This readme discusses DBS wind profiler data that has QC post-
processed using NIMA.
NCAR/EOL operated three 915 MHz boundary layer wind profiler radars
at ISS (Integrated Sounding System) sites at T-REX. These radars
detect scattering from clear-air refractivity gradients (such as
those due to turbulence and inversions) and from precipitation. This
scattering is used to make a measurement of the wind profile above
the radar, typically from about 200 meters through the boundary layer
to 2 to 5 km. The strength of the scattering (reflectivity) and thus
ability to measure wind is a complicated function of temperature,
humidity, turbulence, precipitation, and the presence of unwanted
signals (radio interference, clutter echoes from trees, power lines,
birds, etc). These radars can also measure the virtual temperature
profile (up to 500 to 800 meters) using the Radio Acoustic Sounding
System (RASS) technique.
Two of the three wind profilers were standard DBS (Doppler Beam
Swinging) systems, which provided the data for the accompanying data
set (the other profiler, MAPR, is a research system producing
specialist data and cataloged separated). The DBS profilers at
T-
REX were designated ISS2 and MISS and produced wind measurements
every 30 minutes and also made a 5-minute RASS profile at 30-minute
intervals. (Raw data were recorded every 30 seconds as the radar
antenna was steered along the 5 beam directions used in the Doppler
beam swinging technique used here).
ISS2 was approximately 3 miles up Onion Valley road from Independence at
Lat: 36d 46.676m Lon: 118d 14.911m Alt: 1505m.
The MISS system was a mobile system and moved around 5 sites in the
Owens Valley. These sites are listed below and on our web page
(www.eol.ucar.edu/rtf/projects/trex/iss/)
where they are also mapped.
The raw data on these systems is the standard NOAA/AL and Vaisala/
Radian POP4 spectral data. This data was later reprocessed using the
NCAR/RAL NIMA (NCAR Improved Moments Algorithm) which uses image
processing and fuzzy logic techniques to analyze the spectral data
and separate atmospheric echoes from unwanted signals such as radio
interference and clutter. More information on NIMA is at
www.rap.ucar.edu/technology/profiler/
On previous projects we have found that NIMA processed wind
measurements generally agree with radiosonde soundings to better than
1.5 m/s (standard deviation). RASS virtual temperature measurements
typically agree with soundings to within 1 degree C. The DBS sites at
T-REX did not have soundings with which to make comparisons, however
similar accuracy is expected. NIMA also enables us to recover weak
or noisy data, for example typically extending the range 100 to 300
meters.
The accompanying data files are of three types, wind measurements
(files with extension "windsnc"), RASS virtual temperature
measurements (extension "rassnc"), and spectral moments data
(extension "momnc").
Files nima060325.windsnc, nima060325.rassnc, and d060325.momnc are
the files for March 25, 2006, of winds, RASS, and moments
respectively. The winds and RASS data are generally at 30-minute
intervals. The moments data are the zeroth, first, and second
moments of signals from each 30-second dwell of the steered beam.
These moments are the signal strength (here SNR or Signal to Noise
Ratio which can be used to estimate reflectivity), Doppler shift
(from which the winds are derived), and spectral width (can be used
to estimate turbulence with lots of caveats). We generally
recommend that only experienced profiler users analyze the moment data.
The data files are in netCDF format. This is an advanced binary
format with data self-descriptors widely used in the atmospheric
research community. It was devised by UCAR/Unidata and is described
further on their web site www.unidata.ucar.edu/software/netcdf
The data is arranged in time, height coordinates (the height
coordinate is labeled "x" for compatibility with some legacy
software). For winds (in the *.windsnc files) use variables wspd
and wdir (wdir follows the meteorological convention of the direction
the wind comes from, measured clockwise from north). For RASS
(*.rassnc files), use variable tv (virtual temperature) for calm
conditions or variable tvc when significant vertical velocity is
expected (such as when waves or convection are occurring).
There is a confidence variable (eg, wind_conf or tv_conf), which
describes the degree of confidence (0-1) that the NIMA algorithm
places in the derived data. These variables have the same dimension
as the wind and temperature data. Use only those data points for
which corresponding confidence level exceeds the threshold confidence
level. Usually we use a threshold confidence level of 0.5.
The ISS data are plotted on our project web page
www.eol.ucar.edu/rtf/projects/trex/iss/
where you can also find
documentation such as descriptions of the instruments and a map of
their location during T-REX as well as operator logs.
Please contact Bill Brown (wbrown at ucar.edu or phone 303-497-8774)
for more information.
MISS Sites.
Site: F2 Manzanar Base 36d 43.3m N, 118d 8.5m W, 1166m
Feb 25 - Mar 5 18Z (IOP-1)
Site: F6 Division Creek Road 36d 56.397m N, 118d 16.249m
W , 1259m
Mar 5 22Z - Mar 20 0Z (IOP-2,3,4)
Site: OV2 Onion Valley Rd 36d 47.28m N, 118d 13.32m W,
1335m
Mar 20 3Z - Mar 21 18Z (IOP-5)
Site: F2 Manzanar Base 36d 43.3m N, 118d 8.5m W, 1166m
Mar 21 20Z - Mar 24 0Z (EOP-1)
Site: D Onion Vly Rd & Hwy 395 36d 47.2m N, 118d 12m W, 1249m
Mar 24 5Z - Mar 27 21Z (IOP-6)
Site: F2 Manzanar Base 36d 43.3m N, 118d 8.5m W, 1166m
Mar 28 0Z - Mar 30 23Z (IOP-7, EOP-2)
Site: F6 Division Creek Road 36d 56.397m N, 118d 16.249m
W , 1259m
Mar 31 2Z - Apr 4 2Z (IOP-8,9)
Site: F2 Manzanar Base 36d 43.3m N, 118d 8.5m W, 1166m
Apr 4 22Z - Apr 7 20Z (Aircraft Intercomp)
Site: F6 Division Creek Road 36d 56.397m N, 118d 16.249m
W , 1259m
Apr 7 22Z - Apr 10 19Z (IOP-10,11)
Site: B Mazourka Canyon Rd/Kiersarge Mine 36d 48.5m N, 118d 6.6m
W , 1178m
Apr 10 22Z - Apr 12 21Z (IOP-12)
Site: F2 Manzanar Base 36d 43.3m N, 118d 8.5m W, 1166m
Apr 12 23Z - Apr 14 22Z
Site: OV2 Onion Valley Rd 36d 47.28m N, 118d 13.32m W,
1335m
Apr 14 23Z - Apr 17 21Z (IOP-13)
Site: F2 Manzanar Base 36d 43.3m N, 118d 8.5m W, 1166m
Apr 17 23Z - Apr 24 16Z (EOP-3, IOP-14)
Site: B Mazourka Canyon Rd/Kiersarge Mine 36d 48.5m N, 118d 6.6m
W , 1178m
Apr 24 18Z - Apr 28 11Z (IOP-15)
Site: F2 Manzanar Base 36d 43.3m N, 118d 8.5m W, 1166m
Apr 28 18Z - May 1 (EOP-4,5)
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