1. An inspection system for a metal-reinforced concrete structure, comprising: (a) a radio frequency (RF) system configured to be movable with respect to a surface of the concrete structure in a scan direction, transmit radio signals into the interior of the structure at a plurality of scan locations, and receive reflected radio signals; and (b) a processor configured to process the reflected radio signals by: normalizing each waveform of the reflected radio signals for unity amplitude, performing a principal component analysis to remove a first reflection from a first interface of the radio signals to the metal-reinforced concrete structure, obtaining a first principal component representative of the transmitted radio signals and using the first principal component to filter each waveform, correcting attenuation of the radio signals in the metal-reinforced, concrete structure, creating an analytical signal for each waveform, generating a sub-surface 2D image of the metal-reinforced concrete structure using the magnitude of the waveforms, projecting the 2D image to the scan direction by estimating a maximum value at each scan location to estimate reflection amplitude, for each identified peak location, plotting a phase for each waveform, and estimating a slope of the phase prior to and after a metal-reinforcement, wherein the slope corresponds to the physical condition of the metal-reinforcement.