Arthur Hou NASA Goddard Space Flight Center Space-Based Precipitation Measurements JCSDA-HFIP Workshop, 2-3 December 2010, Miami, Florida

JCSDA-HFIP Workshop, 2-3 December Current Generation of Global Precipitation Products  TRMM radar provided an anchor for rainfall estimates by passive microwave sensors in the tropics and subtropics.  Further advances require better sensors and remote-sensing algorithms (especially for light rain and falling snow). Current multi-satellite products are based on MW or MW+IR observations from uncoordinated satellite missions using a variety of merging techniques 50N 50S TRMM Realtime 3hr global rain map at 0.25 o resolution

JCSDA-HFIP Workshop, 2-3 December  Detailed knowledge of precipitation microphysical properties (particle size distribution, liquid/ice partition, hydrometeor profiles, etc.) is key to improving precipitation retrievals from passive microwave sensors - Dual-frequency or dual-polarimetric radar capabilities  A better understanding of global water fluxes & precipitation characteristics (frequency, intensity, distribution, etc.) in a changing climate requires improved measurements of light rain and snow. - Light rain and snowfall account for ~50% of precipitation events and significant a fractions of precipitation volume outside the Tropics  “High frequency” water vapor channels are key to improving precipitation retrievals over land, especially over frozen terrains  Ground validation must go beyond direct comparison of surface rain rates between ground and satellite measurements to provide the means for improving satellite simulators, retrieval algorithms, & model applications  Near-realtime “asynoptic” observations between those by polar orbiters at fixed local times have high operational values in hurricane monitoring - TMI data account for 16% of all tropical cyclone position fixes made by the Joint Typhoon Warning Center in a typical year Lessons from TRMM

JCSDA-HFIP Workshop, 2-3 December GPM Reference Concept Unify and advance precipitation measurements from space to provide next-generation global precipitation products within a consistent framework GPM Mission Concept Key Advancement Using an advanced radar/radiometer measurement system to improve constellation sensor retrievals Partner Satellites: GCOM-W1DMSP F-18, F-19Megha-TropiquesMetOp, NOAA-19NPP, JPSS (over land) GPM Core Observatory (65 o ) DPR (Ku-Ka band) GMI ( GHz) (NASA-JAXA, LRD 2013) Precipitation physics observatory Transfer standard for inter-satellite calibration of constellation sensors Enhanced capability for ci near realtime monitoring ci of hurricanes & ci midlatitude storms Improved estimation of ci rainfall accumulation Low Inclination Observatory (40 o ) GMI ( GHz)(NASA & Partner, 2014) Coverage & Sampling 1-2 hr revisit time over land < 3 hr mean revisit time over 90% of globe

JCSDA-HFIP Workshop, 2-3 December GPM Observations from Non-Sun-Synchronous Orbits Monthly Samples as a Function of the Time of the Day (1 o x 1 o Resolution) TRMM: 3652 “asynoptic” samples GPM Core+LIO: 6175 samples Core+LIO: 4298 samples Near real-time observations fillinggaps between those of polarorbiters at fixed time of the day for: Intercalibration of polar-orbiting m sensors over wide range of latitudes Near real-time monitoring of m hurricanes & midlatitude storms Improved accuracy of rain volume estimation Resolving diurnal variability in m rainfall climatology m

JCSDA-HFIP Workshop, 2-3 December NASA-JAXA GPM Core Observatory  Increased sensitivity (~12 dBZ) for light rain and snow detection relative to TRMM  Better measurement accuracy with differential attenuation correction  Detailed microphysical information (DSD mean mass diameter & particle no. density) & identification of liquid, ice, and mixed-phase regions Dual-Frequency (Ku-Ka band) Precipitation Radar (DPR): Multi-Channel ( GHz) GPM Microwave Imager (GMI):  Higher spatial resolution (IFOV: 6-26 km)  Improved light rain & snow detection  Improved signals of solid precipitation over land (especially over snow-covered surfaces)  4-point calibration to serve as a radiometric reference for constellation radiometers Combined Radar-Radiometer Retrieval  DPR & GMI together provide greater constraints on possible solutions to improve retrieval accuracy  Observation-based a-priori cloud database for constellation radiometer retrievals Core Observatory Measurement Capabilities

