North Hoyle Windfarm Report
5 QinetiQ radar trials 5.1 Overview There were two parts to the radar trials. The first dealt with the clutter effects on ship-borne radar and the second considered shadowing from wind turbines. The radar shadow trial involved a launch travelling along a predefined course whilst being monitored by an on-shore radar at Prestatyn. The radar clutter (spurious echoes) trial used the launch "Fast Cat" to see what effect the wind turbines have on the radar display at different ranges and gain settings. Full technical details of these tests can be found in the trials plan [2]. 5.2 Radar clutter trial results Four different positions from the centre of the wind farm were used for the spurious radar echo trial. The first position is at the centre of the wind farm. The second and third positions are 1000m and 3000m from the centre of the wind farm respectively. The fourth position is approximately 6000m from the wind farm centre. The radar screens at each of these ranges, when using different gain settings, are shown in Figure 5-1 to Figure 5-6. In all the figures the position of the launch is in the centre of the radar display, at the bottom of the vertical line. At the centre of the wind farm, the radar display when the gain is automatically set and manually adjusted is shown in Figure 5-1. It can be noted that the automatic gain setting is inappropriate in this case. The figure shows significant numbers of false plots (spurious echoes) of turbines and the beginning of ring-around (side lobe echoes). Using manual adjustment to reduce the gain from 60% to just 20%, the spurious echoes are almost removed entirely. In Figure 5-2 the radar display at the second position, 1000m from the wind farm centre is presented. Here it can be observed that at a range setting of 1/2 nm there is effectively no clutter visible. However, with a 3nm range setting there is significant clutter on the radar display. In both cases the radar gain was on the automatic setting. The radar displays at position 2 illustrate how altering settings on the radar system can improve the visible output. In this case moving to a shorter range has lowered the gain. A different pulse length is also used on this range scale. The radar displays observed at position 3 are presented in Figure 5-3. These figures show that the wind turbines are much clearer at the lower gain setting. Furthermore, in both cases there are very few false plots or evidence of side lobe break through originating from the turbines. In Figure 5-4, Figure 5-5 and Figure 5-6 the radar screens observed with gain settings of 64% (automatic setting), 54%, 44%, 34% and 24% are shown. It can be noted that the turbines are visible as discrete plots. The large region of clutter is the coastline. As the gain is reduced, the wind turbines remain on the screen although by a gain of 34% a number of the turbines have disappeared. With a gain setting of 24% the number of visible turbines has reduced significantly. It is interesting to note that the turbines that do disappear are turbines that are shadowed by other turbines. A further consequence of reducing the gain is that small targets at long range may no longer be detectable.
Figure 5-1: Position 1, the wind farm centre, with gain settings of 60% (left) and 20% (right)
Figure 5-2: Position 2, 1000m from wind farm centre, close up (left) and the whole wind farm (right) with an automatic gain setting
Figure 5-3: Position 3, 3000m from wind farm centre, 74% gain (left) 44% gain setting (right)
Figure 5-4: On route to the wind farm with 64%(left) and 54%(right) gain settings
Figure 5-5: On route to the wind farm with 44%(left) and 34% gain settings Figure 5-6: On route to the wind farm with 24% gain setting
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