Mid-Atlantic Baseline Studies: Aerial Surveys

High resolution digital video aerial surveys are a new method for collecting distribution and relative abundance data on animals. HiDef Aerial Surveying. Ltd., a company that developed this approach in the United Kingdom, conducted the surveys for this study. Our study was the first to use these methods on a broad scale in the U.S. 

Surveys were flown in small twin-engine airplanes at 250 km/hr and an altitude of 610 m, which is much faster and higher than traditional visual aerial surveys (flown at altitudes of 60-180 m). Flying at this higher altitude is safer for the flight crew and less disruptive to the animals being counted. We conducted 15 surveys over two years (March 2012–May 2014) along 2,857 km of transects (3,601 including the expansion in Maryland). Four belly-mounted cameras recorded video data, resulting in a 200 m wide transect.

This diagram shows the field of view available during digital video aerial surveys. The twin-engined aircraft flew at an altitude of 610 m with four cameras pointing at an angle to the ocean’s surface; the combined strip width for all four cameras was 200 m.

The study areas for the Mid-Atlantic Baseline Study and Maryland study, with Wind Energy Areas (WEAs) and aerial survey transects. Fine scale aerial transects (20% coverage) were carried out within the WEAs and the Maryland study area.

Video data were analyzed by two teams of observers who located and identified objects in the footage. These processes included multiple quality control procedures. Flight heights were estimated for flying animals using an estimate of parallax.

• Hatch SK, Connelly EE, Divoll TJ, Stenhouse IJ, Williams KA (2013) Offshore observations of eastern red bats (Lasiurus borealis) in the mid-Atlantic United States using multiple survey methods. PLoS One 8(12):e83803. doi:10.1371/journal.pone.0083803 
• Thaxter CB, Burton NHK (2009) High definition imagery for surveying seabirds and marine mammals: a review of recent trials and development of protocols. British Trust for Ornithology Report Commissioned by COWRIE Ltd.