TDRS Observations 
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The TDRS Observation represents an observation of a spacecraft from a site on the ground of a CelestialObject, relayed through a TDRS transponder. The measurement types available for these observations are:
Note: TDRS Twoway Range observations in FreeFlyer are computing by summing the four legs of the measurement and dividing by 2, so that the value represents the average range from ground site to TDRS transponder to spacecraft. When loading Twoway Range data into FreeFlyer for processing, if the input data includes both the forward and return paths, the values should be divided by 2 before processing.
When working with TDRS Observations, you have the option to include the following corrections:
The tropospheric correction calculation relies on the GroundStation.MonthlyRefractivity property, so it is possible to configure different values for the refractivity when simulating the measurements vs. when processing. Similarly, the ionospheric correction calculation relies on the FF_SolarSystem.IonosphereOptions.ScaleFactor property, which can be configured to scale the ionospheric correction values differently for simulating vs. processing. The ground antenna and spacecraft transponder frequencies are also used in computing the ionospheric and tropospheric corrections.
The following tracking data formats supported by FreeFlyer can contain TDRS Observations:
For more information on creating simulated TDRS Observations, see the Simulating Tracking Data page.
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