A method for suppressing the Jet Engine Modulation (JEM) clutter signal returns from compressor blades (26) in data sampled by a system for Foreign Object Debris (FOD) detection in the air intake (30) of a turbine assembly, the method comprising the steps of: (a) identifying in the data the start sample position and length in samples of a single complete shaft rotation; and (b) subtracting from a current rotation dataset the samples from a comparison rotation dataset corresponding to another complete single shaft rotation.