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115
NOUS41 KWBC 141808
PNSNMC
NATIONAL TECHNICAL INFORMATION MESSAGE 96-21...PART 1 OF 2
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
210 PM EDT WED AUG 14 1996
TO - TO WIND PROFILER DATA USERS
FROM - FREDERICK S. ZBAR...CHIEF...TECHNOLOGY AND FORECAST
SYSTEMS CORE...OFFICE OF METEOROLOGY
SUBJECT - NEW QUALITY CONTROL PROCEDURES TO IDENTIFY MIGRATING-
BIRD ERRORS IN PROFILER WINDS...EFFECTIVE 0000 UTC
AUG 15 1996
...PART 1 OF 2-PART MESSAGE...
THE 404 MHZ WIND PROFILER NETWORK OPERATED BY THE NATIONAL
OCEANIC ATMOSPHERIC ADMINISTRATION/S FORECAST SYSTEMS LABORATORY
IN THE CENTRAL USA IS IMPLEMENTING A NEW QUALITY CONTROL /QC/
ALGORITHM EFFECTIVE 0000 UTC AUGUST 15 1996. THE ALGORITHM AND
DETAILS OF THE CHANGES ARE DESCRIBED BELOW.
ON AUGUST 15 1996...A QC ALGORITHM WILL BE IMPLEMENTED ON
THE HOURLY WINDS FROM THE NOAA PROFILER NETWORK /FORMERLY CALLED
THE WIND PROFILER DEMONSTRATION NETWORK/. THE ALGORITHM IS
DESIGNED TO FLAG WINDS THAT ARE SUSPECTED OF BEING BIASED IN WIND
VELOCITY OR DIRECTION BY MIGRATING BIRDS. THE ALGORITHM IS
APPLIED ONLY AT NIGHT...ONLY BELOW 4.5 KM ABOVE MEAN SEA LEVEL
/BELOW ABOUT 570 MB OR 15000 FEET/...AND ONLY DURING THE SPRING
AND FALL MIGRATION PERIODS. NO CHANGE TO THE NATIONAL WEATHER
SERVICE AFOS DISPLAY SOFTWARE FOR PROFILER DATA WILL BE NEEDED.
WINDS SUSPECTED OF BEING BIASED BY MIGRATING BIRDS WILL BE
IDENTIFIED WITH A 1 /QC CHECK FAILED OR NOT PERFORMED/ FLAG ON
THE AFOS TIME-HEIGHT WIND DISPLAY. A MORE DETAILED DESCRIPTION
FOLLOWS COVERING THESE SUBJECTS
A. BIRD MIGRATION PATTERNS
B. ASPECTS OF CONTAMINATION BY BIRDS ON WIND PROFILER DATA
C. EXPERIMENTAL RESULTS ON BIRD IMPACTS
D. THE NEW QC BIRD DETECTION ALGORITHM
E. EVALUATING PERFORMANCE OF ALGORITHM /BARTH ET AL 1996/
A...BIRD MIGRATION PATTERNS
DIFFERENT SPECIES OF BIRDS MIGRATE AT DIFFERENT TIMES OF THE
YEAR. DEFINITE PEAK MIGRATION PERIODS OCCUR AT NIGHT DURING THE
SPRING AND FALL WHEN LOW-LEVEL WINDS ARE FAVORABLE FOR THEIR
DIRECTION OF TRAVEL. SPECIFICALLY...THEY MIGRATE NORTHWARD
DURING THE SPRING USING THE LOW-LEVEL SOUTHERLY JET...AND
SOUTHWARD IN THE FALL.
LARGE MIGRATING GEESE ARE NOT A MAJOR PROBLEM TO THE
PROFILER...AS MIGHT BE EXPECTED. THE BIRDS THAT CAUSE THE
GREATEST IMPACT TO THE PROFILERS ARE SMALL SONGBIRDS /PASSERINES/
THAT FLY IN A DISPERSED PATTERN RATHER THAN A TIGHT FLOCK. THEY
TYPICALLY START FLYING ABOUT 30 MINUTES AFTER SUNSET AND CONTINUE
UNTIL ABOUT 30 MINUTES BEFORE SUNRISE...FLYING AT AN ALTITUDE OF
MOST FAVORABLE TAILWINDS /OR VERY WEAK HEADWINDS/...GENERALLY
LESS THAN 2-4 KM ABOVE THE GROUND. THEIR MAXIMUM HEIGHT APPEARS
TO BE LIMITED BY THE AMBIENT AIR TEMPERATURE /GREATER THAN -2
DEGREES C/. THEY TYPICALLY FLY AT A LOWER MAXIMUM ALTITUDE IN
THE SPRING /USING THE NOCTURNAL LOW-LEVEL SOUTHERLY JET/ COMPARED
TO THE FALL WHEN THEY FLY AT GREATER HEIGHTS IN THE WARMER...
