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| author | Joseph Hunkeler <jhunkeler@gmail.com> | 2015-03-04 21:21:30 -0500 |
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| committer | Joseph Hunkeler <jhunkeler@gmail.com> | 2015-03-04 21:21:30 -0500 |
| commit | d54fe7c1f704a63824c5bfa0ece65245572e9b27 (patch) | |
| tree | afc52015ffc2c74e0266653eecef1c8ef8ba5d91 /src/slalib/sun67.htx/node167.html | |
| download | calfuse-d54fe7c1f704a63824c5bfa0ece65245572e9b27.tar.gz | |
Initial commit
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| -rw-r--r-- | src/slalib/sun67.htx/node167.html | 232 |
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diff --git a/src/slalib/sun67.htx/node167.html b/src/slalib/sun67.htx/node167.html new file mode 100644 index 0000000..f422ec8 --- /dev/null +++ b/src/slalib/sun67.htx/node167.html @@ -0,0 +1,232 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<!--Converted with LaTeX2HTML 97.1 (release) (July 13th, 1997) + by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds +* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan +* with significant contributions from: + Jens Lippman, Marek Rouchal, Martin Wilck and others --> +<HTML> +<HEAD> +<TITLE>SLA_REFRO - Refraction</TITLE> +<META NAME="description" CONTENT="SLA_REFRO - Refraction"> +<META NAME="keywords" CONTENT="sun67"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso_8859_1"> +<LINK REL="STYLESHEET" HREF="sun67.css"> +<LINK REL="next" HREF="node168.html"> +<LINK REL="previous" HREF="node166.html"> +<LINK REL="up" HREF="node13.html"> +<LINK REL="next" HREF="node168.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html2096" HREF="node168.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2094" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2088" HREF="node166.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html2097" HREF="node168.html">SLA_REFV - Apply Refraction to Vector</A> +<BR> +<B>Up:</B> <A NAME="tex2html2095" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2089" HREF="node166.html">SLA_REFCOQ - Refraction Constants (fast)</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H2><A NAME="SECTION0004154000000000000000">SLA_REFRO - Refraction</A> +<A NAME="xref_SLA_REFRO"> </A><A NAME="SLA_REFRO"> </A> +</H2> + <DL> +<DT><STRONG>ACTION:</STRONG> +<DD>Atmospheric refraction, for radio or optical/IR wavelengths. +<DT><STRONG>CALL:</STRONG> +<DD><TT>CALL sla_REFRO (ZOBS, HM, TDK, PMB, RH, WL, PHI, TLR, EPS, REF)</TT> +<P> </DL> +<P> <DL> +<DT><STRONG>GIVEN:</STRONG> +<DD> +<BR> +<TABLE CELLPADDING=3> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>ZOBS</EM></TD> +<TH ALIGN="LEFT"><B>D</B></TH> +<TD ALIGN="LEFT" NOWRAP>observed zenith distance of the source (radians)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>HM</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>height of the observer above sea level (metre)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>TDK</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>ambient temperature at the observer (degrees K)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>PMB</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>pressure at the observer (mB)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RH</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>relative humidity at the observer (range 0-1)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>WL</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>effective wavelength of the source (<IMG WIDTH="26" HEIGHT="25" ALIGN="MIDDLE" BORDER="0" + SRC="img21.gif" + ALT="$\mu{\rm m}$">)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>PHI</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>latitude of the observer (radian, astronomical)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>TLR</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>temperature lapse rate in the troposphere +(degrees K per metre)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>EPS</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>precision required to terminate iteration (radian)</TD> +</TR> +</TABLE></DL> +<P> <DL> +<DT><STRONG>RETURNED:</STRONG> +<DD> +<BR> +<TABLE CELLPADDING=3> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>REF</EM></TD> +<TH ALIGN="LEFT"><B>D</B></TH> +<TH ALIGN="LEFT" NOWRAP>refraction: <I>in vacuo</I> ZD minus observed ZD (radians)</TH> +</TR> +</TABLE></DL> +<P> <DL> +<DT><STRONG>NOTES:</STRONG> +<DD><DL COMPACT> +<DT>1. +<DD>A suggested value for the TLR argument is 0.0065D0. The +refraction is significantly affected by TLR, and if studies +of the local atmosphere have been carried out a better TLR + value may be available. + <DT>2. +<DD>A suggested value for the EPS argument is 1D-8. The result is + usually at least two orders of magnitude more computationally + precise than the supplied EPS value. + <DT>3. +<DD>The routine computes the refraction for zenith distances up + to and a little beyond <IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img22.gif" + ALT="$90^{\circ}$"> using the method of Hohenkerk + & Sinclair (NAO Technical Notes 59 and 63, subsequently adopted + in the <I>Explanatory Supplement to the Astronomical Almanac,</I> + 1992 - see section 