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MICROWAVE RAINFALL RETRIEVALS AND VALIDATIONS R.M. GAIROLA, S. POHREL & A.K. VARMA OSD/MOG SAC/ISRO AHMEDABAD

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Development of algorithms for rain rate retrievals over land and oceans Validation & fine-tuning of algorithm using ground based measurements like Doppler Weather Radar (DWR) & rain gauges etc. over Indian region (land & ocean) Study of some cases of monsoon, flash floods & cyclone rainfall using the developed algorithms Study of hydrological processes to assess the accuracy of the retrievals ISSUES AND OBJECTIVES :

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Physical Approach Forward Modeling (Radiative Transfer Simulations)

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Water vapour versus simulated TBs - TMI Channels For Non-Raining Atmospheres:

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CLW versus Simulated TBs TMI Channels

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Assumption:- For an isotropic field the ratio of the second moment of the radiation field to the mean intensity is everywhere equal to 1/3. RTR for Raining Atmospheres Eddington approximation Assumption:- Cross-polarization is negligible and the scattering phase function follow Henyey-Greenstein equation. Discrete Ordinate Approximation Model used:- Kummerow et al., 1993 Model used:- Liu, 1998

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Observations from TRMM-TMI and PR (V-Blue, H-Red)

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Examples from Data: Tropical Rainfall Measuring Mission (TRMM) TRMM Microwave Imager (TMI); 85.5 GHz Precipitation Radar (PR); 13.8 GHz Data Product (Version 6): 2A25 for Radar Reflectivity 1B11 for Brightness Temperature 2A12 for Latent Heat information

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300 275 250 225 200 Spatial distribution of BT (85.5 GHz, Vertical) over Eastern India

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50 30 20 10 0 Spatial distribution of Near Surface PR Reflectivity (dBZ) over Eastern India

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Number of Pixels (a)Spatial variation of BT(85.5 GHz) for convective and stratiform region and (b) Corresponding vertical cross section of PR Reflectivity (dBZ) (a) (b)

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RETRIEVAL ALGORITHMS FOR OCEAN & LAND (MR Approach) OCEANIC RAINFALL Use of emission (at low frequency) & scattering (at high frequency) signatures with suitable statistical model: R = a0+a1.ln(Tb19vTb19h)+a2.ln(Tb22v 180)+a3.ln(Tb85v-Tb19v) LAND RAINFALL Use of scattering signatures at high frequencies R = c0 + c1.PCT + c2.SI [PCT=1.818TB85v0.818TB85h ], [SI=E 85v (10v,19v,21v) TB85v] E 85v (10v, 19v, 21v) = b0+b1.Tb10v+b2.Tb19v + b3.TB21v (b i coeff. derived for non-raining conditions)

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TRMM-TMI Rainfall from NASA & Present Algorithms NASA TMI Rain (mm/hr)Present TMI Rain (mm/hr) AUGUST 2, 2002

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COMPARISON OF RAINFALL FROM NASA, PR & PRESENT ALGORITHMS NASA TMI RAINRATE NASA PR RAINRATE TMI RAINRATE (PRESENT ALGORITHM) OCTOBER 10, 2002

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TRMM-TMI Rainfall from NASA-GPROF and SAC Algorithm, Aug 2, 2002

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Output Layer Hidden Layer Input Layer ----- Training ----- Testing Fig. ANN architecture having four inputs as brightness Temp and one output as radar rainfall Fig. 3. ANN error distribution for training

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Observed Rain Rate ANN Rain Rate RETRIEVAL ALGORITHMS FOR OCEAN & LAND (ANN Approach)

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Fig. Observed and ANN rain rate for the geographical area used for testing the performance of the ANN. Observed Rain Rate ANN Rain Rate

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VALIDATIONS

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GROUND-BASED OBSERVATIONS BY DOPPLER WEATHER RADAR (CHENNAI) Original Image

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COMPARISON OF TRMM RAINFALL USING DWR DATA OCTOBER 17, 2002 NASA-GPROF RAINFALL PRODUCT

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TRMM Rain (mm/h) Statistics (17-Oct-02) 1.With 0.5 degree elevation r = 0.67 Total Points: 256 rms diff: 4.592406 2. With 1.5 degree elevation r = 0.63 Total Points: 256 rms diff: 4.725613594 SHAR-DWR Rain (mm/h) Ele: 1.5 SHAR-DWR Rain (mm/h) Ele: 0.5 1845Z 1929Z

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IR Image WV Image 17-10-2002, 1500hrs [MetSAT-5]

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Convective Activity on 1-6 th Dec 2002

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Statistics (6-Dec-02) 1.With 0.5 degree elevation r = 0.45 Total Points: 256 rms diff: 3.13 2. With 1.5 degree elevation r = 0.42 Total Points: 256 rms diff: 3.22 SHAR-DWR Rain (mm/h) Ele: 0.5 SHAR-DWR Rain (mm/h) Ele: 1.5 TRMM Rain (mm/h) 0915Z 1015Z

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VALIDATION CAMPAIGN (Oct-Nov. 2003)

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Simultaneous DWR and Disdrometer observations over SHAR on 17-10-03 (0951 IST) SHAR DWR and Disdrometer Observations

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PPI Plot (06 Nov,2003) DWR (SHAR)

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PR Scan (06 Nov, 2003) Orbit No. 34082

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(a) DWR (b) PR Magnified View of near simultaneous Observations of (a) DWR and (b) PR (TRMM) Reflectivity on 06 Nov, 2003

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Scatter plots (a) PR estimated dBZ versus DWR estimated dBZ (b) PR estimated Rainfall intensity versus DWR estimated Rainfall intensity (a) (b)

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TMI DWR-25 km PR DWR-4 km 6 Nov. 2003

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Applications: Some Examples

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TRMM Rainfall Anomalies 1998-2004

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MODIS Water Vapor Obs. 2001-2004

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TRMM Seasonal Rainfall (2001-2004)

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TRMM Rainfall Rates (mm/h) 1998-2004

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Time Latitude Plot of TPW from MODIS 75 0 -85 0

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Time Longitude Plot of TPW from MODIS 5 0 -15 0

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Hydrological Studies from Microwave Measurements: Evaporation Estimates from Microwave Measurements examples from TRMM Precipitation Estimates from Microwave Measurements examples from TRMM Fresh water fluxes (E-P) - examples from TRMM

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E-P for July 1, 2003 (mm/day)

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E-P for July, 2003 (mm/month)

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Conclusions and Concerned Areas: Beam Filling Problem Horizontal and vertical inhomogenity Drop size distribution Melting layer Inversion Techniques

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