Why was SoDAR chosen instead of a wind monitoring mast?

Multiple options were considered for the collection of representative wind data including Light Detection and Ranging (LiDAR), Sonic Detection and Ranging (SoDAR) and anemometry masts. Given the high energy requirements of LiDAR which required an onsite diesel generator and the potential impact to wildlife, specifically in relation to guy lines which are required for the anemometry mast, SoDAR was selected as the most accurate and least impactful solution.

The sound emitted from the SoDAR is of low frequency, which is not typically disturbing for animals. It is high frequency sounds that tend to scare birds and bats away from a site, and instruments which produce high frequency noises are typically in place at airfields to limit the bird strike risk for this reason.

There are four distinct pings emitted from the SoDAR which travel upwards in a vertical column; each ping varies in volume from the last. Sound pressure level can be described subjectively based on the dB scale.

A typical chart showing the range of sound pressure level (and typical sources of the sound) is shown below:

The pings emitted average 45dB (dBA) over 1h, and the absolute maximum peak delivered from the device is <80dBp (the remaining peaks are much lower in volume), which is well within safe hearing limits. The volume emitted is lower than the volume of HGVs passing over the nearby roads (as shown in the chart above).

At 50m distance from the device at ground level the volume is <35dB and, at 100m distance from the device at ground level, the sound is inaudible.

What is the purpose of noise monitoring equipment at the windfarm sites?

Noise monitoring equipment records the average background noise level to understand the baseline noise in an area; this can then be compared with anticipated noise levels if a design was taken to construction. This supports an Environmental Impact Assessment (EIA) and windfarm design as it informs the clearance distances between a property and the nearest wind turbine.

Because of the way sound volume levels diminish with distance, the focus will be on the closest properties. In order to ensure the spacing of turbines and overall design does not unreasonably impact on the residents of a property, the design process will ensure that noise levels at the property from the wind turbine remain below 35dBA (this is typically the volume of whispering in a library).

The equipment does not record individual sounds or record conversations; the equipment only records the volume reached.