Sport · Turf

NDVI and red-edge analysis for sports turf

Managed turf is a harder surface to read than a crop canopy — and the index most people reach for is the one most likely to mislead them.

What NDVI measures

NDVI — the Normalised Difference Vegetation Index — compares reflected near-infrared light against reflected red light:

NDVI = (NIR − Red) / (NIR + Red)

Healthy chlorophyll absorbs red strongly and healthy leaf structure reflects near-infrared strongly, so vigorous vegetation returns a high value. Stressed, thin or senescent turf returns a lower one. Values run from −1 to +1, with dense healthy grass typically sitting well up the scale.

Why NDVI struggles on good turf

Here is the catch for anyone managing a well-kept sward. NDVI saturates: once the canopy is dense and fully closed, red absorption is already nearly complete, so adding more healthy biomass barely moves the number.

On a sparse arable crop that is not a problem, because the index is working in the part of its range where it is sensitive. On a maintained pitch or a golf green — dense, uniform, closed canopy — a great deal of genuinely useful variation gets compressed into the top of the scale, and the map looks flatter than the turf really is.

Where red edge comes in

The red-edge band sits in the steep transition between red and near-infrared, around 700–730 nm. Because it samples the slope itself rather than the saturated ends, red-edge indices such as NDRE stay sensitive in exactly the dense-canopy conditions where NDVI flattens out.

In practice the two are complementary rather than competing: NDVI for the broad picture and for thin or worn areas, red edge for grading stress across turf that is already in good condition. Reading both is how you see the difference between fine and about to stop being fine.

Reading a pitch

Wear on a sports pitch is not random, and a survey tends to confirm the pattern every greenkeeper already suspects — with the advantage of showing its extent and its progression rather than its existence:

Goal mouths, which take concentrated traffic in a small area.
The centre circle and central training zones, where repetitive drills compound wear.
Shaded margins beneath stands and tree lines, where light limits recovery.
Drainage lines, which can show as either stressed or unusually vigorous strips depending on the season.

The useful output is not that these areas are worn. It is how fast they are changing, and whether an intervention worked.

An illustrated multispectral analysis of a sports pitch: true colour with three zones ringed, NDVI and red-edge maps beside it, the four individual bands beneath, and a summary panel of health classes. — One pitch, read every way at once: true colour, NDVI, red edge, and the individual bands underneath them. The zones ringed on the left are the goal mouth and the central training ground, which is where the wear in the list above tends to collect.

Reading a course

A golf course is a larger and more varied problem: greens, approaches, fairways, rough, trees and water, each with different expectations and different tolerances. A survey flown hole by hole gathers the findings from every pass into a single picture of the course, which is difficult to assemble any other way.

Tree health and water features matter here too. Both influence the turf around them, and both benefit from being read in the context of the terrain they sit on rather than as flat shapes on a map.

A golf green with two bunkers in the Terravect viewer, rendered in true colour: an even carpet of turf with no obvious variation across it. — The same green in the Terravect viewer, from one survey. Dense, healthy turf sits at the top of the NDVI scale, which is exactly where NDVI stops separating it: the green reads as one flat block. The red-edge slope samples the transition rather than the saturated end, and pulls the same ground apart.

The same green rendered as NDVI: the turf reads high on the scale and the green sits as one flat block, while the bunkers drop out of it. — The same green in the Terravect viewer, from one survey. Dense, healthy turf sits at the top of the NDVI scale, which is exactly where NDVI stops separating it: the green reads as one flat block. The red-edge slope samples the transition rather than the saturated end, and pulls the same ground apart.

Making passes comparable

An index value is only meaningful against another index value. Sun angle, cloud cover, sensor calibration and flight altitude all shift readings, and a mowing pass immediately before a flight will change the canopy you are measuring.

Consistency is what turns a sequence of surveys into a trend rather than a set of unrelated flights: the same sensor, comparable conditions, a consistent position in the maintenance cycle, and a shared frame of reference to lay each pass over.

Where Terravect fits

Terravect reads NDVI and red-edge indices across pitches and courses, pinpointing stressed turf zone by zone and laying every finding on a 3D digital twin of the grounds.

Common questions

Questions we get asked.

Why does NDVI saturate on sports turf?

Once a canopy is dense and fully closed, red light absorption is already nearly complete, so additional healthy biomass barely changes the value. On a well-maintained pitch or green that compresses a lot of real variation into the top of the scale, which is why red-edge indices such as NDRE are more useful on turf already in good condition.

What is the difference between NDVI and NDRE?

NDVI compares near-infrared against red. NDRE substitutes the red-edge band, around 700 to 730 nm, which sits in the steep transition between the two. Because it samples the slope rather than the saturated ends, NDRE stays sensitive in dense canopy where NDVI flattens out.

Can a drone survey show pitch wear a grounds team doesn't already know about?

Usually it confirms the pattern rather than revealing it — goal mouths, the centre circle, shaded margins. The value is in extent and progression: how far a worn zone has spread since the last pass, whether a renovation, feed or irrigation change actually worked, and a record of it to take to the committee.

Get in touch

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