Mobile laboratories equipped with marine radars were used to study the intensity altitude (above 25m), direction, behavior and ground speed of migrating birds in Alaska, Minnesota and South Dakota. A screen to reduce clutter on the radar display resulting from echoes of surrounding vegetation and other objects was developed. Other modification, including disengagement of the antenna motor use of a side-lobing shield and replacement of the slotted waveguide with a parabolic antenna, improved the system's ability to obtain information on flight altitudes. New features available on radars, such as the color monitor, alarm function, echo stretch function and plotting function, improved the radar system's ability to obtain information on movements of birds.
An improved marine radar system for studies of bird migration
Cooper, B.; Day, R.; Ritchie, R.; Cranor, C. (1991). An improved marine radar system for studies of bird migration. Journal of Field Ornithology, 62(3), 367-377.