To cover a large area, the use of HF radars is preferred to classical radars one because HF radars are not limited by EM horizon. On counterpart, antennas of HF radars are huge and ionospheric and surface clutters disturb the use of such radars. In order to improve radar's performances, we will study, in this paper, electromagnetic signature of sea and ground clutter in HF band by means of radar cross section. Among the calculation methods of radar cross section, we will de¯ne the use condition and the expression of radar cross section estimated by approximate methods which are Small Perturbation Method (SPM), Two Scale Model (TSM) and Small Slope Approximation (SSA). To implement the scattering coe±cients using by those models, we need to know electrical permittivity, magnetic permeability, surface spectrum and surface slope distribution. In this paper, we will consider diamagnetic or paramagnetic surfaces so magnetic permeability is near to vacuum permeability. Thanks to approximate methods we study in this paper, we will observe the e®ects of the polar- ization, of the parameters linked to sea (wind direction and wind speed, salinity and temperature of salt water) and ground (roughness and composition) surfaces, of the transmitter and receiver positions and of the transmitting frequency on the electromagnetic signatures of surface clutter.