In remote sensing, phase is the exact position within a periodic signal with respect to an arbitrary reference point. It is typically expressed as an angle and measured in degrees or radians, where one period corresponds to a phase of 360° or 2π, respectively. Mathematically, phase is the argument of a complex number, that is the angle between its geometric representation in the complex plane and the real axis. For this reason, complex algebra is often used in remote sensing to facilitate phase calculations. Due to its periodic nature, phase can only be measured unambiguously within one period. Consequently, phase measurements are commonly subject to 2π phase ambiguities. These ambiguities can often be resolved in a process called phase unwrapping, using a priori information about the signal, typically related to its continuity. Phase measurements are crucial for the creation of synthetic aperture radar (SAR) images, as well as for many SAR imaging techniques, including interferometric SAR (InSAR).