Terminal Doppler Weather Radar

Last updated
Airports with a TDWR in the US. Another in San Juan, Puerto Rico, is not shown on this map. Map TDWR.svg
Airports with a TDWR in the US. Another in San Juan, Puerto Rico, is not shown on this map.

Terminal Doppler Weather Radar (TDWR) is a Doppler weather radar system with a three-dimensional "pencil beam" used primarily for the detection of hazardous wind shear conditions, precipitation, and winds aloft on and near major airports situated in climates with great exposure to thunderstorms in the United States. [1] As of 2011, all were in-service with 45 operational radars, some covering multiple airports in major metropolitan locations, across the United States & Puerto Rico. [2] [3] Several similar weather radars have also been sold to other countries such as China (Hong Kong). [4] [5] Funded by the United States Federal Aviation Administration (FAA), TDWR technology was developed in the early 1990s at Lincoln Laboratory, part of the Massachusetts Institute of Technology, to assist air traffic controllers by providing real-time wind shear detection and high-resolution precipitation data. [6]

Contents

The primary advantage of TDWRs over previous weather radars is that it has a finer range resolution—meaning it can see smaller areas of the atmosphere. [1] The reason for the resolution is that the TDWR has a narrower beam than traditional radar systems, and that it uses a set of algorithms to reduce ground clutter. [6]

Characteristics

TDWR uses a carrier wave in the frequency band of 5600–5650 MHz (5 cm wavelength), with a narrow beam and angular resolution of 0.5 degrees, and has a peak power of 250 kW. In reflectivity, the resolution in distance is 150 metres (500 ft) within 135 kilometres (84 mi) of the radar and 300 metres (1,000 ft) from 135 kilometres (84 mi) to 460 kilometres (290 mi) to the radar. [1] The reason for this difference is that since the width resolution is angular, at larger range the width of the beam becomes quite large and to obtain a better averaging of data in a resolution volume, one has to increase the number of range pulse bins. This cut off is arbitrarily set for the software at 135 kilometres (84 mi).

In radial velocities, data are available up to 90 kilometres (56 mi) from the radar with the full angular resolution of 0.5 degrees and range resolution of 150 metres (490 ft). [1] Because of the Pulse Repetition Frequency (PRF) used, there is aliasing and the maximum non-ambiguous velocity is 20 to 30 knots (23 to 35 mph; 37 to 56 km/h). [1]

TDWR can perform near-surface scans at a 0.1-0.3 degree angle of inclination from the Earth's surface every minute. It can also perform composite scans in which the radar observes at several different angles of inclination in order to obtain a fuller picture of the atmospheric conditions; each such composite scan requires 6 minutes. [1] [4]

Comparison with NEXRAD

A TDWR return (top) and NEXRAD return (bottom) showing the improved resolution in reflectivity, but also showing the attenuation in the TDWR due to absorption from heavy precipitation as a black gap TDWR and NEXRAD Refl Compared vert.png
A TDWR return (top) and NEXRAD return (bottom) showing the improved resolution in reflectivity, but also showing the attenuation in the TDWR due to absorption from heavy precipitation as a black gap

Advantages

A NEXRAD weather radar currently used by the National Weather Service (NWS) is a 10 cm wavelength (2700-3000 MHz) radar capable of a complete scan every 4.5 to 10 minutes, depending on the number of angles scanned, and depending on whether or not MESO-SAILS [7] is active, which adds a supplemental low-level scan while completing a volume scan. Its resolution is 0.5 degrees in width and 250 metres (820 ft) in range. The non-ambiguous radial velocity is 62 knots (71 mph; 115 km/h) up to 230 kilometres (140 mi) from the radar. [1] [4]

The range resolution of the TDWR is nearly twice that of that classic NEXRAD scheme. This will give much better details on small features in precipitation patterns, particularly in thunderstorms, in reflectivity and radial velocity. However, this finer resolution is only available up to 135 kilometres (84 mi) from the radar; beyond that, the resolution is close to that of the NEXRAD. However, since August 2008, oversampling on NEXRAD has increased its resolution in lower elevations in reflectivity data to 0.25 km (0.16 mi) by 0.5 degree, and increased the range of Doppler velocity data to 300 km (190 mi). [8] [9] This lessens the advantages of TDWR for those elevations.

