How to create a guide file from satellite imagery
The 🛰 Satellite section turns a satellite image into a variable‑rate guide file (prescription map) based on a vegetation index. By comparing different light spectra, satellites let you track biomass growth across a field and apply more or less input where it’s needed.
Where to get the imagery
- Swedish farms — the easiest route is cropsat.se, which creates guide files directly in the browser.
- Other European farms — process an image here in GeoDataFarm. You need to download the band 4 and band 8 raster bands from the EO Browser (powered by Sentinel; free signup), packaged as a ZIP.
The Links row provides quick buttons to cropsat.se, geodatafarm.com and the EO Browser.
Steps
- Select field — choose the field, using Update field list to refresh the list if needed.
- Select index — pick the vegetation index to compute:
- NDVI — the standard normalised difference vegetation index.
- MSAVI2 — a soil‑adjusted index, useful on sparse canopies / bare soil.
- Pick the image date on the calendar. Tick Planned date of usage if you want to tag the guide file with the date you intend to apply it.
- Index value mapping — map index ranges to the output values your machine should apply. The defaults split the index into five bands:
| Index range | Default output |
|---|---|
| 0.1 [0.1–0.2] (10%) | 200 |
| 0.3 [0.2–0.4] (25%) | 180 |
| 0.5 [0.4–0.6] (25%) | 150 |
| 0.7 [0.6–0.8] (25%) | 120 |
| 0.9 [0.8–0.9] (15%) | 100 |
Edit the output values to match your agronomic plan (e.g. more nitrogen where biomass is low, or vice‑versa).
- Select zip file — choose the ZIP containing the Sentinel band‑4 and band‑8 rasters.
- Generate guide file — GeoDataFarm computes the index, applies your mapping and writes the guide file. Use Update graph to preview the index distribution.
Notes
- If the ZIP is missing band 4 or band 8 you’ll get a warning — re‑download both bands from the EO Browser.
- If the chosen day is cloudy there may be no usable data; pick a cloud‑free date.
- The result is a guide file you can load onto your terminal, the same way as a guide file made under 📄 Guide file.