Fast Forward Radiative Transfer

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• Fast Forward Radiative Transfer
• Modeling for Microwave Radiance Assimilation
• Albin J. Gasiewski
• Alex G. Voronovich
• Bob L. Weber
• Dean F. Smith
• Timothy L. Schneider
• Jian-Wen Bao
• NOAA Environmental Technology Laboratory

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NOAA/ETL RT Modeling Group

• Personnel
• Dr. Al Gasiewski (0.2 EFT) - PI, JCSDA Tech
  Liaison
• Dr. Alex Voronovich (0.1 EFT) - Algorithm
  Development
• Dr. Bob Weber (0.7 EFT) - Code Development
• Dr. Dean Smith (0.5 EFT) - Code Assessment
• Tim Schneider (0.2 EFT) - RT Modeling Science
• Dr. Jian-Wen Bao (0.1 EFT) - NWP Modeling
• Dr. Gary Wick (0.1 EFT) - Satellite Data
  Analysis
• Dr. Boba Stankov (0.1 EFT) - RT Graphics
• Dr. Marian Klein (0.1 EFT) - RT Modeling Science
• Total 2.1 EFT contributing
• Also, PI for NESDIS Geostationary Microwave
  Pathway Study

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All-Weather Microwave Assimilation

• Potential capabilities include
• Extended thermodynamic information (water vapor
  and temperature fields) within the
  forecast-sensitive and economically important
  cloud-covered regions
• Improved accuracy of cloud and radiation products
• Short-term prediction of mesoscale convection for
  warnings with high specificity
• Tracking of latent heat exchange within
  precipitation

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Fast Scattering-Based Jacobian Algorithm

• Planar stratified atmosphere
• Liebe MPM 87 93 gaseous absorption model
• Polydispersive Mie solution for five phase of
  water
• Cloud (liquid), Rain (liquid), Graupel (liquid
  solid),
• Snow (solid), Cloud Ice (solid)
• Discrete-ordinate layer-adding solution
• Incremental response to changes in bulk
  absorption
• and scattering coefficients and temperature
• Efficiency compatible with satellite data
  streams
• Applicable for arbitrary wavelengths
• Henyey-Greenstein hydrometeor phase matrix,
  being
• extended to incorporate an exact Mie library
• Interface to JCSDA CRTM developed

Voronovich, A., A.J. Gasiewski, and B.L.
Weber, "A Fast Multistream
Scattering-Based Jacobian for Microwave Radiance
Assimilation," IEEE Trans. Geosci.
Remote Sensing, August 2004.
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ETL DOTLRT Radiative Transfer Model (v2.0)
Dielectric constant e(f,T, tj), ?e/?T
OPTRAN
Consists of two files LIBNAME.CAT and LIBNAME.LIB

Calculates Mie solution and averages it
over azimuthal angles and exponential size
distribution for each hydrometeor phase

Exact Mie Library
DATA
Calculation of scattering (phase) matrix S as
well as its derivatives ST , S?
Numerical Weather Prediction Model
CRTM Profile Setup Routine
Level 1
Calculates brightness temperatures TBV , TBH
along with RT Jacobian
Layer 1
DOTLRT v2.0
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?S
?a
TB
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?S
?a
TB
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Practical Implications(Radiation Jacobian)
Layers Streams CPU Rate (GHz) Calculation Time (ms)
60 8 1.8 4.2

• Recourses
• Further simplified treatment of non-scattering
  layers (acceleration factor 2-3x)
• Parallel processing 2.8 GHz 100-nodes
  (acceleration 200x)
• Statistical 10 scattering cloud cover
  (acceleration 10x)
• gt 1 usec per channel-profile
  (anticipated)
• e.g., NPOESS CMIS data rate 30 channels every
  12 msec
• gt 400 usec per channel-profile

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DOTLRT Development Pathway
Code Attribute DOTLRT version gt v1.0 v1.1 v2.0 v2.1
Atmospheric radiation and geophysical Jacobians Mie spherical scatterer model x x x x
Five hydrometeor phases / exponential size distribution x x x x
Henyey Greenstein phase function x x
Fast Mie lookup library x x
Full Mie scattering phase function x x
Full Stokes Capability
Interface with CRTM x x
Distribution Jan 2005 Sep 2005 (est)
Proposed
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Precipitation Correlation Length - TRMM vs GCI,
Active Months -
TRMM PRgt0.1 mm/hr
GCI TB,IRlt240K
TRMM PRgt1 mm/hr

• Land/water continuity vindicates GPROFS maritime
  classification scheme
• Short scale lengths over land, longer over water
• Short scale behavior within ITCZ and over
  "maritime" continent

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• NWP Precipitation Locking

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NWP Precipitation Locking

• To realize locking of an NWP model onto
  precipitation, observations are needed at time
  and space scales of order 5-15 km and 15
  minutes.
• Locking is analogous to phase-locked loop in
  electrical engineering wherein linear phase
  differencing is achieved only when oscillator and
  signal remain within same phase cycle.
• Similarly, linear NWP model updates can be
  achieved provided that the cloud and
  precipitation state does not decorrelate between
  satellite observations.

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Sampling Requirements for NWP Precipitation
Locking

• The sampling requirements for all-weather
  microwave assimilation using near-term NWP models
  (especially regional models) are well satisfied
  by a large-aperture geosynchronous microwave
  sounder.

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GMSWG? Concept SummaryGEosynchronous Microwave
(GEM) Sensor

• Baseline system using 54, 118, 183, 380, and 424
  GHz with 2 m diameter Cassegrain antenna.
• 16 km subsatellite resolution (12 km using
  oversampling) above 2-5 km altitude at highest
  frequency channels.
• The 380 and 424 GHz channels selected to map
  precipitation through most optically opaque
  clouds at sub-hourly intervals. (Gasiewski, 1992)
• Temperature and humidity sounding channels
  penetrate clouds sufficiently to drive NWP models
  with hourly data.
• Estimated 2005 costs 36M non-recurring plus
  34M/unit.

Geosynchronous Microwave Sounder Working
Group, Chair D.H. Staelin (MIT)
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GeoSTAR Concept2-D Geostationary Sounder/Imager

• GeoSTAR spatial response pattern
• for 298 elements with 2.8lspacing
• 50 km spatial resolution
• Full disk image every one hour
• No moving parts
• 2.5m maximum baseline
• NASA/JPL concept

Y-Array of 300-600 receiver elements and tens of
thousands of one-bit correlators in each of three
bands 50-56, 89, and 183 GHz
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Summary

• FAST RT Jacobian development for multiphase
  precipitation including scattering (DOTLRT)
  Focus is on microwave bands, but applicable to IR
  also.
• Extension to include full Mie library underway
• Extension to full Stokes vector proposed
• Precipitation erorr covariance model development
  underway
• Geostationary Microwave Sounder system studies
  and simulations underway
• All-weather microwave radiance assimilation
  observing system experiments - focus on AMSU
  using the WRF regional model.
• Minimal funds received in FY04 no funding
  received yet in FY05