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

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 :

Physical Approach Forward Modeling (Radiative Transfer Simulations)

Water vapour versus simulated TB’s - TMI Channels For Non-Raining Atmospheres:

CLW versus Simulated TB’s – TMI Channels

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

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

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

Spatial distribution of BT (85.5 GHz, Vertical) over Eastern India

Spatial distribution of Near Surface PR Reflectivity (dBZ) over Eastern India

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)

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(Tb19v–Tb19h)+a2.ln(Tb22v –180)+a3.ln(Tb85v-Tb19v) LAND RAINFALL Use of scattering signatures at high frequencies R = c0 + c1.PCT + c2.SI [PCT=1.818TB85v–0.818TB85h ], [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)

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

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

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

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

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

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

VALIDATIONS

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

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

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

IR Image WV Image , 1500hrs [MetSAT-5]

Convective Activity on 1-6 th Dec 2002

Statistics (6-Dec-02) 1.With 0.5 degree elevation r = 0.45 Total Points: 256 rms diff: 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

VALIDATION CAMPAIGN (Oct-Nov. 2003)

Simultaneous DWR and Disdrometer observations over SHAR on (0951 IST) SHAR DWR and Disdrometer Observations

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

PR Scan (06 Nov, 2003) Orbit No

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

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

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

Applications: Some Examples

TRMM Rainfall Anomalies

MODIS Water Vapor Obs

TRMM Seasonal Rainfall ( )

TRMM Rainfall Rates (mm/h)

Time Latitude Plot of TPW from MODIS

Time Longitude Plot of TPW from MODIS

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

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

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

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