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    Compute atmospheric emission, opacity, system temperatures, etc...,  us-
    ing input parameters provided by the user. Input parameters are the fol-
    lowing 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  addi-
    tional 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.
    Option /PRINT displays all these inputs.

    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)
       TAU_TOT          The total opacity: H2O + O2 (+ minor components for
                        new ATM versions)
       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
       ATM_SIG          The atmosphere temperature in the signal sideband
       ATM_IMA          The atmosphere temperature in the image sideband
       TANT             The antenna temperature
    These  variables can then be used to produce plots of atmospheric trans-
    parency, system temperatures, etc. By default, the command computes  the
    atmospheric  parameters  for  a single pair of signal and image frequen-
    cies. To compute the parameters for a list of  frequencies,  use  option
    /FREQUENCIES (see subtopic for details).

    will do the same calculations, but interpolating the data from the bina-
    ry table (as defined by logical name GAG_ATMOSPHERE). The whole table is
    loaded  in  internal  buffers  which  can  be  accessed in the structure
    ATM%TABLE% for use in procedures.

    ATMOSPHERE MAKE filename nf freqmin freqmax
    will create the binary table filename.bin  for  nf  frequencies  between
    freqmin  and freqmax (in GHz). See subtopic FORMAT for details about the
    binary format used.

    ATMOSPHERE SAVE filename
    will save inside filename.bin the  binary  table  currently  in  memory.
    This  is useful to save with the current machine byte order a table pre-
    viously computed on a different machine with a different byte order.


Gildas manager 2019-12-05