Publishers version - DTU Orbit

Figure 2: Calibration, laboratory work, and real-time Doppler spectrum obtained at Risø DTU
with the experimental bi-static CW sodar “Heimdall” (Mikkelsen et al., 2007). Upper panel:
Combined acoustic horn and parabola antenna for high-yield (+30 dB gain) backscatter receiving
of sound waves. Middle panel: Two researchers at the Risø DTU Laboratory while
testing of the bi-static sodar. Lower panel: A real-time obtainable continuous Doppler spectrum
Heimdall bi-static sodar from wind measurements at 60 m above Risø DTU
static sodar configurations exist as well, where the transmitter and receivers are separated
e.g. 100–200 meters on the ground.
Bi-static configurations have significant C/N-ratio advantages over mono-static configurations
for wind energy applications. Received backscatter in a bi-static configuration is not
limited to direct (180 ◦ ) backscatter from temperature (density) fluctuations only, but enables
also backscatter contributions from the atmospheric turbulence. And the higher the wind
speed the more turbulence.
As a consequence significant improvements of the C/N- ratios can be obtained from a socalled
“bi-static configuration”, in which the transmitter and the receiver are separated from
one another on the ground. This becomes in particular relevant during strong wind situations,
where the background noise level increases with the wind speed.
A particular configuration considered for wind energy applications is therefore the bi-static
continuous wave (CW) sodar configuration. Alternatively to the range gating in a pulsed
system, the range to the wind speed measurement in a CW system can be determined by
well-defined overlapping transmission and receiving antenna functions. At Risø DTU we have
build and investigated such a sodar system for wind energy applications.
1.2.1 RS applications within Wind Energy
Remote sensed wind speed measurements are needed to supplement and extend tall met mast
measurements, on and offshore, and within research to evaluate various wind flow models and
wind atlases for a number of purposes, including:
1. Wind resource assessments
2. Wind park development projects
3. Power curve measurements
4. Bankability
5. Wind model and wind resource (wind atlas) uncertainty evaluation
The common denominator in most of these issues is high accuracy, and with a demand
for reproducible certainty to more than 99% of what can be achieved with a corresponding
DTU Wind Energy-E-Report-0029(EN) 13