A NEW SAR RETRIEVAL METHOD FOR HURRICANE WIND PARAMETERS

Transcription

1 A NEW SAR RETRIEVAL METHOD FOR HURRICANE WIND PARAMETERS Antonio Reppucci, Susanne lehner, Johannes Schulz-Stellenfleth German Aerospace Center (DLR) Oberpfaffenhofen Wessling, Germany.

2 Hurricane Katrina Buoys wind speed : A: Measured=14.4 m/s SAR Retrieved =13.3 m/s B: Measured=15.8 m/s SAR Retrieved =17.1 m/s *A * B Radius of Maximum Wind (70 m/s). Radius of Hurricane force Wind (33 m/s). Strong Convective Cell

3 Overview Measurement of Tropical Cyclone Intensity Wind Speed Error New procedure to estimate TC intensity using SAR data NRCS attenuation in hurricane Conclusion.

4 Dvorak Technique Operational since 1973 The technique utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops from IR images and the fact that cyclones of similar intensity tend to have certain characteristic features. From these measurements a Current Intensity (CI) value is assigned to the storm. [Dvorak, V., 1984: Tropical cyclone intensity analysis using satellite data. NOAA Tech. Report NESDIS 11. Available from NOAA/NESDIS, 5200 Auth Rd., Washington DC, 20233, 47pp. ] CI number ,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 MWS (kts) MSLP (hpa) ,

5 Airplane Measurement Operational NOAA P3 and G4 research aircraft Hurricane Katrina 28/08/2005 GPS dropwindsondes: pressure humidity temperature wind direction and speed Stepped-Frequency Microwave Radiometer Wind speed Rain Rate [Uhlhorn, Eric W., Peter G. Black, James L. Franklin, Mark Goodberlet, James Carswell, Alan S. Goldstein, 2007 : Hurricane Surface Wind Measurements from an Operational Stepped Frequency Microwave Radiometer, Monthly Weather Review, In press]

6 Active Microwave Wind Speed Measurements SeaWinds Hurricane Katrina (c) JPL ASAR Hurricane Katrina K u band C band m/s

7 Rain in Tropical Cyclones

8 Rain Rate by HOAPS Image courtesy UNI Hamburg, MPI

9 SFMR rain rate measurements NOAA HRD Hurricane Katrina 28/08/2005

10 Ku band Rain attenuation C band Delta NRCS Undisturbed NRCS [Ulaby F.T., More R.K., Fung A.K, 1981, Microwave Remote Sensing: Active and Passive (MA: Addison-Wesley), vol. 1.] Delta NRCS Undisturbed NRCS [Z.S. Haddad, David A. Short, Stephen L. Durden, Eastwood Im,Scott Hensley, Martre B. Grable, and Robert A. Black,(1997). A New Parametrization of the Rain Drop Size Distribution, IEEE Trans. Geosci. Remote Sensing, vol. 29,pp , Sept ]

11 NRCS err. on wind speed retrieval CMOD-5 Simulation of NRCS for different wind speed and direction Wind direction [deg] Attenuation of the simulated NRCS of 0.5 db [Hersbach H., 2003, CMOD5 an improved geophysical model function for ERS C- band scatterometry, Internal report, European Centre for Medium- Range Weather Forecast, no ] Retrieval of wind speed using attenuated NRCS

12 CMOD5 Inc.=25 Cross wind Wind Speed error NRCS [db] CMOD5 Inc.=25 Cross wind Att.=0.5 db CMOD5 Inc.=25 Up wind NRCS [db] Second Solution First Solution CMOD5 Inc.=25 Up wind Att.=0.5 db

13 Error Map Wind direction [deg] Inc. Angle 35 Inc. Angle 25 Wind direction [deg]

14 Holland Model AOML-HRD Wind Field V r = A B p n 1 exp A / r B p 2 2 c 2 f r + r f ρ r B 4 2 p c = Central Pressure p n = Environment pressure r = distance from the center f = Coriolis parameter ρ = Air Density A,B = Scaling Parameter related to R mws [G.J. Holland, 1980, An Analytic model of the wind and pressure profiles in Hurricanes, Mon. Weather Rev., vol. 108, pp ] Simulation of Katrina Wind Field

