Estimating sea level, wind direction, significant wave height, and wave peak period using a geodetic GNSS receiver

[weisongwen]

Monitoring oceanographic parameters is essential for marine engineering construction, coastal safety, marine analysis, and climatic analysis. Traditionally, oceanographic parameters have been monitored using different sensors. With the development of global navigation satellite systems (GNSS), signal-to-noise ratio (SNR) observations have been found to oscillate due to the interference between direct and reflected signals. GNSS-interferometry reflectometry (GNSS-IR) utilizes the characteristics of these oscillations to retrieve the parameters of a reflecting surface. For GNSS marine application, GNSS-IR sea-level retrieval technology has considerably improved and is undergoing rapid development; however, only a few studies have estimated significant wave height (SWH) and wind direction using GNSS-IR. The cut-off elevation, an SNR parameter, is the elevation angle at which the dominant power of one SNR arc switches between coherent and incoherent energy and is related to SWH and wind direction. Methods to estimate SWH and wind direction were presented based on the cut-off elevation. Moreover, we introduced the Generalized Shallow Water Wave Growth (GSWWG) model to estimate the wave peak period based on retrieved SWH. The sea level, wind direction, SWH, and wave peak period were estimated using a geodetic GNSS receiver. Data were collected before and after Hurricane Delta using the GNSS site CALC, Louisiana, USA. First, the classical GNSS-IR method was used to retrieve sea levels. Second, the wavelet analysis method was processed to SNR arcs to form wavelet spectra showing the nonstationary power and estimate their cut-off elevations. Third, the lower cut-off elevation was used to estimate the wind direction, and the upper cut-off elevation was used to estimate the SWH. Finally, the wave peak period was estimated from the retrieved SWH based on the GSWWG model. The results showed a root mean square error of 4.72 cm between sea-level measurements and sea-level retrievals, and a correlation coefficient > 80% between wind speed measurements and SWH retrievals estimated from GPS L5 and GLONASS R2. The points of SWH retrievals vs. wind speeds of GPS L5 and GLONASS R2 corresponded well to the wind–SWH relationship deduced from the GSWWG model. These results indicated that GNSS-IR technology could estimate the wave peak period in addition to its previously known applications for retrieving sea level, wind direction, and SWH, providing additional oceanographic services.