Observing Systems by Technology
Acoustic |
Lidar |
Ocean Flux System |
Processors |
Profiling Radar |
Radar |
Radiometer
Infrasonics
Contact: Al Bedard
Infrasonics is the study of sound below the range of human hearing.
These low-frequency signals are produced by a variety of geophysical
processes including earthquakes, severe weather, volcanic activity,
geomagnetic activity, ocean waves, avalanches, turbulence aloft, and
meteors and by some man-made sources such as aircraft and
explosions. Infrasonic and near-infrasonic signatures may provide
advanced warning and monitoring of these extreme events. Infrasonic
sensors invented at ETL are the basis for a demonstration network
which has detected avalanches, tornados, and sprites. They are
also used to study the propagation of sound which can be used
to address such issues as airport and industrial noise.
Lidar (LIght Detection And Ranging) is similar to radar, except that
it uses optical rather than radio frequencies. Light from a pulsed laser is
transmitted into the atmosphere, where molecules, aerosol particles, or
cloud particles scatter the light. A small portion of light backscattered
to the lidar is collected by a telescope and measured. Depending on the
application and lidar wavelength(s), the backscattered intensity, frequency
shift (Doppler or Raman), depolarization, attenuation by molecular
absorption, and/or extinction by particles provide information about the
atmospheric constituents.
Airborne Aerosol Lidar (ABAEL)
ABAEL is designed to detect aerosol layers in the atmosphere from an aircraft. It has been
deployed for air quality missions to locate aerosol layers for in-situ sampling and for
mapping the regional distribution of aerosols.
Depolarization and Backscatter Unattended Lidar (DABUL)
A major development that promises to have significant impact on future
climate research associated with cloud and aerosol climatology is the
Depolarization and Aerosol Backscatter Unattended Lidar (DABUL). Whereas
most lidar systems require significant attention from highly trained
personnel, DABUL is designed to operate without attention for extended
periods. This developmental lidar provides measurements of aerosol
structure and cloud base heights throughout the troposphere. Results are
automatically recorded and can be transferred via phone lines to a central
site. Applications of the instrument include validation and correction of
satellite products, development of climatology of aerosols and clouds in
different regions of the globe, and observation of both mixed-layer height
and aerosol buildup for air quality studies.
Airborne Excimer Ozone DIAL
The airborne ozone lidar obtains 3-dimensional distributions of ozone
over both urban and rural regions, such as during the Southern Oxidant Study.
The system is designed for easy mounting on a wide variety of
moderate-to-large aircraft. This excimer-laser DIAL system views
downward as the plane flies a few kilometers above the surface, but can
also be operated viewing upward from the ground. High pulse rate and good
sensitivity ensure good horizontal resolution. This ETL system provides
critical information for studies of regional pollution transport,
production, and dissipation mechanisms.
Fish Lidar, Oceanic, Experimental (FLOE)
Using pulsed lidar technology initially developed
by the Department of Defense to detect objects in the water, FLOE
is being developed to conduct airborne fisheries surveys to improve
fisheries management and decrease costs.
High Resolution Solid State Doppler Lidar (HRDL)
A solid-state system, designed and constructed at ETL, is intended for
ground-based, airborne, and ship based measurements of wind and turbulence
in the planetary boundary layer with superior spatial resolution and Doppler
accuracy. Completely integrated into an optical table, the system can be
installed into a shipping container or aircraft with minimal effort. The
lidar includes a real-time signal-processing and display system as well as
a computer-controlled scanner with compensation for ship motions. The
all-solid-state composition of the system provides reliability in a very
compact package.
Mini-MOPA CO2 Doppler Lidar
A compact, robust, infrared CO2 lidar developed at ETL for combined Doppler
and molecular species measurements in the planetary boundary-layer and for
cloud studies. Early, single-wavelength versions provided excellent
cloud and subcloud Doppler data measurements. The second wavelength will
permit DIAL profiling of ozone and water vapor, and ice/water discrimination
of clouds. A unique, single-instrument capability for measuring fluxes with
DIAL and Doppler is anticipated.
Nd:YAG-based Ozone Profiling Atmospheric Lidar (OPAL)
The ground-based ozone lidar measures profiles or vertical-plane
distributions of ozone to heights of about 3 km. Designed for air-quality
studies, the instrument is the only one of its kind in the United States
(although several similar instruments exist in Europe). The lidar
is housed in a modified 20-foot-long shipping container for easy domestic or
foreign deployment. This Nd:YAG-laser DIAL system was designed for good minimum
range, temporal resolution, and calibration. The lidar been used to study
pollutant transport in California and Tennesee.