Shortcomings

The TDWRs and NEXRADs complement each other with overlapping coverage, each designed to optimally view different airspace regimes. TDWR's rapid update rate over short range (55 nmi range) captures microscale weather events quickly in terminal airspace. NEXRAD is a long range radar (200 nmi range) designed to serve multiple en route functions at high altitude, above terminal airspace, and far between terminals. NEXRAD's slower update rate covering a wider volume, captures mesoscale weather events. The shorter 5 centimetres (2.0 in) wavelength, which is closer to the size of a raindrop than the 10 centimetres (3.9 in) wavelength, is partially absorbed by precipitation. This is a serious drawback to using TDWR, as the signal can be strongly attenuated in heavy precipitation. This attenuation means that the radar cannot "see" very far through heavy rain and could miss severe weather such as strong thunderstorms which may contain the signature of a tornado, when there is heavy rain falling between the radar and that storm. When heavy rain is falling on the radome, the range of the TDWR is further limited. [1] [4] Finally, hail in a thunderstorm scanned by a TDWR can entirely block the signal as its size is larger than the wavelength. [1] [4]

A second problem is the smaller non-ambiguous radial velocity or Nyquist velocity. In the case of the TDWR, this means the velocity of precipitations moving at a speed beyond 30 knots (35 mph; 56 km/h) away or toward the radar will be analyzed incorrectly because of aliasing. Algorithms to correct for this do not always yield the proper results. NEXRAD has a threshold that is twice as high (62 knots (71 mph; 115 km/h)) and thus less processing and interpretation are needed. Because of this, the resolution of radar reflectivity for small scale features such as mesocyclones might be better in TDWR, but the velocity resolution may be worse, or at the very least incorrectly analyzed.

Thus, it is best to use the TDWR in conjunction with a traditional NEXRAD nearby to ensure that nothing is missed. In contrast to NEXRAD, which has national coverage of the contiguous United States (although with some holes due to terrain), TDWR has sporadic coverage meant for major airports. While certain areas of the country (the Northeast megalopolis, the states of Ohio and Florida, and the southwestern quarter of Tornado Alley in Oklahoma and Texas) have a high density of TDWR units, others (the entire West Coast, the northern Great Plains and Rocky Mountains, portions of the Deep South, and a stretch running from northern Pennsylvania through upstate New York and into northern New England) have no TDWR coverage at all.

Data processing improvements

The National Severe Storms Laboratory (NSSL) has a program of development and improvement of radar products extracted from data obtained from TDWR and NEXRAD radars. The Severe Weather Warning Applications and Technology Transfer (SWAT) group is sponsored by the National Weather Service and the FAA. It is working in 2009 on better filtering of non-weather echoes, better dealiasing algorithms of velocities, techniques to extract the horizontal component of the wind field from one or multiple radars. NSSL has been providing TDWR data to NWS office since the late 1990s. [10] The NWS's Radar Operations Center (ROC), although focused on the NEXRAD network, also works with TDWRs.

See also

Related Research Articles

<span class="mw-page-title-main">Doppler radar</span> Type of radar equipment

A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal. This variation gives direct and highly accurate measurements of the radial component of a target's velocity relative to the radar. The term applies to radar systems in many domains like aviation, police radar detectors, navigation, meteorology, etc.

<span class="mw-page-title-main">Millimeter cloud radar</span> Weather radar tuned to cloud detection

Millimeter-wave cloud radars, also denominated cloud radars, are radar systems designed to monitor clouds with operating frequencies between 24 and 110 GHz. Accordingly, their wavelengths range from 1 mm to 1.11 cm, about ten times shorter than those used in conventional S band radars such as NEXRAD.

