Airborne Multi-AXis Differential Optical Absorption Spectroscopy (AMAX-DOAS) fills an existing gap in observing capabilities from ground-based monitoring networks and satellite measurements (local to global scale) due to several advantages: (1) better sensitivity in the free troposphere by maximizing overlap between photon paths and trace gases (exploiting the mobility of the aircraft); (2) better vertical profiling capabilities: at constant flight altitude the vertical resolution is best near instrument altitude (few 100m); (3) the remote sensing capability enables to measure trace gases above and below the aircraft, thus making AMAX-DOAS measurements sensitive towards the whole tropospheric and stratospheric columns.
Our AMAX-DOAS instruments typically consist of two synchronized spectrograph/CCD detectors that receive scattered light sequentially from any telescope, and simultaneously observe the spectral ranges from ~330 – 470nm (reactive trace gases) and ~340 – 700nm (aerosol properties). Telescopes are housed in different pylons, adapted to the specific aircraft. The forward viewing directions are actively stabilized by a real time motion compensation system to ensure constant lines of sight, which is crucial to optimize vertical profile retrievals. AMAX-DOAS measurements of various trace gases and aerosol have been conducted during several field campaigns: 2008 and 2009 Twin Otter flights in Colorado and California and CALNEX/CARES 2010 in California; GV flights during HEFT-10 2010 and TORERO 2012 over the tropical Pacific Ocean.
Twin Otter Pylon
NSF/NCAR GV Pylon