An X-band radar watching the sea surface in Saco Bay, Maine. Every hour it records a 5-minute movie of the water. This page turns each movie into pictures and numbers anyone can read.
The newest scan, laid over the map. Try the buttons. The coloured image is what the radar picked up; the ๐ก marks the radar and ๐ the Camp Ellis wave buoy, which sits inside the radar's view.
Tap a picture to put it on the map. Newest on the left.
Written automatically from the numbers. It changes as new scans arrive.
Top: how much of the open water bounced the radar signal back (surface roughness). Middle and bottom: waves and wind measured at the Camp Ellis buoy. When the wind picks up, the water gets rougher and more of it shows up on radar. Drag across the chart to zoom; double-click to reset.
Each dot is one hour. If the dots climb from left to right, the radar and the buoy agree.
The average number of moving targets the radar tracks in each scan, by time of day.
Every moving target the radar tracked this week, coloured by speed. Busy lanes show up as bundles of lines.
How much breaking, churning water the radar sees along the shore, in square feet (or square metres), with the tide in the panel above on the same time axis.
How many scans the radar delivered each day. Gaps mean it was offline or being serviced.
When the sea is rough, each patch of water flickers on radar in time with the waves passing through. We time that flicker and compare it with the buoy's wave period. Dots on the dashed line mean a perfect match. Only confident readings are shown.
The antenna spins about once every 1.3 seconds, firing short microwave pulses. "X-band" means the microwaves are about 3 cm long, roughly the size of a wind ripple.
Tiny wind ripples act like millions of little mirrors that send the pulse back to the radar. Bigger waves tilt and hide those ripples, which makes bright and dark stripes. A glassy calm sea reflects the beam away like a mirror, so it looks black.
Each hourly scan stacks 229 sweeps into a 5-minute movie. Things that stay put (land, rocks, moorings) are land; things that move are water and boats.
This page measures every scan: how rough the water surface is, how much it moves, where water is breaking, and what's moving fast. Then it checks those numbers against the wave buoy next door.
A quick guide to each measurement on this page โ no science degree needed.
What it is: The radar antenna spins about once every 1.3 seconds; each turn is one "sweep" โ a single radar picture of everything within about 2.7 km (1.7 miles). About once an hour the radar records a "scan": roughly 229 sweeps in a row, a 5-minute movie of the sea surface.
Why it matters: Watching the same water for 5 minutes lets the radar tell what stays still (land, rocks, moorings) from what moves (waves, breaking surf, boats) โ day or night, in fog or rain.
๐ One scan โ every hour. Gaps in the "Radar diary" chart mean the radar was offline or being serviced.
๐ Here: 982 scans measured so far, over 90 days.
What it is: The share of nearby open water (300โ1,500 m from the radar) that bounces the radar signal back on a typical sweep. The radar's microwaves are about 3 cm long โ the size of tiny wind ripples. Ripples scatter the signal back to the radar, so rough, wind-blown water shows up bright; flat, glassy water reflects the signal away like a mirror and looks dark.
Why it matters: It shows how wind-roughened the whole bay surface is, not just one spot โ a picture between the buoys, at night and in fog. It rises with wind first, and with waves as they build.
๐ Shown as a rank against every scan this radar has taken: Glassy (calmest 15%), Gentle, Choppy, Rough, Wild (roughest 10%). The raw % depends on the radar's settings, so only compare it with this radar โ and it is not a wave height.
๐ Here: a typical scan echoes from 0.9% of the nearby open water; the calmest 15% of scans are under 0.4% and the roughest 10% are over 19.8%.
What it is: How much each spot's radar echo changes during the 5-minute scan. Moving water flickers constantly; land and rocks barely change.
Why it matters: Motion is how the radar maps where the water is active, and it feeds the "Zones" map and the whitewater measurement.
๐ On the Motion map, warm colours = lots of change (waves, surf, boats); cool or clear = steady (land, sheltered water).
What it is: SeaSignals sorts every spot the radar can see into land, open sea, "active" water (bright and moving โ like breaking waves), and shadow (places hidden behind islands or the shore, which the radar cannot see).
Why it matters: The zones decide which pixels count as "open water" for surface roughness and which count as breaking water near the shore.
๐ Shadows are normal: radar travels in straight lines, so it cannot see behind Ram Island or headlands.
What it is: The area of "active" water within 150 m (500 ft) of the shoreline โ mostly breaking, churning surf. Shown in square metres or square feet.
Why it matters: Breaking waves are what move sand and erode beaches and dunes, so more whitewater along the shore means more work being done on the coast. It also tracks surf conditions.
๐ Rises with wave height and changes with the tide: some sandbars and ledges only break at low water. Boat wakes near shore can add a little.
๐ Here: typically 0.42 miยฒ (1.1 kmยฒ); the most so far was 3.3 miยฒ (8.6 kmยฒ).
What it is: Things the radar followed from sweep to sweep during a scan โ usually boats. Speed is in knots (1 knot โ 1.15 mph โ 0.51 m/s).
Why it matters: Shows how busy the bay is, when, and along which routes ("boat highways").
๐ The tracker is automatic, so a track is "probably a boat": occasionally a bird flock, a big wave crest or a buoy swinging on its mooring.
๐ Here: about 3 moving targets per scan on average; fastest so far 42 knots.
What it is: When the sea is rough, each patch of water flickers on radar in time with the waves passing through. Timing that flicker gives an estimate of the wave period โ seconds between wave crests.
Why it matters: If it works, a radar could measure waves over a whole area, not just at a single buoy.
๐ Only shown when the flicker signal is clear enough (quality โฅ 2.2) โ usually in rougher seas. Compare it with the buoy's period: dots on the dashed line mean a perfect match.
What it is: The Camp Ellis wave buoy sits about 700 m (2,300 ft) from the radar, inside its view. Every hour we pair the radar scan with the buoy's wave height and wind, and measure how closely they rise and fall together ("r", the correlation).
Why it matters: If the radar's roughness follows the buoy, we can trust it to describe the rest of the bay where there is no buoy.
๐ r = +1: in perfect step. Around 0.5: clearly related. Near 0: unrelated.
๐ Here: roughness vs. wind at the buoy: r = 0.85 (strongly linked), from 982 matching hours.