<span class="mw-page-title-main">NEXRAD</span> Network of weather radars operated by the NWS

NEXRAD or Nexrad is a network of 159 high-resolution S-band Doppler weather radars operated by the National Weather Service (NWS), an agency of the National Oceanic and Atmospheric Administration (NOAA) within the United States Department of Commerce, the Federal Aviation Administration (FAA) within the Department of Transportation, and the U.S. Air Force within the Department of Defense. Its technical name is WSR-88D.

<span class="mw-page-title-main">WSR-57</span> Weather radar used by the U.S. Weather Bureau

WSR-57 radars were the USA's main weather surveillance radar for over 35 years. The National Weather Service operated a network of this model radar across the country, watching for severe weather.

<span class="mw-page-title-main">Weather radar</span> Radar used to locate and monitor meteorological conditions

Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type. Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.

<span class="mw-page-title-main">Hook echo</span> Weather radar signature indicating tornadic circulation in a supercell thunderstorm

A hook echo is a pendant or hook-shaped weather radar signature as part of some supercell thunderstorms. It is found in the lower portions of a storm as air and precipitation flow into a mesocyclone, resulting in a curved feature of reflectivity. The echo is produced by rain, hail, or even debris being wrapped around the supercell. It is one of the classic hallmarks of tornado-producing supercells. The National Weather Service may consider the presence of a hook echo coinciding with a tornado vortex signature as sufficient to justify issuing a tornado warning.

<span class="mw-page-title-main">Pulse-Doppler radar</span> Type of radar system

A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics.

The National Severe Storms Laboratory (NSSL) is a National Oceanic and Atmospheric Administration (NOAA) weather research laboratory under the Office of Oceanic and Atmospheric Research. It is one of seven NOAA Research Laboratories (RLs).

<span class="mw-page-title-main">Bounded weak echo region</span> Weather feature

The bounded weak echo region, also known as a BWER or a vault, is a radar signature within a thunderstorm characterized by a local minimum in radar reflectivity at low levels which extends upward into, and is surrounded by, higher reflectivities aloft, forming a kind of dome of weak echoes. This feature is associated with a strong updraft and is almost always found in the inflow region of a thunderstorm: it cannot be seen visually. The BWER has been noted on radar imagery of severe thunderstorms since 1973 and has a lightning detection system equivalent known as a lightning hole.

The King City weather radar station is a weather radar located in King City, Ontario, Canada. It is operated by Environment Canada and is part of the Canadian weather radar network, for which it is the primary research station.

<span class="mw-page-title-main">Canadian weather radar network</span> Weather radars used by the Environment and Climate Change Canada

The Canadian weather radar network consists of 33 weather radars spanning Canada's most populated regions. Their primary purpose is the early detection of precipitation, its motion and the threat it poses to life and property.

<span class="mw-page-title-main">ARMOR Doppler Weather Radar</span>

ARMOR Doppler weather radar is a C-Band, Dual-Polarimetric Doppler Weather Radar, located at the Huntsville International Airport in Huntsville, Alabama. The radar is a collaborative effort between WHNT-TV and the University of Alabama in Huntsville. Live data for the radar is only available to a limited audience, such as UAH employees and NWS meteorologists. All ARMOR data is archived at the National Space Science and Technology Center located on the UAH campus.

Volumetric Imaging and Processing of Integrated Radar, known by the acronym VIPIR, is an analysis and display program for Doppler weather radar, created and sold by Baron Services. This software allows improved analysis of radar data for private users, in particular television stations, similar to the Weather Decision Support System program used by the National Weather Service.

Convective storm detection is the meteorological observation, and short-term prediction, of deep moist convection (DMC). DMC describes atmospheric conditions producing single or clusters of large vertical extension clouds ranging from cumulus congestus to cumulonimbus, the latter producing thunderstorms associated with lightning and thunder. Those two types of clouds can produce severe weather at the surface and aloft.

