Thursday 20 March 2025

Environmental remote sensing is a crucial method for observing the impacts of climate change.

In his doctoral thesis, master of science Ankit Regmi has introduced an innovative approach that utilises the reflection of global navigation satellite system (GNSS) signals from the Earth's surface. This enables the study of surface materials and properties, such as the measurement of sea level, sea ice thickness, and soil moisture. 

Sea level and sea ice thickness monitoring in Vihreäsaari harbour, Oulu, Finland. The developed system observed sea surface over various season for 16 months enabling monitoring of sea ice thickness and sea level.

Signal-to-noise ratio

The research employs a cost-effective GNSS reflectometry system (GNSS-R), which uses a specially designed, antenna and commercial GNSS receivers to record both direct and reflected GNSS signals. This enables the determination of reflective surface properties using the signal-to-noise ratio.

The GNSS-R measurements presented in the study examine surface properties across different seasons and conditions. Sea ice thickness is estimated by observing the total height difference between GNSS interferometric reflectometry results and sea level data from the Finnish Meteorological Institute.

Changes in the GNSS signal passing through multi-layer ice are observed in the reflected GNSS parameter, enabling ice thickness measurement. Statistical parameters of the received GNSS data show a correlation with wind speed over open sea, said doctoral candidate Regmi whose theses Dual Circularly Polarized GNSS-Reflectometry for Remote Sensing of Land and Sea Surfaces is now online.

The relative permittivity of the open sea and land is measured by utilising the change in electromagnetic wave polarisation of reflected GNSS signals. The practicality of dynamic measurements with the GNSS-R system is tested using a drone in various remote sensing scenarios.

"Our innovative GNSS-R system offers a cost-effective and versatile tool for environmental monitoring. By providing detailed insights into surface properties and changes, we can better understand and respond to the challenges posed by climate change," said Regmi.

Some potential applications

• Climate change monitoring: The GNSS-R system can provide accurate and timely data on the impacts of climate change, such as sea level rise and ice melt;
• Agriculture: Measuring soil moisture can help farmers optimise irrigation systems and improve crop yields;
• Maritime navigation: Monitoring sea level and ice thickness can enhance maritime safety and route planning;
• Natural disaster management: The GNSS-R system can help predict and monitor natural disasters, such as floods and storms, improving preparedness and response.