A novel approach for the extraction of cloud motion vectors using airglow imager measurements

摘要

The paper explores the possibility of implementing an advancedphotogrammetric technique, generally employed for satellite measurements, onairglow imager, a ground-based remote sensing instrument primarily used forupper atmospheric studies, measurements of clouds for the extraction ofcloud motion vectors (CMVs). The major steps involved in the algorithmremain the same, including image processing for better visualization oftarget elements and noise removal, identification of target cloud, setting aproper search window for target cloud tracking, estimation of cloud height,and employing 2-D cross-correlation to estimate the CMVs. Nevertheless, theimplementation strategy at each step differs from that of satellite, mainlyto suit airglow imager measurements. For instance, climatology of horizontalwinds at the measured site has been used to fix the search window for targetcloud tracking. The cloud height is estimated very accurately, as requiredby the algorithm, using simultaneous collocated lidar measurements.High-resolution, both in space and time (4 min), cloud imageries areemployed to minimize the errors in retrieved CMVs. The derived winds areevaluated against MST radar-derived winds by considering it as a reference.A very good correspondence is seen between these two wind measurements, bothshowing similar wind variation. The agreement is also found to be good inboth the zonal and meridional wind velocities with RMSEs < 2.4 m s?1. Finally, the strengths and limitations of the algorithm arediscussed, with possible solutions, wherever required.