Mission and Goals
Mission and Goals
RSF field activities and sensor developments in FY 96 concentrated on polarimetric-radar precipitation estimation techniques, marine boundary-layer waves, and boundary-layer flux measurements. We continued to strengthen our joint optical remote sensing program with the NOAA Environmental Technology Laboratory (ETL) by deploying three lidars in collaboration with other boundary-layer instrumentation. RSF's new S-Band Dual Polarimetric Radar (S-Pol, 64Kb) was used in its first field program to obtain dual-polarimetric-radar precipitation estimates for comparison with precipitation estimates derived from older methods currently in use with the WSR-88D (NEXRAD) radars operated by the National Weather Service (NWS). A series of similar intercomparisons is planned over the next few years in various seasons and locations around the U.S.
S-Band Doppler Dual Polarimetric Radar
(S-Pol). A team led by Jon Lutz completed development of
this advanced, highly-portable radar in FY 96. The new system has
significantly improved signal-processing and polarization-measurement
capabilities, compared with earlier radars. The need for S-Pol was
well defined at a Polarization Radar Workshop at NCAR in 1994. The
system was assembled from the basic framework of the prototype FAA
Terminal Doppler Weather Radar (TDWR) radar, with the addition of
components from ATD's earlier CP-2 radar. The enhanced system uses a
high-quality antenna with very low sidelobes, a high- reliability
transmitter built around the FAA's ASR-9 system, and parallel
receivers for simultaneous co-polar and cross-polar responses. The
innovative design packages S-Pol into six 20-foot shipping containers
and eliminates the radome. This greatly simplifies transporting and
setting up the
system and significantly lowers shipping costs.
Airborne ELDORA Doppler Radar
(ELDORA)
In FY 96 RSF operated the new S-Pol radar, the airborne Electra
Doppler radar (ELDORA), the airborne ozone Differential Absorption
Lidar (DIAL), the Staring Aerosol Backscatter Lidar (SABL), and a
2-micron Doppler lidar from NOAA/ETL. RSF also took on new
responsibilities for
operation and maintenance of airborne radiometric sensors (formerly in
RAF). Brief descriptions of these remote sensing systems are given
below. Remote Sensors and Capabilities
Airborne Imaging Microwave Radiometer (AIMR). RSF took on new responsibilities for the operation and maintenance of AIMR in FY 96. This radiometer operates from the NCAR/NSF C-130 aircraft, scanning across the flight track through the nadir point. The instrument measures surface and atmospheric radiation emissions at 37 and 90 GHz. Each frequency is separated into horizontally and vertically polarized channels. To date, the instrument has primarily been used for mapping of the polar ice cap (ice and snow change their radiative properties with age). Potential may exist for mapping ground moisture content. During the next year RSF will test and upgrade the system to make it more useful for field programs.
Weather Avoidance Radar Data System (WARDS). This system successfully processed data from the forward-looking weather-avoidance radar on the C- 130 (41Kb) during the Small Cumulus Microphysics Study (SCMS), and on the Electra (45 Kb) during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX). It was upgraded this year by Craig Walther and Tim Rucker to synchronize with the master time signal on board each aircraft. An add-on unit, developed by Rich Neitzel, receives data from WARDS and plots it on an aircraft track display in fixed-earth coordinates. This latter display will greatly enhance the ability of the principal investigator (PI) to direct the flight, by showing weather echoes within 50 to 100 km of the aircraft in all directions. This display will be available at each of the scientific workstations on board the aircraft.
Optical Remote Sensing:
RSF's Optical Remote Sensing program, led by Mike Hardesty, continued
as a joint effort with the NOAA/Environmental Technology Laboratory (ETL). RSF and ETL science and
technical staff together deployed several lidar instruments in field
programs during the year, as described in subsequent sections. During
FY 96, NCAR and NOAA began planning for the joint development of a
ground-based water-vapor profiling lidar. The following three lidar
systems were offered for atmospheric research during the year:
Solid State High Resolution Doppler Lidar
(HRDL). Chris Grund (NOAA)
and Chuck Frush (NCAR) collaborated to optimize the performance
of the NOAA 2-micron
Solid State High Resolution Doppler Lidar in preparation
for the LIFT experiment. The radar was installed in the NCAR mobile optical laboratory (70 Kb)
having the capability of scanning and resolving 30-meter range
increments. An
upgraded signal processor was added to the instrument to provide
accurate real-time wind and backscatter estimates.
