slaRefco -

SYNOPSYS

PARAMETERS

double hm

double tdk

double pmb

double rh

double wl

double phi

double tlr

double eps

double *refa

double *refb

DESCRIPTION

  Determine constants A and B in atmospheric refraction model
  dz = A tan z + B tan3 z (for optical wavelengths).

  z is the "observed" zenith distance (i.e. affected by
  refraction) and dz is what to add to z to give the "topocentric"
  (i.e. in vacuo) zenith distance.

  The constants are such that the model agrees precisely with
  the full integration performed by the slaRefro routine at
  zenith distances arctan(1) and arctan(4).

Given

    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

    *refa double    tan z coefficient (radian)
    *refb double    tan3 coefficient (radian)

Called

 slaRefro

  Typical values for the tlr and eps arguments might be 0.0065 and
  1e-10 respectively.

  Relative to the comprehensive refraction model used by this routine,
  the simple A tan z + B tan3 z formula achieves 0.5 arcsec accuracy
  for ZD < 80 deg, 0.01 arcsec accuracy for ZD < 60 deg, and
  0.001 arcsec accuracy for ZD < 45 deg.

  P.T.Wallace   Starlink   31 October 1993

SEE ALSO

• slalib.3