Phase synchronization from noisy univariate signals
  We present methods for detecting phase synchronization of two unidirectionally coupled, self-sustained noisy oscillators from a signal of the driven oscillator alone. One method detects soft, another hard phase locking. Both are applied to the problem of detecting phase synchronization in von Karman vortex flow meters. 
A. G. Rossberg, K. Bartholome, H. U. Voss, J. Timmer