Staring Aerosol Backscatter Lidar (SABL). The
SABL lidar (72 Kb),
used to measure and map distributions of relative aerosol
concentrations, is a dual-wavelength system operating at 532 and 1064
nm. It can transmit up to 60 pulses per second. Each pulse contains
approximately 75 mJ of 1064 nm energy and 45 mJ of 532 nm energy. The
transmitted energy scattered by aerosols in the atmosphere is received
by a 14-inch-diameter Cassegrainian telescope. The received signal is
digitized to 12 bits at up to 40 Mhz (3.75-meter range resolution), and
recorded to tape. A real-time data display allows scientists to use
SABL for real-time experimental control during field studies.
Ozone Differential Absorption Lidar
(O3 DIAL). This airborne ozone lidar (61 Kb) was jointly acquired by
NOAA/ETL and NCAR/ATD from EPA in FY 94. Designed for down-looking
airborne operation, the lidar measures ozone and aerosol
cross-sections and profiles in the layer below the aircraft. During FY
96, NCAR and NOAA staff continued to improve the lidar and its data
system to provide higher sensitivity and better reliability of
operation. Intercomparisons with ozone data from airborne and
balloon-borne sensors are being used to improve ozone estimation
algorithms.
NEXRAD/S-Pol Precipitation
Measurement Comparison. In its first field deployment, S-Pol
was sited at the Front Range Airport (east of Denver), near the Denver
WSR-88D radar, for the purpose of comparing rainfall estimates from
S-Pol using polarimetric techniques with those from the WSR-88D using
the standard reflectivity-based method. Scientists from Colorado State
U. (Bringi and Chandresekar), NOAA's National Severe Storms Laboratory
(NSSL, Zrnic, and Rhyzkov), NWS Office of Hydrology (Fulton), and NCAR
(Brandes, Vivekanandan, and Wilson) participated in the project. The
Urban Drainage and Flood Control District concurrently operated a
network of 113 telemetering tipping-bucket raingauges, which provided
an excellent precipitation data set for verification purposes. In
addition, Colorado State U. operated three mobile vehicles for
obtaining measurements of drop-size distribution and rainfall.
Coastally Trapped Waves Experiment. This program was
conducted near Monterey, California with David Rogers of Scripps
Institute as the PI. SABL was deployed on the NCAR C-130 to map
aerosols in the marine boundary-layer. The lidar was mounted so it
could be used for either upward- or downward-looking observations.
Lidars in Flat Terrain (LIFT). LIFT was a field
experiment designed and led by visiting ATD scientist Shane
Mayor. Through LIFT, the instrumentation network of the Flatland
experiment (Wayne Angevine, PI) was supplemented by three additional
lidar systems. The purposes of the program were to measure turbulent
structures in the boundary layer and to improve measurements of
vertical fluxes of momentum, heat, and trace gases. The three lidars
that were fielded were SABL, operating at two wavelengths (1064 nm and
532 nm), developed by Craig Walther and Bruce Morley; an ozone UV-DIAL
lidar, developed at NOAA/ETL by Yanzeng Zhao; and the 2-micron Solid
State HRDL, developed at NOAA/ETL by Chris Grund. In addition, Tammy
Weckwerth (NCAR/ASP post-doctoral fellow) operated the U. Oklahoma
Doppler on Wheels (DOW)
radar to investigate convective-roll structures in conjunction with
the optical measurements.
Data were taken in July and August for a period of 5 weeks near
Champaign, IL. The combined data from the co-located,
vertically pointing, high-resolution lidars are expected to provide an
unprecedented look at evolving boundary-layer features. Most of the
data were taken in the vertically pointing mode, allowing a
comparison of the capabilities of the co-located
instruments to resolve small features of the boundary-layer.
