Ulrike Romatschke , Vanda Grubišić 

Stereophotogrammetric images collected during the Terrain-induced Rotor Experiment (T-REX), which took place in Owens Valley, California, in the spring of 2006, were used to track clouds and cloud fragments in space and time. We explore how photogrammetric data complements other instruments deployed during T-REX, and how it supports T-REX objectives to study the structure and dynamics of atmospheric lee waves and rotors. Algorithms for camera calibration, automatic feature matching, and 3D positioning of clouds were developed which enabled the study of cloud motion in highly turbulent mountain wave scenarios.
The dynamic properties obtained with photogrammetric tools compare well with data collected by other T-REX instruments. In a mild mountain wave event, the whole life cycle of clouds moving through a lee wave crest was tracked in space and time showing upward and downward motion at the upstream and downstream side of the wave crest, respectively. During strong mountain wave events the steepening of the first lee wave as it developed into a hydraulic jump was tracked and quantified. Vertical cloud motion increased from ~2 m/s to 4 m/s and horizontal cloud motion decreased from 20 m/s to 16 m/s with the development of the hydraulic jump. Clouds at distinct vertical layers were tracked in other mountain wave events: moderate southerly flow was observed in the valley (~8 m/s), westerly motion of the same magnitude at the Sierra Nevada mountain crest level, and westerlies with speeds of over 20 m/s at even higher altitudes.