function [bt]=rad2bt(nu,B)
%Brightness Temperature 
% nu is wavenumber, B is radiance
%Paolo Antonelli
%Wed Feb 25 16:43:05 CST 1998

c1=1.191066*10^-5;           %W/m^2/ster/cm^-4
c2=1.438833;                 %K*cm
    
bt=c2*nu./(log((c1*nu.^3)./B+1.0));


