Sea ice detection using GNSS-Reflectometry from sub-orbital rocket flight

Global Satellite Navigation Systems Reflectometry (GNSS-R) is a passive bistatic radar technique that exploits the signals broadcasted by GNSS satellites as signals of opportunity. The scattering characteristics of surfaces such as oceans, ice, soil or vegetation are analyzed by comparing the signals received after a reflection off the Earth surface by a GNSS-R sensor to those received directly. Thanks to the global and continuous availability of multiple GNSS satellites signals, GNSS-R allows the simultaneous analysis of several reflections over different surface areas, with varied incidence angles and carrier frequencies.

Traditionally, GNSS-R is performed from ground stations, airborne platforms or Low Earth Orbit satellites. In this work, a GNSS receiving system was set onboard a sub-orbital sounding rocket, allowing for the collection of rare GNSS-R observations from altitudes varying between 310 and 80km in about 7 minutes of ballistic flight. Such configuration allows extending existing methodologies of surface water detection over wetland and sea-ice from airborne to spaceborne scenarios, notably with the specificity of the recording of direct and reflected signals piercing diversely through the ionospheric E- and F- layers along the flight, at grazing angles.

The flight was performed on November 11, 2024, at 7h38 UTC, as the MAPHEUS-15 (MAterials PHysics Experiment Under weightlessnesS) rocket was launched from the Esrange Space Center, in Sweden. A GNSS antenna, linked to a Syntony GNSS L1-L5 bit grabber, was attached at the bottom of the MAPHEUS-15 payload, aiming for the observation of grazing direct signals and of reflected signals at any elevation angle. The bit grabber digitized the raw RF signals at a 25MHz sampling rate for further software-defined processing.

While the receiving antenna suffered from radio interferences that limited the availability of the GPS L1 frequency, successive computations of GPS L5 Delay Doppler Maps (DDM) were successfully performed at a 1Hz rate, aided for 250ms non-coherent integration by a geometrical model of the direct and reflected signals paths. Reflection events were detected in the processed DDMs of 8 different GPS satellites, with elevations ranging from 0 to 70°, over Norway, Sweden, Finland, as well as over the Fram Strait area. The Fram Strait GNSS-R events were observed continuously for 150s, corresponding to a ground trace of about 300km, and further studied for sea and sea ice characterization. A second iteration of this experiment was performed during the MAPHEUS-16 flight on November 12, 2025, also displaying reflections over the Fram Strait area at grazing angles.