Roost Rings via Regular and Dual Polarization Radar Images

Early morning radar imagery can sometimes show birds as they take off from area waterways.  These echoes are referred to as "roost rings".  A loop of the images show the rings getting larger as the birds get further away.

The image below shows an example that occurred shortly before 6 am on Thursday, August 14.  Rings were seen around Lake Vermilion near Danville, around Lake Mattoon, and also Meredosia Lake along the Illinois River.  The top left panel is the standard radar image you are used to seeing. The remaining panels are dual polarization images (created in an analysis of the horizontal vs vertical components of the radar beam). The top right is a radar product called differential reflectivity (difference between the power returned for the two components); the green and red shades around these rings show the larger differences. The lower right product is called correlation coefficient, and measures how similar the two components of the radar beam behave from pulse to pulse. The blue and green shades show biological targets. (The lower left panel, specific differential phase, is not computed for non-meteorological echoes.)


Roost rings on radar image

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