In the framework of the CORTEX EU project, several measurements from different KWU and VVER reactorshave been analyzed. The goal of this project is to develop and test core monitoring techniques todetect possible anomalies and better characterize the information provided by the neutron detectors.In this article, three different signal processing methods are presented: coolant velocity estimation,Singular Spectrum Analysis (SSA) and Operational Modal Analysis (OMA). The first method is based ondetecting travelling perturbations by cross correlating different detectors and obtaining the impulseresponse function. The second method, SSA, reduces the noise and allows a better estimation of the frequencycontent with a high resolution. SSA has been tested both in simulated and plant data. The lastmethod permits distinguishing closely spaced resonances and a multivariate analysis of all the detectors.In this work, the details of each methodology are explained step by step, and the results on each reactorare also presented. Testing these methods during CORTEX project gives valuable information and orientationfor further investigations in reactors diagnostics.