SUBROUTINE sla_AOPPA (DATE, DUT, ELONGM, PHIM, HM, : XP, YP, TDK, PMB, RH, WL, TLR, AOPRMS) *+ * - - - - - - * A O P P A * - - - - - - * * Precompute apparent to observed place parameters required by * sla_AOPQK and sla_OAPQK. * * Given: * DATE d UTC date/time (modified Julian Date, JD-2400000.5) * DUT d delta UT: UT1-UTC (UTC seconds) * ELONGM d mean longitude of the observer (radians, east +ve) * PHIM d mean geodetic latitude of the observer (radians) * HM d observer's height above sea level (metres) * XP d polar motion x-coordinate (radians) * YP d polar motion y-coordinate (radians) * TDK d local ambient temperature (DegK; std=273.155D0) * PMB d local atmospheric pressure (mB; std=1013.25D0) * RH d local relative humidity (in the range 0D0-1D0) * WL d effective wavelength (micron, e.g. 0.55D0) * TLR d tropospheric lapse rate (DegK/metre, e.g. 0.0065D0) * * Returned: * AOPRMS d(14) star-independent apparent-to-observed parameters: * * (1) geodetic latitude (radians) * (2,3) sine and cosine of geodetic latitude * (4) magnitude of diurnal aberration vector * (5) height (HM) * (6) ambient temperature (TDK) * (7) pressure (PMB) * (8) relative humidity (RH) * (9) wavelength (WL) * (10) lapse rate (TLR) * (11,12) refraction constants A and B (radians) * (13) longitude + eqn of equinoxes + sidereal DUT (radians) * (14) local apparent sidereal time (radians) * * Notes: * * 1) It is advisable to take great care with units, as even * unlikely values of the input parameters are accepted and * processed in accordance with the models used. * * 2) The DATE argument is UTC expressed as an MJD. This is, * strictly speaking, improper, because of leap seconds. However, * as long as the delta UT and the UTC are consistent there * are no difficulties, except during a leap second. In this * case, the start of the 61st second of the final minute should * begin a new MJD day and the old pre-leap delta UT should * continue to be used. As the 61st second completes, the MJD * should revert to the start of the day as, simultaneously, * the delta UTC changes by one second to its post-leap new value. * * 3) The delta UT (UT1-UTC) is tabulated in IERS circulars and * elsewhere. It increases by exactly one second at the end of * each UTC leap second, introduced in order to keep delta UT * within +/- 0.9 seconds. * * 4) IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION. * The longitude required by the present routine is east-positive, * in accordance with geographical convention (and right-handed). * In particular, note that the longitudes returned by the * sla_OBS routine are west-positive, following astronomical * usage, and must be reversed in sign before use in the present * routine. * * 5) The polar coordinates XP,YP can be obtained from IERS * circulars and equivalent publications. The maximum amplitude * is about 0.3 arcseconds. If XP,YP values are unavailable, * use XP=YP=0D0. See page B60 of the 1988 Astronomical Almanac * for a definition of the two angles. * * 6) The height above sea level of the observing station, HM, * can be obtained from the Astronomical Almanac (Section J * in the 1988 edition), or via the routine sla_OBS. If P, * the pressure in millibars, is available, an adequate * estimate of HM can be obtained from the expression * * HM ~ -29.3D0*TSL*LOG(P/1013.25D0). * * where TSL is the approximate sea-level air temperature in * deg K (see Astrophysical Quantities, C.W.Allen, 3rd edition, * section 52). Similarly, if the pressure P is not known, * it can be estimated from the height of the observing * station, HM as follows: * * P ~ 1013.25D0*EXP(-HM/(29.3D0*TSL)). * * Note, however, that the refraction is proportional to the * pressure and that an accurate P value is important for * precise work. * * 7) Repeated, computationally-expensive, calls to sla_AOPPA for * times that are very close together can be avoided by calling * sla_AOPPA just once and then using sla_AOPPAT for the subsequent * times. Fresh calls to sla_AOPPA will be needed only when changes * in the precession have grown to unacceptable levels or when * anything affecting the refraction has changed. * * Called: sla_GEOC, sla_REFCO, sla_EQEQX, sla_AOPPAT * * P.T.Wallace Starlink 6 September 1999 * * Copyright (C) 1999 P.T.Wallace and CCLRC *- IMPLICIT NONE DOUBLE PRECISION DATE,DUT,ELONGM,PHIM,HM,XP,YP,TDK,PMB, : RH,WL,TLR,AOPRMS(14) DOUBLE PRECISION sla_EQEQX * 2Pi DOUBLE PRECISION D2PI PARAMETER (D2PI=6.283185307179586476925287D0) * Seconds of time to radians DOUBLE PRECISION S2R PARAMETER (S2R=7.272205216643039903848712D-5) * Speed of light (AU per day) DOUBLE PRECISION C PARAMETER (C=173.14463331D0) * Ratio between solar and sidereal time DOUBLE PRECISION SOLSID PARAMETER (SOLSID=1.00273790935D0) DOUBLE PRECISION CPHIM,XT,YT,ZT,XC,YC,ZC,ELONG,PHI,UAU,VAU * Observer's location corrected for polar motion CPHIM = COS(PHIM) XT = COS(ELONGM)*CPHIM YT = SIN(ELONGM)*CPHIM ZT = SIN(PHIM) XC = XT-XP*ZT YC = YT+YP*ZT ZC = XP*XT-YP*YT+ZT IF (XC.EQ.0D0.AND.YC.EQ.0D0) THEN ELONG = 0D0 ELSE ELONG = ATAN2(YC,XC) END IF PHI = ATAN2(ZC,SQRT(XC*XC+YC*YC)) AOPRMS(1) = PHI AOPRMS(2) = SIN(PHI) AOPRMS(3) = COS(PHI) * Magnitude of the diurnal aberration vector CALL sla_GEOC(PHI,HM,UAU,VAU) AOPRMS(4) = D2PI*UAU*SOLSID/C * Copy the refraction parameters and compute the A & B constants AOPRMS(5) = HM AOPRMS(6) = TDK AOPRMS(7) = PMB AOPRMS(8) = RH AOPRMS(9) = WL AOPRMS(10) = TLR CALL sla_REFCO(HM,TDK,PMB,RH,WL,PHI,TLR,1D-10, : AOPRMS(11),AOPRMS(12)) * Longitude + equation of the equinoxes + sidereal equivalent of DUT * (ignoring change in equation of the equinoxes between UTC and TDB) AOPRMS(13) = ELONG+sla_EQEQX(DATE)+DUT*SOLSID*S2R * Sidereal time CALL sla_AOPPAT(DATE,AOPRMS) END