Synergistic surface current mapping by spaceborne stereo imaging and coastal HF radar

Abstract

[1] Well validated optical and radar methods of surface current measurement at high spatial resolution (nominally <100 m) from space can greatly advance our ability to monitor earth's oceans, coastal zones, lakes and rivers. With interest growing in optical along-track stereo techniques for surface current and wave motion determinations, questions of how to interpret such data and how to relate them to measurements made by better validated techniques arise. Here we make the first systematic appraisal of surface currents derived from along-track stereo Sun glitter (ATSSG) imagery through comparisons with simultaneous synoptic flows observed by coastal HF radars working at frequencies of 13.9 and 24.5 MHz, which return averaged currents within surface layers of roughly 1 m and 2 m depth respectively. At our Tsushima Strait (Japan) test site, we found that these two techniques provided largely compatible surface current patterns, with the main difference apparent in current strength. Within the northwest (southern) comparison region, the magnitudes of the ATSSG current vectors derived for 13 August 2006 were on average 22% (40%) higher than the corresponding vectors for the 1-m (2-m) depth radar. These results reflect near-surface vertical current structure, differences in the flow components sensed by the two techniques and disparities in instrumental performance. The vertical profile constructed here from ATSSG, HF radar and ADCP data is the first to resolve downwind drift in the upper 2 m of the open ocean. The profile e-folding depth suggests Stokes drift from waves of 10-m wavelength visible in the images. Citation: Matthews, J. P., and Y. Yoshikawa (2012), Synergistic surface current mapping by spaceborne stereo imaging and coastal HF radar, Geophys.

Monitoring Intense Oceanic Fronts Using Sea Surface Roughness: Satellite, Airplane, and In Situ Comparison

“…The complementary use of the NRCS ( σ in our notations) of the instrument at 250 m resolution should help reconstructing currents at a resolution higher than 20 km (see Morrow et al., 2019, their Figure 7). Similar reconstruction could be performed as well on the absolute currents provided by the future Wind and Current Mission (WaCM) based on the Doppler scatterometer concept (Rodríguez et al., 2018) or on the absolute currents provided by any other technique (e.g., along track stereo imagery, Matthews & Yoshikawa, 2012).…”

“…More recently, Ohlmann et al. (2017) documented fronts and eddies with convergence/divergence and cyclonic vorticity about 5 to 10 f over 300 m. Matthews and Yoshikawa (2012) used satellite along‐track stereo imagery to calculate surface displacements of slicks between two consecutive images. Their results indicated current fronts less than 100 m wide, but no in situ measurements could confirm those values.…”

Sunglint images of current gradients at high resolution: Critical angle and directional observing strategy

“…Satellites using different cameras at different zenith angles have proven very useful by providing time sequences of sunglint images (e.g. Matthews and Yoshikawa, 2012). Due to the bistatic nature of sunglint measurements, those satellites can also provide a multi-angle geometry favorable to directional mss retrieval.…”

Atmospheric boundary layer rolls: Quantification of their effect on the hydrodynamics in the German Bight

“…As a result, the next challenge is to investigate whether these BLRinduced oceanic responses can be observed directly. Several techniques described in the recent literature (Romeiser et al [2010] ; Matthews and Yoshikawa [2012] (which is a recent paper using very high-resolution HF radar)) hold promise in this regard. However, any attempt to resolve this important issue will require careful event selection, most likely from within a region of little or no tidal flow.…”