**Note:**
A manuscript of this atmospheric code is in preparation and will be submitted to the Monthly Notices of the Royal Astronomical Society (MNRAS) journal before the end of the year (2019). 
If you use this code for your project, please acknowledge this by making a reference to this paper in due course. You can contact me, the author, for the submission and review status.


Author info: *Joost van den Born*, *born@astron.nl*



*Below you can find a set of models describing the atmospheric refraction and dispersion.*

**Contents:**
- atmosphericModel          	: Python model that can be used to calculate the atmospheric refraction and dispersion, the main content of this repository.
- refractionModel.py            : Python script that compares the output of the different refraction models. 
                                  Can be used as an example on how to use atmosphericModel.py
- atmospheric refraction example: jupyter notebook example


**On the contents of the atmosphericModel package**
The package contains the following files:
- 1976USSA.txt 					: Data file of the 1976 US Standard Atmosphere.
- ciddorModel.py 				: Contains the `Observatory()` class to calculate the refractive index of atmospheric air, using the Ciddor (1996) model.
- dispersionModels.py 			: Contains various atmospheric models that can be used to calculate the atmospheric dispersion
- examples.py 					: Contains several quick functions, e.g. to quickly calculate the refractive index.
- refractionModels.py 			: Contains various atmospheric models that can be used to calculate the atmospheric refraction
- refractivityModels.py 		: Contains various functions from literature to calculate the refractive index. Some examples of works included are Ciddor (1996), Barrell & Sears (1939), SLALIB, Owens (1967) and Edlen (1966).


**On the dispersion model:**

Dispersion model from Ciddor, 1996, calculates the index of refraction of air using the following parameters:
- Temperature
- Pressure
- Relative humidity
- CO2 density




**On the atmospheric refraction / atmospheric dispersion models:**

Available models:
- Full integration using the refractive integral (requires detailed information about the atmosphere, e.g. 1976USSA.txt)
- Plane-parallel atmosphere refraction model
- Cassini's homogeneous atmosphere refraction model
- Oriani's theorem ( Atan(z) + Btan^3(z) )
- Oriani's theorem expanded ( Atan(z) + Btan^3(z) + Ctan^5(z)  )
- Error function refraction model




Input parameters for the spherical atmosphere models (all but the first):
- Temperature               [K]
- Pressure                  [Pa]
- Relative humidity
- CO2 density               [ppm]
- Latitude                  [deg]
- Height above sea level    [m]
- Wavelength(s)             [um]
- Zenith angle              [deg]


**Analytical error propagation**

Full analytical error propagation is available for the Ciddor dispersion model (Observatory.dn_tph( ) ), for the Cassini refraction model (refraction.cassiniError( ) ) and for the Cassini dispersion model (dispersion.cassiniError( ) ).
The results agree well with a Monte Carlo simulation, suggesting that if additional errors have not been considered, they are of neglible importance.

Uncertainties that are considered:

Ciddor dispersion model:

| Param. | Description | Unit |
| ------ | ------ | ------ |
| dl | Wavelength | um |
| dT | Temperature | K |
| dP | Pressure | Pa |
| dRH | Relative Humidity |  |
| dCO2 | CO2 density | ppm |
 

Cassini refraction model:

| Param. | Description | Unit |
| ------ | ------ | ------ |
| dn | Refractive index |  |
| dz | Zenith angle | deg |

Cassini dispersion model:


| Param. | Description | Unit |
| ------ | ------ | ------ |
| dl1, dl2 | Wavelength(s) | um |
| dT | Temperature | K |
| dP | Pressure | Pa |
| dRH | Relative Humidity |  |
| dCO2 | CO2 density | ppm |
| dz | Zenith angle | deg |