optimizing multiple scattering calculations in the crtm
DESCRIPTION
Optimizing Multiple Scattering Calculations in the CRTM. Tom Greenwald, Ralf Bennartz and Jim Davies University of Wisconsin. JCSDA 10th Workshop on Satellite Data Assimilation, October 10-12, 2012. Motivation. Address speed/accuracy tradeoffs in CRTM multiple scattering calculations - PowerPoint PPT PresentationTRANSCRIPT
Optimizing Multiple Scattering Calculations in the CRTM
Tom Greenwald, Ralf Bennartz and Jim DaviesUniversity of Wisconsin
JCSDA 10th Workshop on Satellite Data Assimilation, October 10-12, 2012
MotivationAddress speed/accuracy tradeoffs in CRTM
multiple scattering calculationsDevelop a scattering indicator to find a priori
the optimum number of streams for the solver (i.e., minimum streams needed to achieve a desired accuracy)
JCSDA 10th Workshop on Satellite Data Assimilation, October 10-12, 2012 2
MethodsScattering indicator (SI) based on successive order of
scattering (Stephens 1994)Simple analytical functionDepends on optical depth and single-scatter albedo
Enhancements to Stephens formulation Include effects of gas absorptionExtend to multiple layers using a vertically weighted
single-scatter albedo (Bennartz and Greenwald 2011)
3JCSDA 10th Workshop on Satellite Data Assimilation, October 10-12, 2012
Methods Cont’dApply thresholds to the SI to automatically increase the
numbers of streams (aka “selection rules”) Source of cloud profiles: WRF model simulations
Hurricane Katrina (1.5 km) California marine stratocumulus (2 km) South Atlantic frontal system (3 km)
Limit to microwave sensors for now; define target accuracy as 0.5 K (typical radiometric sensitivity)
CRTM 16-stream solution used as a reference to quantify error
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Examples
0.5 K0.5 K
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Results – Hurricane KatrinaTemperature Sounding Channel (55.5 GHz) Water Vapor Sounding Channel (1831 GHz)
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Results - Hurricane Katrina
0 2 4 6 8 16
Tb error Streams
55 G
Hz
183
1 GH
z
Mean Error
% Optimum Streams
7Error (K)
Results – Marine Sc
150 GHz
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Results – Marine Sc
0 2 4 6 8 16
Tb error Streams
37H
GHz
150
GHz
Error (K)
% Optimum Streams
Mean Error
9
Results – Frontal SystemSouth Atlantic
TemperatureSoundingChannel (54.4 GHz)
Water VaporSoundingChannel (1833 GHz)
Queen Mary’s Peak on Tristan da Cunha
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Results – Frontal System
0 2 4 6 8 16
Tb error Streams
54.4
GHz
18
33
GHz
Error (K)
Mean Error
% Optimum Streams
11
AccomplishmentsDeveloped a method of automatically selecting the
optimum number of streams in the CRTM Generally, optimum values achieved 85-100% of the time Suboptimal (40-75%) in water vapor bands Factors of 5-10 speedup for temperature sounding channels
Modified CRTM code to include new method (FWD/TL only) CRTM v2.1
Number of streams option (overrides auto-selection) Successive Order of Interaction (SOI) RT solver
Publication: Bennartz and Greenwald (2011, QJRMS)
12JCSDA 10th Workshop on Satellite Data Assimilation, October 10-12, 2012
PlansFine-tune selection rulesExplore use of other SIs (e.g., Mie size
parameter) in strongly scattering and absorbing conditions
Write adjoint code Extend method to IR sensors for clouds and
aerosolsInclude in CRTM v2.2 release
13JCSDA 10th Workshop on Satellite Data Assimilation, October 10-12, 2012