SLA_AOPPA - Appt-to-Obs Parameters

From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node21.html | 264 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 264 insertions(+) create mode 100644 src/slalib/sun67.htx/node21.html (limited to 'src/slalib/sun67.htx/node21.html') diff --git a/src/slalib/sun67.htx/node21.html b/src/slalib/sun67.htx/node21.html new file mode 100644 index 0000000..13ef3e2 --- /dev/null +++ b/src/slalib/sun67.htx/node21.html @@ -0,0 +1,264 @@ + + + + +SLA_AOPPA - Appt-to-Obs Parameters + + + + + + + + + + + + +

+ +

+
+ Next: SLA_AOPPAT - Update Appt-to-Obs Parameters +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AOP - Apparent to Observed +

SLA_AOPPA - Appt-to-Obs Parameters + +

ACTION: +: Pre-compute the set of apparent to observed place parameters +required by the ``quick'' routines sla_AOPQK and sla_OAPQK. +
CALL: +: CALL sla_AOPPA ( + DATE, DUT, ELONGM, PHIM, HM, XP, YP, + TDK, PMB, RH, WL, TLR, AOPRMS) +

GIVEN: +

+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

DATE	D	UTC date/time (Modified Julian Date, JD-2400000.5)
DUT	D	$\Delta$ UT: UT1-UTC (UTC seconds)
ELONGM	D	observer's mean longitude (radians, east +ve)
PHIM	D	observer's mean geodetic latitude (radians)
HM	D	observer's height above sea level (metres)
XP,YP	D	polar motion $[\,x,y\,]$ coordinates (radians)
TDK	D	local ambient temperature (degrees K; 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 ( $\mu{\rm m}$ , e.g. 0.55D0)
TLR	D	tropospheric lapse rate (degrees K per 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 $\Delta$ UT'' (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, wrong, 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 $\Delta$ UT 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 $\pm$ $0^{\rm s}\hspace{-0.3em}.9$ . The ``sidereal $\Delta$ UT'' which forms + part of AOPRMS(13) is the same quantity, but converted from solar + to sidereal seconds and expressed in radians. +
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 (as in the Astronomical + Almanac before 1984) 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 + $0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.3$ . 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 mB, is available, an adequate + estimate of HM can be obtained from the following expression: +
HM=-29.3D0*TSL*LOG(P/1013.25D0) +
+ where TSL is the approximate sea-level air temperature in degrees K + (see Astrophysical Quantities, C.W.Allen, 3rd edition, + §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. +

+ +

+
+ Next: SLA_AOPPAT - Update Appt-to-Obs Parameters +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AOP - Apparent to Observed +

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +

+ + -- cgit