• Banta, R. M., 1990: The role of mountain flows in making clouds. Atmospheric Processes over Complex Terrain, Meteor. Monogr., No. 45, Amer. Meteor. Soc., 229–283.

    • Search Google Scholar
    • Export Citation
  • Bargen, D. W., and Brown R. C. , 1980: Interactive radar velocity unfolding. Preprints, 19th Conf. on Radar Meteorology, Miami, FL, Amer. Meteor. Soc., 278–283.

    • Search Google Scholar
    • Export Citation
  • Barnes, S. L., 1980: Report on a meeting to establish a common Doppler radar data exchange format. Bull. Amer. Meteor. Soc, 61 , 14011404.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bergen, W. R., and Albers S. C. , 1988: Two- and three-dimensional dealiasing of Doppler radar velocities. J. Atmos. Oceanic Technol, 5 , 305319.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Binder, P., and and Coauthors, 1995: Mesoscale Alpine Programme: Design proposal. MAP Data Centre, ETH Zürich, 65 pp.

  • Bougeault, P., and and Coauthors, 2001: The MAP special observing period. Bull. Amer. Meteor. Soc, 82 , 433462.

  • Browning, K. A., and Wexler R. , 1968: The determination of kinematic properties of a wind field using Doppler radar. J. Appl. Meteor, 7 , 105113.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chong, M., and and Coauthors, 2000: Real-time wind synthesis from Doppler radar observations during the Mesoscale Alpine Programme. Bull. Amer. Meteor. Soc, 81 , 29532962.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Doviak, R. J., and Zrnić D. S. , 1993: Doppler Radar and Weather Observations. 2d ed. Academic Press, 562 pp.

  • Durran, D. R., 1986: Mountain waves. Mesoscale Meteorology and Forecasting, P. Ray, Ed., Amer. Meteor. Soc., 472–492.

  • Eilts, M. D., and Smith S. D. , 1990: Efficient dealiasing of Doppler velocities using local environment constraints. J. Atmos. Oceanic Technol, 7 , 118128.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Georgis, J-F., Roux F. , and Hildebrand P. H. , 2000: Observation of precipitating systems over complex orography with meteorological Doppler radars: A feasibility study. Meteor. Atmos. Phys, 72 , 185202.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Germann, U., 1999: Vertical wind profile by Doppler radars. MAP Newsletter, No. 11, 6–7. [Available from Swiss Meteorological Institute, CH-8044 Zurich, Switzerland.].

    • Search Google Scholar
    • Export Citation
  • Hennington, L., 1981: Reducing the effects of Doppler radar ambiguities. J. Appl. Meteor, 20 , 15431546.

  • Houze, R. A. Jr, 1993: Cloud Dynamics. Academic Press, 573 pp.

  • James, C. N., Brodzik S. R. , Edmon H. , Houze Jr. R. A. , and Yuter S. E. , 2000: Radar data processing and visualization over complex terrain. Wea. Forecasting, 15 , 327338.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jing, Z., and Wiener G. , 1993: Two-dimensional dealiasing of Doppler velocities. J. Atmos. Oceanic Technol, 10 , 798808.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Joss, J., and and Coauthors, 1998: Operational use of radar for precipitation measurements in Switzerland. Final Rep., NRP 31, ETH Zürich, 108 pp.

    • Search Google Scholar
    • Export Citation
  • Merritt, M. W., 1984: Automatic velocity dealiasing for real-time applications. Proc. 22d Conf. on Radar Meteorology, Zurich, Switzerland, Amer. Meteor. Soc., 528–533.

    • Search Google Scholar
    • Export Citation
  • Ray, P., and Ziegler C. , 1977: Dealiasing first moment Doppler estimates. J. Appl. Meteor, 16 , 563564.

  • Schär, C., and Durran D. R. , 1997: Vortex formation and vortex shedding in continuously stratified flows past isolated topography. J. Atmos. Sci, 54 , 534554.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Smith, R. B., 1979: The influence of mountains on the atmosphere. Advances in Geophysics, Vol. 21, Academic Press, 87–230.

  • Whiteman, C. D., 1990: Observations of thermally developed wind systems in mountainous terrain. Atmospheric Processes over Complex Terrain, Meteor Monogr., No. 45, Amer. Meteor. Soc., 5–42.

