G O D D A R D S P A C E F L I G H T C E N T E R TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop TRMM Ground Validation Some Lessons and Results David B. Wolff, David Marks, David Silberstein & Richard Lawrence TRMM Satellite Validation Office NASA/GSFC

G O D D A R D S P A C E F L I G H T C E N T E R 2 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop TRMM GV Data Processing is up-to-date Major issues are gauge data problems and (especially at KWAJ) radar calibration uncertainties. GSFC is developing an automated method of correcting relative calibration of the KWAJ radar to salvage historical KPOL data. Comparisons of GV estimates to TRMM (3G68) show good agreement, when radar calibration is not major issue. Comparisons of GV estimates to other datasets (e.g. MPA) also show good agreement and bode well for GPM era sampling expectations Summary

G O D D A R D S P A C E F L I G H T C E N T E R 3 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Calibration is a Major Issue for TRMM GV Houze et al. (2004) cite the error associated with a ± 2 dB calibration error is ± 30%, in rain rate, respectively. Actual calibration uncertainty at KWAJ frequently well over ±2 dB and sometimes > 10 dB! Absolutely critical that proper calibration procedures be in place for GPM. Calibration uncertainty is the single largest source of error in Kwajalein rainfall estimates. While absolute calibration is not always possible using conventional radars, stable calibration is essential. GSFC is developing a method to correct historical calibration uncertainties using probability distributions of clutter area reflectivity. Importance of Stable Calibration

G O D D A R D S P A C E F L I G H T C E N T E R 4 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop GV v5: Kwajalein Monthly Radar/Gauge Rainfall Statistics Independent Dependent

G O D D A R D S P A C E F L I G H T C E N T E R 5 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Detrimental Effects of Unstable Radar Calibration Waveguide change occurred on or around July 1, 2003

G O D D A R D S P A C E F L I G H T C E N T E R 6 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Ground Clutter Locations 50 km 100 km TRMM GV uses a “clutter-map” in quality control step at KWAJ. This map provides a lookup table for areas (r,  ) that have a high probability of echo when no precipitation is present. Given KPOL resolution, there are ~4000 points per VOS. Calculate daily PDF of Clutter Area Reflectivity (CAR). Fond that upper percentiles (e.g. 95th) are remarkably stable when the radar calibration is stable, even when precipitation is present. Statistical/Automated Correction of Calibration

G O D D A R D S P A C E F L I G H T C E N T E R 7 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Statistical/Automated Correction of Calibration May 07, 2006 UTCMay 07, 2052 UTC Calibration changes are often traceable to engineering changes to the radar system… here a +7 dB gain was applied.

G O D D A R D S P A C E F L I G H T C E N T E R 8 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Statistical/Automated Correction of Calibration 95th % 95 th Percentile Reflectivity in Clutter Areas is Stable Silberstein et al (32 nd Radar Conference)

G O D D A R D S P A C E F L I G H T C E N T E R 9 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Relative Calibration Adjustment (RCA) PFN replaced 12/12/00 PFN replaced (spare) 11/19/00 Calibration study; Antenna gain decrease Early April 2001 Antenna gain increase Early June 2001 Calibration baseline (Aug dBZ) RCA vs. Engineering Changes

G O D D A R D S P A C E F L I G H T C E N T E R 10 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Statistical/Automated Correction of Calibration UW estimates based on comparison to TRMM PR (Houze et al. 2004)

G O D D A R D S P A C E F L I G H T C E N T E R 11 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Quantifying RCA Effects vs. Z-R Changes Marks et al (32 nd Radar Conference) V5: 2002 WPMM, no RCA V6: Seasonal WPMM, RCA

G O D D A R D S P A C E F L I G H T C E N T E R 12 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop V5 Biases - KWAJ GV vs. TRMM

G O D D A R D S P A C E F L I G H T C E N T E R 13 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop V5 Monthly Means - KWAJ

