Abstract
This paper evaluates the capability of interferometric global navigation satellite system reflectometry (GNSS-R) to perform sea surface altimetry in a synoptic scenario. Such purpose, which requires the combination of the results from different GNSS signals, constitutes a unique characteristic of this approach. Interferometric GNSS-R group delay altimetry has been proven to be more precise than conventional GNSS-R. However, the self-consistency and accuracy of their synoptic solutions (simultaneous multi-static results) have never been proved before. In our work, we analyze a dataset of GNSS signals reflected off the Baltic Sea acquired during an airborne campaign using a receiver that was developed for such a purpose. Among other features, it enables beamformer capability in post-processing to get multiple and simultaneous GNSS signals under the interferometric approach’s restrictions. In particular, the signals from two GPS and two Galileo satellites, at two frequency bands (L1 and L5), covering an elevation range between 28° and 83°, are processed to retrieve sea surface height estimations. The results obtained are self-consistent among the different GNSS signals and data tracks, with discrepancies between 0.01 and 0.26 m. Overall, they agree with ancillary information at 0.40 m level, following a characteristic height gradient present at the experimental site.
Highlights
The use of signals of opportunity represents a low cost means towards remote sensing of geophysical parameters
The aforementioned spaceborne systems were designed for scatterometry applications as a primary target, several studies show the potential of the global navigation satellite system reflectometry (GNSS-R) technique for altimetry from their datasets (e.g., [10,11,12,13,14,15,16])
This paper describes the work done towards the fulfilment of that last requirement: to check the capability of interferometric GNSS-R (iGNSS-R) to perform multi-static sea surface altimetry by keeping the same accuracy levels previously obtained
Summary
The use of signals of opportunity represents a low cost means towards remote sensing of geophysical parameters. The aforementioned spaceborne systems were designed for scatterometry applications as a primary target, several studies show the potential of the GNSS-R technique for altimetry from their datasets (e.g., [10,11,12,13,14,15,16]) As it was initially envisaged in [1], the multi-static geometry nature of this approach represents a good opportunity towards ocean altimetry. Unlike conventional GNSS-R, this method takes profit of all codes present in the GNSS signal regardless of their encryption status, increasing the effective bandwidth employed For this reason, this approach, known as interferometric GNSS-R (iGNSS-R), was selected for different European Space Agency’s proposed GNSS-R altimetric missions: the PARIS in-orbit demonstrator (PARIS IoD) [19], the GNSS REflectometry, radio occultation, and scatterometry onboard the International Space Station (GEROS-ISS) [20] and the GNSS transpolar Earth reflectometry exploring system (G-TERN) [21].
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