ELDORA. This year the
ELDORA radar was upgraded to use
SCSI-2 for higher-rate data recording. The radar is now capable of
recording data at a rate of nearly 1 Mb/sec. Eric Loew added a MiniRIMS
inertial reference unit inside the spinning antenna structure
(rotodome) mounted in the rear of the aircraft. This device will more
accurately register the ELDORA data within the earth's reference frame. A
video distribution system was developed by Mike Strong that allows
both of the ELDORA real-time displays to be available at all five
scientific work areas on board the Electra. Improvements to the
stability and usability of the user interface were also implemented.
Doppler on Wheels (DOW).
Cloud Physics Radar (CPR). In collaboration with Robert
MacIntosh and Andrew Pazmany (U. Massachusetts), RSF is investigating
a cloud physics radar that could be used for a variety of
applications. The system could be deployed either on the ground, on
the Electra in conjunction with ELDORA, or in a C-130 wing
pod. Pazmany has delivered recommendations that are being evaluated by
RSF.
Airborne Radar Techniques. Wen-Chau Lee and Peter
Hildebrand continued to improve algorithms for the efficient
processing of ELDORA data. Lee and Susan Stringer led an effort to
automate the technique of using ground echoes to validate and correct
ELDORA radar beam-pointing angles and to minimize navigation
errors. Hildebrand investigated retrieval of sea-surface wind
direction and speed from the sea-surface returns obtained by ELDORA.
Radar Surface Refractivity Mapping. Frederic Fabry
(NCAR/ ASP post doctoral fellow), with the assistance of Chuck Frush,
developed a technique to measure refractive index and water-vapor
concentrations near the ground using radar returns from fixed ground
targets. A differential analysis of the propagation time to multiple
ground targets caused by changes in index of refraction (due to
changes in density and humidity) provides measurements of
surface-level refractivity. Preliminary tests using data from the
McGill radar in Montreal and from NCAR's S-Pol radar located south of
Denver International Airport indicate good agreement with independent
in situ measurements at selected points. The preliminary
data show patterns in the refractivity field that drift
through the observation area but are not always linked to observable
reflectivity features. Work is continuing at McGill U. where
Fabry is now employed.
SOLO Perusal and
Editing Software. Dick
Oye (RDP), Sherrie Smith, and Wen-Chau Lee continued their development
of the SOLO program to peruse data from various research radars and
lidars, including NEXRAD and TDWR. SOLO also translates a variety of
data formats during ingest, for compatibility purposes. New and
efficient editing and examining functions have been added. SOLO has
been ported to a number of platforms including LINUX.
NEXRAD Data Quality. A team led by Frank Pratte is
developing techniques that can be readily applied to the NEXRAD
WSR-88D radar network. These include a procedure for consistent
reflectivity calibration of the radar, an optimized approach to
anomalous propagated clutter processing, an access platform for the
digital Archive I (time-series) data, and an instrumentation system
for testing modifications and improvements of the Operational Support
Facility (OSF) testbed radar. A new effort to develop a robust
range/velocity-ambiguity removal technique is being led by Chuck
Frush, in collaboration with NOAA/NSSL. Under a joint agreement, RSF and
the NOAA Forecast Systems Laboratory (FSL) support OSF tasks relating
to radar data quality and product improvements and their application to
hydrology.
PC and VME Integrated Radar Acquisition System (PIRAQ and
VIRAQ). The new VIRAQ radar data acquisition system was
developed in FY 96 by Eric Loew and Mitch Randall. This system extends
the PIRAQ system with a dual-channel, digital, intermediate-frequency
signal processor and a digital signal-processor (DSP). The principal
advantage of PIRAQ and VIRAQ is that they can convert an ordinary,
non-Doppler radar into a sophisticated Doppler system. The main
difference in the two systems is that the VIRAQ plugs into a VMEBus
and has two DSPs, while the PIRAQ requires a conventional personal
computer and uses one DSP. A quad-DSP processor board allows
additional DSPs to be added to increase computing power. A video
display board allows more flexible and usable video displays than are
provided by commercial video controllers. These boards were tested
successfully as part of the S-Pol radar during the NEXRAD/S-Pol
Precipitation Measurement program, and are also used in WARDS.
