2023-10-13 15:15:33
On October 9, 2023, the small PRETTY spacecraft of the European Space Agency (ESA) was launched into space aboard the Vega rocket from French Guiana and will soon capture satellite navigation signals (GNSS).
A team from the Institute of Space Studies of Catalonia (IEEC) and the Institute of Space Sciences (ICE), dependent on the Higher Council for Scientific Research (CSIC), in Spain, participates in the scientific consortium of this nanosatellite that will test forms innovative and economical ways to monitor sea surface and ice levels from space.
PRETTY is a 3U CubeSat-type nanosatellite, a small cube-shaped satellite, equipped with a pair of forward-facing antennas to capture signals from near-horizon navigation satellites. 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 height of the ice and the sea can be calculated with an accuracy of at least 50 centimeters from an orbital altitude of 550 kilometers.
From GNSS signals reflected in the sea, it is possible to accurately measure the topography of the sea at very low angles. The ICE Earth Observation group, led by Estel Cardellach, including Serni Ribó and Weiqiang Li (all 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 ICE, IEEC, the German Center for Geosciences Research (GFZ) and the German Aerospace Center (DLR).
The ICE and the IEEC have helped define the parameters of the GNSS receiver on board the nanosatellite and will be in charge, together with the DLR and the GFZ, of generating the first altimetric solutions from the signals collected by PRETTY during the initial phases of The mission.
Artistic recreation of PRETTY in action. (Illustration: ESA)
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,” says Estel Cardellach, researcher at ICE and IEEC. “In our group we have the responsibility of providing the first altimetric results, during the initial phases after launch,” she adds.
“In addition, PRETTY is making use of a new GNSS frequency for the first time, employing the longer wavelength E5/L5 transmitted by the European Galileo and US 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 ICE and IEEC in 2021, with the participation of the Mediterranean Institute for Advanced Studies (IMEDEA), attached to the CSIC, and funded by ESA, to investigate reflectometry at grazing angles. 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. . (Source: Alba Calejero / ICE / CSIC)
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