Joint Polarization Experiment

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Joint Polarization Experiment
NWS Office Slidell LA NEXRAD.JPG
A WSR-88D, the subject of JPOLE
Country of originUSA
Introduced1988
No. built160 [1]
TypeWeather radar
Frequency2900 MHz (S-band)
PRF 300 - 1200 Hz
Beamwidth 0.95° [2]
Range460km
Diameter8.51 m
Azimuth 0-360°
Elevation-1°— 20°
Power750 kW

The Joint Polarization Experiment (JPOLE) was a test for evaluating the performance of the WSR-88D in order to modify it to include dual polarization. This program was a joint project of the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the US Air Force Meteorological Agency (AFWA), which took place from 2000-2004. It has resulted in the upgrading of the entire meteorological radar network in the United States by adding dual polarization to better determine the type of hydrometeor, and quantities that have fallen. [3]

Contents

History

During the years preceding JPOLE, the National Center for Atmospheric Research (NCAR) was among the first centers in the field to utilize dual polarization for a weather radar, with staff Dusan S. Zrnic and Alexander V. Ryzhkov. In July 2000, the first planning meeting for JPOLE was held at the National Severe Storms Laboratory (NSSL), and it was determined that the project would take place in two stages:

Description

JPOLE was introduced using a testbed NEXRAD mounted in Norman, Oklahoma, on the grounds of the NSSL. The signal from its transmitter was split in two to obtain a conventional horizontal polarization and a vertical polarization. [4] The signals were sent to the antenna by two waveguides and could simultaneously transmit the two signals and furthermore receive the echoes returned by the precipitation in the emitted or orthogonal planes. [5]

In general, most hydrometeors have a larger axis in the horizontal (for example, drops of rain become oblates when falling because of the resistance of the air). Because of this, the dipolar axis of the water molecules therefore tends to align in the horizontal and, as such, the radar beam will generally be horizontally polarized to take advantage of maximum return properties. If we send at the same time a pulse with vertical polarization and another with horizontal polarization, we can note a difference of several characteristics between these returns: [6]

Differential Reflectivity ()

Correlation Coefficient ()

Differential Phase Shift ()

Related Research Articles

Polarization (waves) Property of waves that can oscillate with more than one orientation

Polarization is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string (see image); for example, in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves in solids.

Doppler radar 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.

Millimeter cloud radar

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.

Parabolic antenna Type of antenna

A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves to the receiver in its focal point. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct radio waves in a narrow beam, or receive radio waves from one particular direction only. Parabolic antennas have some of the highest gains, meaning that they can produce the narrowest beamwidths, of any antenna type. In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the wavelength of the radio waves used, so parabolic antennas are used in the high frequency part of the radio spectrum, at UHF and microwave (SHF) frequencies, at which the wavelengths are small enough that conveniently-sized reflectors can be used.

Ice crystals Solid frozen water molecules

Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust.

NEXRAD Nationwide network of Doppler weather radars operated by the U.S. National Weather Service

NEXRAD or Nexrad is a network of 160 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.

Synthetic-aperture radar Form of radar used to create images of landscapes

Synthetic-aperture radar (SAR) is a form of radar that is used to create two-dimensional images or three-dimensional reconstructions of objects, such as landscapes. SAR uses the motion of the radar antenna over a target region to provide finer spatial resolution than conventional stationary beam-scanning radars. SAR is typically mounted on a moving platform, such as an aircraft or spacecraft, and has its origins in an advanced form of side looking airborne radar (SLAR). The distance the SAR device travels over a target during the period when the target scene is illuminated creates the large synthetic antenna aperture. Typically, the larger the aperture, the higher the image resolution will be, regardless of whether the aperture is physical or synthetic – this allows SAR to create high-resolution images with comparatively small physical antennas. For a fixed antenna size and orientation, objects which are further away remain illuminated longer - therefore SAR has the property of creating larger synthetic apertures for more distant objects, which results in a consistent spatial resolution over a range of viewing distances.

Weather radar 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.

Polarimetry Measurement and interpretation of the polarization of transverse waves

Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or have been reflected, refracted or diffracted by some material in order to characterize that object.

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).

dBZ (meteorology) Unit of measure used in weather radar

dBZ stands for decibel relative to Z. It is a logarithmic dimensionless technical unit used in radar, mostly in weather radar, to compare the equivalent reflectivity factor (Z) of a remote object to the return of a droplet of rain with a diameter of 1 mm. It is proportional to the number of drops per unit volume and the sixth power of drops' diameter and is thus used to estimate the rain or snow intensity. With other variables analyzed from the radar returns it helps to determine the type of precipitation. Both the radar reflectivity factor and its logarithmic version are commonly referred to as reflectivity when the context is clear. In short, the higher the dBZ value, the more likely it is for severe weather to occur in the form of precipitation.

