Thermospheric neutral density variations from Low Earth Orbit accelerometers and precise orbits

The thermosphere is located above the mesosphere and below the exosphere, and its highly ionized state increases the complexity of its geophysical processes due to the magnetosphere-ionosphere-thermosphere (MIT) coupling. Therefore, accurate measurement of neutral density variations is essential for atmospheric research, Precise Orbit Determination (POD), and radio wave propagation. However, it is difficult to quantify and interpret the upper atmospheric variations due to large uncertainty in the models and lack of measurements from the limited traditional technologies of observation. Nowadays, thermospheric neutral densities estimated from accelerometers and GNSS onboard LEO satellites provide a unique opportunity to study the upper atmosphere with new observational data. In this thesis, thermospheric neutral density variations are inferred and investigated from accelerometers and precise orbits of GRACE (Gravity Recovery and Climate Experiment) for the period 2003-2016.