TEA CO2 Doppler Lidar
The mobile 1-J infrared Doppler lidar system invented at ETL measures wind
flow and turbulence parameters in optically clear air to distances of
typically 15 to 30 km. This scanning lidar is used in a variety of research
investigations, including air-quality-related studies of flows in complex
terrain, climate studies of cloud properties and stratospheric aerosol,
and severe weather events such as wind shear and damaging downslope winds.
Miniature Water Vapor DIAL
The goal of this project is to develop a compact, low-cost, eye-safe,
automated remote-sensing instrument which can continuously profile water
vapor. This lidar can be widely deployed resulting in considerably more
data for improved forecasting and modeling.
Ship-based Near-Surface Bulk and Flux Data Package
The University of Colorado and NOAA ETL Air-Sea Interaction Group
have spent more than a
decade developing techniques for accurate direct covariance ship-based
measurements of the
turbulent heat, mass, and momentum fluxes (Fairall et al., 1996a; 1997).
Improved measurement techniques,
studies of fundamental physical processes, and development of simplified
representations of flux processes are
essental to improving analyses and forecasts of weather, climate, and
environmental conditions over the oceans and in coastal zones.
Flux instrument packages are configured to meet operational and experimental
goals. Observations
generally include the following.
- High resolution wind components and temperature are measured with an ultrasonic
anemometer/thermometer (sonic) with full motion corrections.
This information is used to compute the sensible heat flux and wind stress over the water.
-
Information from a fast response infrared H2O/CO2 sensor is combined with the corrected
sonic signal to compute estimates of the fluxes of latent heat and carbon dioxide. The direct covariance
and inertial-dissipation fluxes are computed at 10-min and 1-hr time intervals. Flow distortion by the ship's
structure is also applied and is based on computational fluid dynamics (CFD)
calculations with empirical tuning.
-
Downwelling radiative flux components are also measured, and these sensors are calibrated and
cross checked against a similar resident systems.
-
The flux system mean temperature and humidity measurements are accurate to better than 0.2 C
and 0.3 g/kg, and the near surface ocean temperature is measured with a floating temperature
sensor (seasnake) which samples at a depth of about 5 cm. This sensor
fully resolves all diurnal
warm layers, and the true interface temperature is obtained by subtracting a cool-skin correction.
-
The capability for measurement of direct covariance carbon dioxide fluxes is a recent addition.
Radar wind profilers transmit pulses of radio energy which scatter off
refractive index inhomogeneities in the atmosphere. In the clear air
these inhomogeneities are typically caused by variations in temperature or
humidity of atmosphere. By measuring the Doppler shift, the wind speed and
direction can be calculated as a function of height.
Profilers designed at different frequencies can observe regions of the
atmosphere from the boundary-layer to the stratosphere. Combining
profiler data with measurements taken by an acoustic sensor call a
RASS (radio acoustic sounding system), temperature profiles of the
atmosphere can also be derived.
Platteville 50-MHz Rardar Wind Profiler with RASS
This ETL radar was built in the mid
1980's and is part of the first "operational" network of wind profilers (the "Colorado Network")
that predates the present Wind Profiler Demonstration Network (WPDN) in ERL's Forecast Systems
Laboratory (FSL). It is collocated with the 404-MHz WPDN profiler at Platteville, Colorado, and
it continues to operate unattended, providing wind profiles to l8-km ASL and temperature profiles
to 6-km AGL. The radar is often used by meteorologists as part of local research projects and by
the University of Colorado in meteor trail studies. It is also used by SDID staff as a test bed
to validate and intercompare with other sensors as part of ongoing advancement of technology.
915-MHz Radar Wind Profiler with RASS
This instrument is nearly identical to the Platteville 50-MHz
instrument in cost of maintenance and operation. Its height coverage is not as great as the
50-MHz system, but it is used more frequently by the National Weather Service (NWS) and FSL for
regional forecasts. It is the most sensitive 915-MHz system in existence. Because it is located
next to the NWS rawinsonde release point, it is frequently used for sensor intercomparisons by a
number of agencies.