    • Search Google Scholar
    • Export Citation
  • Yamada, Y., and Chong M. , 1999: VAD-based determination of the Nyquist interval number of Doppler velocity aliasing without wind information. J. Meteor. Soc. Japan, 77 , 447457.

    • Crossref
    • Search Google Scholar
    • Export Citation
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A Real-Time Four-Dimensional Doppler Dealiasing Scheme

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  • 1 Department of Atmospheric Sciences, University of Washington, Seattle, Washington
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Abstract

A new dealiasing scheme uses the full four-dimensionality available in an operational Doppler radar data stream. It examines one tilt angle at a time, beginning at the highest elevation where clutter is minimal and gate-to-gate shear is typically low compared to the Nyquist velocity. It then dealiases each tilt in descending order until the entire radial velocity volume is corrected.

In each tilt, the algorithm performs six simple steps. In the first two steps, a reflectivity threshold and filter are applied to the radial velocity field to remove unwanted noise. The third step initializes dealiasing by attempting to adjust the value of each gate by Nyquist intervals such that it agrees with both the nearest gate in the next higher tilt and the nearest gate in the previous volume. The gates that pass the third step at a high confidence level become the initial values for step four, which consist of correcting the neighboring gates within the scan, while preserving environmental shear as much as possible. In step five, remaining gates are compared to an average of neighboring corrected gates, and anomalous gates are deleted. As a last resort, step six uses a velocity azimuth display (VAD) analysis of the wind field to interpret and correct any remaining isolated echoes.

This scheme uses all available data dimensions to interpret and dealias each tilt and is efficient enough to operate on a continuous data stream. It performs reliably even in difficult dealiasing situations and at low Nyquist velocity. During two complex events observed by low-Nyquist Doppler radar in the European Alps, 93% of 4300 tilts were dealiased without error. When errors did occur, they were usually confined to small regions and most frequently resulted from the occurrence of gate-to-gate shear that was impossible to resolve by the Nyquist velocity.

* Current affiliation: Meteorology Lab, Embry-Riddle Aeronautical University, Prescott, Arizona.

Corresponding author address: Professor R. A. Houze Jr., Department of Atmospheric Sciences, Box 351640, University of Washington, Seattle, WA 98195-1640. Email: houze@atmos.washington.edu

Abstract

A new dealiasing scheme uses the full four-dimensionality available in an operational Doppler radar data stream. It examines one tilt angle at a time, beginning at the highest elevation where clutter is minimal and gate-to-gate shear is typically low compared to the Nyquist velocity. It then dealiases each tilt in descending order until the entire radial velocity volume is corrected.

In each tilt, the algorithm performs six simple steps. In the first two steps, a reflectivity threshold and filter are applied to the radial velocity field to remove unwanted noise. The third step initializes dealiasing by attempting to adjust the value of each gate by Nyquist intervals such that it agrees with both the nearest gate in the next higher tilt and the nearest gate in the previous volume. The gates that pass the third step at a high confidence level become the initial values for step four, which consist of correcting the neighboring gates within the scan, while preserving environmental shear as much as possible. In step five, remaining gates are compared to an average of neighboring corrected gates, and anomalous gates are deleted. As a last resort, step six uses a velocity azimuth display (VAD) analysis of the wind field to interpret and correct any remaining isolated echoes.

This scheme uses all available data dimensions to interpret and dealias each tilt and is efficient enough to operate on a continuous data stream. It performs reliably even in difficult dealiasing situations and at low Nyquist velocity. During two complex events observed by low-Nyquist Doppler radar in the European Alps, 93% of 4300 tilts were dealiased without error. When errors did occur, they were usually confined to small regions and most frequently resulted from the occurrence of gate-to-gate shear that was impossible to resolve by the Nyquist velocity.

* Current affiliation: Meteorology Lab, Embry-Riddle Aeronautical University, Prescott, Arizona.

Corresponding author address: Professor R. A. Houze Jr., Department of Atmospheric Sciences, Box 351640, University of Washington, Seattle, WA 98195-1640. Email: houze@atmos.washington.edu

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