DEEPER MIXED LAYER. THE BIRDS TYPICALLY FLY WITH AN AIRSPEED OF
ABOUT 8-15 M/S /15-30 KNOTS/ /WILCZAK ET. AL. 1995/.
B...ASPECTS OF CONTAMINATION BY BIRDS ON WIND PROFILER DATA
WIND PROFILING RADARS ARE DESIGNED TO MEASURE THE EXTREMELY
WEAK SIGNALS FROM THE CLEAR AIR THROUGHOUT THE TROPOSPHERE AND
LOWER STRATOSPHERE. THESE WEAK SIGNALS REQUIRE A LONG AVERAGING
TIME /1-MINUTE/ IN EACH OF THE THREE FIXED BEAM POSITIONS USED BY
THE PROFILERS /GENERALLY POINTING TOWARD THE EAST...NORTH...AND
VERTICAL/. THE REFLECTED ENERGY FROM A SINGLE BIRD FLYING
THROUGH THE RADAR BEAM EVEN FOR JUST A FEW SECONDS IS MUCH
GREATER THAN THE CLEAR-AIR SIGNAL AVERAGED OVER THE 1-MINUTE
DWELL TIME. THEREFORE...THE PROFILER REPORTS A VELOCITY EQUAL TO
THE FLYING SPEED OF THE BIRD/S/ TOWARD OR AWAY FROM THE PROFILER
/MOST NOTED IN THE NORTHWARD POINTING BEAM/.
THE EXISTING HOURLY CONSENSUS AVERAGING ALGORITHM /USED FOR
THE PAST 10 YEARS/ EFFECTIVELY REMOVES ISOLATED /A FEW PER HOUR/
ERRONEOUS VELOCITY MEASUREMENTS BEFORE AVERAGING THE REMAINING
GOOD POINTS. PROBLEMS OCCUR WHEN CONSISTENT BAD DATA /IN TIME/
ARE COMPETING WITH...OR OVERWHELMING...THE GOOD WIND DATA. IN
ADDITION...BECAUSE THE BIRDS PRODUCE HIGHER REFLECTIVITY THAN
CLEAR-AIR...THEY CAN ALSO BE DETECTED AS THEY FLY THROUGH THE
PROFILER/S ANTENNA SIDELOBES. THIS CAUSES DIFFERING VELOCITY AND
SPECTRAL WIDTH COMPONENTS TO BE MEASURED AND AVERAGED TOGETHER.
HOWEVER...THE ERRONEOUS POSITIVE AND NEGATIVE VELOCITY
MEASUREMENTS MAY AVERAGE OUT TO NEARLY THE CORRECT BACKGROUND
WIND...WHILE THE WIDER THAN NORMAL SPECTRAL WIDTHS REMAIN /A KEY
ELEMENT IN THE QC ALGORITHM/.
C...EXPERIMENT TO DETERMINE IMPACT OF BIRDS ON WIND PROFILER DATA
IN ORDER TO MEASURE THE EXTENT OF THE CONTAMINATION...DATA
FROM FOUR PROFILERS IN KANSAS AND OKLAHOMA WERE COMPARED WITH
DATA FROM COLLOCATED RAWINSONDES THAT WERE LAUNCHED EVERY 3 HOURS
DURING THE SPRING AND FALL OF 1994. THE AVERAGE ERRORS CAUSED BY
THE BIRD MIGRATIONS WERE 8-9 M/S...WITH LARGER ERRORS POSSIBLE UP
TO THE AIRSPEED OF THE BIRDS /15 M/S/. IN TOTAL...IT WAS FOUND
THAT DURING THE SPRING AND FALL MIGRATION PERIODS THAT ONLY ABOUT
2 PERCENT OF ALL THE PROFILER WIND DATA WERE BEING CONTAMINATED
BY BIRDS /WHEN CONSIDERING ALL WIND MEASUREMENTS IN TIME AND
HEIGHT/.
END OF PART 1 OF 2
PART 2
139
NOUS41 KWBC 141810
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NATIONAL TECHNICAL INFORMATION MESSAGE 96-21...PART 2 OF 2
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
210 PM EDT WED AUG 14 1996
TO - TO WIND PROFILER DATA USERS
FROM - FREDERICK S. ZBAR...CHIEF...TECHNOLOGY AND FORECAST
SYSTEMS CORE...OFFICE OF METEOROLOGY
SUBJECT - NEW QUALITY CONTROL PROCEDURES TO IDENTIFY MIGRATING-
BIRD ERRORS IN PROFILER WINDS...EFFECTIVE 0000 UTC AUG
15 1996
...PART 2 OF 2-PART MESSAGE...
