Combined microwave and optical remote sensing of clouds: a review

Joint cloud remote sensing research using radar, lidar, and passive optical and microwave techniques began over 25 years ago, not long after the development of field-worthy laser systems. Concurrent field measurements of thunderstorm clouds and anvils were made in 1970 by a polarization ruby (0.69 μm) lidar transported from New York University and a scanning 10-cm radar system from the South Dakota School of Mines and Technology near Rapid City. At about the same time, a program was initiated at the NOAA Wave Propagation Laboratory in Boulder, CO, primarily from laser eye-safety concerns, to coalign a K-band radar with a scanning mirror assembly used to point the laser beam. Although polarization lidar findings from this early research phase were published (1), serious intercomparisons with the radar data were not attempted. However, since that time the multiple remote sensor approach has steadily gained acceptance in the cloud physics research community with the recognition of the synergistic qualities of diverse, multiwavelength datasets. Examples of the integration of active and passive optical and microwave remote sensing methods, which currently constitute a major meteorological research emphasis, as applied to cloud research programs are reviewed