On October 9, 2023, the Pretty mission of the European Space Agency (ESA) aboard the Vega rocket from French Guiana and will soon capture satellite navigation (GNSS) signals. A team from the Institute of Space Sciences (ICE-CSIC) and the Institute of Space Studies of Catalonia (IEEC) participates in the scientific consortium of this nanosatellite that will test innovative and economical ways to monitor sea surface and ice levels from space.
The Pretty mission (Passive Reflectometry and Dosimetry) is a CubeSat 3U type nanosatellite, a miniature cuboidal satellite, equipped with a pair of forward-facing antennas to capture signals from navigation satellites close to the horizon. The antenna on the front face of Pretty will receive the signal from a GNSS satellite that travels through two ray paths: a direct path from the GNSS system and a path that has previously bounced off Earth’s cryosphere or oceans. After analyzing and comparing both signals, the mission will be able to calculate the height of the ice and sea with an accuracy of at least 50 centimeters from an orbital altitude of 550 kilometers.
How the nanosatellite operates to monitor the seas and ice
This nanosatellite operates from GNSS signals reflected in the sea, which make it possible to accurately measure the topography of the sea at very low angles. The ICE-CSIC Earth Observation group, led by Estel Cardellachincluding Serni Ribó and Weiqiang Li – all of them also members of the IEEC – has been developing altimetry techniques based on GNSS signals since the late 1990s. The team participates in the scientific consortium coordinated by the Norwegian University of Science and Technology (NTNU), in collaboration with the ICE-CSIC, the IEEC, the German Center for Research in Geosciences GFZ and the German Aerospace Center (DLR-SO).
The ICE-CSIC and the IEEC have helped define the parameters of the GNSS receiver on board the nanosatellite and will be in charge, together with DLR-SO and GFZ, of generating the first altimetric solutions from the signals collected by Pretty during the phases initials of the mission.
GNSS signals, a new approach to reflectometry
“At Pretty we will try to demonstrate different aspects of GNSS altimetry at very low angles. It is a technique with great potential, but it also presents complicated challenges”, indicates Estel Cardellach, researcher at the ICE-CSIC and the IEEC. “In our group we have the responsibility of providing the first altimetric results, during the initial phases after launch,” she adds.
“Besides, Pretty is making use of a new GNSS frequency for the first time, using the longer wavelength E5/L5 transmitted by the European Galileo and American GPS satellites. The Pretty team made this change at an advanced stage of mission development, guided by ground tests that showed greater precision using this frequency band,” explains ESA engineer Manuel Martín Neira.
The ground experiment was led by the ICE-CSIC and the IEEC in 2021, with the participation of the Mediterranean Institute for Advanced Studies (IMEDEA-CSIC), and funded by the ESA, to investigate reflectometry at grazing angles. Researchers Estel Cardellach and Serni Ribó installed a navigation satellite receiver at the top of Puig Major, in Mallorca. The campaign and the data analyzed served to explore a clearer way of monitoring sea level, offering appropriate advice for the Pretty mission, as well as for future missions that use cost-effective altimetry techniques and GNSS signals.
Exploring the shape of the sea surface, its height and the processes that alter it will allow better applications at a scientific and social level in climate research, prediction of marine currents, prediction of cyclones, fisheries management, monitoring of debris and plastics, etc. .
The Pretty mission, funded through ESA’s General Support Technology Program by Austria, has been developed by an Austrian consortium consisting of Beyond Gravity Austria, Seibersdorf Laboratories and the Graz University of Technology.