GNSS (Global Navigation Satellite System) signals propagating through the Earth's atmosphere experience complex interactions such as scattering, refraction, and diffraction with the propagation medium. These propagation effects will highly affect the accuracy of the precise positioning using the GNSS receiver. To study these effects and avoid them, it is essential to understand well the Earths atmosphere structure. The NTU Satellite Research Centre (SaRC) utilized a near equatorial Low Earth Orbit (LEO) satellite, VELOX-CI, to carry out radio occultation(RO) experiment. The RO data was then used to derive the ionospheric TEC profile and refractivity profile for the neutral atmosphere. It was investigated whether accurate estimation of TEC is feasible from a platform such as VELOX-CI. Of particular interest was the challenges that pervade data from LEO off-the-shelf receiver occultation platforms such as VELOX-GNSS (Global Navigation Satellite System) signals propagating through the Earth's atmosphere experience complex interactions such as scattering, refraction, and diffraction with the propagation medium. The conclusion is that accurate ionosphere profiles will generally be difficult to obtain from such data. Several reasons were identified: 1) severe cycle-slips and loss-of-lock occurring for satellites outside the main lobe of the antenna, 2) multipath on code observations making correction of carrier ambiguities difficult, especially under frequent loss-of-lock conditions, 3) poor data continuity at top of TEC profiles due to transition of satellite geometry from main lobe of side-facing antenna to zenith-facing antenna. In addition, Dr.Jade Morton (U.S.) and her team conducted mountain-based RO (MRO) experiment.