out the measurement campaigns in cooperation with Dong Energy (Denmark), DTU (Denmark), EOLFI (France), and ECN (Netherlands), etc.
The example of some campaign results is as bellows,
The slope and offset of wind speed at 100m is 1.0006 and +0.029 m/s, respectively.
The slope and offset of wind direction at 100m is 0.990 and +1.515deg, respectively.
The data availability at 430m height is 84.3% (in case that without above function, the availability is 55.9 %). (note)430m height is the highest altitude in that campaign


Conclusion

We developed a new concept of wind lidar system with automatic adapting parameters function. Moreover, we have carried out the measurement campaign in Europe. Consequently, the good results in accuracy and data availability have been obtained for each campaign. We could confirm that these functions provide the lidar performance which fits best to the user’s needs. Especially, this function is very powerful to keep high data availability even in severe atmospheric conditions for lidar (for example, low aerosol density conditions). Therefore, it could contribute the stable measurement for wind resource assessment.


Learning objectives
Since our work contributes to the better wind sensing devices, the wind farm developers and consultant companies, who need better tool for wind resource assessment, can have benefits for participation in this conference.