статья в журнале

En

Remote Sensing

ISSN:20724292
eSSN:2072-4292

2022

10.3390/rs14143364

A commercial unmanned aerial vehicle (UAV) is used for coastal submesoscale current estimation. The measurements were conducted in the Black Sea coastal area with a DJI Mavic quadcopter operated in self-stabilized mode at different look geometry (200–500-m altitude, 0–30 (Formula presented.) incidence angle). The results of four flights during 2020–2021 are reported. Some scenes captured a train of or individual eddies, generated by a current flowing around a topographic obstacle (pier). The eddies were optically visible due to the mixing of clear and turbid waters in the experiment area. Wave dispersion analysis (WDA), based on dispersion shell signature recognition, is used to estimate the sea surface current in the upper 0.5-m-thick layer. The WDA-derived current maps are consistent with visible eddy manifestations. The alternative method, based on 4D-variational assimilation (4DVAR), agrees well with WDA and can complement it in calm wind conditions when waves are too short to be resolved by the UAV sensor. The error of reconstructed velocity due to the uncontrolled UAV motions is assessed from referencing to static land control points. At a 500-m altitude and 7–10 m s (Formula presented.) wind speed (reported by a local weather station for 10-m height), the UAV drift velocity, or the bias of the current velocity estimate, is about (Formula presented.) m s (Formula presented.), but can be reduced to (Formula presented.) m s (Formula presented.) if the first 10 s of the UAV self-stabilization period are excluded from the analysis. The observed anticyclonic eddies (200–400 m in diameter with 0.15–0.30 m s (Formula presented.) orbital velocity) have an unexpectedly high Rossby number, (Formula presented.) ∼15, suggesting the importance of nonlinear centrifugal force for such eddies and their significant role in coastal vertical transport

4D-variational assimilation, coastal eddy, sea surface, submesoscale currents, unmanned aerial vehicle, vortex street, wave dispersion

2022-10-17 14:22:01