3.281). + <DT>4. +<DD>The code is based on the AREF optical/IR refraction subroutine + of C.Hohenkerk (HMNAO, September 1984), with extensions to + support the radio case. The modifications to the original HMNAO + optical/IR refraction code which affect the results are: + <UL> +<LI> Murray's values for the gas constants have been used + (<I>Vectorial Astrometry,</I> Adam Hilger, 1983). +<LI> A better model for <I>P</I><SUB><I>s</I></SUB>(<I>T</I>) has been adopted (taken from + Gill, <I>Atmosphere-Ocean Dynamics,</I> Academic Press, 1982). +<LI> More accurate expressions for <I>Pw</I><SUB><I>o</I></SUB> have been adopted + (again from Gill 1982). +<LI> Provision for radio wavelengths has been added using + expressions devised by A.T.Sinclair, RGO (private + communication 1989), based on the Essen & Froome + refractivity formula adopted in Resolution 1 of the + 12th International Geodesy Association General Assembly + (Bulletin Géodésique <B>70</B> p390, 1963). + </UL> + None of the changes significantly affects the optical/IR results + with respect to the algorithm given in the 1992 <I>Explanatory + Supplement.</I> For example, at <IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img174.gif" + ALT="$70^\circ$"> zenith distance the present + routine agrees with the ES algorithm to better than + <IMG WIDTH="31" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" + SRC="img175.gif" + ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.05$"><P> +for any reasonable combination of parameters. However, the + improved water-vapour expressions do make a significant difference + in the radio band, at <IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img174.gif" + ALT="$70^\circ$"> zenith distance reaching almost + <IMG WIDTH="17" HEIGHT="17" ALIGN="BOTTOM" BORDER="0" + SRC="img130.gif" + ALT="$4\hspace{-0.05em}^{'\hspace{-0.1em}'}$"> for a hot, humid, low-altitude site during a period of + low pressure. + <DT>5. +<DD>The radio refraction is chosen by specifying WL >100 <IMG WIDTH="26" HEIGHT="25" ALIGN="MIDDLE" BORDER="0" + SRC="img21.gif" + ALT="$\mu{\rm m}$">. Because the algorithm takes no account of the ionosphere, the + accuracy deteriorates at low frequencies, below about 30MHz. + <DT>6. +<DD>Before use, the value of ZOBS is expressed in the range <IMG WIDTH="25" HEIGHT="25" ALIGN="MIDDLE" BORDER="0" + SRC="img47.gif" + ALT="$\pm \pi$">. If this ranged ZOBS is negative, the result REF is computed from its + absolute value before being made negative to match. In addition, if + it has an absolute value greater than <IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img176.gif" + ALT="$93^\circ$">, a fixed REF value + equal to the result for ZOBS <IMG WIDTH="43" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img177.gif" + ALT="$=93^\circ$"> is returned, appropriately + signed. + <DT>7. +<DD>As in the original Hohenkerk and Sinclair algorithm, fixed values + of the water vapour polytrope exponent, the height of the + tropopause, and the height at which refraction is negligible are + used. + <DT>8. +<DD>The radio refraction has been tested against work done by + Iain Coulson, JACH, (private communication 1995) for the + James Clerk Maxwell Telescope, Mauna Kea. For typical conditions, + agreement at the + <IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" + SRC="img25.gif" + ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.1$"> level is achieved for moderate ZD, + worsening to perhaps + <IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" + SRC="img83.gif" + ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.5$"> - + <IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" + SRC="img178.gif" + ALT="$1\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.0$"> at ZD <IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img179.gif" + ALT="$80^\circ$">. At hot and humid sea-level sites the accuracy will not be as good. + <DT>9. +<DD>It should be noted that the relative humidity RH is formally + defined in terms of ``mixing ratio'' rather than pressures or + densities as is often stated. It is the mass of water per unit + mass of dry air divided by that for saturated air at the same + temperature and pressure (see Gill 1982). The familiar + <IMG WIDTH="75" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img180.gif" + ALT="$\nu=p_w/p_s$"> or <IMG WIDTH="75" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img181.gif" + ALT="$\nu=\rho_w/\rho_s$"> expressions can differ from + the formal definition by several percent, significant in the + radio case. + </DL></DL> +<BR> <HR> +<A NAME="tex2html2096" HREF="node168.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2094" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2088" HREF="node166.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html2097" HREF="node168.html">SLA_REFV - Apply Refraction to Vector</A> +<BR> +<B>Up:</B> <A NAME="tex2html2095" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2089" HREF="node166.html">SLA_REFCOQ - Refraction Constants (fast)</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<ADDRESS> +<I>SLALIB --- Positional Astronomy Library<BR>Starlink User Note 67<BR>P. T. Wallace<BR>12 October 1999<BR>E-mail:ptw@star.rl.ac.uk</I> +</ADDRESS> +</BODY> +</HTML> |