• Amayenc, P., , and Testud J. , 2001: Preliminary analysis of the interest and feasibility of Doppler measurements with the spaceborne cloud radar in Earth’s CARE. ESA Final Rep. 13358/99/NL/GD, 46 pp.

  • Amayenc, P., , Testud J. , , and Marzoug M. , 1993: Proposal for a spaceborne dual-beam rain radar with Doppler capability. J. Atmos. Oceanic Technol., 10 , 262276.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bringi, V., , and Chandrasekar V. , 2001: Polarimetric Doppler Weather Radar: Principles and Applications. Cambridge University Press, 636 pp.

    • Search Google Scholar
    • Export Citation
  • Doviak, R., , and Zrnić D. , 1993: Doppler Radar and Weather Observations. Academic Press, 562 pp.

  • Fishman, G., 1996: Monte Carlo: Concepts, Algorithms, and Applications. Springer Series in Operations Research and Financial Engineering, Springer-Verlag, 698 pp.

    • Search Google Scholar
    • Export Citation
  • Golub, G., , and van Loan C. F. , 1996: Matrix Computations. John Hopkins University Press, 694 pp.

  • Harris, R., , and Battrick B. , 2001: EarthCARE—Earth Clouds, Aerosols and Radiation Explorer. ESA Rep. SP-1257 (1), 130 pp.

  • Horie, T., , Iguchi T. , , Hanado H. , , Kuroiwa H. , , Okamoto H. , , and Kumagai H. , 2000: Development of an airborne cloud profiling radar at 95 GHz (Spider). IEICE Trans. Commun., 83 , 20102020.

    • Search Google Scholar
    • Export Citation
  • Kobayashi, S., , Kumagai H. , , and Kuroiwa H. , 2002: A proposal of pulse-pair Doppler operation on a spaceborne cloud-profiling radar in the W band. J. Atmos. Oceanic Technol., 19 , 12941306.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kobayashi, S., , Kumagai H. , , and Iguchi T. , 2003: Accuracy evaluation of Doppler velocity on a spaceborne weather radar through a random signal simulation. J. Atmos. Oceanic Technol., 20 , 944949.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kristjansson, J., , Edwards J. , , and Mitchell D. , 2000: Impact of a new scheme for optical properties of ice crystals on climates of two gems. J. Geophys. Res., 105 , 1006310079.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lucas, C., , MacKinnon A. D. , , Vincent R. A. , , and May P. T. , 2004: Raindrop size distribution retrievals from a VHF boundary layer profiler. J. Atmos. Oceanic Technol., 21 , 4560.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Meneghini, R., , and Kozu T. , 1990: Spaceborne Weather Radar. Artech House, 199 pp.

  • Ohsaki, Y., 2003: Simulation-based error analysis of Doppler velocity measured by a spaceborne cloud-profiling radar in the W-band. J. Meteor. Soc. Japan, 81 , 425435.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Peebles, P., 1980: Probability, Random Variables and Random Signal Principles. McGraw-Hill Series in Electrical Engineering, McGraw-Hill, 480 pp.

    • Search Google Scholar
    • Export Citation
  • Potter, G. L., , and Cess R. D. , 2004: Testing the impact of clouds on the radiation budgets of 19 atmospheric general circulation models. J. Geophys. Res., 109 .D02106, doi:10.1029/2003JD004018.

    • Search Google Scholar
    • Export Citation
  • Rajopadyaya, D., , May P. , , and Vincent R. , 1993: A general approach to the retrieval of raindrop size distributions from wind profiler Doppler spectra: Modeling results. J. Atmos. Oceanic Technol., 10 , 710717.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schafer, R., , Avery S. , , May P. , , Rajopadhyaya D. , , and Williemas C. , 2002: Estimation of rainfall drop size distributions from dual-frequency wind profiler spectra using deconvolution and a nonlinear least squares fitting technique. J. Atmos. Oceanic Technol., 19 , 864874.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Sirmans, D., , and Bumgarner B. , 1975: Numerical comparison of five mean frequency estimators. J. Appl. Meteor., 14 , 9911003.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Slingo, A., 1990: Sensitivity of the Earth’s radiation budget to changes in low clouds. Nature, 343 , 4951.

