Abstract
As compared to GPS L1C/A signals, L5/E5a Global Navigation Satellite System-Reflectometry (GNSS-R) improves the spatial resolution due to the narrower auto-correlation function. Furthermore, the larger transmitted power (+3 dB), and correlation gain (+10 dB) allow the reception of weaker reflected signals. If directive antennas are used, very short incoherent integration times are enough to achieve good signal-to-noise ratios, allowing the reception of multiple specular reflection points without the blurring induced by long incoherent integration times. This study presents for the first time experimental evidence of the wind and swell waves signatures in the GNSS-R waveforms, and it performs a statistical analysis, a time-domain analysis, and a frequency-domain analysis for a unique data set of waveforms collected by the UPC MIR instrument during a series of flights over the Bass Strait, Australia.
Highlights
The Microwave Interferometric Reflectometer (MIR) is an airborne multi-constellation, dual-beam, and dual-band (L1/E1 and L5/E5a), conventional and interferometric Global Navigation Satellite System-Reflectometry (GNSS-R) [1] instrument (Figure 1)
The peak of the reflected signal is not blurred, and re-tracking is not required. This has allowed that multiple peaks systematically appear in the Delay-Doppler Maps (DDM) and waveforms (WF), provided they occur within the antenna footprint
The last section showed three examples of three different waveforms retrieved from Track 1 Beam 1, where the location of the second peak varies with time
Summary
The Microwave Interferometric Reflectometer (MIR) is an airborne multi-constellation, dual-beam, and dual-band (L1/E1 and L5/E5a), conventional and interferometric GNSS-R [1] instrument (Figure 1) It has two very directive antenna arrays to pick the direct and reflected GNSS signals [2,3]. The peak of the reflected signal is not blurred, and re-tracking is not required This has allowed that multiple peaks systematically appear in the Delay-Doppler Maps (DDM) and waveforms (WF), provided they occur within the antenna footprint. As it is presented in this study, these multiple peaks are related to sea wave information, produced by multiple reflections on consecutive waves, producing a forward Bragg scattering in consecutive wave crests. The use of a higher spatial resolution signal, such as the GNSS L5 (with a spatial resolution of 30 m), opens the possibility to measure the swell spectra, as the spatial resolution provided by these signals is comparable to the swell wavelength, as will be covered
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