The Interference Pattern Technique (IPT) is a new GNSS-R technology, which mainly utilizes the interference of GNSS direct signals and reflected signals. This technique requires a specially made interference-type receiver, which utilizes the polarization characteristics of the reflected signal. In addition, based on the Z-V model and MSS model, the delay-Doppler map (DDM), and the inversion of the scattering coefficient σ0, surface roughness parameters can be obtained, such as sea surface roughness (the higher the wind speed is, the greater the surface roughness is, the larger the DDM in the delay and frequency domain is), ocean wind field, sea surface temperature, ocean salinity, hurricane detection, sea surface oil spill, etc. This chapter introduces the interference pattern technique and delay Doppler map as well as their applications, starting from the Fresnel reflection coefficient.