Maritime Applications for Small Sats: Observations of ocean waves, currents, tides, and navigational hazards

Small satellites are ideal platforms for ocean observations due to their high pixel resolution (~meters), and high revisit frequency (~hours). The paper will discuss three Maritime applications: (1) Ocean wave spectra from weather to sub-seasonal temporal scales. (2) Nearshore bathymetry and navigational hazards. (3) Internal waves, currents, and tides.

Both single pushbroom images and framing video systems can be used. We focus on video because of its relative novelty on commercial space systems. Four enterprises have deployed video in Earth orbit: Skybox Imaging (2013-2015), Urthecast (2015-2017, Earth-I (2017-), and Planet (2017-).

Video has clear advantages in Maritime observations. Video enables space-time processing methods that invert wave celerity into depth (up to about 20 m), and map surface currents and tides. Or the ocean waves can be filtered out to enhance visibility of navigational hazards below the surface. From motion of surf one can infer changes in the beach morphology. These applications have been implemented with traditional high resolution satellites (WorldView, Sentinel 2). Small sats will enable better temporal sampling of ocean phenomena and at locations further from land. Examples will be presented with video from Skybox Imaging and Urthecast.

The paper will discuss trade-off between resolution, footprint size, image compression, and frame rate; 1-3 fps (vs. 30 fps typical) is adequate in most applications. We explain how and where color bands are useful.

This paper is an update of “Urthecast video imaging from Earth orbit: a new tool for mapping coastal bathymetry,” presented at Coastal GeoTools 2017.