Instrumentation
Boundary Layer Profiler Network
Publications
The NOAA/ETL boundary layer windprofiler network is a portable, configurable
network of wind profilers, meteorological observation towers and RASS units
for the observation of regional weather systems impacting air quality and severe weather.
Disdrometers
The Distromet LTD Model RD-80 disdrometer uses the momentum of falling
raindrops to measure the size distribution of rain. The amplitude of the
pulse generated as a drop hits the disdrometer's electromechanical
transducer is roughly proportional to the drop's momentum
and, ultimately, the drop's diameter. The size range of drops that can
be measured spans from 0.3 mm to 5 mm. Drops larger than 5 mm are rare
because they tend to be unstable and breakup into smaller drops. By
comparing disdrometer measurements from coastal and
inland mountain sites, we will learn more about the microphysical
processes associated with orographic precipitation, one of the underlying
goals of PACJET. The disdrometer measurements will also shed light on the
microphysical information derived from the X-band polarimetric scanning
radar and the S-band vertically pointing radars deployed for PACJET-2003.
The integrated size distribution measured by the disdrometer is a direct
measurement of the rainfall intensity, which will be compared to the
rainfall intensities measured by a variety of other rain gauges and
estimated by the radars. These comparisons will be used to
diagnose the strengths and limitations of various in situ and remote
sensing measurement techniques used to provide rainfall intensity.
S-band Profiler
The S-band vertical profiler is based on existing S-band and UHF profiler
technology which has been modified for research. It's dynamic range has
been extended to study moderate to heavy precipitation which would not be
otherwise possible. The S-band has been calibrated through a side-by-side
comparison with the Ka-band radar. In a typical cloud profiling mode of
operation, the sensitivity is -14 dBZ at 10 km. Examples taken from a
recent field campaign illustrate the profiler's ability to measure vertical
velocity and radar reflectivity profiles in clouds and precipitation.
Water Content Reflectometers
Volumetric soil water content measurements are made using the Campbell Scientific
CS 616 water content reflectometers. These instruments estimate soil water
content by measuring the time it takes an electromagnetic pulse to traverse a
30 cm waveguide formed in the soil by two parallel rods spaced 3.0 cm apart.
At the Rio Nido, Cazadero, Healdsburg, and Hopland locations the reflectometers
are buried horizontally at a depth of 15 cm. The Lake Sonoma and Big Sulfur Creek
probes are buried at 7.5 cm because the soils in these elevated locations are
thinner and contain large amounts of gravel.
Individual calibrations are developed for each site based on drying and weighing
soil samples taken in the immediate vicinity of the probe. The measurements are
also corrected for variations in soil temperature using a themistor buried at
the same depth as the refectometer.
X-band Polarimetric Radar
ETL developed this state-of-the-art X-band radar primarily for observations
of the ocean surface, rain, snow, storm airflow patterns, and for
hydrological applications. It has Doppler, dual-polarization, and full
scanning capability, including the ability to scan downward beneath the
horizon for ocean work. Fine-scale measurements are possible with selectable
range resolution from 7.5 to 150 meters. Polarization options include
switching between H and V, or using the "split" H/V, configuration that has
been proposed for future NEXRAD upgrades. The polarization measurements
include differential phase (Kdp), and differential reflectivity (ZDR),
which can used for more accurate estimates of rainfall rate and
identification of precipitation particle types. The radar uses ETL's new
Radar Acquisition and Display System (RADS), which allows various options
for scan control and computing derived parameters in realtime. The radar
is transportable in North America on its own trailer bed or it can be
shipped overseas in standard sea containers. ETL engineers are working
toward implementing fully automated, unattended operation and remote
control of this system.
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