[Vineyard & Winery Elf EN](https://help.vineyardelf.com/index.md) / [VineyardElf](https://help.vineyardelf.com/vineyardelf.md) # [Satellite data (NDVI): parcel health from Sentinel-2 imagery](https://help.vineyardelf.com/satellite-data-ndvi-parcel-health-from-sentinel-2-imagery.md) A satellite photographs your parcels every few days, and it costs you nothing. Elf turns those images into a health reading for every parcel and shows how it changes through the season. It does not replace walking the rows, but it tells you which parcel to walk first. You will find the screen in the menu as **Satellite (NDVI)**, under the VineyardElf brand. ## What you need 1. **A free Copernicus account** (European Space Agency). Register at dataspace.copernicus.eu, then open OAuth clients in your user settings, create a client and save the **Client ID** and **Client Secret**. The secret is shown only once. 2. **Credentials in Elf**: Settings, Sensors section, Copernicus block. Enter both keys, click Save and then Test. 3. **Parcel boundaries** drawn in the Parcels and rows module. The satellite computes indices strictly from the outline, so a parcel without a boundary is skipped. After that there is nothing to do. Whenever you open the screen, Elf checks for new images and adds them to the history. ## What the screen shows **The pass selector** at the top lists the days on which the satellite photographed your parcels. Next to it are three figures: the pass date, the average NDVI across the vineyard and the average cloud-free coverage. **The trend chart** is the most important part of the screen. It shows how each parcel changes and which one is drifting away from the rest. A hollow circle marks a day when clouds covered the parcel; such a point is not joined by a line, because it must not be read as a change in the vineyard. You can switch the range between 60 days, the season, the full history and a season-to-season comparison. **The map** overlays the image from the pass date on your parcels, on top of detailed aerial imagery. You can choose the coloured NDVI map, true colour, or the base map alone. The opacity slider reveals the base map so you can get your bearings on the ground. **The parcel card** gathers the figures and ratings: NDVI with its average and range, water (NDWI), moisture (NDMI) and cloud-free coverage. ## How to read the indices **NDVI** reflects the amount of green, active leaf mass. **NDWI** responds to water, **NDMI** to the moisture of the vegetation. A drop in NDMI while NDVI stays flat can be an early sign of water stress. The key rule is: **watch the change, not the number itself**. A satellite pixel is 10 metres across while vine rows sit 2.5 to 3 metres apart, so most of what that pixel sees is the ground between the rows rather than the vines. That is why Elf shows two relative ratings: - **Against this parcel's history** - whether today's NDVI is weaker or stronger than usual for this time of the season in previous years. This needs at least five comparable passes, so at first you will see "not enough history" until you download past seasons. - **Against the other parcels** - the position in the ranking from the same pass and the deviation from the vineyard median. The general rating with fixed thresholds is only an extra, and you can switch it off in the view settings. ## When Elf tells you not to trust it This is what separates an honest tool from a pretty one. Elf flags the situations in which its numbers are a weak basis for a decision: - **Clouds** - when less than half of the parcel is visible a warning appears, and the point on the chart stays hollow. - **A small parcel** - below 0.5 ha the surroundings of the parcel enter the average, so a low reliability label appears. The same applies to narrow parcels. - **Outside the growing season** - the worded ratings disappear, because the satellite is then looking at the cover between the rows rather than at dormant vines. Only the figures remain, with a clear note about what is actually visible. Elf works the window out from the latitude of your parcels, not from the country on your account: roughly mid November to the end of March in the southern hemisphere, mid May to the end of September in the northern one. ## Past seasons and season-to-season comparison On its own Elf reaches 60 days back. To compare this season with earlier ones, use the **Past seasons** panel at the bottom of the screen and choose 1, 2 or 3 seasons. Elf shows the date range, the number of parcels and an estimate of how much of the Copernicus monthly quota it will use. For a few small parcels two seasons is usually a few dozen units out of the 10,000 available per month. You can interrupt the download, and the days already fetched are kept. Once you have two seasons, the parcel card gains a line about NDVI a year ago at the same point in the season, and the chart gains the season-to-season mode. A southern hemisphere season starts on 1 October and is labelled across two years, for example 2026/27; a northern one starts on 1 April and carries a single year. The comparison runs on a shared day-of-season axis, so both hemispheres line up without any setting. ## Vigour zones For parcels of 0.5 ha and up (and wide enough) Elf can compute **vigour zones**: a split of the parcel into three parts by condition, from a 30 day composite. Zones can be exported to a GeoJSON or KML file and opened in QGIS or in a task mapping application. If you also compute zones in the following season, at roughly the same point in it (Elf only pairs windows no more than a month apart in the season calendar), it shows what percentage of the area stayed in the same class. A stable pattern usually comes from the soil, a shifting one more likely from weather or a treatment. At 10 metres per pixel a small parcel holds only a few dozen pixels, so treat zones as a hint about where to look closer, not as a map for a machine. ## Ranking before a heat wave When the forecast for the coming week exceeds the threshold you set (35 °C by default, and 38 °C is worth setting in hot inland regions), a list appears at the top of the screen ranking parcels by the drop in moisture over recent passes. It suggests where to start checking your probes and irrigation. Elf sends no notifications, so the banner is visible only when you open the screen. A parcel gets a value when it has at least two passes visible through the clouds, no more than 45 days apart - after a longer gap the difference would describe the changing season rather than drying out. ## Common questions **What does it cost?** The data is free. A Copernicus account has a monthly limit of 10,000 processing units, and ordinary use of the screen consumes a fraction of it. **Does it work outside Europe?** Yes. Copernicus is a European programme, but Sentinel-2 images the whole world on the same schedule, Australia included, and the free monthly quota is the same wherever your vineyard is. **Why are there no new passes?** Usually clouds. Elf only saves days on which at least one parcel was visible. **Will I see individual vines?** No. At 10 metres per pixel the smallest meaningful object is a parcel of roughly 0.1 ha. **How does Elf know my parcels?** From the Parcels and rows module. After you change a boundary, new passes are computed from the new outline. ## Video: how it works