Locating RFID Tags Under Snow and Vegetation

We investigated the use of passive RFID tags for subsurface localization in challenging environments such as vegetation and snow. A synthetic aperture radar (SAR)-based RFID system was developed, combining high-precision GNSS tracking with phase-based localization methods. Two cost functions were evaluated: a standard complex phasor correlation and a guided phase unwrapping approach. Validation experiments were conducted with tags buried under vegetation layers (hay, bark) and snow covers (dry snow, 1.8-meter-thick wet snowpack). Localization errors were consistently below 5 cm horizontally and 15 cm vertically, even under deep wet snow. The guided phase unwrapping method improved robustness in distorted signal environments at the expense of higher computation time. These results demonstrate the feasibility of passive RFID localization in real-world environmental conditions, opening new perspectives for remote sensing and monitoring applications.