Understanding Swath Width
The swath, resolution and revisit trade-off
Every imaging mission balances three competing goals: how wide an area it sees (swath), how finely it resolves detail (ground sample distance), and how often it returns to a spot (revisit time). Because a detector array carries a fixed pixel count, widening the swath spreads those pixels over more ground and coarsens resolution — but it also shortens revisit, since fewer passes are needed to cover everywhere. Designers pick a point on this curve to suit the task, from continental weather maps to a single building.
| Sensor | Swath width | Resolution | Typical role |
|---|---|---|---|
| VIIRS (Suomi NPP) | 3,040 km | 375–750 m | Daily global cover |
| MODIS (Terra/Aqua) | 2,330 km | 250–1,000 m | Daily global cover |
| Sentinel-3 OLCI | 1,270 km | 300 m | Ocean & land colour |
| Sentinel-2 MSI | 290 km | 10–60 m | Land monitoring |
| Landsat 8/9 OLI | 185 km | 15–30 m | Land imaging |
| SPOT 6/7 | 60 km | 1.5–6 m | Regional mapping |
| WorldView-3 | 13 km | 0.31 m | High-detail tasking |
What determines swath width
For a sensor looking straight down, the swath is roughly twice the altitude multiplied by the tangent of half the field of view, so both a wider optical field and a higher orbit broaden the strip — though Earth's curvature complicates this for very wide swaths. Most modern optical satellites use a push-broom design: a fixed linear array of detectors laid across-track that records a continuous ribbon as the spacecraft flies forward. Older instruments used a whisk-broom scanning mirror sweeping side to side. Either way, the practical limit is the optics, detector count and the distortion that grows toward the swath edges, where the viewing angle steepens and pixels smear.
SAR: a swath you can change
Synthetic-aperture radar (SAR) satellites are unusual in trading swath for resolution electronically, by steering the radar beam rather than being fixed at launch. Stripmap mode holds the beam steady for a narrow, sharp strip; ScanSAR sweeps it across several sub-swaths to widen coverage at coarser resolution; spotlight mode dwells on one small patch for the finest detail of all. Europe's Sentinel-1, for example, images most land in a 250 km Interferometric Wide swath but widens to 400 km over oceans and ice.
| Sentinel-1 mode | Swath | Resolution |
|---|---|---|
| Stripmap | 80 km | 5 × 5 m |
| Interferometric Wide (IW) | 250 km | 5 × 20 m |
| Extra-Wide (EW) | 400 km | 20 × 40 m |
| Wave | 20 × 20 km | 5 × 5 m |
Swath width, orbit and global coverage
To build seamless global mosaics, Earth-observation satellites almost always fly in Sun-synchronous, near-polar orbits, so each swath lays down an evenly-lit strip as the planet turns beneath. The narrower the swath, the more orbits — and days — pass before those strips overlap enough to cover everywhere. That is why high-resolution satellites either accept long revisit gaps or fly as large constellations to close them. Adjacent passes are planned to overlap slightly so no gaps open at the swath edges.