Wen-Chau Lee continued his collaboration with the NOAA Hurricane
Research Division (HRD)
and the National Taiwan U. on the VTD and GBVTD
radar data-analysis techniques. These methods use a single airborne or
ground-based Doppler radar to retrieve the primary circulation of a
hurricane or typhoon. Mean perturbation pressure and temperature have
been successfully retrieved from the mean tangential winds obtained
using the VTD and GBVTD techniques.
Lee and Peter Hildebrand computed vertical profiles of momentum,
apparent sensible heat source, and apparent moisture sink for
several tropical convective systems using ELDORA data collected during
TOGA COARE. The results showed good agreement with conventional
methods using rawinsonde data.
Lee collaborated with David Chen (U. Chicago) in using TAMEX data to
study the formation of a barrier jet and its relationship to heavy
rainfall in northwestern Taiwan. In addition, Lee participated in
planning for the use of ELDORA radar in several future field
experiments.
Shane Mayor, with Raul Alvarez (NOAA/ETL) and Christoph Senff
(U. Colorado), analyzed airborne lidar observations from the 1995
Southern Oxidants Study to map regional ozone and aerosol
distributions over the experimental area. They also studied diurnal
transport and evolution of the Nashville metropolitan ozone plume
during a major air stagnation event, and characterized ozone titration
in power-plant plumes. In combination with concurrent in situ
measurements, the airborne lidar data provide important information on
generation and transport of ozone in an isolated metropolitan area.
Jeffrey Keeler and Hildebrand maintained a collaboration with Robert
Macintosh and Andrew Pazmany (U. Massachusetts) on dual-polarization
mm-wave radar applications for the scientific community. Their goal is
to provide access by NSF-supported scientists to airborne and
ground-based mm-wave radar systems for application to various research
topics such as cloud evolution, clouds and radiation, cloud physics,
and boundary-layer processes.
RSF field support activities during FY 96 are listed in Table ATD-4
and briefly summarized below: Field Support Activities
User (Affiliation)
Project
Location
Sensor
Period
Brandes, et al. (NCAR/RAP
and other)
NEXRAD/S-Pol Precipitation
Measurement
Front Range Airport, CO
S-Pol
Jun-Aug 96
Rogers
(Scripps)
Coastally Trapped Waves
Monterey, CA
SABL
Jun-Jul 96
Mayor
(NCAR/ATD)
LIFT
Champaign, IL
SABL, HRDL, DOW
Jul-Aug 96
Considerable effort was spent by RSF staff on sensor development
during FY 96. These activities spanned developments in ground-based
and airborne radar systems, as well as optical systems. Several
developments in the areas of data systems and signal processing were
common to multiple sensor systems. Sensor Development Activities
Polarimetric Rainfall Estimation. Real-time algorithms
for estimating rainfall amount were implemented on S-Pol during summer
1996. For this purpose, Frederick Fabry and Mitch Randall modified
computer code obtained from Colorado State U. and the NOAA/NSSL.
Three algorithms were prepared.
The first is based on horizontal (ZH) and vertical
(ZV) radar reflectivity factors, the second on specific
propagation phase (KDP), and the third on the Z-R (radar
reflectivity-rainfall rate) relationship used by the NEXRAD WSR-88D
radars. Studies are underway to determine optimum procedures for
applying these different relationships for different rainfall regimes.
Based on these studies, precipitation estimates are expected to become
a routine real-time product from S-Pol. Technique Development Activities
Jim Wilson continued his research into the factors affecting the
initiation, organization, and decay of convective storms in Florida. A
paper on the subject was prepared and accepted for publication in
Monthly Weather Review. His research has shown that the
initiation of storms is related to the magnitude and depth of
boundary-layer convergence and the low-level wind-shear profile. The
lifetime and organization of the convection is related to the relative
motion between the storms and the convergence lines. Research Activities
