Doppler Weather Radars and Wind Turbines - Doppler Radar Observations: Weather Radar, Wind Profiler, Ionospheric Radar, and Other Advanced Applications - page 350

Possible mitigation measures for wind turbine clutter include a) placing wind turbines out
of the radar's line of sight b) reducing the wind turbines' radar cross section using stealth
material c) development and application of adaptive clutter filters, d) use of gap-filling radars
to cover areas contaminated by clutter and e) adapting the radar scan strategy to pass over the
wind turbines.
Blockage is caused by any obstacle in line of sight of a radar and is not specific to wind
turbines. For a weather radar, blockage leads to an underestimation of the precipitation
behind the blocking obstacle. Blockage caused by wind turbines is difficult to analyse using
reflectivity data due to spatial variation of precipitation and clutter tails that are generated
behind wind turbines. Model results can, however, be compared with observations of
blockage caused by stationary obstacles such as towers, masts, or wind turbines that are not
in operation.
Concepts for mitigating blockage include a) placing wind turbines radially from the radar b)
use of a gap-filling radar to cover affected areas and c) adapting the radar scan strategy to
pass over the wind turbines.
The Doppler function of a radar detects movements in echoes such as those from the rotating
blades of a wind turbine. Although such measurements are correct, the interpretation by the
radar may still be wrong. For example, an air traffic control radar may interpret echoes from
rotating wind turbine blades as a moving aircraft and a weather radar may interpret such
measurements as an approaching thunderstorm.
A weather radar uses Doppler-shifted echoes to estimate the wind speed. Doppler-shifted
echoes from wind turbine blades may therefore lead to erroneous wind measurements.
Observations of wind measurements over wind farms occasionally show extremely large
wind speeds but most often the wind measurements are close to zero. The non-synchronised
movements of the many rotor blades of a wind farm also lead to large spectrum widths.
Mitigation measures for wind measurements are the same as those presented for wind turbine
clutter.
5. References
Aarholt, E. & Jackson, C. A. (2010). Wind farm gapfiller concept solution, European Radar
Conference , EuRAD, Paris, pp. 236-239.
Agence National des Fréquences (2005). Perturbations du fonctionnement des radars
meteorologiques par les eoliennes, Technical Report Rapport CCE5 No.1 , Commision
Consultative de la Compatibilité Electromagnétique. In French.
Anon. (1890). Mr. Brush's windmill dynamo, Scientific American 63(25): 54.
Appelton, S. (2005). Design & manufacture of radar absorbing wind turbine blades, Final
Report W/44/00636/00/REP, DTI PUB URN 05/1409 , QinetiQ.
Bachmann, S., Al-Rashid, Y., Bronecke, P., Palmer, R. & Isom, B. (2010a). Suppression
of the windfarm contribution from the atmospheric radar returns, 26th Conference
on Interactive Information and Processing Systems for Meteorology, Oceanography, and
Hydrology , American Meteorological Society, pp. 81-86.