Global Navigation Satellite System (GNSS) has been widely used to provide positioning, navigation and timing services in civil and military domains since it became fully operational in 1993. In addition to these fundamental services and applications, GNSS could be also used for remote sensing of atmospheric parameters; for instance, by launching LEO satellites and observing refraction signals from GNSS satellites with negative elevation angles. This GNSS-based remote sensing technique termed GNSS radio occultation (GNSS-RO) could be used to estimate the tropospheric water vapor, temperature, pressure, and ionospheric total electron content (TEC) with a high resolution. Meanwhile, GNSS signal reflection over a specific surface, a source of positioning error, which cannot be easily neutralized, could be used to retrieve the surface geophysical parameters. This remote sensing technique is termed GNSS Reflectometry (GNSS-R). The ocean’s surface characteristics (ie. ocean surface height, roughness, wind speed and wind direction) could be estimated by GNSS-R. It could be also applied for land applications such as the retrieval of ground vegetation condition and soil moisture. This study focuses on sea ice detection using GNSS-R.