Researchers: : Dongju Peng, Emma M. Hill and Adam D. Switzer, Nanyang Technological University; Linlin Li, University of Singapore; and Kristine M. Larson, University of Colorado
Written by Linda Rowan
1 June 2020
Geodetic stations at two coastal sites in Hong Kong were able to measure storm surge from Typhoon Hato in 2017 and Typhoon Mangkhut in 2018. The sites used signal to noise ratio measurements from Global Navigation Satellite Systems (GNSS) signals that reflected off of the nearby water into the station antennae. The technique, GNSS Interferometric Reflectometry (GNSS-IR), can help with measuring water levels changes under many conditions. Adding more satellite signals and GNSS ground stations would provide greater coverage in space and time and greater accuracy to geodetic, storm-resistant, ground-based measurements of sea level, storm surge and even tsunami height.
Storm surge, an increase of water height and water inundation on land caused by wind and severe weather conditions, can cause serious damage to coastal communities and coastal lands. Tide gauges, which are typically used to measure sea surface rise and fall can be damaged or provide no measurements during extreme events because of their precarious positions at water level. In addition, a tide gauge only provides a point measurement of how a large body of water is changing.
Previous work has shown that GNSS stations installed on the ground or on structures near coastlines or other bodies of water can be utilized to measure the rise and fall of the water surface. Using the reflected satellite signal that bounces off of the water surface and into the station antenna, the signal to noise ratio can be related to height of the water relative to the height of the antenna. The GNSS station measures the precise position of the ground level from direct satellite signals. Combining these measurements provides the absolute water level. Depending on the geometry of the site, the antenna can capture signals for tens of satellites and track water changes over a large area and over a long time.
Here the authors use two GNSS stations, HKPC and HKQT, in Hong Kong that are attached to buildings and near the coastline. They utilized the L1, L2P, L2C and L5 signals from the Global Positioning System (GPS) and the signal from GLONASS. The stations were not installed to be tide gauges, so the authors tested whether the sites could accurately measure sea level changes using GNSS-IR for a year. The yearlong measurements were just as accurate as the nearby tide gauge measurements. Next they measured the storm surge for typhoons Hato and Mangkhut.
The GNSS stations were able to accurately record the storm surge for two typhoons in Hong Kong using GNSS-IR in very strong wind conditions. The L5 GPS signal was the most accurate for recording sea level and the L1, L2C and L5 signals accurately recorded the storm surges. The GLONASS signal by itself was a bit noisier than expected, but combining multiple signals from many constellations will enhance any measurements of the water level over time and space. GNSS-IR is more than capable of monitoring normal to extreme water level changes in calm and severe conditions and will be useful for tracking severe weather.
Peng, D., Hill, E.M., Li, L. et al. Application of GNSS interferometric reflectometry for detecting storm surges. GPS Solut 23, 47 (2019), doi: 10.1007/s10291-019-0838-y.
Storm surge, sea level, GNSS interferometric reflectometry, signal to noise ratio
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Last modified: 2020-06-01 13:43:47 America/Denver