To observe changes in tidal flats and coastal area, sedimentation process and biomass are needed to be understood. To monitor such an active change, surface conditions and high precision DEMs with an accuracy of better than 20 cm are required in tidal flats. In this study, C-band radar scattering model and the feasibility of ERS SAR applications to tidal flat monitoring were investigated. R.m.s. height was the most significant parameter in C-band SAR backscattered signals. C-band HV-polarization was the most effective combination to observe Korean tidal flats for studying surface conditions. Surface water cover by remnant seawater specifically on the ebb tide is another important factor on SAR imaging in the tidal flats. Coherence of ERS-1/2 tandem pair was about 0.6 in Korean tidal flats. However, coherence depends on tidal conditions rather than time interval between an interferometric pair.