Looking at the Earth as a planet: Passive microwave remote sensing of land surfaces

Multi-frequency microwave radiometry from satellite is an excellent tool for providing a continuous monitoring of land surfaces, which is crucial in making decisions about land management in terms of water resources, agriculture, forestry, energy, tourism, transportation and similar activities, as well as in rapidly detection of natural and anthropic disasters. Microwave radiometers are highly sensitive, stable receivers that measure thermal emission from the observed surfaces. One of the greatest challenges of remote sensing involves inverting the measurements and retrieving the quantities of interests from the observed data. After a short description of the principles of microwave radiometry, observation instruments, and techniques, this paper addresses the issue of retrieving significant quantities of land surfaces which affect the water cycle and are important indicators of climate changes.