We group 4,719 locations on a stretch of Japanese coast by how their brightness temperature changed over one day, then put the groups back on the map.
A weather satellite measured 4,719 locations on a stretch of Japanese coast 142 times in one day. If a computer groups the locations only by how their readings rose and fell, without being told where any of them are, do the groups trace the coastline?
Some groups do: put back at their real positions, they look like parts of the coastline. Reveal the basemap and compare.
How to read this figure. In “The computer's view”, each dot is one location. Dots sit close together when their brightness temperature (the temperature the satellite works out from the infrared light it receives) followed similar curves through the day; the computer then split them into k clusters, shown as colours. “The same locations on the map” puts every dot back at its real position, in the same colour. If a colour forms a patch that follows the coast, the daily curves alone carried that information. The arrangements were computed in advance by three methods (Embedding); n_neighbors and Perplexity are settings of those methods.
Clusters are numbered from coldest (C1) to warmest by their average brightness temperature; the number on each button counts its locations. Hover over a button to show only that cluster; click it to hide or show it. With many clusters, neighbouring colours look alike, so use the buttons to tell them apart.
Colour shows each location's brightness temperature in the current scene. The scale is the same for every scene, so a change in colour is a change in value. It spans the 2nd–98th percentile of all values; values beyond it take the end colours.
Press play, or drag the slider, to step through the day's 142 saved scenes; both panels then show each location's value in that scene. Times are the scheduled scan slots in UTC; the satellite scans this stretch of coast about 100 s after each slot begins.
The curve is this location's brightness temperature through the day. Hover over a dot in either panel to preview another location; click it to keep it. Hover over the curve to read single values.