At the same time, an airplane or satellite with the radar antenna moves forward and radar pulse is repeated. In SAR, the antenna must be designed to make azimuthal resolution as small as half the antenna length. This can be done if the antenna does not travel more than half of the along-track antenna length between the two successive pulses. It is also called the along-track resolution. The cross-track resolution and the along-track resolution determine the size of a ground pixel. Distance from the antenna to the ground is recorded in a rough form of slant range with additional information in the form of phase in the SAR image.

The general expression for the electric field of a plane electromagnetic wave, which is a solution of the Maxwell equations, is:E=E0(R, t)ei(k?R?��t)=E0(R, t)ei��(1)where E0(R,t) is the amplitude of the EM pulse and the phase angle is:��=k?R?��t(2)where k = k�� is the complex wave vector (�� is a unit vector in the propagation direction), k is the complex wave number, depending on dielectric constant. The wave propagates along space vector R (slant range). �� is the wave angular frequency and t the time. Thus, the echo received by the antenna of an imaging radar from a ground pixel is characterized by two quantities: amplitude and phase, as shown in Figure 2.Figure 2.The relationship among amplitude, phase, and wavelength of a radar signal. The intensity of the radar signal is proportional to the squared amplitude.The digitized signal from a ground pixel is conveniently represented as a complex number, thus giving a complex image.

Complex images are generated from the signal data received by each antenna. The amplitude of an image pixel represents the backscattering capability of the terrain of the corresponding ground pixel to send the incident energy back to the antenna. The pictorial representation of the amplitude of the EM pulses received by the Drug_discovery antenna is called amplitude image. Backscattering and reflection are two different concepts. A very reflective calm water surface is very reflective but the least backscattering, so in a radar image, calm water surfaces correspond to the dark pixels.The phase records the history of the signal from its emission to its return. The pictorial representation of the phase of the EM pulse is called phase image. In practice, however, an interferometric system does not measure the total pixel phase.

Rather, it measures only the phase that remains after subtracting all full intervals present (module-2��). The phase image is thus called wrapped. Conversion from wrapped phase to continuous true phase is called phase unwrapping.1.3. Factors That Impact the Phase of an Image PixelAn image pixel is a pixel in a radar image, while a ground pixel is the corresponding surface area on the ground.