Over the past fifty years, advances in space flight and radar technology have revolutionized the way we view the Earth. Today, satellites thousands of kilometers up are mapping its entire surface quite literally meter-by-meter. Applications for Earth observation data abound. From aquifer and oil field measurements to crop health monitoring, its importance will continue to grow as human needs increasingly strain our planet's resources. In my talk, I will explore the physics that underlie detailed Earth observation. Starting with atmospheric effects that restrict our choice of imaging frequencies, I will apply that knowledge to radar systems, devoting particular attention to Synthetic Aperture Radar (SAR), the technique responsible for many of the recent advances in ultrahigh-resolution imaging.