JCSDA-HFIP Workshop, 2-3 December JAXA/NICT Dual-Frequency Precipitation Radar heavy rain Rain-rate light rain/snow Rainrate Occurrence mid- & high- latitude rain & snow Measurable range by GHz radar Measurable range by 13.6GHz radar tropical rain Courtesy Z. Haddad GPM TRMM ~12.5 mm/h ~1.5 mm/h Rain Rate (mm/h) Simulated Error Std Dev in Rain Retrieval Percent DPR capabilities relative to TRMM PR CloudSat data show that light rain rates between mm/hr account for 16% of the rain volume < 2.0 mm/hr. With Ku and Ka bands, GPM will capture ~98% of total global rain volume. Courtesy of Wes Berg 40N-40S

JCSDA-HFIP Workshop, 2-3 December GMI capabilities 4 in/hr G. Skofronick-Jackson AMSU-B 89 GHz AMSU-B ± 7 GHz NOAA NEXRAD Data Snow Retrieval g m 3 Radar reflectivity of the March 5-6, 2001 New England blizzard (75 cm of snow fell on Burlington, VT) Cannot distinguish surface from cloud effects. Surface effects screened by water vapor. Snowfall appears as low brightness temperatures Feasibility demonstration of snowfall retrieval using HF channels AMPR (Aircraft) GMI (Core) AMSR-E TMI SSMIS Comparison of GMI resolution with other radiometers Synthesized Brightness Temperatures (R. Hood)

JCSDA-HFIP Workshop, 2-3 December Constellation microwave sensor channel coverage Mean Spatial Resolution (km) Different center frequencies, viewing geometry, and spatial resolution must be reconciled Channel6 GHz 10 GHz 19 GHz 23 GHz 31/36 GHz GHz 89/91 GHz150/166 GHz 183/190 GHz AMSR-E6.925 V/H V/H 18.7 V/H 23.8 V/H 36.5 V/H 89.0 V/H GMI10.65 V/H18.70 V/H23.80 V36.50 V/H89.0 V/H165.5 V/H V MADRAS18.7 V/H23.8 V36.5 V/H89.0 V/H157 V/H SSMIS19.35 V/H V37.0 V/H V/H91.65 V/H150 H183.31H MHS89 V157 V H V ATMS V – Vertical PolarizationH – Horizontal Polarization Channel6 GHz10 GHz19 GHz 23 GHz 31/36 GHz GHz 89/91 GHz 150/166 GHz 183 GHz AMSR-E GMI MADRAS SSMIS MHS17 ATMS Passive Microwave Sensor Characteristics in the GPM Era

JCSDA-HFIP Workshop, 2-3 December Inter-Satellite Calibration of Microwave Radiometers Objective: Quantify and reconcile differences between similar but not identical microwave radiometers to produce self-consistent global precipitation estimates X-Cal (Imagers): Convert observations of one satellite to virtual observations of another using non-Sun-synchronous satellite as a transfer standard (e.g. TMI or GMI) GPM International X-Cal Working Group (NASA, NOAA, JAXA, CNRS, EUMETSAT, CMA, CONAE, GIST, & universities) in coordination with WMO/CGMS GSICS -Develop corrections for recurring instrument errors and implementation strategy for routine intercalibration of constellation radiometers -Bias correction a function of orbital phase and solar beta angle -Agreement between different methods ~ 0.3 K TMI Bias Correction Table (K) X-Cal (Sounders): -Double differencing using forecast residual as primary transfer standard to provide a basis for calibration consistency -Collaboration with NWP centers NOAA ±3 GHz (Ocean) (MHS-ECMWF)- (AMSU_B-ECMWF) Courtesy of Bauer (ECMWF) Hanna, Weng, & Yan (NOAA)

JCSDA-HFIP Workshop, 2-3 December GPM Strategy to Global Precipitation Estimation RAIN SNOW Meneghini et al., NASA/GSFC - Radar for vertical structural details - Radiometers for horizontal coverage - A radar-radiometer system for a common transfer standard DPR Retrievals: A characteristic size parameter (D 0 ) of the PSD estimated from the difference (in dB) between Ku- and Ka-band radar reflectivity factors Ambiguities include unknown shape parameter (  ) of the gamma PSD distribution and the snow mass density (  ) Characteristic number concentration of PSD is given by D 0 and the radar equation Step-by-step estimation of attenuation correction based on PSD estimates Precipitation rate and the equivalent water content are derived from the PSD for an assumed velocity distribution

