Added Mathars exponential refraction model

README.md

@@ -2,7 +2,7 @@
 
 **Note:**
 It would be appreciated if a reference to the following work, for which this package was originally build, is included whenever this code is used for a publication: 
-*Quantification of the expected residual dispersion of the MICADO Near-IR imaging instrument*, van den Born & Jellema, 2020, MNRAS. Accepted 2020 June 23. Received 2020 June 23; in original form 2020 January 24.
+*Quantification of the expected residual dispersion of the MICADO Near-IR imaging instrument*, van den Born & Jellema, 2020, MNRAS, DOI: [10.1093/mnras/staa1870](https://doi.org/10.1093/mnras/staa1870).
 
 
 **Author info**: *Joost van den Born*, *born@astron.nl*
@@ -41,7 +41,7 @@ disp = dispersion(lat, h)
 disp.setReducedHeight(P, rho)
 
 # Calculation of the atmopheric dipsersion
-atm_dispersion = ref.cassini(n1, z0) * 3.6e6
+atm_dispersion = disp.cassini(n1, z0) * 3.6e6
 print ('The dispersion is %.03f milli arc seconds' %(atm_dispersion))
 ```
 
@@ -95,6 +95,7 @@ The available models in this package:
 - `oriani()` - Oriani's theorem ( Atan(z) + Btan^3(z) )
 - `tan5()` - Oriani's theorem expanded ( Atan(z) + Btan^3(z) + Ctan^5(z)  )
 - `corbard()` - Error function refraction model
+- `matharExponential()` - Barometric exponential model by R. Mathar.
 
 
 Input parameters for the spherical atmosphere models (all but the first):