MotionLeaf: Fine-grained Multi-Leaf Damped Vibration Monitoring for
  Plant Water Stress using Low-Cost mmWave Sensors
In this paper, we introduce MotionLeaf , a novel mmWave base multi-point
vibration frequency measurement system that can estimate plant stress by
analyzing the surface vibrations of multiple leaves. MotionLeaf features a
novel signal processing pipeline that accurately estimates fine-grained damped
vibration frequencies based on noisy micro-displacement measurements from a
mmWave radar. Specifically we explore the Interquartile Mean (IQM) of coherent
phase differences from neighboring Frequency-Modulated Continuous Wave (FMCW)
radar chirps to calculate micro-displacements. Furthermore, we use the
measurements from multiple received antennas in the radar to estimate the
vibration signals of different leaves via a Blind Source Separation (BSS)
method. Experimental results demonstrate that MotionLeaf can accurately measure
the frequency of multiple leaves in a plant with average error of 0.0176 Hz,
which is less than 50% of that (0.0416 Hz) of the state-of-the-art approach
(mmVib). Additionally, the estimated natural vibration frequencies from
MotionLeaf are shown to be an excellent feature to detect the water stress in
the plant during 7-day drought experiments.
Mark Cardamis Chun Tung Chou Wen Hu