G-CLASS is a space mission currently under feasibility study (Phase A). It was selected by the ESA’s Advisory Committee for Earth Observation (ACEO) to compete as the tenth Earth Explorer mission together with two different mission concepts. G-CLASS involves many universities and remote sensing research centers from all over Europe including Africa.
The main limitation of current low Earth orbit synthetic aperture radars (LEOSAR), such as Sentinel-1 or TerraSAR-X, is related to their revisit time of several days or weeks. They cannot provide continuous monitoring over the same area.
G-CLASS (GEOSAR) Mission Concept
The introduction of the geosynchronous synthetic aperture radar (GEOSAR) concept aims to provide permanent illumination of a wide zone of the planet. Potential applications that require continuous monitoring are, for instance, inundation monitoring and forecasting, glacier motion and snow cover and mass monitoring, earthquakes, volcanoes and landslides forecasting, and subsidence monitoring due to anthropogenic or natural motion.
G-CLASS is designed to help scientists unravel the details of the daily water cycle. Some of the main challenges come from processes which occur over periods of a few hours at a local, kilometer scale. For instance, prediction of local storms require the detailed observation of the local weather during the early stages. Monitoring of variations in the soil moisture, snow melting in mountains, river flows and water supplies would also benefit from the GEOSAR concept.
Microwave sensors are well-suited for measuring water in solid, liquid or gaseous phases. G-CLASS uses a single satellite with a synthetic aperture radar (GEOSAR). The inherent relative motion of the spacecraft with respect to Earth due to the GEO orbit allows to obtain radar echo data acquisitions providing images after Synthetic Aperture Radar processing. Different compromises between time (from minutes to hours) and spatial resolutions (from 10 m to 1 km) are possible when imaging continental areas of the visible Earth’s scene excluding the nadir point below the satellite position. By choosing an appropriate orbit configuration, imaging can be provided over most of Europe and North or South Africa.