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VCPs for Staggered PRT

VCPs for Staggered PRT. Sebastián Torres and David Warde CIMMS/NSSL. Data Quality MOU – Technical Interchange Meeting Spring 2009. Outline. Designing VCPs for SPRT (recap) Importance Performance indicators PRT choice Recommended VCPs for SPRT Design criteria Trade-offs

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VCPs for Staggered PRT

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  1. VCPs for Staggered PRT Sebastián Torres and David Warde CIMMS/NSSL Data Quality MOU – Technical Interchange Meeting Spring 2009

  2. Outline • Designing VCPs for SPRT (recap) • Importance • Performance indicators • PRT choice • Recommended VCPs for SPRT • Design criteria • Trade-offs • Performance analysis • Recommendation andFuture Work Staggered PRT ra = 184 km, va = 45.1 m/s

  3. VCPs for SPRT • VCP design for SPRT is crucial • SPRT algorithm performance is intimately tied to acquisition parameters • VCP design should follow the algorithm evolution • PRT ratio • Ground clutter filter • Overlaid echo recovery • More trade-offs than with other techniques • We want everything we’ve had and more! • SPRT will complement SZ-2 in VCPs that achieve a “complete solution” for the mitigation of R/V ambiguities

  4. VCP Performance Indicators • Acquisition time • Dwell times • Maximum unambiguous range • Surveillance (Z) • Doppler (V & W) • Maximum unambiguous velocity • Spectrum width saturation • Errors of estimates • Statistical errors • Dealiasing errors • Clutter suppression

  5. PRT Selection Trade-offs • Shorter PRTs • Larger Nyquist • Larger maximum spectrum width • More samples for the same dwell times • Lower errors of estimates • Lower rate of catastrophic errors • Better clutter suppression • Longer PRTs • Longer unambiguous range

  6. New VCP Design Criterion • We can trade shorter PRT for increased likelihood of overlaid echoes • Benefits are realized for elevations above 2.4 deg Solid: old Dashed: new

  7. Choosing the PRTs (I) • PRT ratio: 2/3 • Required for SACHI clutter filter • Choose the PRTs as short as possible • Maximum overlay condition • ra,2 = rmax • T1 = 4rmax / 3c • The proposed SPRT algorithm can handle overlaid echoes • ra,D = ra,S = ra,2

  8. Choosing the PRTs (II) • Minimum short PRT: 0.88 ms • Required to maintain 0.5 m/s velocity resolution • Maximum va for 0.5 m/s resolution is 63 m/s • Maximum va is obtained for minimum frequency • Using fmin= 2700 MHz and a PRT ratio of 2/3 • T1,min = c/(4 fmin va,max) • Maximum short PRT: 1.74 ms • Required to match rmax at the lowest SPRT elevation • Using lowest SPRT elevation of 1.8 deg and maximum rmax of 392 km • T1,max = 2rmax,max /c

  9. Choosing the PRTs (III) • SPRT short PRTs are selected from a set of 8 PRTs uniformly distributed between T1,min and T1,max

  10. Choosing the Dwell Times (I) • Dwell times must be chosen to… • Meet error requirements for reflectivity, velocity, and spectrum width • Meet clutter filtering requirements • Satisfy operational needs

  11. Choosing the Dwell Times (II) • Excessively long dwell times seem to be needed to meet “High Suppression” clutter filtering velocity requirements • Feasible, but operationally not acceptable • Recommend using dwell times to meet • System Specification standard error requirements and • “Medium Suppression” clutter filtering requirements • Most clutter contamination at SPRT elevations is through the antenna sidelobes • ~30 dB of clutter suppression should be adequate Batch?

  12. SPRT VCPs • Operational VCPs that have advanced R/V ambiguity mitigation schemes • VCP 121: SZ-2 & MPDA • R/V ambiguity mitigation on all tilts • VCP 211: VCP 11 with SZ-2 on split cuts • VCP 212: VCP 12 with SZ-2 on split cuts • VCP 221: VCP 21 with SZ-2 on split cuts

  13. Standard VCP 211

  14. Proposed VCP 211 • 1.3 min longer update time • Double va • Up to one half SD(Z ) • Use CDX at the upper tilts • Allow increased errors of estimates • Reduce clutter supp. at the upper tilts

  15. Standard VCP 212

  16. Proposed VCP 212 • 2.1 min longer update time • Double va • Up to one third SD(Z ) • SD(v ) ≤ 1 m/s

  17. Standard VCP 221

  18. Proposed VCP 221 • Same update time • Double va • Up to one half SD(Z )

  19. Proposed VCP Performance • Acquisition time • Same or longer dwell times • Some trade-offs can be made • Maximum unambiguous range and velocity • Great improvement w.r.t legacy VCPs • Spectrum width saturation • Acceptable • Errors of estimates • Statistical errors meet requirements • Much better reflectivity estimates! • Clutter suppression • Meets requirements for “Medium Suppression” filter

  20. Summary • Staggered PRT provides significant benefits … • Longer unambiguous range • Larger Nyquist velocity • More accurate reflectivity estimates • … that must be traded for … • Longer acquisition times • Operationally acceptable (trade-offs available!) • “Catastrophic” velocity dealiasing errors • Handled by ORPG’s VDA

  21. Future Work • Recommendation • Implement proposed VCPs • Collect several data cases • Process data using recommended SPRT algorithm including SACHI and modified ORPG velocity dealiasing algorithm • Assess data quality

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