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/node24.html | 213 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 213 insertions(+) create mode 100644 src/slalib/sun67.htx/node24.html (limited to 'src/slalib/sun67.htx/node24.html') diff --git a/src/slalib/sun67.htx/node24.html b/src/slalib/sun67.htx/node24.html new file mode 100644 index 0000000..aecbb98 --- /dev/null +++ b/src/slalib/sun67.htx/node24.html @@ -0,0 +1,213 @@ + + + + +SLA_ATMDSP - Atmospheric Dispersion + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: SLA_AV2M - Rotation Matrix from Axial Vector +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AOPQK - Quick Appt-to-Observed +

+

+

SLA_ATMDSP - Atmospheric Dispersion +   +

+
+
ACTION: +
Apply atmospheric-dispersion adjustments to refraction coefficients. +
CALL: +
CALL sla_ATMDSP (TDK, PMB, RH, WL1, A1, B1, WL2, A2, B2) +

+

+
GIVEN: +
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
TDKDambient temperature at the observer (degrees K)
PMBDpressure at the observer (mB)
RHDrelative humidity at the observer (range 0-1)
WL1Dbase wavelength ($\mu{\rm m}$)
A1Drefraction coefficient A for wavelength WL1 (radians)
B1Drefraction coefficient B for wavelength WL1 (radians)
WL2Dwavelength for which adjusted A,B required ($\mu{\rm m}$)
+

+
RETURNED: +
+
+ + + + + + + + + +
A2Drefraction coefficient A for wavelength WL2 (radians)
B2Drefraction coefficient B for wavelength WL2 (radians)
+

+
NOTES: +
+
1. +
To use this routine, first call sla_REFCO specifying WL1 as the +wavelength. This yields refraction coefficients A1, B1, correct +for that wavelength. Subsequently, calls to sla_ATMDSP specifying + different wavelengths will produce new, slightly adjusted + refraction coefficients A2, B2, which apply to the specified wavelength. +
2. +
Most of the atmospheric dispersion happens between $0.7\,\mu{\rm m}$ 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 $0.4\,\mu{\rm m}$.
3. +
The accuracy, for this set of conditions:
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
height above sea level 2000m
latitude $29^\circ$
pressure 793mB
temperature $290^\circ$K
humidity 0.5 (50%)
lapse rate $0.0065^\circ m^{-1}$
reference wavelength $0.4\,\mu{\rm m}$
star elevation $15^\circ$
+
+
+is about 2.5mas RMS between 0.3 and $1.0\,\mu{\rm m}$, and stays + within 4mas for the whole range longward of $0.3\,\mu{\rm m}$ (compared with a total dispersion from 0.3 to $20\,\mu{\rm m}$ of about $11\hspace{-0.05em}^{'\hspace{-0.1em}'}$). These errors are typical for ordinary + conditions; in extreme conditions values a few times this size + may occur. +
4. +
If either wavelength exceeds $100\,\mu{\rm m}$, 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 sla_REFRO routine, and then scaling of the two refraction + coefficients according to classical refraction theory. This + amounts to scaling the A coefficient in proportion to $(\mu-1)$ and + the B coefficient almost in the same ratio (see R.M.Green, + Spherical Astronomy, Cambridge University Press, 1985). +
+
+ +next + +up + +previous +
+ Next: SLA_AV2M - Rotation Matrix from Axial Vector +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AOPQK - Quick Appt-to-Observed +

+

+

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