10.5061/DRYAD.45GB4
Urmy, Samuel S.
Stony Brook University
Warren, Joseph D.
Stony Brook University
Data from: Quantitative ornithology with a commercial marine radar:
standard-target calibration, target detection and tracking, and
measurement of echoes from individuals and flocks
Dryad
dataset
2017
Radar
Ornithology
Sterna dougallii
radar cross-section
Sterna dougalli
Sterna hirundo
2017-10-26T00:00:00Z
2017-10-26T00:00:00Z
en
https://doi.org/10.1111/2041-210x.12699
686768877 bytes
1
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Marine surveillance radars are commonly used for radar ornithology, but
they are rarely calibrated. This prevents them from measuring the radar
cross-sections (RCS) of the birds under study. Furthermore, if the birds
are aggregated too closely for the radar to resolve them individually, the
bulk volume reflectivity cannot be translated into a numerical density. We
calibrated a commercial off-the-shelf marine radar using a standard
spherical target of known RCS. Once calibrated, the radar was used to
measure the RCS of common and roseate terns (Sterna hirundo L. and Sterna
dougallii Montagu) tracked from a land-based installation at their
breeding colony on Great Gull Island, NY, USA. We also integrated echoes
from flocks of terns, comparing these total flock cross-sections with
visual counts from photos taken at the same time as the radar
measurements. The radar's calibration parameters were determined with
1% error. RCS measurements made after calibration were expected to be
accurate within ±2 dB. Mean tern RCS was estimated at -28 dB relative to
one square meter (dBsm), agreeing in magnitude with a simple theoretical
model. RCS was 3-4 dB higher when birds’ aspect angles were broadside to
the radar beam compared with head- or tail-on. Integrated flock
cross-section was linearly related to the number of birds. The slope of
this line, an independent estimate of RCS, was -32 dBsm, within an order
of magnitude of the estimate from individual birds, and near the middle of
the frequency distribution of RCS values. These results indicate that a
calibrated marine radar can count the birds in an aggregation via echo
integration. Field calibration of marine radars is practical, enables
useful measurements, and should be done more often.
Raw radar files from tern colony on Great Gull Island, NYZipped archive
containing 200 raw radar sweeps recorded as NetCDF files on 22 July 2014
on Great Gull Island, NY. Each file contains a single sweep of the
radar's antenna, with three variables. The variable
"amplitude" contains 2-D array of radar reflectivities in polar
coordinates. Amplitudes are recorded as 16-bit signed integer values from
the digitizer: to convert them to voltages, divide by the variable's
"max_counts" metadata value (which is equal to 32764 for all
files in this archive). The other two variables, "pulse_number"
and "range", are the values corresponding to the amplitude
array's azimuth and radial axes. Analysis scripts for these files are
found in the article's supplementary online information.raw_radar.zip
New York
Block Island Sound
Long Island Sound
72.1192W
41.2018N
Great Gull Island