<span class="mw-page-title-main">GRLevelX</span>

GRLevelX is a suite of data processing and display programs developed by Gibson Ridge Software, LLC (GRS), to view weather radar data. It went on the market in March 2005. It comes in three versions, all of which ingest raw data: GRLevel2 and GRLevel2 Analyst Edition for viewing Level II data of the National Weather Service (NWS), and GRLevel3 for viewing Level III data. All programs are capable of rendering dual polarization data.

The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.

<span class="mw-page-title-main">Radar Operations Center</span>

The Radar Operations Center (ROC) is a National Weather Service (NWS) unit that coordinates the development, maintenance, and training for the NEXRAD weather radar network. It is located at the National Weather Center (NWC) in Norman, Oklahoma and run by the National Oceanic and Atmospheric Administration (NOAA) in the Department of Commerce with partners at the Department of Defense and the Department of Transportation.

<span class="mw-page-title-main">Multifunction Phased Array Radar</span>

Multifunction Phased Array Radar (MPAR) was an experimental Doppler radar system that utilized phased array technology. MPAR could scan at angles as high as 60 degrees in elevation, and simultaneously track meteorological phenomena, biological flyers, non-cooperative aircraft, and air traffic. From 2003 through 2016, there was one operational MPAR within the mainland United States—a repurposed AN/SPY-1A radar set loaned to NOAA by the U.S. Navy. The MPAR was decommissioned and removed in 2016.

<span class="mw-page-title-main">Glossary of meteorology</span> List of definitions of terms and concepts commonly used in meteorology

This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.

<span class="mw-page-title-main">National Weather Service Gray/Portland, Maine</span>

The National Weather Service Gray/Portland, Maine (GYX) is a local office of the National Weather Service responsible for monitoring weather conditions over western Maine and all of New Hampshire. It is situated in Gray, Maine, in the metropolitan area of Portland, in a rural setting.

References

  1. 1 2 3 4 5 6 7 8 9 "Terminal Doppler Weather Radar - Supplemental Product Generator (TDWR-SPG)". National Weather Service. Retrieved August 5, 2017.
  2. ↑ "Search Proximity to Terminal Doppler Weather Radars (TDWRs)". Spectrum Bridge, Inc. Archived from the original on 7 March 2012. Retrieved 4 August 2011.
  3. ↑ "TDWR Locations and Frequencies". WISPA. Retrieved 18 July 2017.
  4. 1 2 3 4 5 "Wunderground launches high-definition radar product". Dr. Jeff Masters' WunderBlog. Weather Underground. 15 December 2008. Retrieved 2018-06-21.
  5. ↑ Chi M. Shun and Sharon S. Y. Lau (2000). "Terminal Doppler Weather Radar (TDWR) observation of atmospheric flow over complex terrain during tropical cyclone passages". Proc. SPIE. 4152 (42): 42. Bibcode:2000SPIE.4152...42S. CiteSeerX   10.1.1.551.3486 . doi:10.1117/12.410622. S2CID   130709921.
  6. 1 2 "Terminal Doppler Weather Radar (TDWR)". MIT Lincoln Laboratory. Retrieved 4 August 2009.
  7. ↑ https://www.roc.noaa.gov/wsr88d/PublicDocs/NewTechnology/MESO-SAILS_Description_Briefing_Jan_2014.pdf [ bare URL PDF ]
  8. ↑ "Build10FAQ". Radar Operations Center. National Oceanic and Atmospheric Administration. Archived from the original on 2008-07-04.
  9. ↑ "RPG SW BUILD 10.0 – INCLUDES REPORTING FOR SW 41 RDA". Radar Operations Center. National Oceanic and Atmospheric Administration.
  10. ↑ "WSR-88D/TDWR Operational Product Development and Improvement". Warning Applications Research. National Severe Storms Laboratory. 2009. Archived from the original on 2011-05-19. Retrieved 2009-09-18.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.