The 915 MHz radar operating characteristics are defined in Table
1. In clear air, the transmitted signal is backscattered most effectively
from turbulent entities of 16 cm spatial scale (Bragg scatter, most effective
near one-half the radar wavelength). Thus, the height to which wind profiles
are obtained is dependent on the both the turbulent kinetic energy and the
variability of refractive index, which are in turn dependent on the depth
and concentration of water vapor, atmospheric stability, and various turbulent
mixing processes. The operating parameters are adjustable: pulse length
options are 60, 105, 210 and 420 m; pulse coding can be implemented, and
gate spacing equal to pulse length for pulse coding, and variable when pulse
coding is not implemented During the summer months over the Southeast, we
have observed that wind profiles usually extend to 4 km altitude, and sometimes
to 7 km in the long (440 m) pulse mode. Raw data are used to create a vertical
profile of horizontal wind speed and direction over a selectable averaging
period (5-60 min). When the consensus averaging period is completed, the
system processes other data products (time vs. height sections of wind and
spectral moments are generated by an independent PC linux workstation to
display the time history of wind profiles, vertical motion and other ABL
parameters. NOAA scientists have shown that the accuracy of retrieved one-hour
consensus winds is about 1 m s-1 in speed and 10 deg in direction under
normal conditions. The microwave frequency is also sensitive to all liquid
and ice-phase hydrometeors, including raindrops, snow and ice crystals.
In the precipitation environment, a strong signal is usually obtained throughout
the depth of the cloud system. During mobile operations, the clutter panels
are not used, but we have found that the performance is not significantly
compromised in low-clutter locations. The 915 MHz antenna is an electrically
steerable micropatch phased array, formatted by four 0.9 m and 0.9 m antenna
panels. The current system has five fixed beams, one at zenith, and four
beams 23 deg from zenith in orthogonal directions. With the 9 deg beamwidth,
the sample volume width is approximate 15% the value of range. Thus, at
a height of 4 km, the width of the sample volume is ~600 m. Operating parameters
during IHOP_2002 are provided in Table
1. Archived data include consensus winds (u,v,w) and spectral the
spectral moments backscattered power (SNR), Doppler velocity, and width
of the Doppler spectrum.
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