A conventional nautical radar, operating at grazing incidence and horizontal polarization in transmit and receive, is used as a ocean surface wave sensor. Radar-image sequences, with their high spatial resolution and large coverage, offer an opportunity to derive and study individual waves and wave fields in space and time. However, rainfall effect cannot be avoided in traditional X-band wave monitoring system. Instead of X-band radar, present study utilizes S-band radar as the surface wave sensor. During intensive operation period (IOP) experiment, it is clearly to see that S-band radar can be used in rainfall conditions, and from radar signal to noise ratio (SNR) and modulation transfer function (MTF) comparisons, S-Band radar indeed has good performance on surface wave measurement.