Validation of Bird Movement Signatures in Weather Radar Wind Profiles using a Dedicated Bird Radar

It is well known that non-hydrometeor targets such as insects and birds are also detected by Doppler weather radar. While some insects can provide a help in defining the boundary layer wind, birds and actively flying insects, like moths or grasshoppers, are a major source of error for wind retrieval algorithms. Alternatively, Doppler weather radar can be employed to study bird movements and flight behavior of insects in the atmosphere.

KNMI operates two C-band Doppler weather radars which are, amongst others, used for obtaining wind profiles. An extensive quality control of the radial velocity and wind vector data is applied during the retrieval of the wind profiles.

RNLAF employs a Flycatcher tracking radar which is modified to operate as a dedicated bird radar. The radar is performing both PPI scans and RHI scans perpendicular to the main direction of the bird migration. The PPI scans provide speed and flight-direction data, while the RHI scans provide the bird densities at various altitudes. The distance between the KNMI and RNLAF radars is approximately 80 km.

Here we present a quantitative comparison of "wind data" from the Doppler weather radar with data from the dedicated bird radar over a period March to May 2003. It is found that the standard deviation of the radial velocity can be used to separate the profile data from the Doppler weather radar into "true" wind vectors and bird movement vectors. This implies that high quality wind vector data, i.e., without bird signatures, can be obtained. Moreover, our results show that the profiles from Doppler weather radars contain information on the temporal and vertical distribution of migrating birds. This creates an opportunity for developing a warning system for avoiding airplane-bird strikes, based on Doppler radar networks.