Towards GPS-Denied Spotlight SAR Image Formation

Synthetic Aperture Radar (SAR) systems emit pulses of (Radio Frequency) RF energy from an antenna into the environment over short intervals in time. Reflected RF energy is received coherently by a receiving antenna and signal processing focusing algorithms process the received signals using one of many potential focusing algorithms to form 2D images of the scene. Formation of these images requires highly accurate knowledge of the antenna state, e.g., the position, orientation and their velocities, when transmitting and receiving RF signals. This information is typically obtained using a combination of a high-quality Global Positioning System (GPS) receiver and a highly-accurate Inertial Navigation System (INS). SAR dependence on GPS and INS data prohibit SAR image formation in GPS-denied contexts which limit the application of this technology. This work investigates approaches for focusing SAR images when GPS is unavailable.