The Center for Analysis and Prediction of Storms (CAPS) was established at the University of Oklahoma in 1989 as one of the first eleven National Science Foundation Science and Technology Centers. Located at the National Weather Center in Norman, Oklahoma, its mission is the development of techniques for the computer-based prediction of high-impact local weather, such as individual spring and winter storms, with the NEXRAD (WSR-88D) Doppler weather radar serving as a key data source.

ARMOR Doppler Weather Radar

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.

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.

Tornado vortex signature

A tornadic vortex signature, abbreviated TVS, is a Pulse-Doppler radar weather radar detected rotation algorithm that indicates the likely presence of a strong mesocyclone that is in some stage of tornadogenesis. It may give meteorologists the ability to pinpoint and track the location of tornadic rotation within a larger storm, but it is not an important feature in the National Weather Service's warning operations.

OU-PRIME

OU-PRIME was an advanced Doppler weather radar. It was completed in January 2009 after a ten-month construction period and commissioned on April 4, 2009. It is operated by the Advanced Radar Research Center (ARRC) at the University of Oklahoma (OU). The radar was manufactured by Enterprise Electronics Corporation to provide OU students and faculty a platform for research and education in the field of radar meteorology. This C-band polarimetric radar has some of the highest resolution data of any C-band weather radar in the United States.

Tornado debris signature

A tornadic debris signature (TDS), often colloquially referred to as a debris ball, also colloquially "debris spike", is an area of high reflectivity on weather radar caused by debris lofting into the air, usually associated with a tornado. A TDS may also be indicated by dual-polarization radar products, designated as a polarimetric tornado debris signature (PTDS). Polarimetric radar can discern meteorological and nonmeteorological hydrometeors and the co-location of a PTDS with the enhanced reflectivity of a debris ball are used by meteorologists as confirmation that a tornado is occurring.

NSSL Doppler

NOAA's 10 cm Doppler Weather Radar was a 10 cm wavelength S-band Doppler Weather Radar commonly referred to as NSSL Doppler, and was used to track severe weather and related meteorological phenomena. The radar became operational soon after its donation, collecting its first data in May 1971. Data was collected on magnetic tapes and processed on a NASA computer post event due to the lack of real-time capability at the time.

Multifunction Phased Array Radar

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.

Present weather sensor

The present weather sensor (PWS) is a component of an automatic weather station that detects the presence of hydrometeors and determines their type and intensity. It works on a principle similar to a bistatic radar, noting the passage of droplets, or flakes, between a transmitter and a sensor. These instruments in automatic weather stations are used to simulate the observation taken by a human observer. They allow rapid reporting of any change in the type and intensity of precipitation, but include interpretation limitations.

References

  1. "NOAA NEXt-Generation RADar (NEXRAD) Products - Data.gov". catalog.data.gov.
  2. Weather Radar Technology Beyond NEXRAD. 31 July 2002. doi:10.17226/10394. ISBN   978-0-309-08466-6.
  3. Scharfenberg, Kevin A.; Miller, Daniel J.; Schuur, Terry J.; Schlatter, Paul T.; Giangrande, Scott E.; Melnikov, Valery M.; Burgess, Donald W.; Andra, David L.; Foster, Michael P.; Krause, John M. (1 October 2005). "The Joint Polarization Experiment: Polarimetric Radar in Forecasting and Warning Decision Making". Weather and Forecasting. 20 (5): 775–788. Bibcode:2005WtFor..20..775S. doi:10.1175/waf881.1.
  4. Service, US Department of Commerce, NOAA, National Weather. "Contact Us". www.weather.gov.
  5. Ryzhkov, Alexander V.; Schuur, Terry J.; Burgess, Donald W.; Heinselman, Pamela L.; Giangrande, Scott E.; Zrnic, Dusan S. (1 June 2005). "The Joint Polarization Experiment: Polarimetric Rainfall Measurements and Hydrometeor Classification". Bulletin of the American Meteorological Society. 86 (6): 809–824. Bibcode:2005BAMS...86..809R. doi:10.1175/bams-86-6-809.
  6. "Archived copy" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2018-08-22.{{cite web}}: CS1 maint: archived copy as title (link)
  7. "Polarimetric Radar Page". www.cimms.ou.edu.