15 Along Track Cut Holland simulated NRCS Radius maxmimum wind speed Measured NRCS

16 New Method to Estimate the Maximum Hurricane Wind Speed Holland Model(p c,v M ) o CMOD5 (θ,φ) σ ( p, v ) c M J o σ i o σ ( p, v ) ( p,v ) c c = Measured NRCS M M = = Holland simulated NRCS p c = central pressure v M = maximum wind speed i [ ( ) ] o o σ i pc, vm σ i [ ] o σ 2 i 2 Holland fitted wind speed tropical storm force winds CMOD5 Retrieved wind speed

17 New Method to Estimate the Maximum Hurricane Wind Speed Acquisition Time Image center Coordinates Measured Max Wind Speed SAR Retrieved Max Wind Speed Measured Central Pressure SAR Retrieved Central Pressure Hurricane Katrina :50 26,1 N, 87.7 W 70 m/s 68 m/s 905 mb 901 mb Hurricane Rita : N, 85.5 W 75 m/s 70 m/s 897 mb 890 mb Typhoon Kiko : N, 131 E 45 m/s 48 m/s 955 mb 950 mb Typhoon Kiko Typhoon Songda SAR Retrieved Max Wind Speed : : N, E 28.8 N, E 55 m/s 44 m/s SAR Retrieved Central Pressure 60 m/s 40 m/s 945 mb 945 mb 930 mb 946 mb Measured Max Wind Speed Measured Central Pressure

18 NRCS att. Katrina NRCS [db] NRCS meas [db] Inc. Angle: 33.9 Delta NRCS [db]

19 NRCS att. Kiko NRCS [db] NRCS meas [db] Inc. Angle: 37 Delta NRCS [db]

20 Conclusions and future steps Wind Speed retrieval in Hurrican force winds shows a Limited skill in intensity analysis. Rain contamination can partly explain the strong damping but also the foam layer must be taken into account. A new Procedure for the estimation of Tropical Cyclone Intensity using SAR data and parametric model results has been developed. First analysis of the NRCS predicted by the CMOD5 GMF seems not agree with SAR measurements for high wind speed conditions. Validation of the developed algorithm using more SAR Hurricane images. Estimation of a possible correction to apply to the GMF CMOD5 for Tropical Cyclones conditions. Application to extratropical Cyclones.

21 Thanks for your Attention

22 Ocean Surface in a Hurricane Images courtesy NOAAA HRD 200 m Wind speed ~28m/s 200 m Wind Speed ~ 46 m/s

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24 Rain Attenuation Attenuation Coefficient Volume Backscattering Coefficient Reflectivity Factor [J. Tournadre, Y. Quilfen, 2003]

25 Objective Estimation of TC parameter using SAR data. Improve the existing models for the wind speed retrieval In Tropical Cyclones conditions.

26 Experimental techniques Objective Estimation of Tropical Observational Cyclone Analyses of North Atlantic Wind Structure from Infrared Satellite Tropical Data. Cyclones from NOAA Polar-Orbiting KIMBERLY J. MUELLER, MARK DEMARIA, JOHN KNAFF, JAMES P. Satellite Microwave Data KOSSIN, THOMAS H. VONDER HAAR. WEATHER AND FORECASTING,dec Christopher S. Velden, Journal of Applied Meteorology, Volume 28, Issue 1 (January 1989). [Katsaros K. B., Vachon P. W., Black P. G., Dodge P. P.,. Uhlhorn E. W., 2000, Wind Fields from SAR: Could They Improve Our Understanding of Storm Dynamics?, Johns Hopkins APL Technical Digest, vol 21, No. 1]

27 CMOD5 Inc.=35 Cross wind Wind Speed error CMOD5 Inc.=35 Up wind NRCS [db] CMOD5 Inc.=35 Cross wind Att.=0.5 db NRCS [db] CMOD5 Inc.=35 Up Att.=0.5 db

28 Along Track Cut Possible explanation: Strong Nrcs Strong Rain Attenuation inside the Foam Layer on the sea surface Tropical Storm force winds area Holland simulated NRCS Measured NRCS

29 C-Band Rain Attenuation 20 mm/h 30 mm/h 40 mm/h 50 mm/h Ku-Band Sigma Naugth [db] Attenuation [db]

30 Holland Fitting Holland wind speed Retrieved wind speed Wind Speed [m/s]

31 Holland Fitting

32 Conclusion and Future Steps Wind Speed retrieval In Hurrican force winds using the Scatterometer GMF is not accurate. Rain can partly explain the strong damping but also the foam and layer must be taken into account. Estimates of Hurricanes wind field can be made fitting an appropriate Holland profile that match the retrieved wind speed in the range below 17 m/s.

33 Thanks for Your Attention

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35 Central press =951 V max =52