Find and measure vessels in Sentinel-1 radar, in your own browser. The satellite data is fetched straight from the archive by this page, so nothing about where you look reaches my server — though the box you draw does reach Microsoft, whose archive serves the radar, and the basemap tiles come from OpenStreetMap.
Not for navigation or targeting. Estimates from 10 m radar pixels. A contact is a bright thing on the water, and the class is a guess from its shape. This page has no AIS, so it can never confirm what a vessel actually is.
What you are looking at. Sentinel-1 is a radar satellite, so it makes its own illumination and sees through cloud and darkness. Steel hulls are corner reflectors and come back far brighter than water, which is what makes ships findable at all. The image is gamma0 backscatter in decibels, not a photograph.
How a contact is found. A two-parameter CFAR: for every pixel, measure the sea in a box 1.2 km across with a 510 m hole punched in the middle (so the ship cannot contaminate its own background), then keep pixels five standard deviations above that. Terrain is masked out first by area, because land is separable from ships by size and not by brightness. Near the shore the bar rises to 5.5 sigma, because surf is a few dB over the sea and a hull is twenty.
How it is measured. Length is the along-axis spread of the bright core. Beam is the contiguous cross-section at each station along the hull, which matters: a bright ship throws a starburst of sidelobe flare, and measuring across the whole blob reported 46 m hulls at 158 m. Every beam is quoted with a real plus-or-minus, because at 10 m pixels it deserves one.
What this is not. It is a preview of a desktop tool, not the tool. Missing here: AIS correlation (the only thing that can confirm what a vessel is), video and contact-card export, tiling for areas bigger than about 1.4 megapixels, cross-pass persistence, and the charted-water veto that tells a breakwater from a hull. Sentinel-1 RTC is also only processed where a terrain model exists, so there is no mid-ocean coverage at all.
What it cannot do. It cannot tell you a ship is military. A flight deck is a flat plate, so it mirrors radar away rather than back, and twelve passes over the carrier piers at Norfolk turned up nothing wider than 32 m. The desktop tool does not answer that question either — it just narrows it, using AIS asymmetrically: a hull broadcasting its own name and dimensions is near-certainly civilian, while silence is only suspicion, because a warship and a fishing boat with the set switched off look the same.