Radar ornithology adds to wind farm data gathering

Copyright ©2002, The Martha’s Vineyard Times. Reprinted with permission.

By Matt Pelikan

Anyone visiting Cape Poge or boating in adjacent waters recently could hardly have missed the presence of a radar installation perched on the north-facing cliff near the Cape Poge lighthouse. No, it isn’t a high-tech attempt by derby fishermen to zero in on breaking bonito; rather, it’s an innovative effort to study bird activity over Nantucket Sound. The radar has been in place throughout September; a previous, five-week phase of the study took place last May and June. The project is taking place with the cooperation of the Trustees of Reservations, which has substantial conservation holdings on Chappaquiddick.

The purpose is not just to gratify idle curiosity. The radar is collecting data for the exhaustive review process for a proposed wind farm in Nantucket Sound. A Yarmouth-based company, Cape Wind Associates, hopes to erect a phalanx of 170 wind turbines on Horseshoe Shoal, a shallow portion of the sound northeast of the Vineyard. Anchored in the sea floor and rising more than 400 feet from the ocean surface to the tops of the arc of their blades, the turbines of the proposed project would derive electricity from the rarely faltering winds that sweep these waters. The project would represent a significant source of renewable energy: Cape Wind estimates that with strong winds cranking the turbines up to their maximum output, the proposed wind farm could produce an amount of electricity almost equaling the combined demand of the Cape and Islands.

Although virtually everyone acknowledges the merits of renewable energy sources, objections to this specific proposal have come from many quarters. Among the concerns is the possibility that birds could be killed, conceivably in large numbers, by collisions with the pylons or the turbine blades themselves. Birds of many kinds unquestionably cross Nantucket Sound by the thousands during migration, and some rare species, like the threatened roseate tern, frequent these waters. But while decades of observations have produced a sense of the numbers and species of birds moving between the Cape and the Island, little is known about the precise paths they follow or the altitudes at which they travel — vital questions for assessing what impact the wind farm might have on birds.

Mark Rogers, a spokesman for Cape Wind, said the company is serious about “filling in some of the gaps in our knowledge of the patterns of movements of birds” and will spend about $400,000 on avian research “to really get a handle on what the bird activity is in Nantucket Sound.” For example, Mr. Rogers said that migrating songbirds typically fly between 1,000 and 5,000 feet off the ground, which would put them safely above the turbine blades. But do they fly that high when crossing water, and how soon after taking off from Cape Cod do they reach cruising altitude? Does weather affect the height at which they fly? To address questions like these, Cape Wind Associates hired Avian Radar, a division of Florida-based Geo Marine, to conduct radar surveys of birds flying over the sound.

Technical and Innovative
The radar system in place on Cape Poge leavens standard technology with innovation. One radar antenna, roughly eight feet across and mounted on 16-foot tower, rotates in the normal horizontal plane; a second unit, on a somewhat lower tower, rotates in the vertical plane, like a pinwheel. According to Avian Radar’s Edward Zakrajsek, the identical units are essentially off-the-shelf radars made by Furuno, a well-known marine electronics manufacturer, for use on large seagoing vessels. Adjacent to the towers, a 20-foot-long trailer houses computers, a tiny office, and an onboard generator.

However, instead of simply displaying data on a screen like a standard marine unit, these radars have been modified to input data directly into desktop computers. Operating 24 hours a day, unless halted for maintenance or repairs, the radars pump a continuous record of what they see into a gigantic database. For each target, 23 separate attributes, such as size, shape, and reflectivity, are recorded, Mr. Zakrajsek said. Under ideal conditions, the horizontal unit can spot birds as far as six nautical miles away; together the two units can determine the position, altitude, and speed of nearly everything moving over a wide swath of Nantucket Sound.

The amount of data produced during the month-long monitoring period will be enormous (two PCs are needed to receive the data just from the horizontal antenna, according to Mr. Zakrajsek). To make sense of this mountain of information, Avian Radar has developed computer programs that automatically recognize characteristics marking a radar blip as, say, an airplane, a dragonfly, or a bird. Once the results have been fully processed, researchers believe, the project will yield a detailed count of every bird that crossed the study area, from sea level to about 8,500 feet.

Studies of coastal bird migration, especially of large birds such as ducks and gannets, have been conducted for years using human observers, positioned on good vantage points and counting or estimating how many birds fly past. This method has its advantages, according to Jeff Burm of Environmental Science Services, the company retained by Cape Wind to assess possible environmental impacts of the wind farm. For one thing, experienced human observers can precisely identify flying birds and determine what type of activity they are engaged in. But there are drawbacks to human counters, as well. Under foggy conditions, or at night (when most songbird migration takes place), only imprecise counts based on the numbers of birds heard calling are possible. And human counters are subjective: different observers often come up with widely varying estimates of the size of a flock or the altitude at which it is flying.

Radar, in contrast, is undeterred by darkness. And, just as important, it is more consistent than human observers.

“Although radar has biases,” said Avian Radar’s Edward Zakrajsek, “they can be measured and they stay constant,” making it much easier to factor in corrections. Because of its objectivity and reliability, radar is gaining a prominent place in the study of bird movements. For example, the National Oceanographic and Atmospheric Administration’s nationwide network of weather radar has proven to be a powerful tool for detecting and even estimating the numbers involved in large-scale movements of migratory birds. And a number of projects have used portable radar to study birds concentrating in nocturnal roosts.

One of Several Study Efforts
Cape Wind’s Mark Rogers emphasizes that radar is only one tactic being used to study birds on Nantucket Sound.

“We are also doing more conventional studies with human observers operating from boats or airplanes,” he said, to verify some of the radar data and add additional information about the species involved. But the ability of radar to count birds 24 hours a day appears to give the Cape Poge installation particular importance. Measures such as building pylons that lack attractive perch sites and coloring rotors with bright or contrasting patterns reduce the impact modern wind farms have on diurnal birds, which can usually see and avoid the hazard. But towers of all kinds can pose risks for birds migrating at night — when human data collectors are at their greatest disadvantage. So, for estimating the likely effects of the Cape Wind project, reliable counts conducted at night are both especially important and especially hard to perform by traditional methods.

While existing technology is impressive, Mr. Zakrajsek described even more ambitious plans for the future. Work is underway to give radar the capacity not just to count birds, but to identify them. Environmental Science Service’s Jeff Burm noted that one facet of the Cape Poge project involves having ground-based observers identify birds as they are being recorded by radar. By linking the characteristics of radar signatures with the known identities of particular birds, researchers hope to give computers the ability to reliably recognize at least the general family to which a bird belongs. The Cape Poge radar can’t separate closely related species such as common and roseate terns, according to Mr. Burm, but it readily picks out birds like gannets that are distinctive in size, shape, or manner of flight.

The results of the Cape Poge radar study will be scrutinized during the wind farm review process. And data on current bird movements may not remove concerns about how the turbines, if built, might alter the behavior of birds. But with its innovative combination of newfangled radar and old-style human observers, the Cape Poge project illustrates the vast potential of the emergent field of radar ornithology. And it will undoubtedly furnish the most detailed picture ever of what goes on over Nantucket Sound.