SAR stands for Synthetic Aperture Radar, which is a type of satellite-based radar that uses microwave signals to create images of the Earth's surface. It works by transmitting a pulse of microwave energy towards the surface and then measuring the time it takes for the pulse to bounce back to the satellite. The resulting data is processed to form an “image” of the Earth that is quite different from an optical image. As SAR images are not affected by the visible light spectrum, they deliver in grayscale, rather than color.

SAR is particularly useful because it can be used in all weather and lighting conditions, including cloudy or foggy weather, and at night, because the microwave signals are not affected by atmospheric interference. SAR can also penetrate through vegetation, ice, and snow, allowing it to capture images of the Earth's surface that may not be visible using other types of satellite imaging.

SAR images can be used for a wide range of applications, including monitoring changes in the Earth's surface, mapping land use and land cover, water and flood extents, and detecting natural disasters such as earthquakes and landslides. SAR can also be used for military and intelligence purposes, such as identifying equipment or monitoring activity in remote areas.