Home > SPlaC v1_0 > Mie > PWE > PweQcoeff.m

PweQcoeff

PURPOSE ^

Calculates the Mie extinction, scattering and absorption coefficients for PWE from the Mie susceptibilities.

SYNOPSIS ^

function stQ=PweQcoeff(x,stGD)

DESCRIPTION ^

 Calculates the Mie extinction, scattering and absorption coefficients for PWE from the Mie susceptibilities.
 The relevant formulae are given in  Eqs. H.76, H.77, H.78.

 Parameters:
 - x:      column vector [L x 1]
           wavelength-dependent x=kM*a (Eq. H.45)
 - stGD:  structure with two fields, Gamma and Delta
           each a matrix [L x nNmax]
           with suceptibilities Gamma_n and Delta_n
           can be obtained from function GenSuscepGDAB

 Returns: structure stQ with three fields
          each a matrix [L x 1]
 - stQ.Qext: [L x 1] wavelength-dependent extinction coefficient
 - stQ.Qsca: [L x 1] wavelength-dependent scattering coefficient
 - stQ.Qabs: [L x 1] wavelength-dependent absorption coefficient

 This file is part of the SPlaC v1.0 package (copyright 2008)
 Check the README file for further information

CROSS-REFERENCE INFORMATION ^

This function calls: This function is called by:

SOURCE CODE ^

0001 nNmax=size(stGD.Gamma,2);
0002 
0003 n=transpose(1:nNmax); % [nNmax x 1]
0004 cc = 2.*n+1; % [nNmax x 1]
0005 
0006 % From Eq. H.76
0007 Gamma2=abs(stGD.Gamma).^2;
0008 Delta2=abs(stGD.Delta).^2;
0009 scamat= Gamma2 + Delta2; % [L x nNmax]
0010 stQ.Qsca= 2./((x).^2) .* (scamat * cc); % [L x 1]
0011 % no checksum required since this is a sum of positive numbers
0012 
0013 % Calculation of Qext
0014 % This may result in loss-of-precission warnings for non-absorbing sphere,
0015 % for which real(\Delta)=-|\Delta|^2 exactly
0016 % These are not an issue since in this case Qext=Qsca, and only
0017 % the calculation of Qsca should therefore be trusted.
0018 
0019 % take real part and check for loss of precision
0020 GammaR=GenCheckSumReal(stGD.Gamma,'GammaR','PweQcoeff'); % [L x nNmax]
0021 DeltaR=GenCheckSumReal(stGD.Delta,'DeltaR','PweQcoeff'); % [L x nNmax]
0022 % From Eq. H.77
0023 stQ.Qext= - 2./((x).^2) .* ((GammaR+DeltaR) * cc); % [L x 1]
0024 % sum is on negative numbers only, no loss of precision
0025 
0026 % From Eq. H.78
0027 stQ.Qabs = stQ.Qext - stQ.Qsca; % [L x 1]
0028

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