D...THE NEW QC BIRD DETECTION ALGORITHM
THE ALGORITHM CHECKS FOR THE FOLLOWING CONDITIONS AT EACH
MEASUREMENT HEIGHT /RANGE GATE/ IN THE HOURLY AVERAGED PROFILER
DATA -
SPRINGTIME /FEBRUARY 15 - MAY 15/ AND 0200 - 1200 UTC
OR FALL /AUGUST 15 - NOVEMBER 30/ AND 0000 - 1300 UTC
HEIGHT LESS THAN 4.5 KM ABOVE MSL
WIND DIRECTION FROM THE SOUTH DURING SPRINGTIME OR FROM THE
NORTH DURING THE FALL
NORTH BEAM VELOCITY VARIANCE GREATER THAN 1 M/S SQUARED
VERTICAL VELOCITY LESS THAN 3 M/S /WIDER SPECTRAL WIDTHS
NATURALLY OCCUR DURING PRECIPITATION/.
THE WIND IS FLAGGED AS BAD /IDENTIFIED WITH A 1 ON THE AFOS
DISPLAY/ AT EACH HEIGHT WHERE ALL CONDITIONS ARE MET.
E...EVALUATING PERFORMANCE OF ALGORITHM
THE RAWINSONDE DATA WERE ALSO USED TO STATISTICALLY EVALUATE
THE ALGORITHM. THE PROBABILITY OF DETECTION /POD/ WAS GENERALLY
GOOD...SUCCESSFULLY FLAGGING OVER 60 PERCENT OF THE BIRD
CONTAMINATED WIND DATA. /BIRD CONTAMINATION WAS DEFINED BY
COMPUTING THE STANDARD DEVIATION OF WIND COMPONENT VELOCITY
DIFFERENCES /APPROXIMATELY 2 M/S/ DURING NON-BIRD MIGRATION
PERIODS...AND USING TWO TIMES THIS STANDARD DEVIATION AS THE
THRESHOLD FOR IDENTIFYING VELOCITY CONTAMINATION IN THE SPRING
AND FALL./ A RATHER HIGH FALSE ALARM RATE /FAR/ OF 44 PERCENT
WAS NOTED. THIS APPEARS TO BE DUE TO THE POSITIVE AND NEGATIVE
VELOCITY ERRORS /CAUSED BY BIRDS IN THE SIDELOBES/ AVERAGING OUT
TO NEAR THE TRUE WIND VELOCITY...WHILE THE SPECTRAL WIDTH AVERAGE
REMAINS HIGH AND TRIPS THE BIRD DETECTION ALGORITHM.
THEREFORE...THE FAR APPEARS TO BE SOMEWHAT FICTITIOUSLY HIGH.
FURTHER EVALUATION AND ADJUSTMENTS TO THE ALGORITHM ARE EXPECTED.
AN OBVIOUS CHANGE AFTER THE ALGORITHM BECOMES OPERATIONAL ON
AUGUST 15...WILL BE AN INCREASE IN THE NUMBER OF WINDS BELOW 4.5
KM BEING FLAGGED AS FAILING QC. USE YOUR BEST JUDGMENT TO
INTERPRET THESE WINDS.
FOR FURTHER INFORMATION...CONTACT DOUG VAN DE KAMP AT
/303/ 497-6309 OR VANDEKAMP@xxxxxxxxxxxx /SMALL CASE
LETTERS/...OR THE PROFILER CONTROL CENTER AT /303/ 497-6033.
FOR A COPY OF THE REPORT DOCUMENTING THE
EXPERIMENT...CONTACT MIKE BARTH AT /303/ 497-6589 OR
BARTH@xxxxxxxxxxxx /SMALL CASE LETTERS/.
REFERENCES
BARTH...M.F P.A. MILLER J.R. SMART AND L.A. BENJAMIN
1996 QUALITY CONTROL OF HOURLY PROFILER WINDS FOR BIRD
CONTAMINATION. MEMORANDUM FOR THE RECORD.
WILCZAK...J.M. R.G. STRAUCH F.M. RALPH B.L. WEBER
D.A. MERRITT J.R. JORDAN D.E. WOLFE L.K. LEWIS
D.B. WUERTZ J.E. GAYNOR S.A.MCLAUGHLIN R.R. ROGERS
A.C. RIDDLE AND T.S. DYE...
1995 CONTAMINATION OF WIND PROFILER DATA BY MIGRATING BIRDS -
CHARACTERISTICS OF CORRUPTED DATA AND POTENTIAL SOLUTIONS. J.
ATMOS. OCEANIC TECHNOL....12...449-469.
...WEB NOTE...
THIS AND ALL OTHER PENDING NWS SERVICE CHANGE NOTIFICATIONS ARE
AVAILABLE ON THE NWS OFFICE OF METEOROLOGY/S HOME PAGE IN THE
NOTIFICATION SECTION. THE ADDRESS OF THE NOTIFICATION SECTION
/IN SMALL CASE LETTERS/ IS HTTP://WWW.NWS.NOAA.GOV/OM/NOTIF.HTM
END OF PART 2 OF 2
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