# Tropospheric Model: Saastamoinen

**URL:** https://learn.safran-navigation-timing.com/t/tropospheric-model-saastamoinen/119
**Category:** Skydel Discussion
**Created:** [December 12, 2020, 8:13pm UTC](https://learn.safran-navigation-timing.com/t/tropospheric-model-saastamoinen/119 "2020-12-12T20:13:07Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Astrosogi](https://yyz2.discourse-cdn.com/flex030/user_avatar/learn.safran-navigation-timing.com/astrosogi/32/39_2.png) [@Astrosogi](https://learn.safran-navigation-timing.com/u/Astrosogi)
#### Post date: [December 12, 2020, 8:13pm UTC](https://learn.safran-navigation-timing.com/t/tropospheric-model-saastamoinen/119/1 "2020-12-12T20:13:07Z")

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Hi Everyone! I hope you are having a great weekend! 🙂

I was looking at the tropospheric models that are available in _(Setting → Global → Atmosphere → nominal )_ and I have a question about the Saastamoin model.

I read up a little on atmospheric models and to my understanding STANAG mostly uses the station coordinates and respective elevation angle to calculate the tropospheric delay. (so I am assuming the coordinate of the gnss receiver is used for this model in Skydel)

However, I read that the Saastamoinen model requires local meteorological parameters like temperature, atmospheric pressure and humidity. Do you know where skydel gets these information from? Since I don’t see a place where the user can input these parameters for a certain coordinate and time.

P.S: Atmospheric models are not my specialty and I just read up on them a little bit. So please feel free to correct me if I made a mistake in my understanding of these models 🙂

Cheers,  
Sogand

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### Author: ![Boumediene](https://avatars.discourse-cdn.com/v4/letter/b/4bbf92/32.png) [@Boumediene](https://learn.safran-navigation-timing.com/u/Boumediene)
#### Post date: [December 14, 2020, 7:10pm UTC](https://learn.safran-navigation-timing.com/t/tropospheric-model-saastamoinen/119/2 "2020-12-14T19:10:29Z")

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Hi !,

Indeed, there are models which require meteorological parameters in order to calculate tropospheric delay. however, the way to get these values ​depends on the model.  
Example: model tropo-Do-229 uses elevation, altitude and latitude values ​​and a predefined “Meteorological parameters for tropospheric delay” table to compute the meteorological params.

Talking about the Saastamoinen model, we have meteorological constants. We do not give the possibility of editing them.  
Below, you can see the meteorological params values for the Saastamoinen model.

Gravitational acceleration, m/s^2; = 9.784  
Lapse rate, K/m - Kelvin per meter; = 0.00558  
Gas constant for air (287 m2/s2/K); = 287  
Standard sea level temperature (288 K); = 283.15  
Pressure at sea level, kPa - Kilopascal. For millibar = 101.3  
Relative humidity at antenna location = 50_exp(-0.0006396_h)