Earth, seen
through its echo.
Cameras need sunlight and clear skies. Radar brings its own light. NISAR, the joint NASA–ISRO satellite, sends microwave pulses through cloud, smoke, rain and night, and listens for the echo. When the ground changes, the echo changes. This is the story of seven places whose echo changed: a flood, a drying lake, a mountain hazard, a wildfire, a volcano, a melting ice cap and a glacier.
How radar sees change
NISAR records two echoes per pass: HH (sent and received horizontally) and HV (sent horizontally, returned vertically). Each surface answers in its own way, and every layer in this app is built on one of these six rules.
Three kinds of statement, never mixed
Every sentence in a chapter wears one of these styles, so you always know what the radar showed and what is our reading of it.
Numbers computed from the data shown here; its source is unverified. Solid frame.
Reports from agencies and news, linked to their source. Neutral frame.
What we think explains the change. Could be wrong. Dashed frame.
Natural or human?
The radar cannot see people, but it can see what they do. Crops greening up and being harvested change the HV echo on cropland on a farming calendar, while floods, fire and ice follow their own. Each bar is the changed area in one place, coloured by the proposed driver; grey hatching is what we refuse to guess.
What the radar cannot tell us
An echo is evidence, not an answer. These are the limits that apply everywhere in this story; each chapter lists its own as well.
What NISAR makes possible next
Free, open data, all of it
NISAR is the measurement. Every other dataset only adds context (land cover, terrain, tree height) and is named wherever it is used. Every source below is free to download, and the processing code is open source.