Abstract
Currently, GNSS reflectometry based on the signal-to-noise ratio (SNR) has become an established tool in ocean remote sensing. Here, the distance between an antenna and the water surface is measured by analyzing the oscillation of the SNR observation. Due to the antenna gain pattern, this oscillation is more pronounced for satellite signals coming from low elevation angles. Additionally, the sea surface roughness is related to the attenuation of the SNR oscillation. Hence, the significant wave height (SWH) can be estimated by analyzing the SNR signal. In this work, a method is presented with which the SWH can be calculated from the attenuation’s damping coefficient of the SNR observations measured with surface-based receivers. The method’s usability is demonstrated using data from a static antenna operated in the German Bight and with data from a ship-based antenna. The estimated SWH values were validated against numerical wave model data. For both experiments, a high correlation was found.
Highlights
The oceans are of major importance for the global climate and life on Earth
During the last few years, the interference of the direct and the reflected signal that creates a characteristic oscillation in the signal-to-noise ratio (SNR), which is observed by the majority of GNSS receivers, has been shown to be a useful tool for observing the distance between a GNSS antenna and the reflecting water surface [8]
While a GNSS satellite moves along its orbit, the specular point moves over the water surface, yielding an interference variation with the direct signal, which results in an oscillation of the GNSS SNR observables
Summary
The oceans are of major importance for the global climate and life on Earth. In addition to their ecological impact, they play an important role in civil and economic life. A standard technique for doing in situ SWH observations is moored wave buoys where the SWH is calculated from vertical acceleration measurements [1] Such observations can be used to generate SWH time series for a specific location, which are important for calibration and validation of remote sensing techniques like satellite altimetry [2], marine radar [3], or SAR satellites [4]. Alonso-Arroyo et al used a short-time Fourier transform of the attenuated SNR oscillation to calculate the cutoff angle, at which the signal coherence is lost [11] They found a non-linear relation between the cutoff angle and the SWH that was observed in parallel by a radar-based instrument.
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