How to see a satellite image of your own field for free: Copernicus Browser, NASA Worldview and ISRO Bhuvan

Which free tools show my field?

Three free tools: Copernicus Browser, NASA Worldview and ISRO's Bhuvan. For a single field, Copernicus Browser is the right one, because it serves 10 m detail from the European Sentinel-2 satellites.

The main layers that NASA Worldview shows (MODIS) have 250 m pixels. One pixel is then about 15 acres (250 m by 250 m is 62,500 square metres). That is good for the weather over a district, not for one field. Bhuvan is the Indian government (ISRO) map and satellite viewer; it is useful for finding and looking at your field. We have not checked the dates of its images, so do week-to-week comparisons in Copernicus Browser.

How do I find my field in Copernicus Browser?

The words on the screen change from time to time, but the steps are:

• Open browser.dataspace.copernicus.eu. On the welcome screen choose 'Log in' (a free account) or 'Use anonymously'. An account unlocks extras such as timelapse.
• Type your village in the search box at the top right and zoom in until you recognise your field and the road beside it.
• In the Visualise tab on the left, Sentinel-2 L2A is already selected and a 30 per cent cloud limit is already applied.
• Pick a date. Choose a recent one with no cloud, and open the dates before and after it as well.
• Pick a layer: first True color (the picture as the eye sees it), then NDVI (the greenness layer) and, if your list has it, false colour (infrared). Layer names can look slightly different.
• Draw a polygon around the field and compare it across other dates.

What does one 10 m pixel mean in acres?

A Sentinel-2 pixel is 10 m by 10 m, which is 100 square metres. One acre is about 4,047 square metres, so a pixel is about 0.025 acre and one acre is about 40 pixels. One guntha is about 101 square metres, so a pixel is almost exactly one guntha. One hectare is 100 pixels.

A square one-acre field is about 64 m across, roughly 6 pixels wide. The edge pixels blend with the road or the bund, so only about 19 pixels are pure field. In an orchard planted 6 m by 6 m, one pixel covers about 2.8 trees' worth of area: part tree, part ground between the trees. All of this is our arithmetic.

How do I pick a good image and date?

Choose an image without cloud. Cloud or its shadow over the field gives a wrong greenness number. The European Space Agency says two Sentinel-2 satellites together pass over the same place about every five days. But in the monsoon (June to September), cloud can leave you without a clean image for weeks.

Remember that the image is not 'today'. It is from the last pass, often a few days old. A live image is not available in the free tools.

What does a satellite image show, and not show?

It shows whether a field is green or bare; whether a strip of the field differs from the rest; whether greenness rose or fell compared with recent weeks. It does not show a single tree, the name of a disease, pests, or a fertiliser shortage. In small fields and near bunds the pixels blend, so the numbers are less reliable.

VarshaKrishi's weekly message does this for you: has your orchard's greenness changed from the last image, with the date and the cloud situation. The decisions remain yours and the KVK's.