ATMOSPHERE

        [ASTRO\]ATMOSPHERE [INTERPOLATE|MAKE]

    Compute atmospheric  emission,  opacity,  system  temperatures,  etc...,
    using  input  parameters  provided by the user. Input parameters are the
    following SIC variables:
       TEMPERATURE      Outside temperature
       ZERO_PRESSURE    Pressure at sea level.
       AIRMASS          Number of air masses
       WATER            Precipitable water vapor
       FORWARD_EFF      Forward efficiency
       GAIN_IMAGE       Receiver gain ratio
       TREC             Receiver temperature
       FREQ_SIG         Signal frequency (in GHz)
       FREQ_IMA         Image frequency (in GHz)
    These variables  can  be  assigned  using  the  SIC  command  LET.   The
    additional input variables
       ALTITUDE         Site altitude
       FREQ_SIG         Signal frequency (in GHz)
       FREQ_IMA         Image frequency (in GHz)
    are modified by the ASTRO OBSERVATORY and LINE commands.

    The output of the command consists in the following variables
       TRUE_PRESSURE    Local pressure, derived from the site altitude and
                        the sea level pressure by the scale height of 5.5 km.
       TSYS             The system temperature in the signal sideband
       TAU_H2O          The water vapor opacity
       TAU_O2           The dry atmosphere opacity (mostly due to Oxygen,
                        but minor constituents like Ozone may also play a role)
       EMIS_SIG         The atmospheric emission (Kelvin) in the signal sideband
       EMIS_IMA         The atmospheric emission (Kelvin) in the image sideband
       PATH_SIG         The atmospheric excess optical path length (mm)
                        in the signal sideband
       PATH_IMA         The atmospheric excess optical path length (mm)
                        in the image sideband
    These variables can  then  be  used  to  produce  plots  of  atmospheric
    transparency, system temperatures, etc...

    ATMOSPHERE INTERPOLATE
    will do the same calculations,  but  interpolating  the  data  from  the
    binary table (logical name GAG_ATMOSPHERE).

    ATMOSPHERE MAKE filename nf freqmin freqmax
    will create the binary table filename.bin  for  nf  frequencies  between
    freqmin and freqmax (in GHz).