915-MHz Profiler Network
ETL has developed a network consisting of 14 portable 915-MHz radar wind
profilers with RASS. Data transmission and communications are accomplished
via phone lines and satellite systems to a central data hub in Boulder,
Colorado. These profilers are used in a variety of ways including
individual installations to extend the technology in new environments,
deployment as a mesoscale research network, and acquiring data for
initialization of test models for air-quality transport studies.
Radars Data Acquisition and Processors |
Radar Acquisition and Display System (RADS)
The Radar Acquisition and Display System (RADS) is a configurable system
designed to record and display data from a research Doppler radar with
polarization diversity. Constructed primarily from commerically available
components, the VME-based processor controls radar operations, data
acquisition and display through a graphical interface. Incorporating GPS
navigation directly into the data stream, it can be configured
for ground, aircraft and ship based radars. The programmable processor
allows for real-time calculation and display of custom data fields and
monitoring of data quality.
Precipitation and Cloud Radars |
ETL designs and operates high-performance, transportable, Doppler
radars for atmospheric and oceanic research. These radars use higher
frequencies (shorter wavelengths) and are smaller than storm surveillance
radars. Our radars have been used extensively in field research projects
at dozens of locations in the United States and other
countries. The radars were designed and built in-house and are in a
continuous state of development as latest state-of-the-art
capabilities are added. The Ka-band "cloud" radars have superb sensitivity
that allows them to detect tiny cloud particles in addition to
precipitation. In combination with radiometers, these cloud radars are
used to estimate microphysical features of the nearby clouds,
including ice crystal and water droplet sizes and mass contents.
Polarization measurements from the scanning cloud radar allow the
particle shapes and types (plate crystals, column crystals, droplets,
etc.) to be identified in the clouds. Polarization capabilities recently
implemented in the scanning X-band "hydro-radar" allow new possibilities
for more accurate estimation of rainfall and snowfall rates. Both
scanning radars have also been used for studies of the ocean surface and
both are equipped with the new RADS processor that was
designed at ETL.
Precipitation and Cloud Radars
ETL Suite Overview
|
Radar | Wavelength |
Scanning? | Dual-polarization? |
Primary Use |
NOAA/D (hydro-radar) |
3.2 cm (X-band) |
yes | yes |
rain, snow, storms, ocean surface |
NOAA/K (cloud radar) |
8.7 mm (Ka-band) |
yes | yes |
clouds, boundary layer, ocean surface |
NPCO (cloud radar+) |
8.7 mm (Ka-band) |
no | no |
unattended, long-term cloud profiling |
MMCR-ARM (cloud radar) |
8.7 mm (Ka-band) |
no | planned |
unattended, long-term cloud-monitoring |
Ron Brown
(ship-based precip radar)
|
5-cm (C-band) |
yes | no |
ocean precipitation measurement |
S-PROF
(precip profiler)
|
10-cm (S-band) |
no | no |
unattended, precipitation measurement |
NOAA D 9.3-GHz Atmosphere & Ocean 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.
NOAA/K 35GHz Scanning Cloud Radar
ETL has developed a Ka-band (8.7-mm wavelength) system designed primarily
for observations of non-precipitating and weakly
precipitating clouds. By virtue of its short wavelength, it has excellent
sensitivity to very small hydrometeors and is insensitive to ground clutter.
The radar has been used extensively for research of the radiative effects of
clouds for climate change programs and for observations of
winter storms. A rotating quarter-wave plate allows transmission of a
continuous sequence of polarizations from circular to elliptical to linear
to examine hydrometeor types. The radar transmits 85-kW of peak power in a
0.5-degree conical beam width using a 1-m parabolic
antenna with an offset Cassegrain feed. Radial velocity, reflectivity,
and depolarization are measured at 256 gates with 37.5m resolution using
PPI and RHI or fixed beam scans. Sensitivity is about -30 dBZ at 10-km range.
In another configuration H,V, or slant-linear dual-polarization is available
with a 1.8 meter antenna for even greater sensitivity. The radar uses ETL's
new Radar Acquisition and Display (RADS) system.
NOAA Portable Cloud Observatory (NPCO)
The NPCO is a unified single unit that combines active and passive remote sensinginstruments for observing clouds overhead. It was formerly called the MMCR package. This
observatory is housed in a standard 20-foot sea container for automated operations on land or
on research ships at sea. The heart of the NPCO is a 35-GHz cloud radar that is identical to
the MMCR cloud radar built by ETL for the U.S. Department of Energy. This radar is able
to detect extremely weak clouds overhead with resolution as fine as 45 m. Dual-channel
microwave radiometers and a narrow-band infrared radiometer also point vertically along side
of the radar s beam. Standard surface meteorological instruments complete the suite of
sensors in the container. Estimates of cloud microphysical properties, such as vertical profiles
of hydrometeor median size, total concentration, and mass content are computed from the
combined radar and radiometer data using retrieval techniques developed at ETL.
