The Mapper is an interactive map viewer for the Sentinel-1 SAR archive. Draw an area of interest, search for the acquisitions that cover it over a date range, and stack the resulting scenes as map layers to compare them through time.
Tip: Backscatter values are stored as gamma-nought × 1000 (uint16, NODATA = 0). The viewer applies a display stretch automatically.
The Search panel is where you define where and when to look, then run the query against the Sentinel-1 archive.
The map-tools row at the top of the panel controls how you mark the area:
| Tool | What it does |
|---|---|
| DRAW AOI | Draw a rectangular area of interest by dragging on the map. |
| RESIZE AOI | Adjust the existing AOI rectangle. |
| MARK POINT | Drop a single point of interest. |
| DRAW POLYGON | Draw a free-form polygon for irregular areas. |
| DELETE | Remove the current AOI / point / polygon. |
The fine-zoom buttons (± in 0.5 steps) and the sync AOI button help you frame the area precisely.
The matching acquisitions are listed in the Results panel. A tile-progress indicator shows loading while scenes render on the map.
Tip: A smaller AOI and a tighter date range return faster and keep the results list manageable.
After a search, the Results panel lists every Sentinel-1 acquisition (STAC item) that covers your area in the chosen date range.
Ascending and descending passes view the ground from opposite sides, so backscatter from the same field can differ between them. For a clean time series, compare scenes of the same orbit direction.
Tip: Add several scenes of the same orbit direction, then use the time slider to flick through them in date order.
The second toolbar row is marked sort and contains only view controls — nothing on that row adds anything to the map.
Date lists in acquisition order, oldest first (the default). Coverage lists by measured AOI coverage, highest first, which is what you want when a long search returns a mix of full frames and swath edges; rows not yet measured sort last, because not yet known is not the same as zero. The active one is highlighted in blue, the same as the orbit filter above it — blue controls change what you see, green controls load layers.
Sorting changes the display only. + Add and + All always work through the acquisitions in date order, so the sort never changes which scenes a click loads.
⭳ CSV — the outlined button at the right of the sort row — downloads what is listed, in the order shown: date, time, orbit, polarisation, measured coverage, how it was measured, whether it was sampled, the number of datasets merged into that day, and the dataset id. The AOI and polarisation are written into the file header.
Coverage of your AOI by each acquisition is something the archive does not record — the Mapper measures it. The CSV is how that leaves the browser, so a choice of dates can be justified or reproduced without re-running the search.
link in the Results header copies a URL that restores the AOI, the date range, polarisation, orbit filter, zoom and the exact set of loaded acquisitions.
Opening such a link re-runs the search — the scene list has to be fetched before any layer can be drawn — and then adds the linked acquisitions. Scenes are remembered by date, not by dataset id, so a link keeps working after a scene is reprocessed. If a date is no longer returned by the search (archived, reprocessed out of the AOI, or the AOI itself was edited), the status line names it rather than restoring silently.
Add ?diag=1 to the URL, and a panel shows the same report mapperDiag() prints to the console: AOI size, the probe window and its pixels-per-degree against the OWS floor, and one line per acquisition with its coverage, how it was measured and any error. copy puts it on the clipboard for pasting into a bug report.
The Layers panel controls everything you've added to the map from the Results list.
When two or more scene layers are loaded, a time slider appears over the map. Drag it (or step it) to move through the acquisitions in date order — an easy way to watch how backscatter changes over a field or water body across the season.
Hover any pixel to read its backscatter value. Remember values are gamma-nought × 1000, so a reading of, say, 1850 corresponds to γ⁰ ≈ 1.85 (before dB conversion). NODATA pixels read 0.
Tip: Pair opacity with the time slider — set a reference scene semi-transparent on top of the stack to see change "bleed through" as you slide.
⭳ PNG in the Results toolbar — beside CSV, because both write a file — exports the frame currently shown as three files:
| File | Contents |
|---|---|
sagris_<date>_<pol>_z<zoom>.png | the SAR frame with the boundary framework over it |
….pgw | ESRI world file — places the PNG geographically |
….prj | the CRS (EPSG:3857) as WKT, so QGIS does not ask |
Drop the PNG into QGIS with the two sidecars beside it and it lands in the right place at the right scale. Your browser may ask permission for multiple downloads.
The image is the tiles already on screen, not a re-render, so what you exported is what you approved. Boundaries are stroked more heavily than on the map — a hairline that reads on a monitor vanishes in a scaled-down figure — with a dark halo so they stay legible over both bright speckle and dark water, and the selected polygon is drawn at two and a half times the normal weight.
Polygons you have just drawn are included even before save drawn — the export is what you see on screen, and an unsaved boundary is on screen. The status line says how many unsaved drawings went into the file. Labelled scratch points are not exported: they are annotation for you, not part of the framework.
Field interiors are never filled — the SAR texture inside a boundary is the data, so the framework is fully transparent. The selected field carries a third, white outer ring on top of the dark halo, so which field the figure is about is unmistakable even where neighbouring boundaries differ in colour.
The date is burnt into the image, bottom-left, with polarisation, orbit and pixel size beneath it. It is on an opaque plate in a corner, so it can be cropped away in one action if the pixels are needed clean; the world file still describes the whole image and the filename repeats the date.
Export works at whatever zoom you are on, including the quarter-zoom steps this map allows: tiles are scaled exactly as on screen and the world file uses the matching resolution.