JCSDA-HFIP Workshop, 2-3 December Combined DPR+GMI retrievals Using GMI radiance measurements as additional constraints on the DPR profiling algorithm: Assumptions regarding the particle size distribution, ice microphysics, cloud water andwater vapor vertical distribution are refined using a variational procedure that minimizesdepartures between simulated and observed brightness temperatures - according to thesensitivity of simulated brightness temperatures to assumptions in DPR retrievals. Retrievals are consistent with both DPR reflectivities and GMI radiances w within a maximum-likelihood estimation framework. Construction of an a-priori database that relates hydrometeors to b brightness temperatures over the range of observed T b values for p precipitation retrievals from constellation radiometers. Pre-launch algorithm advances focus on retrievals of solid precipitation p and physical retrievals over land: - Modeling of nonlinear, under-constrained relationships between physical characteristics of precipitation particles and microwave observations - Characterization of land surface variability/emissivity

JCSDA-HFIP Workshop, 2-3 December GPM Joint Field Campaigns: Joint campaign with Brazil on warm rain retrieval over land in Alcântara, 3-24 March 2010 Light Precipitation Validation Experiment (LPVEx): CloudSat-GPM light rain in shallow melting layer situations in Helsinki, Finland, 15 Sept - 20 Oct 2010 Mid-Latitude Continental Convective Clouds Experiment (MC3E): NASA-DOE field campaign in central Oklahoma, Apr-May 2011 High-Latitude GPM Cold-Season Precipitation Experiment (GCPEX): Joint campaign with Environment Canada on snowfall retrieval in Ontario, Canada, Jan-Feb 2012 Hydrological validation with NOAA HMT in 2013 (under development) International Collaborations on GPM GV Pre-CHUVA (2010) MC3E (2011) NASA-EC Snowfall (2012) LPVEx (2010) 15 Active International Projects Joint field campaigns National networks and other ground assets (radar, gauges, etc.) Hydrological validation sites (streamflow gauges, etc.)

JCSDA-HFIP Workshop, 2-3 December Intercalibrated constellation radiometric data reconciling differences in center frequency, viewing geometry, resolution, etc. -Converting observations of one satellite to virtual observations of another using non-Sun-synchronous satellite as a transfer standard -GMI employs an encased hot load design (to minimize solar intrusion) and noise diodes for nonlinearity removal to attain greater accuracy & stability Unified precipitation retrievals using a common cloud database constrained by DPR+GMI measurements from the Core Observatory GPM Core: Reference Standard for Constellation Radiometers Next-Generation Global Precipitation Products Optimally matching observed T b with simulated T b from an a priori cloud database Simulated T b Observed T b TRMM uses a model-generated cloud database GPM uses a DPR/GMI-constrained database Prototype GPM Radiometer Retrieval Comparison of TRMM PR surface rain with TMI rainretrieval using an cloud database consistent with PRreflectivity and GMI multichannel radiances

JCSDA-HFIP Workshop, 2-3 December GPM Data Products

JCSDA-HFIP Workshop, 2-3 December Applications for hurricane monitoring & prediction Hurricane Tracking Numerical Weather Prediction ECMWF Hurricane Charley track forecasts from analysis Cyclone disappeared in operational forecast without rain assimilation Rain Ass Courtesy of P. Bauer/ECMWF Position Error in Nautical Miles Precipitation observations are in operational use at ECMWF, NCEP, JMA, and other NWP centers.

JCSDA-HFIP Workshop, 2-3 December GPM is an international satellite mission that will unify and advance precipitation measurements from a constellation of microwave sensors for scientific research and societal applications. – GPM is in the implementation phase at NASA and JAXA – Core Observatory Launch Readiness Date: 21 July 2013 Key advances include – More accurate instantaneous precipitation information, especially light rain & solid precipitation – Better space-time coverage through international partnership – High spatial resolution (DPR & GMI on Core Observatory) – Next-generation global precipitation products building on intercalibrated constellation radiometric measurements and unified physical retrievals using a common observation-constrained hydrometeor database NASA Precipitation Processing System is currently producing – Prototype intercalibrated L1 products for TMI, SSMI, AMSR-E, SSMIS, & WindSat – L3 merged global precipitation products using TMI, SSMI, AMSR-E, AMSU, & MetOp in near real-time for research & applications Summary (1/2)

JCSDA-HFIP Workshop, 2-3 December GPM is a science mission with integrated applications goals: –MW imaging and precipitation rates available within 1 hr of observation from two GMI’s in non-Sun-synchronous orbits for near real-time applications –DPR reflectivity and combined DPR+GMI precipitation products available within 3 hr of observation Ground validation is key to pre-launch algorithm development and post-launch product evaluation. - NASA is conducting a series of joint field campaigns with domestic & international partners to refine algorithm assumptions & parameters. - Synergy with NWP in areas such as radiometer intercalibration, observation operator development, and model physics improvement Summary (2/2)