  • Stephens, G., and Coauthors, 2002: The CloudSat mission and the A-train. Bull. Amer. Meteor. Soc., 83 , 17711790.

  • Tanelli, S., , Im I. , , Durden S. , , Facheris L. , , and Giuli D. , 2002: The effects of nonuniform beam filling on vertical rainfall velocity measurements with a spaceborne Doppler radar. J. Atmos. Oceanic Technol., 19 , 10191034.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zrnić, D., 1975: Simulation of weatherlike Doppler spectra and signals. J. Appl. Meteor., 14 , 619620.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 32 32 6
PDF Downloads 26 26 4

Simulated Doppler Radar Observations of Inhomogeneous Clouds: Application to the EarthCARE Space Mission

View More View Less
  • 1 NICT, Tokyo, Japan
© Get Permissions
Restricted access

Abstract

A new simulation technique for spaceborne Doppler radar observations that was developed specifically for inhomogeneous targets is presented. Cloud inhomogeneity affects Doppler observations in two ways. First, line-of-sight velocities within the instantaneous field of view are unequally weighted. As the large forward motion of a spaceborne radar contributes to these line-of-sight velocities this causes biases in observed Doppler speeds. Second, receiver voltages now have time-varying stochastical properties, increasing the inaccuracy of Doppler observations. The new technique predicts larger inaccuracies of observed Doppler speeds than the traditional random signal simulations based on the inverse Fourier transform.

The accuracy of Doppler speed observations by a spaceborne 95-GHz radar [as part of the proposed European Space Agency (ESA)/Japan Aerospace Exploration Agency (JAXA)/National Institute for Information and Communications Technology (NICT) EarthCARE mission] is assessed through simulations for realistic cloud scenes based on observations made by ground-based cloud-profiling radars. Close to lateral cloud boundary biases as large as several meters per second occur. For half of the cloud scenes investigated, the distribution of the in-cloud bias has an rms of 0.5 m s−1, implying that a bias in excess of 0.5 m s−1 will not be uncommon.

An algorithm to correct the bias in observed Doppler observations, based on the observed gradient of reflectivity along track, is suggested and shown to be effective; that is, the aforementioned rms bias reduces to 0.14 m s−1.

Corresponding author address: Nick Schutgens, CCSR, Tokyo University, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568, Japan. Email: schutgen@ccsr.u-tokyo.ac.jp

Abstract

A new simulation technique for spaceborne Doppler radar observations that was developed specifically for inhomogeneous targets is presented. Cloud inhomogeneity affects Doppler observations in two ways. First, line-of-sight velocities within the instantaneous field of view are unequally weighted. As the large forward motion of a spaceborne radar contributes to these line-of-sight velocities this causes biases in observed Doppler speeds. Second, receiver voltages now have time-varying stochastical properties, increasing the inaccuracy of Doppler observations. The new technique predicts larger inaccuracies of observed Doppler speeds than the traditional random signal simulations based on the inverse Fourier transform.

The accuracy of Doppler speed observations by a spaceborne 95-GHz radar [as part of the proposed European Space Agency (ESA)/Japan Aerospace Exploration Agency (JAXA)/National Institute for Information and Communications Technology (NICT) EarthCARE mission] is assessed through simulations for realistic cloud scenes based on observations made by ground-based cloud-profiling radars. Close to lateral cloud boundary biases as large as several meters per second occur. For half of the cloud scenes investigated, the distribution of the in-cloud bias has an rms of 0.5 m s−1, implying that a bias in excess of 0.5 m s−1 will not be uncommon.

An algorithm to correct the bias in observed Doppler observations, based on the observed gradient of reflectivity along track, is suggested and shown to be effective; that is, the aforementioned rms bias reduces to 0.14 m s−1.

Corresponding author address: Nick Schutgens, CCSR, Tokyo University, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568, Japan. Email: schutgen@ccsr.u-tokyo.ac.jp

Save