| Description: | Subject: Bird contamination of 915 MHz profiler winds
DQR No: Platform: 915rwp-cf
Subject: Contamination of wind fields by birds
Date Submitted:19 Oct 1994
Submitted By:Richard L. Coulter _X_ Instrument Mentor
___ EST Member
___ Science Team Member
___ Other _____________________________
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509-375-6898 or via email at dqr@arm.gov.
Platform/Measurement:
What level data: (raw,a0,a1,b1,c1 etc):
raw,a0,a1
What location was the data collected at:
Central Facility
Period of time in question
Begin Date 1 /1 /93 Time : (GMT)
End Date ?? / / Time : (GMT)
Data should be labeled:
_ x__ questionable ___ All data fields affected
___ incorrect ___ Only some data fields affected
___ wrong calibration
___ others
Discussion of Problem:
We now have fairly conclusive evidence that migratory birds flying through the
915 Profiler beam are leading to bogus values of wind speed and direction. This
problem is not unique to the CART, it is inherently possible in all 915 and 404
MHz wind profilers, since the size of some birds are approximately the same as
the profiler wavelength. By comparing the 50 MHz winds with the 915 we have
an excellent check since the wavelength of the 50 MHz profiler will not sense
any birds smaller than a pterodactyl. We found significant overestimates of
wind speeds with the 915 profiler during nighttime with winds mainly from the
south, with increasingly large mean differences as time progressed from June
through August. The mean difference decreased with height above 4 km.
This is consistent with migratory patterns of birds: they fly
mainly when the wind is in the direction they want to go, when it is not too
turbulent, during nighttime, and less above 4 km.
Further analysis of the data indicates that individual instances can have
differences of 5 m/s or more. Thus, to sum up, nighttime data is most suspect;
seasonal differences are expected, i.e. south winds overestimated near
summer's end, north winds overestimated near winter's end;
RASS temperatures should not be affected.
Other observations/measurements impacted by this problem:
Suggested Corrections of the Problem: (e.g. change calibration factor and
recompute, flag data with this comment, etc.)
It is quite possible that much of the data can be corrected. However, it will
require analysing all the raw spectral data and developing an algorithm to
locate problems.
The vendor (Radian) promises that the next software release will have a bird-
sensing algorithm included that is successful much, but not all, of the time.
This new version may be available by Jan., 1995 (my guess).
Note that this type of problem is inherent to all the radar profilers, including
NEXRAD, which is contaminated by insects., with the possible exception of the
50 MHz system.
Data Processing Notes Date |