ARM Millimeter-Wave Cloud Radar (MMCR)
ETL designed and built the
MMCR in the 1990's for the U.S. Department of
Energy's Atmospheric Radiation Measurement (ARM) program to monitor
cloud conditions over Cloud and Radiation Testbed (CART) sites. Using
data from many instruments at these sites, scientists are examining how
clouds affect climate and climate change through their
interactions with radiant energy in the atmosphere. The MMCR is an
unattended 35-GHz Doppler radar that has the ability to detect extremely
weak clouds as well as precipitation overhead. It uses a 6-ft or 10-ft
antenna and sophisticated signal processing methods to attain
exceptionally good sensitivity and a low-power transmitter for dependable
long-term operations. Height resolution of the data is as good as 45 m.
The first MMCR was installed at the site in Oklahoma in 1996, followed by
others in Alaska and the tropical western Pacific. An upgraded data
system and dual-polarization hardware are now being constructed
at ETL for the ARM MMCRs.
Ron Brown Scanning Precipitation Radar
NOAA/ETL serves as instrument mentor for the Doppler C-band radar which was
built and installed by Radtec Engineering, Inc.. The instrument is
available to principle investigators for a wide variety of marine
studies sponsored by NOAA and other agencies. C-band represents a
compromise between more heavily attenuated higher radar frequencies,
such as X-band, and the larger size and weight requirements of lower
frequency S-band weather radars, such those used for the land-based
WSR-88D (NEXRAD) systems. In many respects, this radar is the equivalent
of an oceangoing NEXRAD that can provide research-quality observations,
in addition to routine storm surveillance. Rain statistics at sea
derived from its data are well suited for evaluating assumptions used in
satellite precipitation algorithms.
S-band Precipitation 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.
Ground-Based Radiometers
Radiometers are passive instruments which receive energy signals that
are naturally emitted from objects within the instrument's viewing angle. A
radiometer antenna pointed upward into the air receives infrared and radio
frequency emissions from the atmosphere's various chemical constituents.
Each constituent possesses a unique emission spectrum that
corresponds exactly to its absorption spectrum. Radiometers "listen" at
selected frequencies to best sort out the constituents and measure their
abundances.
Airborne Microwave Radiometers
System |
Frequency (GHz) |
Bandwidth (GHz) |
Beamwidth (deg.) |
Sensitivity K @ 1 sec |
Polarization |
R05 Radiometer |
60.0 |
2.0 |
6 |
0.04 |
linear |
RP08 Polarimeter |
37.0 |
1.0 |
6 |
0.05 |
-45, 0, +45 |
RP20 Polarimeter |
15.0 |
0.8 |
8 |
0.05 |
-45, 0, +45 |
RP30 Polarimeter |
10.0 |
0.8 |
8 |
0.05 |
-45, 0, +45 |
R20/30 Radiometer |
23.87/31.65 |
0.5 |
3.6/3.6 |
0.064 |
linear H/V |
Ground-Based Microwave Radiometers
System |
Frequencies (GHz) |
Beamwidth (deg.) |
Spinning Flat? |
Scanning Capability |
Additional Sensors |
Radiometer Sea Container |
23.87, 31.65,90.0* |
2.5 |
yes |
Elevation |
Surface Met |
MMCR Sea Container |
20.6, 31.65, 90.0* |
5.0 |
yes |
Zenith only |
Surface Met
IR Radiometer |
Portable Building |
20.6, 31.65 |
5.0 |
no |
Zenith only |
Surface Met |
Four Channel 50 GHz System |
53.85, 56.02, 54.94, 57.97 |
|
|
|
|
Prototype Mailbox Radiometer |
23.8, 31.6 |
5.0 |
|
|
|
Prototype Mailbox Radiometer |
90 |
|
|
|
|
* = optionally available on Radiometer or MMCR container units
|
Ground-Based Infrared Radiometers in Operation
System |
Spectral Sensitivity |
Field of View |
Heitronics |
10.61 - 11.27 microns |
2 Degrees |
Barnes PRT-5 |
9.95 - 11.43 microns |
2 Degrees |
|