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INFLUENCE OF NON-UNIFORM BEAM FILLING ON ATTENUATION CORRECTION AT C- AND X-BAND

ERAD 2006 - Barcelona. INFLUENCE OF NON-UNIFORM BEAM FILLING ON ATTENUATION CORRECTION AT C- AND X-BAND. A. BERNE LTHE, Grenoble, France. R. UIJLENHOET HWM Group, Wageningen, The Netherlands. Motivation. Example of Z profile. 25 m. 500 m. Attenuation Z a (r) = A(r) Z(r) and

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INFLUENCE OF NON-UNIFORM BEAM FILLING ON ATTENUATION CORRECTION AT C- AND X-BAND

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  1. ERAD 2006 - Barcelona INFLUENCE OF NON-UNIFORM BEAM FILLING ON ATTENUATION CORRECTION AT C- AND X-BAND • A. BERNE LTHE, Grenoble, France. • R. UIJLENHOET HWM Group, Wageningen, The Netherlands.

  2. Motivation Example of Z profile 25 m 500 m Attenuation Za(r) = A(r) Z(r) and Attenuation correction (non dual-pol) Z = akbb≠1 Z and k are assumed to be uniform within radar sampling volume → What is the influence of NUBF on attenuation correction accuracy? (e.g. Nakamura, 1991; Gosset and Zawadzki, 2001; Zhang et al., 2004)

  3. Approach • Limit our analysis to single-frequency non-polarimetric incoherent radar systems. • Stochastic simulation approach • → generate 1000 DSD profiles → Z and k profiles. • → Monte Carlo technique to quantify NUBF effect. • C- and X-band.

  4. DSD simulator • Principle • N(D) = NtL exp(-LD) (Nt,L) lognormally distributed. • Spatial structure → vector auto-regressive process order 1. • Parameterization • Intense Mediterranean rainfall: 45 min at <R> ~60 mm h-1 • (DSD data from OSP) • Example of generated profile Z and Za (using Mie theory)

  5. Attenuation correction algorithms • Forward implementation algorithm: Hitschfeld and Bordan (1954) • - Easy to implement, fast computation. • - Instability when strong attenuation occurs. • Backward implementation algorithm: Marzoug and Amayenc (1994) • Stable. • Requires an additional piece of information (PIA).

  6. Method • DSD simulator • 1000 DSD profiles (derived Z and k profiles) at 25-m resolution. • Averaging at 50, 125, 250, 500, 1000, 1500, 2000 and 2500 m. • Monte Carlo technique • Attenuation correction (2 algorithms) on the 1000 profiles. • Comparison between corrected (Zc) and true (Z) reflectivity profiles: • Evolution of the 2 criteria as a function of dr/q (ratio between resolution and characteristic scale of rainfall) and PIA, at C- (5.6 cm)and X-band (3.2 cm).

  7. Distributions of PIA and Z-k coef. for the generated profiles At C-band At 25-m resolution Prefactor a Exponent b PIA Mean = 1.09 Std = 0.03 Mean = 5.7 105 Std = 6.0 104 At X-band Mean = 1.32 Std = 0.06 Mean = 1.1 105 Std = 9.5 103

  8. MBE HB MBE MA RMSE MA RMSE HB Results at C-band

  9. RMSE HB RMSE MA MBE MA MBE HB Results at X-band

  10. Conclusions Quantification of NUBF influence on attenuation correction accuracy for 2 algorithms for single-frequency non-polarimetric incoherent radars. Simulated 1000 DSD profiles (and derived Z and k profiles at X- and C-band). Analysis of RMSE and MBE as a function of PIA and ratio between radar spatial resolution and rainfall characteristic scale. → if dr/q < 0.2, NUBF has a limited influence on attenuation correction accuracy (in our case, q ~ 4 km → dr < 1000 m). We intend to extend this approach to polarimetric attenuation correction algorithms.

  11. Thank you for your attention!

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