I. Introduction
Blade health monitoring (BHM) is a technique of monitoring the condition of blades for an aero-engine rotor to identify abnormal changes and prewarn the development of faults [1]. The increasing demand for higher compressor performance and efficiency poses huge challenges for the rotor blades [2]. Engine blades abnormal conditions such as high cycle fatigue (HCF), foreign object damage, and flutter usually cause catastrophic failure [3]. Damages in engine blades generally have indications on blade vibration especially the blade tip. Blade tip timing (BTT) [4], [5] is a vibration measurement technique developed in recent years for blade tip displacement monitoring, whose principle and superiority over strain gauges have been illustrated in [6].