Turbine blade monitoring

A blade monitoring system and method for monitoring a turbine assembly comprising rotating blades. The system comprising at least one sensor 10, 12 for transmitting a signal towards said rotating blades and detecting a time-varying return signal therefrom. One or more processors are configured to calculate the time derivative of said return signal, generate a phase variation signal for said time derivative, determine minima points within said phase variation signal and measure said signal at said minima points so as to identify data representative of respective minimum path lengths. Each said minimum path length corresponding to the returned signal as each respective blade passes said sensor, and generate, using said minimum path lengths, a time series of data representing the returned signal from individual blades as they pass the sensor. Said data may be used to determine the health of the turbine and offer a complete solution for monitoring blade vibration, cracked discs, foreign object debris and tip clearance. The transmitted signal may be a wideband signal to enable a return signal to be collected from a complete blade and the signal may be a radar signal.