Reading NDVI Patterns: A Guide to Planning Field Checks
The shape of a vegetation pattern can help organise a field visit. It does not identify the cause. Several problems can produce similar shapes, and image artefacts can resemble field variation. Treat each pattern below as a question to investigate.
First check the observation
Read the satellite date, confirm the field boundary and consider cloud or shadow. Compare another suitable date if available, but do not delay an urgent inspection. At 10-metre native resolution, fine strips and small hotspots may not be resolved reliably. Display enlargement does not add ground detail.
Straight stripes
Question to investigate: does the pattern follow a sowing, irrigation or machinery operation?
Compare it with operation records and actual equipment paths. Inspect stand density, soil moisture and crop symptoms on both sides. A stripe near the width of a satellite pixel is particularly difficult to interpret. Do not apply a corrective input merely because a line appears on the map.
Arcs or wedges
Question to investigate: does the pattern coincide with the irrigation layout or a change in management?
Check the relevant equipment, pressure or water distribution where appropriate. Compare soil conditions and crop cover across the pattern. A similar shape can arise from field boundaries or previous land use, so the geometry is a clue rather than confirmation.
A patch in lower ground
Question to investigate: is the patch associated with drainage, ponding, soil differences or uneven establishment?
Inspect after considering recent rain and irrigation. Record standing water, stand and soil observations. If salinity or sodicity is suspected, suitable sampling and local advice are needed. NDVI cannot justify a soil amendment or drainage design by itself.
A patch on only one date
Question to investigate: could cloud, shadow, processing or a recent field operation explain the change?
Compare another date and any available field observations. A disappearing pattern is not proof that there was no real problem: management and weather can also change rapidly. If there are visible symptoms or a farmer report, inspect rather than waiting for the map to settle.
A patch that expands
Question to investigate: is the changing area supported by observations on the ground?
Record its location and compare plants inside, at the margin and outside it. Water distribution, crop development, pests, disease and image conditions may all need consideration. The map cannot determine which explanation applies. Seek local specialist advice when symptoms cannot be identified confidently.
Variation along an edge
Question to investigate: does the satellite pixel include a road, canal, trees or a neighbouring crop?
Check the drawn boundary and compare interior pixels. Also inspect for actual edge effects such as shade, turning areas or different crop establishment. Do not dismiss a real edge problem merely because mixed pixels are possible.
A decline across the whole field
Question to investigate: has the crop matured, been harvested, experienced a management change, or been observed under different conditions?
Record the growth stage and recent operations. Nearby vegetation can provide context, but is not an infallible atmospheric reference: it can change too. A field-wide decline requires interpretation alongside the crop and image dates.
Build a field-specific reference
Save a dated map, your observations and any explanation that was actually verified. Keep unconfirmed explanations labelled as possibilities. Over time, this record helps distinguish recurring patterns from new ones without inventing certainty.
Use the field checklist to compare locations and plan follow-up. Read the methodology for cloud-filtering and summary-value limitations.
Interpretation and references
The map is a scouting aid. Displayed summaries are colour-derived estimates; cloud and shadow may remain after scene filtering. Check how ndvi.us works, and use the field checklist to record observations. Examples and suggested workflows are not verified field trials or guarantees of savings.