Thermokarst Lake Gyre Flow Speed and Direction Derivation Using Image Matching from Sequential Satellite Images
Thursday, 18 December 2014
Thermokarst lakes on the Arctic Coastal Plain of northern Alaska are closely coupled with the regional climate through energy, water and carbon budgets. These lakes exhibit striking elongated shapes perpendicular to the prevailing wind direction. This has led to the hypothesis that the expansion of lakes is caused by thermomechanical processes induced by wind-driven water circulation. The predominant bimodal wind regime in the region (easterly and westerly wind) redistributes lake sediment towards the west and east shores to form protective littoral shelves while the north and south shores are preferentially eroded. Previous research on wind-driven circulation in thermokarst lakes was mainly based on in situ studies which can only collect sparse measurements and is time-consuming. Examination of satellite imagery clearly reveals the wide-spread presence of gyres in thermokarst lakes. It allows the study of gyres and other circulation patterns at both lake and regional scales. This study examines the movement (speed, direction) of a 10-km-wide gyre using a Landsat-7 and an ASTER scene taken about 40 minutes apart. These two images are matched using a robust image matching technique based on cross-correlation. Flow speed and direction for the gyre are extracted from the images and are compared with the in situ measurements collected during previous field work. This study provides insight into the evolution of thermokarst lakes and their interaction with the local climate by quantifying gyre circulation rates over entire lakes.