Advances in Microwave Limb Sounding—An Update on the Compact AdaptableMicrowave Limb Sounder (CAMLS) Project

Spaceborne instruments employing the microwave limb sounding technique provide daily near-global observations of atmospheric composition and other parameters including temperature, geopotential height, and cloud properties from the upper troposphere through the mesosphere. Such measurements provide valuable scientific insights into issues surrounding ozone layer stability, climate change and climate feedbacks, and pollution transport. NASA's Compact Adaptable Microwave Limb Sounder (CAMLS) project is developing a new class of microwave limb sounding instrument to extend and augment the record of measurements from NASA's Microwave Limb Sounder (MLS) sensors on the UARS and Aura spacecraft, launched in 1991 and 2004, respectively. Under the CAMLS project, we have developed a new 340 GHz receiver and a set of CMOS digital spectrometers, and have incorporated them into an airborne instrument for high altitude testing. Using CAMLS-developed subsystems, an "MLS follow on" instrument could be developed in a far smaller mass/power envelope than was needed for Aura MLS (e.g., 20kg, 80W compared to 350 kg, 370 W). Alternatively, cooling the new 340 GHz receiver to ~50 K provides greatly improved signal to noise compared to previous sensors, enabling 2D (vertical and across track) scanning of the limb, providing dramatic improvements in horizontal and temporal resolution. We review CAMLS progress to date and outline future plans for CAMLS, A-SMLS and the MLS-class of spaceborne instruments.