c==========================================================
c
c NAME: lza
c
c PURPOSE:  Computes local zenith angle for HIRS observation
c
c INPUTS:
c           alt.......Altitude in km
c           isp.......HIRS scan position (1-56)
c
c OUTPUT:
c           local zenith angle in degrees
c
c HISTORY:  Darren Jackson CIRES/ETL April 2002
c
c=========================================================
c
      function lza(alt,isp)

      implicit none

      real    alt,scan_angle,lza,sinzen
      integer isp

c      external sind,asind

      scan_angle=-49.5+1.8*float(isp-1)
      sinzen=abs((alt+6371.)*sind(scan_angle)/6371.)
      lza=asind(sinzen)
      return
      end