Kazumasa Aonashi MRIJMA

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Oct.24, 2006
3rd IPWG Workshop
Developnemt of Passive Microwave Precipitation
Retrieval Algorithm Towards the GPM Era

• Kazumasa Aonashi (MRI/JMA)
• Takuji Kubota (Osaka Pref. Univ.)
• Nobuhiro Takahashi (NICT)

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Satellite Microwave Radiometers
Aqua AMSR-E
TRMM TMI PR
DMSP SSM/I
ADEOS-II AMSR
MWRs with window channels
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Passive Microwave Precipitation Retrieval

• GSMaP Retrieval Algorithm
• Global Satellite Mapping of Precipitation Project
  started in 2003.
• Leader Prof. Kenich Okamoto (Osaka Pref. Univ.)
• Funded by JST/CREST
• The goal is to produce accurate precip map using
  mainly satellite microwave radiometer.
• Passive microwave precip retrieval algorithm is
  based on Aonashi and Liu (2000).

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Outline

• Introduction
• GSMaP MW Retrieval Algorithm
• Retrieval Algorithm (V4.7.2)
• Validation using radar and gauge data
• Improvement of the Scattering part

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GSMaP MW Retrieval Algorithm

• Retrieval Algorithm (V4.7.2)

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GSMaP Precip Retrieval Algorithm

• Over Land
• Scattering by frozen particles
• (TBs at 37 85GHz)
• Over Ocean
• Scattering (37 85GHz)
• Radiation from Rain
• (TBs at 10 19 GHz)

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Passive microwave precipitation retrieval
Forward calculation
Retrieval Calculation
parameters
Observed TBs
Look-up Table
FLH Precip Profiles DSD inhomogeneity

Precip.
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Forward Calculation

• Lius RTM (1998) is used to calculate TBs
• Mixed-phase precip is parameterized with
  Takahashi Awaka (2005).
• Parameters (FLH, precip profiles) are given as
  the a priori information.

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Nishitsuji Model (N model)
Implicitly including break-up/coalescence
processes

• On the basis of the filed experiment, the
  following parameters are modeled
• Volume liquid water fraction (Pw)
• shape parameter of the dielectric constant (U)
• DSD parameter (B) is a function of Pw
• Density ?vPw
• Fall velocity Magono-Nakamura(1965) for snow and
  Foot and Du Toit for rain

Pw and U profile
Relationship between B and Pw
B
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Lookup table (TB-R) for variable Freezing Level
Height (FLH)
Procedure Rain rate from PR is integrated within
TMIs 10 GHz footprint weighted by the antenna
pattern.

• Melting layer model shows slightly better
  representation than rain only model.

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Forward Calculation

• Lius RTM (1998) is used to calculate TBs
• Mixed-phase precip is parameterized with
  Takahashi Awaka (2005).
• Parameters (FLH, precip profiles) are given as
  the a priori information.

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Parameters used in the AlgorithmPrecipitation
Types and Profiles (TRMM PR)
Classification of types
Database for types
2.5 deg. grid Seasonal 8types(Sea 3, Land 5)

Type-1
Profile for each Types
Height (km)
Database for Profile
For precip. types surface precip.
Precip mm/h
Precipitation profiles for Type 1 0.5, 1, 2, 3,
4, 6, 8, 10, 15, 20, 30, 40, 60, 80, 120, 160,
200 mm/h
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Parameters used in the AlgorithmAtmospheric
variables (GANAL)

• Atmospheric variables (FLH, SSW, SST) are
  derived from the Global Analysis data of JMA

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Basic Idea of the Retrieval Algorithm
Forward calculation
Retrieval Calculation
parameters
Observed TBs
Look-up Table
FLH Precip Profiles DSD inhomogeneity

Precip.
To find the optimal precipitation that gives
RTM-calculated TBs fitting best with the observed
TBs.
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Precipitation Retrival Algorithm
Observed TBs
Screening of Precip Areas
LOOK-UP TABLE (LUT)
rain flag
Scatter-based Precip Estimation
rain37 ? PCT37LUT rain85 ? PCT85LUT
sigma (inhomogeneity)
First-guess of over-sea Precipitation
rain10V ? TB10VLUT (sigma)
rain19V ? TB19VLUT (sigma)
Minimization of S(TBc-TBo)2
Retrivals
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Rain85 Rain.v4.7.2 vs Rainsurf over Tropical
land, July, 1998
Rain85
W85Rain85W37Rain37
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Validation using Radar gauges

• Comparison with
• PR.2A25
• Ground radar
• (Okinawa, KWAJ)
• GPCC (rain gauge)

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Relative Error with PR (1998-2004)
Error100 TMI PR/PR Average over
(19982004)
Tropic (15S15N) Mid (lt15S or gt 15N)
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Zonal Mean Precip over Ocean(19982004)
PR3G68, GPROF.v6, GSMaP.v4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
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Zonal Mean Precip over Land (19982004)
PR3G68, GPROF.v6, GSMaP.v4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
3G68 V6 PR GPROF V6 TMI GSMaP V4.7 GSMaP V4.7.2
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Comparison with ground-based radar
COBRA(Okinawa)
KWAJ
Corretation0.79(No253) RMSE1.46 mm/hr
Correlation0.65(No1139) RMSE1.78 mm/hr
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Integrated 6-hour Microwave radiometer
Precipitation Map(TMIAMSRAMSR-EF13,F14,F15
SSM/I Jul., 2003)
Missing Values
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Comparison with GPCC data
GSMaP_MWRmonthly mean preciptation (1x1
deg) GPCC Monthly Precipitation (Monitoring)
Product (Rudolf et al. 2006)
Correlation0.80 (Number5974)
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Improvement of the Scattering part

• Retrieval Algorithm (V5.1)

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(rainsurf/rain.4.7.2).vs.stdlgpr and Toplev over
Tropical Land, July, 1998
STDLGPR (inhomo)
Precip. Top level
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Scattering part (V5.1)

• Dual-frequency (37,85GHz)
• Retrieval of rain37 uses parameters from rain85
• Horizontal inhomogeneity
• Precipitation top level

Sigma85 vs STDLGPR
PCT85 vs Precip. top
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Comparison with PR 3G68 over Land (July, 1998)
V4.7.2
V5.1
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Comparison with PR 3G68 over Ocean (July, 1998)
V5.1
V4.7.2
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Summary

• GSMaP passive microwave precipitation retrieval
  algorithm.
• The retrieved precipitation agreed well with PR,
  radar data over ocean.
• The over-land algorithm underestimated the strong
  precipitation.
• Introduction of the retrieved inhomogeneity
  alleviated the underestimation.

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END

• Thank you.