JCSDA-HFIP Workshop, 2-3 December Additional Information

JCSDA-HFIP Workshop, 2-3 December * Minimum detectable rainfall rate is defined by Ze=200 R 1.6 (TRMM/PR: Ze=372.4 R 1.54 ) ItemKuPR at 407 kmKaPR at 407 kmTRMM PR at 350 km Antenna TypeActive Phased Array (128) Frequency & GHz & GHz & GHz Swath Width245 km120 km215 km Horizontal Reso5 km (at nadir) 4.3 km (at nadir) Tx Pulse Width 1.6  s (x2)1.6/3.2  s (x2)1.6  s (x2) Range Reso250 m (1.67  s) 250 m/500 m (1.67/3.34  s) 250m Observation Range 18 km to -5 km (mirror image around nadir) 18 km to -3 km (mirror image around nadir) 15km to -5km (mirror image at nadir) PRF VPRF (4206 Hz  170 Hz)VPRF (4275 Hz  100 Hz) Fixed PRF (2776Hz) Sampling Num 104 ～ ～ Tx Peak Power> 1013 W> 146 W> 500 W Min Detect Ze (Rainfall Rate) < 18 dBZ ( < 0.5 mm/hr ) < 12 dBZ (500m res) ( < 0.2 mm/hr ) < 18 dBZ ( < 0.7 mm/hr ) Measure Accuracy within ±1 dB Data Rate< 112 Kbps< 78 Kbps< 93.5 Kbps Mass< 365 kg< 300 kg< 465 kg Power Consumption < 383 W< 297 W< 250 W Size2.4×2.4×0.6 m1.44 ×1.07×0.7 m2.2×2.2×0.6 m DPR Instrument Characteristics

JCSDA-HFIP Workshop, 2-3 December GMI Instrument Characteristics Frequency Beam NEDT Req. (K) Expected* NEDT (K) Expected Beam Efficiency (%) Expected Cal. Uncertainty (K) Resolution (km) GHz (V & H) K x (V & H) x (V) x (V & H) x (V & H) x (V & H) x ±3 (V) x ±7 (V) x 7.3 Data Rate: ~30 kbps Power: 162 Watts Mass: 166 kg * Analysis data as of May 2010 Deployed Size: 1.4 m x 1.5 m x 3.5 m Antenna Size: 1.2 m Swath: 885 km Resolution and swath for GMI on Core

JCSDA-HFIP Workshop, 2-3 December Baseline Constellation Schedule Hour Prime Life Extended Life Current Capability: < 3h over 45% of globe GPM (2015): < 3h over 90% of globe GPM Constellation Sampling and Coverage GPM Core Launch 1-2 hr revisit time over land with inclusion of sounders

JCSDA-HFIP Workshop, 2-3 December Three complementary approaches: Direct statistical validation (surface): - Leveraging off operational networks to identify and resolve first-order discrepancies between satellite and ground-based precipitation estimates Physical process validation (vertical column): - Cloud system and microphysical studies geared toward testing and refinement of physically-based retrieval algorithms Integrated hydrologic validation/applications (4-dimensional): - Identify space-time scales at which satellite precipitation data are useful to water budget studies and hydrological applications; characterization of model and observation errors Role of GPM Ground Validation Pre-launch algorithm development & post-launch product evaluation - Refine algorithm assumptions & parameters - Characterize uncertainties in satellite retrievals & GV measurements “Truth” is estimated through the convergence of satellite and ground-based estimates

JCSDA-HFIP Workshop, 2-3 December Science Partnership with NOAA on GPM Level 1 radiometer intercalibration (partnership through GSICS & PMM) - Using NWP forecast residuals for sounder intercalibration Level 2 precipitation algorithms (NOAA PI’s on PMM Science Team) -Land surface characterization for physically based retrieval -Precipitation microphysical properties Statistical validation - Collaboration with NOAA NMQ for validation and product enhancement Hydrological applications/validation - Joint field campaigns with NOAA HMT (e.g. HMT-SE) Level 3 multi-satellite product development -Moving towards U.S. national products (global & regional) -Combined satellite & ground-based measurements Level 4 dynamic downscaling -WRF ensemble data assimilation using NOAA operational data streams