Environmental Engineering Reference
In-Depth Information
detected bird flocks (and other moving targets such as boats and planes). To do this
surveillance radars have what is known as an echo trail feature. This feature makes
each radar point location visible for a given amount of time, allowing a trail, or
trajectory, to be built up of the target being tracked. Each echo on the radar monitor
corresponds to a single bird or a flock in the study area, and in this way the spatial
pattern of bird movement in the area was described during both the day and night.
At the outer limits of radar detection, only large flocks were able to be detected.
Weather also affected the distance at which the radar could detect passing birds.
In addition, “clutter”, for example breaking waves offshore and prominent hills and
ridges onshore, tended to mask trail detection to varying degrees. Additionally,
horizontal radar cannot determine the height birds are flying, and coverage is limited
to a degree by the relief of the surrounding land and the roughness of the sea. These
various weaknesses in the use of radar were addressed by using observers on the
ground to supplement radar data. In addition an extensive terrain modelling analysis
was commissioned to determine potential non-detection due to terrain topography
as well as radar clutter.
Observers were positioned at strategic stations to provide the optimal view over
each proposed turbine cluster and to provide a view of areas that the radar could not
“see”. Visual observations of flocks provided supplemental data on flock movement
patterns for comparison with radar and allowed confirmation of the validity of the
survey technique. Observers and radar stations were linked by radio in order to
communicate about bird/flock direction, number and species. Each trail was given a
unique code when first sighted by which all three radars and all observers could
track a flock through the wind farm.
Throughout each survey, radars were run for an average of 12 h per day for
5 days a week, with a 24 h run being conducted once a week. Field observers
initially worked between 7.00 am and 7.00 pm, but this was modified with each
subsequent survey as patterns in the timing of peak migration emerged between the
winter and summer seasons and indicated that a shift in observation periods would
give better coverage. Although, the observers did not work the same hours as the
radar stations, the correlation of the daytime observation data with radar data
collected during these periods provided a sample from which trends in the types of
species moving through the site, flock size, flock species mix (generally SIPO but
sometimes wrybill and also red knot were also observed in a mixed flock) and from
which flock flight heights were determined. In addition, running the radar 24 h a day
gave an overall indication of the total number of birds moving through the site.
Several 60 m high metrological masts provided useful reference points for
observers to determine flock flight height. In addition, training was provided for all
observers using model aircraft of a similar size to SIPO. With sufficient training it
was found that observers could provide height estimates within a 10 m range.
The metrological masts also provided real time data from which the effects of
climatic factors on flock direction and height as they flew through the site were able
to be determined.
