Monsoon cloud over one Vidarbha field: one clear view in 20 passes

How often did the satellite see the field in the monsoon?

Between 21 June and 2 September 2026, Sentinel-2 passed over one 3.2-acre field near Katol, Nagpur district, 20 times. The whole field was clear on one pass, 14 July 2026. Between 14 July and 7 September, 55 days, no pass gave a usable view of the field, although 13 passes went over it.

Over the whole year the picture is different. From 7 October 2025 to 12 October 2026 there were 91 passes and 56 were clear; from October 2025 to May 2026, 46 of 56 passes were clear. The monsoon, not the satellite, decides how often a field can be seen.

Month by month

A pass counts as clear only when at least 90 per cent of the field is usable after the cloud and shadow mask. Three clear-looking readings that fell far below their neighbours were set aside as suspected haze and are counted separately.

Why is the cloud figure for a whole image a poor guide to one field?

Each Sentinel-2 image tile covers a wide area of countryside and comes with one cloud percentage for the whole tile. This field is 129 pixels of 10 m inside it. On 21 December 2025 the image was 47.5 per cent cloud and the field was fully clear. On 5 January 2026 the image was 1.6 per cent cloud and none of the field was usable. On 27 September 2026 the image was 10.6 per cent cloud and the field was still not usable.

So VarshaKrishi checks cloud and shadow on the field's own pixels, pass by pass, instead of trusting the image-wide figure.

What does a weekly message say in weeks like these?

It says that the field could not be seen, instead of guessing. If a field has no clean optical pass for 15 days in the monsoon, its state switches to radar only: standing water and the growth trend, never a stress call of the kind an optical image would support. The message still goes out every week, so silence never stands for a healthy field.

VarshaKrishi is testing before its first season: no farmer receives these messages yet. The rules above are the published rules for when it does.

What radar adds, and what it cannot

Sentinel-1 is a radar satellite that images the ground day and night regardless of the weather, so cloud does not hide the field from it. Radar does not measure leaf greenness the way an optical image does, which is why VarshaKrishi uses it in cloudy weeks only for standing water and the growth trend.

Check it yourself

Every pass in this article is a row in the open data file, with the image identifier, the image-wide cloud figure, the usable share of the field and the field's greenness (NDVI). The file is free under CC BY 4.0, and the method is open source, so anyone can rebuild the same series for this or any other field.

Download the CSV