Weather Radar Technology Beyond NEXRAD (2002) / Chapter Skim
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3. Advanced Radar Technologies - Capabilities and Opportunities
3. Advanced Radar Technologies - Capabilities and Opportunities
Pages 23-35
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From page 23... ...
The remaining sections deal with valuable improvements over the current system and describe several related technologies. Topics include means of improving data quality to reduce interpretive uncertainties, quantifying precipitation and improving precipitation classification via polarimetric measurements, use of phased array antennas to reduce volume sampling times and enable agile beam steering, and use of innovative signal processing schemes to improve radar performance.
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From page 24... ...
These potential revised spectrum allocations could limit or preclude radar operation in any of our existing "weather bands," in particular the low-attenuation S-band. FREQUENCY ALLOCATION Retaining the allocation of weather radar frequencies, particularly at S-band wavelengths with their relatively small attenuation in heavy rainfall, is critically important to maintaining the operational integrity of the NEXRAD radar system as well as preserving its capabilities for any future replacement system.
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From page 25... ...
Data corruption usually results from such factors as range folding, normal and anomalous propagation ground clutter, velocity aliasing, radio frequency (RF) interference, improper maintenance procedures, and nonatmospheric reflectors such as birds or chaff.
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From page 26... ...
that can be used to detect and filter contamination from noise as well as from nonmeteorological echoes such as surface clutter, chaff, birds and insects. Third, the differential polarization parameters, such as differential reflectivity and specific differential propagation phase, are immune to absolute calibration errors.
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From page 27... ...
Advanced radar technology can reduce, but not completely eliminate, data corruption due to ground clutter. Electronically scanned phased array radar has the flexibility to suppress ground clutter entering the main beam by steering the main beam immediately above clutter objects appearing on the horizon (moun
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From page 28... ...
An alternative architecture utilizing a rotating single array appears entirely satisfactory for the next generation weather radar. A simple rotating slotted waveguide array has been proposed for a one-dimensional elevation steering concept of a single agile beam (Smith, 1974; Keeler and Frush, 1983; Josefsson, 1991; Holloway and Keeler, 1993~.
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From page 29... ...
For example, multiple transmit beams, each having relatively high sidelobes using a high-power transmit antenna, could be coupled with a precision, low-power receive phased array capable of high overall isolation between the individual beams. Frequency steering techniques or digital beam forming technology would allow the same rapid VCP coverage while using longer dwell times on each beam.
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From page 30... ...
This phased array test bed, cumbersome by present standards, will be operated to test and evaluate phased array scanning techniques that will likely employ modern, cost-effective array technologies for a future implementation. Slotted waveguide antenna technology offers a viable technology for phased array radar steerable in one dimension.
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From page 31... ...
may be employed to acquire independent samples in range that may be averaged to obtain statistically accurate information in a short dwell time. For many aviation and military applications, an extended waveform using a form of pulse compression is entirely acceptable.
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From page 32... ...
Pulse compression of long, low peak power waveforms is a natural resolution; however, range sidelobe contamination in high-reflectivity gradients may limit the quality of the measurements. A definitive feasibility demonstration is needed for pulse compression techniques for weather radars before low peak power solid-state transmitters can be seriously considered for the next generation radars.
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From page 33... ...
In summary, technological advances in signal processor and receiver technologies are expected to meet or exceed needs of the next generation weather radar. Adaptive Waveform Selection and Scanning Fully adaptive 2D beam steering capability allows extreme flexibility in developing waveforms not only to enhance data quality, but also to acquire rapid update data and to allocate transmit power where it is most needed.
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From page 34... ...
Recommendation Far-Term Adaptive waveform selection, which may even be applied to present systems, and agile beam scanning strategies, which require an electronically scanned phased array system, should be explored to optimize performance in diverse weather. Tomographic Processing Tomographic processing has not been extensively applied to surface radars; however, it has extensive potential with path-integrated measurements (i.e., attenuation and differential propagation phase)
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From page 35... ...
An example of such specialized processing is the measurement of the nearsurface refractive index of air using fixed ground targets (Fabry et al., 1997~. As the refractive index of air in the propagation path changes, the time of travel of radar waves between the antenna and the fixed ground target varies slightly and causes a change in the measured ground target echo's absolute phase.
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