Discrimination of Bird and Insect Radar Echoes in Clear Air Using High-Resolution Radars

Abstract

The source of clear-air reflectivity from operational and research meteorological radars has been a subject of much debate and study over the entire history of radar meteorology. Recent studies have suggested that bird migrations routinely contaminate wind profiles obtained at night, while historical studies have suggested insects as the main source of such nocturnal clear-air echoes. This study analyzes two cases of nocturnal clear-air return using data from operational Weather Surveillance Radar-1988 Doppler (WSR-88D) and X-and W-band research radars. The research radars have sufficient resolution to resolve the echo as point targets in some cases. By examining the radar cross section of the resolved point targets, and by determining the target density, it is found for both cases of nocturnal clear-air echoes that the targets are almost certainly insects. The analysis of the dependence of the echo strength on radar wavelength also supports this conclusion.

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

“…Angevine (1997) reports a downward bias in mean UHF profiler vertical velocities up to 0.3 m s −1 in the daytime PBL due to the subsidence of particulate scatterers, and Geerts and Miao 2005 show that insects can actively oppose PBL upward vertical motions. Concentration of insects in the southern Plains peaks in the mid-afternoon and overnight, with minima near sunrise and dusk (Martin and Shapiro 2007). We estimate a similar diurnal insect pattern at our study location, based on informal inspection of ARMOR dual-polarimetric data over several years.…”

“…Insects are widely acknowledged as the main generator of clear-air radar return in the PBL, and birds can also contaminate radar velocities (e.g. Wilson et al 1994;Martin and Shapiro 2007). Angevine (1997) reports a downward bias in mean UHF profiler vertical velocities up to 0.3 m s −1 in the daytime PBL due to the subsidence of particulate scatterers, and Geerts and Miao 2005 show that insects can actively oppose PBL upward vertical motions.…”

An Objective Prototype-Based Method for Dual-Polarization Radar Clutter Identification

“…For Doppler radar data, insect echoes are a passive tracer for air motion. However, birds/bats have different Doppler velocity characteristics from wind fields [32][33][34]. Zhang et al [35] and Liu et al [36] identified the velocity contamination of migrating birds for WSR-88D radars.…”

Aviation Bird Hazard in NEXRAD Dual Polarization Weather Radar Confirmed by Visual Observations

“…It is typically presented in units of dBZ-decibels of reflectivity. However, non-precipitation objects in the environment can also reflect microwave radiation and have been documented in weather radar, including birds, insects, and bats (Martin and Shapiro, 2007), ashes in smoke plumes (Jones, et al 2009), tornado debris (Magsig & Snow 1998;Burgess, et al 2002, Ryzhkov, et al 2005, chaff (Maddox, et al 1997), and ground-based objects such as trees, buildings and even wind turbines (Isom, et al 2009). Collectively, these are known as "clear-air echoes."…”

“…There is controversy, in fact, about whether some clear-air echoes are birds or insects. When radar is used in the emerging scientific discipline of aeroecology (Chilson, et al 2012), Martin and Shapiro (2007) point out that ornithologists are biased toward the interpretation that the targets are birds, while entomologists are likely to assume they are insects.…”