Abstract
Ground-based interferometric radar systems have numerous environmental monitoring applications in geoscience. Development of a relatively simple ground-based interferometric real-aperture FMCW radar (GB-InRAR) system that can be readily deployed in field without an established set of corner reflectors will meet the present and future need for real-time monitoring of the expected increased number of geohazard events due to climate changes. Several effects affect electromagnetic waves and limit the measurement accuracy, and a careful analysis of the setup of the deployed radar system in field is essential to achieve adequate results. In this paper, we present radar measurement of a moving square trihedral corner reflector from experiments conducted in both the field and laboratory, and assess the error sources with focus on the geometry, hardware and environmental effects on interferometric and differential interferometric measurements. A theoretical model is implemented to assess deviations between theory and measurements. The main observed effects are variations in radio refractivity, multipath interference and inter-reflector interference. Measurement error due to radar hardware and the environment are analyzed, as well as how the geometry of the measurement setup affects the nominal range-cell extent. It is found that for this experiment the deviation between interferometry and differential interferometry is mainly due to variations in the radio refractivity, and temperature-induced changes in the electrical length of the microwave cables. The results show that with careful design and analysis of radar parameters and radar system geometry the measurement accuracy of a GB-InRAR system without the use of deployed corner reflectors is comparable to the accuracy of differential interferometric measurements. A GB-InRAR system can therefore be used during sudden geo-hazard events without established corner reflector infrastructure, and the results are also valid for other high-precision interferometric radar systems.
Highlights
The all-weather capability of radar makes it the natural instrument for real-time monitoring in geosciences for potential life-threatening natural events like rock and mountain slides; clay and snow avalanches; volcanoes; open pit mines [1]; and structural monitoring of dam fronts [2], buildings and bridges [3,4,5]
We present radar measurement of a moving square trihedral corner reflector from experiments conducted in both the field and laboratory, and assess the error sources with focus on the geometry, hardware and environmental effects on interferometric and differential interferometric measurements
The results show that with careful design and analysis of radar parameters and radar system geometry the measurement accuracy of a GB-InRAR system without the use of deployed corner reflectors is comparable to the accuracy of differential interferometric measurements
Summary
The all-weather capability of radar makes it the natural instrument for real-time monitoring in geosciences for potential life-threatening natural events like rock and mountain slides; clay and snow avalanches; volcanoes; open pit mines [1]; and structural monitoring of dam fronts [2], buildings and bridges [3,4,5]. In a recent 8-year study of monitoring an unstable mountainside [6], it was found that atmospheric decorrelation was the major factor limiting the measurement accuracy when monitoring submillimeter motion at distances of 3 to 4 km. It is not always possible to introduce radar reflectors due to the nature of the monitored area or from a safety point of view, typically for an unstable mountain with a lot of motion and occasional rock falls. There is, a need for a thorough assessment of GB-InRAR systems, including radar hardware, measurement geometry and environmental effects, to find ways to compensate for the interferometric measurements for the environmental and geometrical effects in order to achieve accuracies comparable to differential interferometry
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