Geoscience Reference
In-Depth Information
Karlskrona
Vara
0.05
0.04
0.03
0.02
0.01
0
−0.01
Radar cells
Radar cells
Fig. 5. Median wind turbine clutter together with first and third quartiles observed by two
Swedish weather radars (Karlskrona and Vara).
Wind turbine clutter has also been observed from radar cells in which no wind turbines are
located. An example of such area effects of wind turbine clutter is shown in Fig. 6. The wind
turbine clutter in this figure comes from the same wind farm as in Fig. 4. All together this
wind farm consists of five wind turbines with total heights of 150 m above the ground. Three
of the five wind turbines are located within the same radar cell, the other two turbines each
occupy a different radar cell. In Fig. 6 it is seen that not only the radar cells in which the wind
turbines are located show an increase in clutter but also that several radar cells cross- and
downrange of the turbines are affected.
Wind turbine clutter downrange from wind turbines (cf. Figs. 6a and b) has been observed
in several other works (e.g. Crum et al. (2008); Haase et al. (2010); Isom et al. (2009); Toth
et al. (2011); Vogt et al. (2011)). Such clutter tails can be visible for tens of kilometres behind
wind turbines. No theoretical model has been put forward to explain this phenomenon but it
has been suggested that the tails are caused by multiple scattering effects (scattering between
multiple turbines and/or scattering between turbine and ground) (Crum et al., 2008; Isom
et al., 2009; Toth et al., 2011). Clutter tails are not considered a problem for wind farms located
further than 18 km from the weather radar (Crum & Ciardi, 2010; Vogt et al., 2009).
Cross-range clutter may also occur, as is seen in Figs. 6a and c. For the case shown in Fig. 6,
the cross-range clutter is a direct result of the way the reflectivities are stored in the radar data
matrix (the azimuthal resolution of the actual radar measurements is lower than the azimuthal
spacing of the data matrix). However, for wind turbines generating very strong echoes it has
been suggested that clutter may be seen well outside the half-power width of the radar beam,
generating cross-range clutter spanning tens of degrees (Agence National des Fréquences,
2005).
