CFRSL A STATISTICAL ALGORITHM FOR INFERRING RAIN RATE FROM THE QUIKSCAT RADIOMETER. Yanxia Wang

Transcription

1 A STATISTICAL ALGORITHM FOR INFERRING RAIN RATE FROM THE QUIKSCAT RADIOMETER Yanxia Wang M.S.E.E. Wuhan Technical University of Surveying&Mapping Wuhan, China, 1996 Advisor: W. Linwood Jones 1

2 Rain Rate Algorithm Algorithm provides two products Instantaneous rain rate > 0.5 mm/hr 25 km x 25 km spatial resolution Global weekly to monthly average rain rates Uses SeaWinds remote sensor on the QuikSCAT satellite Microwave brightness temperatures Retrieved wind speeds 2

3 SeaWinds Measurement Geometry 3

4 Physical Basis of Rain Algorithm 4

5 Brightness Temperature Rain Rate Relationship The polarized microwave excess brightness (D T bp ) is proportional to the integrated rain rate DT b p T b meas p T b ocean p T b w. speed p T b ocean = ocean background (includes atmos. emissions without rain) based upon 7 year SSMI climatology T b w.speed = wind speed brightness bias 5

6 Brightness Temperature, K Brightness Temperature, K CFRSL Tb-RR Relationship H-pol V-pol Integrated Rain Rate (km*mm/hr) Integrated Rain Rate (km*mm/hr) 6

7 Rain Measurement Theoretical Basis 7

8 Block diagram Rain Tap - Tap Tb = Tap + Gaussian Noise Rain Rate Radiometer Rain Rain Rate Algorithm Measurement Relationship Non-linear ERROR = Rain - Rain 8

9 Monte Carlo Simulation Assume a rain rate pdf and use the Tb-RR relationship to simulate "noise-free" Tap. Noisy radiometer measurements (Tb) are created by adding Gaussian noise Process Tb using the rain rate algorithm and output an estimated rain rate Comparisons are made between the assumed rain rate pdf and the rain rate retrieval pdf 9

10 Normalized frequency Normalized frequency CFRSL Ocean Assumed Rain and noise-free Tex Rain Rate (mm/hr) Tex (K) 10

11 Normalized frequency CFRSL Noisy Tex Noisy Tex with 1K std Noisy Tex with 10K std Tex (K) 11

12 Normalized frequency CFRSL Rain Rate pdf Noise-free rain noisy rain with 10K std noisy rain with 1K std Rain Rate, mm/hr 12

13 Rain Accumulation, mm CFRSL Rain cdf 1K std noise 10K std noise True rain Rain rate, mm/hr 13

14 Rain Rate Algorithm Instantaneous Rain Rate Global Average 14

15 Instantaneous Rain Rate Algorithm QRad Tb L2A Ocean Tb Calc Excess Brightness Temperature Calc Rain Index Calc Instantaneous Rain Rate Instantaneous Rain rate Product QScat Wind Speed L2B Spatial Filter Calc Rain Probability RI p DTb p p DT 0 p # pulses Where: DTb = excess Tb, K; DT 0 = offset based upon a linear regression between TMI integrated rain rate and DTb, K; = the QRad measurement standard deviation p = polarization. # pulses = the number of pulses averaged 15

16 TMI int..rain rate (km*mm/hr) TMI int..rain rate (km*mm/hr) CFRSL TMI Integrated Rain Rate Qrad Rain Index Relationship Rain Index (a) H-pol Rain Index (b) V-pol 16

17 Rain Probability Rain Probability CFRSL Rain Index Probability H-pol V-pol Rain Index Rain Index 17

18 Latitude Latitude CFRSL Instantaneous Rain Rates Comparison (km*mm/hr) TMI QRad Longitude Longitude 18

19 Instantaneous Rain Rates Comparison QRad SSMI Time Difference 19

20 Rain Rate Algorithm Instantaneous Rain Rate Global Average 20

21 Global Avg Rain Rate Algorithm QScat Wind SpeedL2B QRad Tb L2A Ocean Tb Calc Excess Brightness Calculate Instantaneous Rain Rate Earth Locate & Average Weekly Average Rain Rate Product 21

