A comparison of techniques for space-borne Doppler velocity estimation

A comparison of  techniques for space-borne Doppler velocity estimation

V. Venkatesh ^1,2, L. Li, M. McLinden ¹, G. Heymsfield¹ , M. Coon ¹

1 – NASA Goddard Space Flight Center, Greenbelt, MD.

2 – Science Systems and Applications Inc., Lanham, MD.

      Space-borne Doppler velocity measurements, if proven practical, are a potential means to 3-D latent heat retrievals [1] and improved microphysical parameterization [2]. However, large platform speeds and the use of a limited antenna size act to reduce the coherence of the received signal on time-scales of the order of a PRT. This effect, referred to as beam broadening decorrelation, reduces the fidelity of traditional Doppler measurements. Prior approaches to mitigate this issue include adopting a higher than usual dwell time to accumulate traditional pulse-pair covariance measurements [3] and using polarization diversity [4] to overcome the range-Doppler ambiguity dilemma. We propose a novel frequency-diverse method for space-borne Doppler measurements. In this approach, the loss of coherence induced by frequency-diversity is compensated by the highly anti-correlated phases of interleaved frequency-reversed pairs.

    In this study, Monte-Carlo simulations of the backscattered electric field are employed to investigate the error space of space-borne Doppler velocity estimation algorithms.  To initialize the simulator, radar and meteorological parameters like platform speed, antenna size, range to resolution cell, pulse repetition frequency, dwell-time, mean and turbulent velocity components are prescribed. From these values, an enclosing volume centered on the finite footprint is defined. This bounding volume is then populated with a large number of scatterers whose positions are updated at each time-step based on the specified velocity components [5]. The propagated error from beam broadening decorrelation is studied by sweeping design variables of interest. Results from the frequency and polarization diversity pulse-pair estimation algorithms are compared.

REFERENCES

[1] W-K. Tao et al., 2006"Retrieval of latent heating from TRMM measurements", Bull. Amer. Meteor. Soc., 87, 1555-1572.

[2]D.R. Wilson et al. 1997: "Differential Doppler velocity: A radar parameter for charactering hydrometeor size distributions", J. App. Meteor., 36, 649-663.

[3] A. Battaglia, S. Tannelli, P. Kollias, 2013: "Polarization diversity for millimeter spaceborne radars: An answer for observing deep convection ? ", J. Atmos. Oceanic Technol., 30, 2768-2787.

[4] S. Kobayashi et al. 2002: "A proposal for pulse-pair observation on a spaceborne cloud profiling radar in the W band", J. Atmos. Oceanic Technol., 19, 1294-1306.

[5] V. Venkatesh, S.J. Frasier, 2013: "Simulation of spaced-antenna wind-retrieval performance on an X-band active phased-array weather radar", 30, 1447-1459.