• Andsager, K., Beard K. V. , and Laird N. F. , 1999: Laboratory measurements of axis ratios for large raindrops. J. Atmos. Sci., 56 , 26732683.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Beard, K. V., and Jameson A. R. , 1983: Raindrop canting. J. Atmos. Sci., 40 , 448454.

  • Bringi, V. N., and Chandrasekar V. , 2001: Polarimetric Doppler Weather Radar: Principles and Applications. Cambridge University Press, 636 pp.

    • Search Google Scholar
    • Export Citation
  • Hendry, A., Antar Y. M. M. , and McCormick G. C. , 1987: On the relationship between the degree of preferred orientation in precipitation and dual-polarization radar echo characteristics. Radio Sci., 22 , 3750.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Huang, G., Hubbert J. C. , and Bringi V. N. , 2001: Precipitation canting angle distribution estimation from covariance matrix analysis of CSU-CHILL radar data. Preprints, 30th Int. Conf. on Radar Meteorology, Munich, Germany, Amer. Meteor. Soc., 11B.6. [Available online at http://ams.confex.com/ams/pdfpapers/22111.pdf].

  • Huang, G., Bringi V. N. , and Hubbert J. C. , 2003: An algorithm for estimating the variance of the canting angle distribution using polarimetric covariance matrix data. Preprints, 31st Int. Conf. on Radar Meteorology, Seattle, WA, Amer. Meteor. Soc., 8B.5. [Available online at http://ams.confex.com/ams/pdfpapers/64005.pdf].

  • Hubbert, J. C., and Bringi V. N. , 1996: Specular null polarization theory: Applications to radar meteorology. IEEE Trans. Geosci. Remote Sens., 34 , 859873.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kruger, A., and Krajewski W. F. , 2002: Two-dimensional video disdrometer: A description. J. Atmos. Oceanic Technol., 19 , 602617.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mardia, K. V., 1972: Statistics of Directional Data. Academic Press, 357 pp.

  • McCormick, G. C., Hendry A. , and Barge B. L. , 1972: The anisotropy of precipitation media. Nature, 238 , 214216.

  • Metcalf, J. I., 1988: A new slant on the distribution and measurement of hydrometeor canting angles. J. Atmos. Oceanic Technol., 5 , 571578.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Randeu, W. L., Schönhuber M. , and Lammer G. , 2002: Real-time measurements and analyses of precipitation microstructure and dynamics. Proc. Second European Conf. on Radar Meteorology (ERAD), Delft, Netherlands, Copernicus Gesellschaft, 78–83.

  • Ryzhkov, A. V., Zrnic D. S. , Hubbert J. C. , Bringi V. N. , Vivekanandan J. , and Brandes E. A. , 2002: Polarimetric radar observations and interpretation of co-cross-polar correlation coefficients. J. Atmos. Oceanic Technol., 19 , 340354.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schauer, G., 1998: Distrometer-based determination of precipitation parameters for wave propagation research. M.S. thesis, Technical University of Graz, 98 pp.

  • Schönhuber, M., Randeu W. L. , Urban H. E. , and Poiares Baptista J. P. V. , 2000: Field measurements of raindrop orientation angles. Proc. AP2000 Millennium Conf. on Antennas and Propagation, Davos, Switzerland, IEE, CD-ROM.

  • Schönhuber, M., Lammer G. , and Randeu W. L. , 2007: One decade of imaging precipitation measurements by 2D video disdrometer. Adv. Geosci., 10 , 8590.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thurai, M., and Bringi V. N. , 2005: Drop axis ratios from 2D video disdrometer. J. Atmos. Oceanic Technol., 22 , 966978.

  • Thurai, M., Huang G. J. , Bringi V. N. , Randeu W. L. , and Schönhuber M. , 2007: Drop shapes, model comparisons, and calculations of polarimetric radar parameters in rain. J. Atmos. Oceanic Technol., 24 , 10191032.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wang, P. K., 1982: Mathematical description of the shape of conical hydrometeors. J. Atmos. Sci., 39 , 26152622.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 159 101 4
PDF Downloads 92 51 0

Orientation Angle Distributions of Drops after an 80-m Fall Using a 2D Video Disdrometer

View More View Less
  • 1 Colorado State University, Fort Collins, Colorado
Restricted access

Abstract

This note reports on the use of a 2D video disdrometer to estimate the orientation of drops (>2 mm) that were generated artificially and allowed to fall 80 m from a bridge with no obstruction and under calm conditions. This experimental setup enabled a large number of drops to be generated, up to 10 mm in horizontal dimension.

The distribution of the canting angles for all drops >2 mm was found to be nearly symmetric about 0° with standard deviation between 7° and 8°. From the canting angle distributions derived from the two orthogonal camera view planes, the distributions of the polar (θ) and azimuth (ϕ) angles were deduced; these two angles describe the 2D orientation of the symmetry axis. The azimuthal angle distribution was found to be nearly uniform in the range (0, 2π), whereas the distribution of pΩ(θ) = p(θ) sinθ was similar in shape to a special form of the Fisher distribution that is valid for describing the statistics on a spherical surface. The standard deviation of pΩ(θ) showed that larger drops are more stably oriented than smaller ones. This is in agreement with previous radar-based results of standard deviation of the canting angle decreasing with increasing Zdr.

Corresponding author address: V. N. Bringi, Dept. of ECE, Colorado State University, Fort Collins, CO 80523-1373. Email: bringi@engr.colostate.edu

Abstract

This note reports on the use of a 2D video disdrometer to estimate the orientation of drops (>2 mm) that were generated artificially and allowed to fall 80 m from a bridge with no obstruction and under calm conditions. This experimental setup enabled a large number of drops to be generated, up to 10 mm in horizontal dimension.

The distribution of the canting angles for all drops >2 mm was found to be nearly symmetric about 0° with standard deviation between 7° and 8°. From the canting angle distributions derived from the two orthogonal camera view planes, the distributions of the polar (θ) and azimuth (ϕ) angles were deduced; these two angles describe the 2D orientation of the symmetry axis. The azimuthal angle distribution was found to be nearly uniform in the range (0, 2π), whereas the distribution of pΩ(θ) = p(θ) sinθ was similar in shape to a special form of the Fisher distribution that is valid for describing the statistics on a spherical surface. The standard deviation of pΩ(θ) showed that larger drops are more stably oriented than smaller ones. This is in agreement with previous radar-based results of standard deviation of the canting angle decreasing with increasing Zdr.

Corresponding author address: V. N. Bringi, Dept. of ECE, Colorado State University, Fort Collins, CO 80523-1373. Email: bringi@engr.colostate.edu

Save