Geoscience Reference
In-Depth Information
Fig. 3. Wind turbine clutter caused by two wind farms near Dodge City, Kansas, at 0149 GMT
on February 23, 2007. One wind farm is located approximately 40 km to the southwest of the
radar; the other near 20 km to the northeast. Range rings in white are at 10-km spacing.
Adapted from Crum et al. (2008). This image was obtained from NOAA/National Climatic
Data Center.
>
60 dBZ) (Agence National des Fréquences, 2005; Crum et al., 2008; Toth et al., 2011; Tristant,
2006a).
<
of the observed clutter can range from barely visible (
0 dBZ) to near saturation levels (
An example of clutter, originating from two wind farms near Dodge City, Kansas, is shown
in Fig. 3. One wind farm consists of 170 wind turbines and is located approximately
40 km southwest of the radar; the other wind farm consists of 72 wind turbines, located
approximately 20 km northeast of the radar. On this otherwise clear day reflectivity values
close to 30 dBZ can be seen at the location of both wind farms.
Images such as Fig. 3 convincingly demonstrate that wind turbine clutter exists and that it
may indeed cause problems for weather radars. However, in order to obtain a quantitative
estimate of wind turbine clutter long time series of data should be studied.
In the remainder of this section we present results from a study based on long time series of
wind turbine clutter. In the study operational reflectivity data from the four lowest scans of all
Swedish weather radars were analysed over a period of more than three years (November 1,
2007 to March 31, 2011). In order to estimate the amount of wind turbine clutter observed by
the weather radars, precipitation echoes were filtered out using a custom-designed weather
filter. To further increase the quality of the wind turbine clutter, all other clutter — here
referred to as background clutter — was removed from the weather-filtered reflectivity data.
Finally the wind turbine clutter (z) was converted to rain rate (R) assuming the relation
z
200
R
1.5
(Michelson et al., 2000).
=
The weather filter removed precipitation echoes from the lowest elevation angle by comparing
reflectivity data cellwise to reflectivities froma higher elevation angle. If an echo froma higher
