- Geo-Marine, Inc. (GMI) conducted an offshore avian radar baseline study for Oregon Wave Energy Trust (OWET) for a wave energy study located northwest of Reedsport, Oregon from 25 August through 29 October 2010. The study was conducted from shore with GMI’s Mobile Avian Radar System (MARS®). The MARS® was equipped with a 3-centimeter (cm) wavelength 50-kilowatt (kW) radar with a 2.5-degree (°) parabolic antenna for horizontal scanning, and a 3-cm, 25-kW radar with an open array antenna for vertical scanning. Diurnal land-based nearshore and diurnal and nocturnal boat-based radar validation surveys were conducted specifically to determine whether the radar could detect birds flying at low attitudes above the water.
Comparison between the nearshore and offshore (study area) observer bird passage rates and the nearshore and offshore radar passage rates revealed low correlation between diurnal observations and radar data. The correlation analysis values were all too low (<.307) to develop a correction factor to apply to the radar data.
Sea clutter was identified as the limiting factor. When algorithms to reduce false tracks from sea clutter were applied, tracks of real birds were eliminated because they could not be separated from sea clutter false tracks. At present there is no technology known that can accurately remove bird detections from sea clutter. This problem was further magnified in this study because radar visual validation surveys revealed that a major portion of the bird movement both nearshore and offshore occurred at altitudes from 1-30 feet (ft) above sea level. At that altitude it is impossible to separate birds from wind-driven waves and high swells that are common in the study area during fall. The visual validation data documented that the radar was ineffective when birds were flying close to the surface.
In addition to providing data to facilitate passage rate comparisons between observer and the radar, the radar validation surveys provided data on bird flight behaviors within and adjacent to the study area. These data, which were requested to be collected for this study, included information on nearshore and offshore (study area) bird species occurrence, passage rates, flight altitudes and speeds, flight directions, and flock sizes.
During the diurnal land-based nearshore avian surveys 43 bird species were identified; 32 bird species were observed during the boat-based offshore surveys. One federally-listed bird species, Marbled Murrelet (threatened), was observed occasionally during nearshore and offshore surveys.
Diurnal nearshore bird passage rates ranged from 30-390 birds/nautical mile (NM)/hour (hr) from 0 to 1 NM offshore and from 10-142 birds/NM/hr from 1 to 2 NM offshore. Offshore (study area) passage rates ranged from 142-268 birds/NM/hr; offshore nocturnal passage rates ranged from 3-53 birds/NM/hr.
The majority of birds flying over both nearshore (94%) and offshore (93%) waters were flying from 1-100 ft above sea level (asl). The majority of these birds were flying from 1-30 ft asl (nearshore, 75%; offshore, 83%). The dominant flight directions were to the south and the majority of birds sighted were in the 1-5 flock category.
This Avian Radar Baseline Study was contracted to assist in collecting data that could potentially be used to meet these requirements. Avian radar validation surveys were designed specifically by GMI for this study to determine the accuracy of the radar data in predicting the number of birds that would potentially collide with the 30-ft tall wave buoys. The results of the avian radar validation surveys from this study indicate that avian radar is not able to collect accurate altitude flight data within the potential bird-wave power buoy collision zone (1-30 ft asl) because of the presence of sea clutter (high wind waves and/or swells) in the study area; however, diurnal avian radar validation bird survey data collected from shore and from a boat in the study area provided information requested by the Scope of Work including on nearshore and offshore (study area) species occurrence, avian passage rates (number of bird tracks/NM/hr), frequency of avian flight altitudes within and above the bird-wave power buoy collision zone, flock size frequency, and flight direction frequency. In addition, a nocturnal thermal imaging camera was used to conduct nighttime avian studies and provided data on nighttime bird passage rates.
GMI recommends, based on the findings of this Avian Radar Baseline Study, that seasonal radar studies recommended by the FERC Study Plan be replaced with diurnal boat surveys and nocturnal boat surveys using stabilized remote sensing technologies (e.g., thermal imaging, high definition cameras). These methods will, in GMI’s opinion, provide the best data on nocturnal passage rate (bird abundance) and altitude use within the potential bird-wave power buoy collision zone (1-30 ft asl).