function res=rayleigh(lambda,p);
% Rayleigh calculation given by Deschamps et al, 1983
A=8436.e-6;
B=-1225.e-7;
C=14.e-5;
p0=1013;
lambda=lambda*1.e-3;
res=p/p0*(A*lambda.^(-4)+B*lambda.^(-5)+C*lambda.^(-6));