GNSS Interferometric Reflectometry (IR) is a well-studied technique for determination of water surface levels, snow levels and soil moisture. It can be further split into two sub-techniques. First one uses the signal-to-noise ratio (SNR) of a surface-reflected signal received by a GNSS receiver to derive the vertical distance between the GNSS receiver phase centre and the underlying reflecting surface and this will be used for the purposes of this thesis. Second technique uses zenith and nadir antenna and compares phase difference between direct signal received by former and reflected signal received by the latter. Signal transmitted by a GNSS satellite passes through several atmospheric layers. One of these layers is the ionosphere, which can significantly impact signal propagation. Ionosphere consists of charged particles which have a gradient that is evolving through time and can be influenced by external force i.e. solar (Schwabe) cycles. Currently, in 2024 and 2025, we are experiencing peak (solar maximum) of 11-year solar cycle. Metric used for evaluation of this gradient is total electron content (TEC) for which world-wide model is available for fetching through an API. The effect of TEC on the GNSS signal is studied for positioning purposes, however, at the time of writing this thesis no scientific work, to the author's knowledge, has explored extreme ionospheric events on GNSS IR. The aim of the study is to explore the effect of temporal variability of TEC and its effects on the accuracy and precision of Sea Surface Height (SSH) determination. Comparison is made between SSH derived by a nearby tide gauge observations, heights derived during periods of extreme TEC levels (at the time of solar maximum) and normal TEC levels (during solar minimum). Results of the analysis show a rather weak correlation between TEC and the quality of the GNSS-IR measurement, however they uncover modality in the both metrics which warrant further research into the issue of ionospheric effects on GNSS-IR.