(IVAR) - Final Report - Strategic Environmental Research and ...

Comparing the performance of dish vs. array antennas is complicated due to the complexity of
the radar equation. While the large vertical beam width of the array antenna (nominally 20°)
may seem attractive for sampling larger volumes of the sky, it illuminates the ground directly
and hence must deal with much more clutter – and clutter is the dominant limiting factor in
detecting birds with marine radars. Dish antennas on the other hand are usually raised a couple
degrees above the ground, and hence have much less ground clutter to deal with. In typical
installations, radars using dish or array antennas will actually detect and track similar numbers of
birds.
However, like all radar systems, avian radars must be optimized to meet the requirements of the
tasks at hand. If those tasks require knowing the altitude of the targets in exchange for a slight
decrease in horizontal resolution, then dish antennas can provide height information that array
antennas, because of their broad 20° vertical beam width, cannot.
Conclusion
The studies summarized in this section demonstrate successful performance of the metric for
PA1.1; namely, that visual observers were able to confirm at three geographic locations that at
least 100 targets tracked by the Accipiter® DRP were birds, both single birds and flocks of two
or more. During the spring 2007 studies, 915 targets were confirmed to be birds at three
locations, while in the fall 2008 studies 616 were confirmed at four locations.
6.1.1.1.2 Validation by Thermal Confirmation
Methods
The detailed descriptions of the methods for using thermal imagery to confirm targets being
tracked by an avian radar are presented in Appendix B. We employed those methods and a
Thermal Imager-Vertically Pointed Radar (TI-VPR; Gauthreaux and Livingston 2006) system to
confirm the identification of targets tracked by an eBirdRad avian radar unit at night and during
the day at Edisto Island, South Carolina in the fall of 2008. The procedure cross-validated the
radar data gathered with eBirdRad with respect to type of target (i.e., bird, bat, insect), density of
targets, altitudinal distribution of targets, and direction of movement.
Figure 6-3 shows the positions of the eBirdRad and the TI-VPR units at the study location. The
eBirdRad radar was the same as those used elsewhere in IVAR validation studies: a Furuno FR-
2155BB with an Accipiter® DRP. However, the parabolic antenna employed at Edisto Island
had a beam width of 2.5°, whereas the other eBirdRad units have a 4° beam parabolic antenna.
72