An empirical inversion method is presented for determination of time series of ocean surface elevation maps from nautical radar-image sequences. The method is based on the determination of the surface tilt angle in antenna look direction at each pixel of the radar images. Thereby in situ sensors are not required. An external calibration is not necessary. A conventional nautical X-band radar, operating at grazing incidence and horizontal polarization in transmit and receive, is used as a sensor. Radar-image sequences, with their high spatial resolution and large coverage, offer a unique opportunity to derive and study individual waves and wave fields in space and time and therefore allow the measurement of individual wave parameters and wave groups. For validation of the inversion scheme, the significant wave heights derived from the inverted radar data sets and from colocated wave records are compared. It is shown that the accuracy of the radar-retrieved significant wave height is within the accuracy of the in situ sensors. Furthermore, a wave elevation time series is directly compared to a buoy record to show the capabilities of the proposed method.