Observation of Birds on the WSR-88D

Observation of Birds on the WSR-88D
Overview

Basic WSR-88D information

Acronyms

Radar structure and theory (in 3 minutes or less)

Base data and algorithm products

WSR-88D history/deployment

Biological contamination of weather targets

WSR-88D Information

Acronyms

NEXRAD Next Generation Weather Radar (program)

WSR-88D Weather Surveillance Radar, 1988 - Doppler

OSF Operational Support Facility

Radar Structure and Theory

Radar continuously rotates through a fixed series of elevation scans

Transmits pulsed "S" band (10 cm) microwaves

~750 kilowatts
~1 microsecond
phase coherent

"Listens" for returned/reflected microwave signals

from ~10^-3 to 10^-12 watts
~1 millisecond

8+ meter parabolic antenna shapes beam to ~1 degree

Returned information analyzed for 3 basic "moments"

Radar Base Data

Reflectivity (Z) - Sum of power reflected by targets within the radar reflectivity resolution bin

Frequently displayed in decibel units (dBZ = 10 Log Z)

Resolution ~1 degree by 1 kilometer

Indicator of rainfall intensity and/or storm severity

Doppler velocity - Power weighted average radial motion (toward or away from the radar) of the targets in the radar Doppler resolution bin

Resolution ~1 degree by 250 meters

Identifies storm scale circulations (mesocyclones) that precurse strong tornadoes

Shows tornadic circulations at close range

Used to detect and track atmospheric boundary layer wind patterns related to storm initialization

Used to generate vertical wind profiles (VWP)

Spectrum width - Power-weighted distribution of the motion of the targets in the radar Doppler resolution bin.

Indicates small scale shears and turbulence

Can be used to verify the tornadic circulations at longer ranges.

Algorithm Products

Velocity Azimuth Display algorithm Wind Profile (VWP)

A sine wave is fitted to the Doppler radial velocities measured at a fixed range from the radar during a complete 360-degree azimuthal scan

The amplitude and phase of the sine wave define the speed and direction of the meanwind at the radar beam height corresponding to that fixed range

Every 5 - 10 minutes

Vertical profile of winds above radar

WSR-88D History/Deployment

1981 - NEXRAD Program Office formed to procure WSR-88D network

1988 - First WSR-88D delivered to Norman OK

1996 - WSR-88D network fully deployed

160+ radars, more than 135 within the CONUS

Biological Contamination

The idea that WSR-88D products were being contaminated by biological targets was initially met with resistance and some derision by many meteorologists.

Pre NEXRAD

Anomalous radar targets frequently termed "angels"

1988 - Initial WSR-88D installed in Norman, OK

OSF personnel note bird signatures on base data products, predominantly early morning expanding "rings" (blackbirds?) and "clumps" that moved contrary to wind patterns (egrets?)

Numerous other "anomalous" targets were noted

September, 1989

Ron Larkin presented a seminar at OSF titled "Flying Animals on Weather Radar: the Bird Hazard Algorithms," explaining several anomalies including signatures associated with widespread areas of migrating birds and insects

Beginning in the Fall, 1991 - operational deployment of WSR-88Ds

Sites began reporting significant discrepancies between the ballon-derived (rawinsonde) and the radar-based (VWP) wind profiles

Sterling VA, Houston TX, and Altus AFB OK early sites

Similar symptoms - radar wind profiles reasonable in the afternoon, then beginning to change near sunset, worsening after sunset, and then continuing through the night

Altus AFB reported a near accident caused by a false low-level wind shear alert

Early investigation determined that the discrepancies were likely caused by the radar observation of migrating birds (overwhelming the normal clear air echoes)

Various OSF scientist/supervisors disagreed, overruled that evaluation, and suggested that "another cause" be found for the discrepancies

OSF funded a national research laboratory to disprove the WSR-88D products were being contaminated by biological targets

By Summer, 1994 the biological hypothesis was accepted by OSF scientists/supervisors

In the Fall, 1995 OSF presented "Anomalous WSR-88D Wind Profiles - Migrating Birds?" at the American Meteorological Society 27^th Conference on Radar Meteorology

The reception turned from mostly disbelief to acceptance

With a few exceptions, NWS radar personnel now routinely consider biological targets as potential contaminants

"One man's meat is another man's poison"
paraphrased
One scientist's contamination is another scientist's data.