Unmanned aerial systems (UAS) carrying long-wave infrared (LWIR) cameras enable mapping of near-surface currents during low-light and nighttime conditions. We use LWIR video from a UAS over nearshore waters at Texas City Dike, Texas, to estimate surface currents and compare them with in situ Acoustic Doppler Current Profiler (ADCP) measurements.  Two approaches are applied. At night, billow-like thermal patterns appeared on the sea surface. After suppressing wave-related signals with locally adaptive thresholding, these temperature features can be tracked using Particle Image Velocimetry (PIV), yielding coherent current vector fields. At the ADCP site, PIV-derived mean velocities closely match the observations, showing that thermal structures act as effective tracers.  Near dawn, as surface temperature becomes more homogeneous, wave signatures become the primary tracer. Under these conditions, CopterCurrents (Streßer et al., 2017; Bae et al. 2025), a spectral method based on Doppler wave dispersion, is applied to the LWIR imagery. Prior to this, low-temperature striping that interferes with CopterCurrents is filtered out using Proper Orthogonal Decomposition (POD), which clarifies wave signals and improves the resulting vector maps. The mean current estimates again agreed with the ADCP data in both magnitude and direction.  These results show that UAS-based LWIR imaging can resolve coastal surface currents under varying environmental conditions. PIV tracking of thermal tracers enables nighttime current estimation, while CopterCurrents remains effective when only wave patterns are visible. Together, these approaches support continuous monitoring of nearshore hydrodynamics using UAS platforms.

Acknowledgment:  This work is a result of research funded by the Texas General Land Office’s Oil Spill Prevention and Response Program under Award No. 24-016-004-D951.

References

Bae, S.B., Chang, K.-A., Huang, H.-Y., Socolofsky, S.A. (2025). Comparison of surface current measurement techniques and observations of tidal Inlet dynamics using unmanned aerial systems.  Journal of Atmospheric and Oceanic Technology, 42, 1403-1418. https://doi.org/10.1175/JTECH-D-24-0118.1

Streßer, M., Carrasco, R., & Horstmann, J. (2017). Video-Based Estimation of Surface Currents Using a Low-Cost Quadcopter. IEEE Geoscience and Remote Sensing Letters, 14(11), 2027–2031. https://doi.org/10.1109/LGRS.2017.2749120