;*******************************************
;  Convert radiances to brightness temp
;*******************************************

pro rad_to_tb,radiances,tb,channel

h=6.62606876e-34 ;Js   ;Planck
k=1.3806503e-23  ;J/K  ;Boltzmann
c=3.0e8          ;m/s  ;speed of light

;  lambda	 ;um   ;wavelength of radiances
if channel eq 31 then lambda=11.03 else $
if channel eq 33 then lambda=13.34 else $
if channel eq 36 then lambda=14.24 else begin
  print,'no lambda for this wavelength'
  print,'no tb conversion possible'
  stop
endelse


lambda=lambda*1e-6     ;convert to meters
wvnum=1.0/lambda ;wavenumber

do_lam='yes'
if do_lam eq 'yes' then begin
  part1=(h*c)/(k*lambda)
  part2=(2.0*h*(c^2.0))/(lambda^5.0*radiances*1e6)
  part2=alog(part2+1.0)
  tb=part1/part2
endif 

do_wvnum='no'
if do_wvnum eq 'yes' then begin
  part1=(h*c*wvnum)/k
  part2=2.0*h*(c^2.0)*(wvnum^5.0)
  part2=part2/(radiances*1e6)
  part2=alog(part2+1.0)
  tb=part1/part2
endif

;  Put the missing flag in the tb array
result=where(radiances le -8888,count)
if count gt 0 then tb[result]=-8888

return
end