Research

In support of the Coastal Land Air Sea Interaction (CLASI) ONR departmental research initiative, we developed a method to measure near-surface current maps and vertical current profiles at high spatiotemporal resolution. The results presented here are based on optical video data acquired with the 3DR H520-G hexacopter. The camera must be calibrated to determine its focal length, optical center, and distortion coefficients. The currents are computed from the ~1 m scale surface wave signal within the camera footage. Here, we used ground control points to invert the camera pose. This approach resulted in a measurement repeatability of ~1 cm/s with an analysis period of 8 s and analysis window radius of 5 m. Over the open water, we have developed an alternative method that uses the wave signal to correct for errors in the UAS heading, altitude, and horizontal position (Lund et al., 2021).

The Stratified Ocean Dynamics of the Arctic (SODA) experiment on R/V Sikuliaq aimed to study the vertical and horizontal water properties in the Arctic and their impacts on ocean circulation and sea ice growth. This movie illustrates the sea ice drift along a Beaufort Sea ice edge that is forced by the radiation stress gradient of oblique waves. The sea ice drift velocity, calculated from marine X-band radar image sequences using an optical flow technique, decays rapidly with distance from the ice edge. The resulting lateral shear is a source for instabilities that shape the ice edge (Thomson et al., 2021) . This study demonstrates the importance of waves in a marginal ice zone.

During the Arctic Sea State cruise on R/V Sikuliaq in the Chukchi and Beaufort Seas in the fall of 2015, we observed a rapidly evolving ice edge. This movie shows a sequence of temporally averaged marine X-band radar images acquired on 4 Oct 2015, from 10:30 to 19:30 UTC. The images are shown in a fixed reference frame. The strongest radar return is due to first and multiyear ice floes. For more information on the field campaign, see Thomson et al. (2018).

We developed an algorithm to retrieve sea ice drift maps from the marine X-band radar (MR) data collected during the Arctic Sea State R/V Sikuliaq cruise. The movie shows the MR sea ice drift results in 30 min intervals covering the entire 1 month cruise period starting from 4 October 2015. More information on this research can be found in Lund et al. (2018).

During the CARTHE LAgrangian Submesoscale ExpeRiment (LASER) experiment in the Gulf of Mexico near the Mississippi river mouth in early 2016, R/V Walton Smith was equipped with a Doppler marine X-band radar (MR) provided by Jochen Horstmann's radar hydrography group at the Helmholtz Zentrum Geesthacht, Germany. This video shows temporally averaged MR images depicting a submesoscale density front and current convergence zone (visible as narrow bands of enhanced backscatter). The front can be seen slowly propagating westward. The movie also includes the track of several CARTHE drifters (Novelli et al., 2017) that were deployed in the vicinity. Most of the drifters were trapped inside the front. We used the MR and drifter data from this cruise to validate our radar-based near-surface current mapping, see Lund et al. (2018) for details.