The chart

A paddy season, in one curve.

NDVI (Normalised Difference Vegetation Index) is a number between zero and one that says how leafy a square of land is. Plot it month-by-month and a paddy season draws itself: flooded planting low, vegetative high, mature peak, harvest dip, fallow back to baseline. Abandoned paddy never draws that curve. It is the absence we look for.

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Active paddy (seasonal rhythm)

Inactive paddy (flat trace)

Four phases the satellite can see, and the one phase it can't.

01 · Flooded

Planting

Months 1–2 · NDVI ≈ 0.20

Standing water, freshly transplanted seedlings. The pixel looks dark and wet to the satellite.

02 · Vegetative

Growing

Months 2–3 · NDVI 0.45–0.65

Tillering and canopy closure. NDVI climbs sharply as chlorophyll fills the field.

03 · Mature

Peak

Months 3–4 · NDVI ≈ 0.75

Full canopy, ripening grain. The seasonal high. If a field never reaches this, the model flags it.

04 · Harvest

Drop

Months 4–5 · NDVI ≈ 0.30

Cutting, drying, removal. The signal collapses fast, then the cycle resets.