Update README.md

README.md

 # REFRACTION
 
 Astronomical Refraction Routines For Solar Astrometry
+
+## Overview
+Please refer to the following research note:
+
+T Corbard, R Ikhlef, F Morand, M Meftah, C Renaud, **On the importance of 
+astronomical refraction for modern solar astrometric measurements**, 
+[Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 3, 
+March 2019, Pages 3865–3877, ](https://doi.org/10.1093/mnras/sty3391)
+
+[arXiv:1304.0147 [astro-ph.SR]](https://arxiv.org/abs/1304.0147)
+
+### Example 1: Get the observed zenith distance from the true one and back
+```
+;Get station latitude and elevation from its name
+calern=station('Calern')
+;
+;Get standard (Ciddor, 1996) atmospheric condition
+std_atm=meteo()
+;
+;Select a refraction model
+std_refrac=refrac_model('NAO63Ciddor') ;exact integral calculation from Standard atmosphere
+;
+;Choose a true zenith distance
+zt=70.D0*!DPI/180.D0
+;
+;Choose a wavelength
+lbda=535.7d-9
+;
+;Get the observed zenith distance
+z=zt-refrac_all_p(zt,lbda,calern,std_atm,std_refrac,/true)
+print,z*180.D0/!DPI
+;
+;Get back the true zenith distance
+zt=z+refrac_all_p(z,lbda,calern,std_atm,std_refrac)
+print,zt*180.D0/!DPI
+
+69.956757
+70.000000
+```
+
+### Example 2: Compare curvature radius estimates using either geodetic latitude / elvation above the reference ellipsoid or astronomic latitude and elevation above sea level
+```
+;provide geodetic latitude and elvation above the WGS84 reference ellipsoid
+calern=station('Calern') 
+;
+;astronomic latitude and elevation above sea level
+calern2=station('Calern2',h=1271.d0,lat=[43.D0,44.D0,53.D0]) 
+;
+;Print the difference (in meters) for various curvature radius estimates (see curvature_radius.pro)
+print,round(curvature_radius(calern2.lat,calern2.h)-curvature_radius(calern.lat, calern.h))
+
+-56 -53 -55 -51
+
+```
+### Example 3: Compare reduced height either assuming ideal gaz law or from full air density calculation
+```
+;Get average weather conditions at Calern observatory
+atm=meteo(model='Calern_mean') 
+;
+;Get the air density from Ciddor (1996) equations
+print,'Air Density: ',atm.density,' kg/m^2',format='(a,d5.3,a)'
+g=9.802155492d0 ; m/s^2 Measured gravity acceleration at Calern
+print,'Reduced height (Full density calculation): ',round(reduced_height([atm.P,atm.density,g])),' m'
+print,'Reduced height (Assuming ideal gaz law ): ',round(reduced_height([atm.T])),' m'
+
+Air Density: 1.054 kg/m^2
+Reduced height (full density calculation): 8467 m
+Reduced height (assuming ideal gaz law ): 8430 m
+```
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