Oregon State University

Thermal-IR imagery may help map cold-air drainage in complex terrain

Thermal-Infrared image of mouth of Lookout Creek valley (HJA) Research:As part of the Advanced Resolution Canopy Flow Observation (ARCFLO) 2012 study at the HJ Andrews LTER site funded by the National Science Foundation, a tandem camera system was installed on Blue River Ridge that looks down on the lower Lookout Creek Valley. The system consists of a thermal infrared (IR) and a visible & near infrared camera which take an image every 5 min. The scientific idea is to use the thermal signal of the foliage as a proxy for air temperature to study and map the dynamics of the nocturnal, weak-wind boundary layer in this mountain valley. Valley-scale cold air drainage and cold pools are important features in complex terrain. The tandem camera system also complements extensive efforts to characterize the valley-scale air circulation using acoustic ground-based remote sensing (VALCEX). The core of the experimental efforts during ARCFLO 2012 takes place in Watershed 1, where a dense network of wind, temperature, carbon dioxide, and water vapor sensors will be installed to investigate how wind, heat, carbon dioxide and water vapor communicate across the landscape in this steep mountaineous terrain. This experiment is a central reearch activity of the NSF Career award in Physical and Dynamical Meteorology.

A sequence of images taken by the tandem camera system on 27 and 28 June 2012 is shown as an exmaple:

(First panel): Cold-air drainage and pooling dominate temperatures in the bottom of the valley early at night, while higher elevations and indiviudal tall trees show up as warm.

(Second panel): Early in the morning before sunrise, temperature differences are smaller, while the general trend of lower temperatures in the bottom of the valley compared to the sloped is conserved. A secondary gradient of decreasing temperatures deeper into the Lookout Creek valley (into the foreground of the image) is noted.

(Third panel): The sunlight heats up the foliage of indivdiual tall trees towering above the main canopy and the north-facing slope of the Blue River Ridge. A very cold, cloud-topped inversion above the Blue Lake reservoir can be seen near the top of the image.

(Fourth panel): Surface heating has lead to higher temperature in the bottom of the valley.

Sequence of images taken by the tandem camera system installed on the Rd130 tower at the HJA LTER site, (c) bmm group

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