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diff --git a/math/slalib/doc/atmdsp.hlp b/math/slalib/doc/atmdsp.hlp new file mode 100644 index 00000000..eaa2b411 --- /dev/null +++ b/math/slalib/doc/atmdsp.hlp @@ -0,0 +1,75 @@ +.help atmdsp Jun99 "Slalib Package" +.nf + + SUBROUTINE slATMD (TDK, PMB, RH, WL1, A1, B1, WL2, A2, B2) + + - - - - - - - + A T M D + - - - - - - - + + Apply atmospheric-dispersion adjustments to refraction coefficients. + + Given: + TDK d ambient temperature, degrees K + PMB d ambient pressure, millibars + RH d ambient relative humidity, 0-1 + WL1 d reference wavelength, micrometre (0.4D0 recommended) + A1 d refraction coefficient A for wavelength WL1 (radians) + B1 d refraction coefficient B for wavelength WL1 (radians) + WL2 d wavelength for which adjusted A,B required + + Returned: + A2 d refraction coefficient A for wavelength WL2 (radians) + B2 d refraction coefficient B for wavelength WL2 (radians) + + Notes: + + 1 To use this routine, first call slRFCO specifying WL1 as the + wavelength. This yields refraction coefficients A1,B1, correct + for that wavelength. Subsequently, calls to slATMD specifying + different wavelengths will produce new, slightly adjusted + refraction coefficients which apply to the specified wavelength. + + 2 Most of the atmospheric dispersion happens between 0.7 micrometre + and the UV atmospheric cutoff, and the effect increases strongly + towards the UV end. For this reason a blue reference wavelength + is recommended, for example 0.4 micrometres. + + 3 The accuracy, for this set of conditions: + + height above sea level 2000 m + latitude 29 deg + pressure 793 mB + temperature 17 degC + humidity 50% + lapse rate 0.0065 degC/m + reference wavelength 0.4 micrometre + star elevation 15 deg + + is about 2.5 mas RMS between 0.3 and 1.0 micrometres, and stays + within 4 mas for the whole range longward of 0.3 micrometres + (compared with a total dispersion from 0.3 to 20.0 micrometres + of about 11 arcsec). These errors are typical for ordinary + conditions and the given elevation; in extreme conditions values + a few times this size may occur, while at higher elevations the + errors become much smaller. + + 4 If either wavelength exceeds 100 micrometres, the radio case + is assumed and the returned refraction coefficients are the + same as the given ones. + + 5 The algorithm consists of calculation of the refractivity of the + air at the observer for the two wavelengths, using the methods + of the slRFRO routine, and then scaling of the two refraction + coefficients according to classical refraction theory. This + amounts to scaling the A coefficient in proportion to (n-1) and + the B coefficient almost in the same ratio (see R.M.Green, + "Spherical Astronomy", Cambridge University Press, 1985). + + P.T.Wallace Starlink 6 October 1995 + + Copyright (C) 1995 Rutherford Appleton Laboratory + Copyright (C) 1995 Association of Universities for Research in Astronomy Inc. + +.fi +.endhelp |