A Rough Guide to the Interpretation of WSR-88D Base Reflectivity Images

From the theory of the base reflectivity it can be shown that 28*Z = average density of the targets* average radar cross-section of the targets.

A reasonable estimate of a radar bird cross-section would be 10 cm2.

We then see that the average density of targets with a cross-section of 10 cm2 in the WSR-88D beam would be given by 2.8*Z or approximately 3*Z.

The table below indicates the type of information one can estimate from the value of dBZ obtained from the base reflectivity images. I have used the value of dBZ at 46 km (the range at which the present studies were made). A similar table could be set up for dBZ at other ranges.

Density and Migration Traffic Rate (MTR) at 46 km from Buffalo

 WSR-88D dBZ WSR-88D Z Beam Density Landing Density Migration Traffic Rate Landing Density 250-950 m Birds/km3 250-950 m Birds/km2 Rate 250-950 m Birds/km/hr All Heights Birds/km2 dBZ Z 3.0*Z 2.0*Z 100*Z 4.0*Z 0 1 3 2 100 4 2.5 1.8 5.3 3.6 177.8 7.1 5 3.2 9.5 6.3 316.2 12.6 7.5 5.6 16.9 11.2 562.3 22.5 10 10.0 30.0 20.0 1000.0 40.0 12.5 17.8 53.3 35.6 1778.3 71.1 14 25.1 75.4 50.2 2511.9 100.5 15 31.6 94.9 63.2 3162.3 126.5 17.5 56.2 168.7 112.5 5623.4 224.9 20 100.0 300.0 200.0 10000.0 400.0 22.5 177.8 533.5 355.7 17782.8 711.3 25 316.2 948.7 632.5 31622.8 1264.9 27.5 562.3 1687.0 1124.7 56234.1 2249.4 30 1000.0 3000.0 2000.0 100000.0 4000.0 32.5 1778.3 5334.8 3556.6 177827.9 7113.1 35 3162.3 9486.8 6324.6 316227.8 12649.1 37.5 5623.4 16870.2 11246.8 562341.3 22493.7 40 10000.0 30000.0 20000.0 1000000.0 40000.0