SAR technological advancements allow space-borne devices to achieve extremely high levels of ground-range resolution. Using high-resolution optical sensors can identify the magnitude of earthquakes. Radar systems allow for the delivery of data within 24 hours. All of these advancements prompted the development of new processing algorithms, products, and applications capable of fully utilizing the new sensor capabilities (e.g., wide spectral band, multi-angle view, short revisit time). The extensive and constantly updated the SAR data (Bovenga, 2020). Real aperture radars (RAR) and synthetic aperture radars (SAR) are the two types of remote sensing radars. Real aperture radars use a fixed-length antenna to transmit and receive microwave signals, as is the case with the Russian Resurs-O series satellite. Because it is difficult to transport a very long antenna, they are limited in ability to produce resolutions fine enough for most remote sensing applications. Synthetic aperture radars were created to address this issue. Physically, SARs have shorter antennas that simulate or synthesize very long antennas. Modified data recording and signal processing techniques are used to accomplish this. The received signal is complex, which means it includes both a phase and an amplitude component (Hanssen 2001). Because the components of the complex signal must be stored for processing, both components must be stored. Synthetic aperture radar (SAR) is an active imaging instrument that is capable of measuring the earth's properties (Bamler and Hartl 1998). Electromagnetic radiation is first transmitted from the SAR instrument in pulses, after which pulses striking objects on the ground are scattered in all directions, and a small portion of the pulses are reflected back to the SAR-receiver instrument's antenna.
The SAR sensor has several advantages:
Microwave sensors rely on microwave illumination, while optical sensors rely on solar illumination or thermal radiation from the sun.
The microwave energy from SAR can penetrate clouds and be used at night and in all weather conditions. Furthermore, depending on polarization and frequency, it may penetrate vegetation, dry sand, and snow to some extent.
It is possible to produce SAR images at various frequencies and with different polarizations
The wavelength of radar is sensitive to surface roughness and dielectric constant.
Coseismic deformation mapping has become a focus of SARs (see Table 2.1 for examples of current and upcoming SAR instruments).
In this section, the basic concepts of synthetic aperture radar (SAR), interferometric synthetic aperture radar (InSAR), LOS ambiguity, and Landsat 8 OLI, as well as the DInSAR, MAI, and 3D surface deformation techniques, are discussed.
Table (2.1): The current and near-future commercial SAR sensors for earth observation
