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/node165.html | 176 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 176 insertions(+) create mode 100644 src/slalib/sun67.htx/node165.html (limited to 'src/slalib/sun67.htx/node165.html') diff --git a/src/slalib/sun67.htx/node165.html b/src/slalib/sun67.htx/node165.html new file mode 100644 index 0000000..1fadca0 --- /dev/null +++ b/src/slalib/sun67.htx/node165.html @@ -0,0 +1,176 @@ + + + + +SLA_REFCO - Refraction Constants + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: SLA_REFCOQ - Refraction Constants (fast) +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_RDPLAN - Apparent of Planet +

+

+

SLA_REFCO - Refraction Constants +   +

+
+
ACTION: +
Determine the constants a and b in the +atmospheric refraction model + $\Delta \zeta = a \tan \zeta + b \tan^{3} \zeta$, where $\zeta$ is the observed zenith distance + (i.e. affected by refraction) and $\Delta \zeta$ is + what to add to $\zeta$ to give the topocentric + (i.e. in vacuo) zenith distance. +

CALL: +
CALL sla_REFCO (HM, TDK, PMB, RH, WL, PHI, TLR, EPS, REFA, REFB) +

+

+
GIVEN: +
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
HMDheight of the observer above sea level (metre)
TDKDambient temperature at the observer (degrees K)
PMBDpressure at the observer (mB)
RHDrelative humidity at the observer (range 0-1)
WLDeffective wavelength of the source ($\mu{\rm m}$)
PHIDlatitude of the observer (radian, astronomical)
TLRDtemperature lapse rate in the troposphere +(degrees K per metre)
EPSDprecision required to terminate iteration (radian)
+

+
RETURNED: +
+
+ + + + + + + + + +
REFAD$\tan \zeta$ coefficient (radians)
REFBD$\tan^{3} \zeta$ coefficient (radians)
+

+
NOTES: +
+
1. +
Suggested values for the TLR and EPS arguments are 0.0065D0 and +1D-8 respectively. +
2. +
The radio refraction is chosen by specifying WL >100 $\mu{\rm m}$.
3. +
The routine is a slower but more accurate alternative to the + sla_REFCOQ routine. The constants it produces give perfect + agreement with sla_REFRO at zenith distances + $\tan^{-1} 1$ ($45^\circ$) and $\tan^{-1} 4$ ($\sim 76^\circ$). + At other zenith distances, the model achieves: +

$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.5$ accuracy for $\zeta<80^{\circ}$,

$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.01$ accuracy for $\zeta<60^{\circ}$, and +

$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.001$ accuracy for $\zeta<45^{\circ}$.

+
+ +next + +up + +previous +
+ Next: SLA_REFCOQ - Refraction Constants (fast) +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_RDPLAN - Apparent of Planet +

+

+

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