22 TMI int. rain rate (km*mm/hr) TMI int. rain rate (km*mm/hr) CFRSL TMI Integrated Rain Rate Qrad Tex Relationship (a) H-pol (b) V-pol Tex (K) Tex (K) 22

23 Normalized frequency CFRSL Rain Rate pdf Rain-free 5 x 5 Areas Gaussian fit QRad Rain rate (mm/hr) Mean = and std =

24 Rain Accumulation (mm) CFRSL Monthly Average Global Rain Accumulations TMI 3A11 QRad TMI 2A12 Rain Rate (mm/hr) 24

25 Normalized frequency CFRSL Monthly Average Rain Rates TMI 2A12 QRad TMI 3A11 Rain Rate, mm/hr 25

26 QRad Monthly Avg Rain Rates (Jun x 0.5 ) TMI 26

27 Monthly Avg Rain Rates (Jun x 5 ) Qrad TMI 27

28 Delta-Rain Rate, mm/hr CFRSL QRad minus TMI Mo. Avg Rain Rates Mean = 0.04 Std = 0.17 (0.5 x 0.5 ) Delta-RR 28

29 Delta-Rain Rate, mm/hr CFRSL QRad minus TMI Mo. Avg Rain Mean = Std = Rates (5 x 5 ) Delta-RR 29

30 Rain Rate Scatter Diagram TMI vs. Qrad (5 x 5 ) 30

31 Rain Rate ( mm / hr ) CFRSL Weekly Zonal Avg Rain Rate for 20 N - 10 N IO MC TC CP EP AO TMI Qrad Time ( day of year 2000)

32 SSMI Rain Rate Adjustment Monthly Average Global Rain Accumulations TMI SSMI *

33 Normalized frequency CFRSL Monthly Avg. Rain Rate SSMI TMI Rain Rate (mm/hr) 33

34 Mon. Avg. Global Rain Rates for Qrad and SSMI, 1 x 1 QRad SSMI 34

35 Delta-Rain Rate (mm/hr) CFRSL QRad minus SSMI global Mo. Avg Rain Rates (1 x 1 ) Mean = Std = Delta-RR 35

36 Normalized frequency Rain Accumulation (mm) CFRSL QRad and SSMI Monthly Global Rain Rates SSMI QRad SSMI QRad Rain Rate (mm/hr) Rain Rate (mm/hr) 36

37 Conclusions Based upon my thesis: QRad provides quantitative estimates of instantaneous rain rate over oceans JPL has implemented this algorithm in science data processing Good comparisons of instantaneous rain rate with TMI and SSMI when collocation times are ± 1 hr 37

38 Based upon my thesis: Conclusions cont. QRad provides quantitative estimates of global average rain rate over oceans Weekly to monthly time scales Monthly average comparisons with TMI and SSMI rain rates are good QRad underestimates high rain rates and slightly over estimates low rain rates Differences in over pass times may influence the weekly to monthly averages 38

39 Publication Wang, Y., Jones, W. L., Park, J. and J. Zec, " Quantitative Rain Rate Estimates over Oceans using QuikSCAT," Oceanology Americas 2001, NASA Oceanography Scientific Conference, April 3-4, 2001, Miami, FL. Jones, W. L., Kasparis, T., Wang, Y. and J. Park, "Global Ocean Rain Rates from QuikSCAT," 7th International Conference on Precipitation, June 30 -July 3, 2001, Samoset Resort, Rockport, ME. Susanj, Mladen, Jones, W. L., Wang, Y., Zec J., and Jun-Dong Park, "A Rain Flag over Oceans for the SeaWinds Scatterometer on QuikSCAT", AGU Spring meeting, May 30 - June 3, 2000, Wash DC Jones, W. L., Zec, J., Park, J. D. and Yanxia Wang, "Review of NSCAT Hurricane Research and Application to SeaWinds, SeaWinds Performance in Extreme Winds and Ambiguity Removal and Directional performance Workshop, Jet propulsion Lab, Aug , 2000, Pasadena, CA 39