G O D D A R D S P A C E F L I G H T C E N T E R 14 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop V6r Biases - KWAJ

G O D D A R D S P A C E F L I G H T C E N T E R 15 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop V6r Monthly Means - KWAJ

G O D D A R D S P A C E F L I G H T C E N T E R 16 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop A similar comparison was done using the Multi-Satellite Precipitation Analysis (3B42) Rain Estimate (Huffman et al. 2005) 0.25° x 0.25° gridded product, available every 3-hours GV gridded similarly Compared the 3-hour accumulations from both GV and MPA over these pixels. Comparing GV to Other Rain Estimates (MPA)

G O D D A R D S P A C E F L I G H T C E N T E R 17 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop KWAJ: Comparisons to Other Datasets (MPA)

G O D D A R D S P A C E F L I G H T C E N T E R 18 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop MELB: Comparisons to Other Datasets (MPA)

G O D D A R D S P A C E F L I G H T C E N T E R 19 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Summary – TRMM GV data processing is current for all sites – Calibration issues at Kwajalein a major source of error – Relative Calibration Adjustment (RCA) shows promise but is still a work in development. – Comparisons to TRMM over MELB generally within ± 10% on year-to-year basis – Comparisons to other estimates (MPA) also show good agreement in MELB and KWAJ (during period when radar calibration is mitigated). – TRMM GV is providing GPM GV a significant number of “lessons learned”, which are being applied in GPM GV development

G O D D A R D S P A C E F L I G H T C E N T E R 20 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Backup Slides

G O D D A R D S P A C E F L I G H T C E N T E R 21 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Statistical/Automated Correction of Calibration Diurnal Differences in 95 th Percentile Clutter Reflectivity Data was chosen from 1 st 100 days in 2002 when radar calibration appeared stable

G O D D A R D S P A C E F L I G H T C E N T E R 22 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Probability distributions of rain rate were derived from TRMM (PR, TMI and COM) and GV estimates TRMM --> global (land or ocean) for Feb 1998 (ITE110 - official V6, thanks to S. Yang) GV --> KWAJ (Ocean) and MELB (Land) for period 07-12/1999 Over ocean all PDFs nearly log-normal with some exceptions. Over land, there remains work to be done, especially for 2A12 (TMI). Comparison of Rain Intensity Distributions

G O D D A R D S P A C E F L I G H T C E N T E R 23 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop TRMM GV Processing Status

G O D D A R D S P A C E F L I G H T C E N T E R 24 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Statistical/Automated Correction of Calibration Benefits of “clutter map” approach: 95 th percentile clutter-area reflectivity is remarkably stable even in the presence of precipitation. Little or no diurnal effect Easily calculated for near-real-time monitoring of the current state of the relative radar calibration Current effort: determine the best means of applying these relative calibration changes to historical data to develop improved GV products Signal is strong, amplitude is in question. Under further investigation.

G O D D A R D S P A C E F L I G H T C E N T E R 25 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop DARW KWAJ HSTN MELB Version 6 GV Site Surface Masks

G O D D A R D S P A C E F L I G H T C E N T E R 26 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop 3G68 & GV Land/Coast/Ocean Masks

G O D D A R D S P A C E F L I G H T C E N T E R 27 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop Notes on Bias Calculations Two references (GV and Satellite) – GV_Ref = Mean 0.5° GV rain intensity – Sat_Ref = (PR + TMI + COM)/3 Bias = (Reference - Measurement) / Measurement Comparing GV and TRMM Data

G O D D A R D S P A C E F L I G H T C E N T E R 28 TRMM Tropical Rainfall Measuring Mission 2nd GPM GV Workshop TRMM 3G68 (gridded PR, TMI and COM) rain intensity estimates compared to similarly gridded TRMM GV estimates. All TRMM estimates are Version 6! 0.5° x 0.5° over land, coast and ocean Analysis of TRMM-v6 has been completed Comparing TRMM and GV Rain Intensities