slaRefro -

SYNOPSYS

PARAMETERS

double zobs

double hm

double tdk

double pmb

double rh

double wl

double phi

double tlr

double eps

double *ref

DESCRIPTION

  Atmospheric refraction for radio and optical wavelengths.

Given

    zobs    double  observed zenith distance of the source (radian)
    hm      double  height of the observer above sea level (metre)
    tdk     double  ambient temperature at the observer (deg K)
    pmb     double  pressure at the observer (millibar)
    rh      double  relative humidity at the observer (range 0-1)
    wl      double  effective wavelength of the source (micrometre)
    phi     double  latitude of the observer (radian, astronomical)
    tlr     double  temperature lapse rate in the troposphere (degK/metre)
    eps     double  precision required to terminate iteration (radian)

Returned

    ref     double  refraction: in vacuo ZD minus observed ZD (radian)

  Typical values for the tlr and eps arguments are 0.0065
  and 1e-9 respectively.

  This routine computes the refraction for zenith distances up to
  and a little beyond 90 deg using the method of Hohenkerk and
  Sinclair (NAO Technical Notes 59 and 63).  The C code is an
  adaptation of the Fortran optical refraction subroutine AREF
  of C.Hohenkerk (HMNAO, September 1984), with extensions to support
  radio wavelengths.  Most of the modifications to the HMNAO optical
  algorithm are cosmetic;  in addition the angle arguments have been
  changed to radians, any value of zobs is allowed, and other values
  have been limited to safe values.  The radio expressions were
  devised by A.T.Sinclair (RGO - private communication), based on
  the Essen & Froome refractivity formula adopted in Resolution 1
  of the 13th International Geodesy Association General Assembly
  (Bulletin Geodesique 1963 p390).

  The radio refraction is chosen by specifying wl > 100 micrometres.

  Before use, the value of zobs is expressed in the range +/- Pi.
  If this ranged zobs is -ve, the result ref is computed from its
  absolute value before being made -ve to match.  In addition, if
  it has an absolute value greater than 93 deg, a fixed ref value
  equal to the result for zobs = 93 deg is returned, appropriately
  signed.

  Fixed values of the water vapour exponent, height of tropopause, and
  height at which refraction is negligible are used.

Called

 slaDrange, atmt, atms

  Defined in slamac.h:  TRUE, FALSE

  Original version by C.Hohenkerk, HMNAO, September 1986.
  Starlink version by P.T.Wallace, revised 22 December 1993.

SEE ALSO

• slalib.3