Center-pivot and line inspection with drones: what you can automate

A 100 ha center pivot has hundreds of meters of pipe, dozens of emitters, several towers with gear motors and tires, and a pump on the other side of the farm. Some part of it fails every year, and the failure is usually spotted late: in a yellowing band of the crop or on the power bill.

This article covers a way to look at the whole pivot at once, from above, and how to combine that with the sensors the pivot already has. It is written for people who run pivots and for those who look after several.

What the aerial image shows

Each type of defect leaves its own mark on the field or on the equipment:

• Clogged nozzle or wrong nozzle size. A drier circular band, concentric with the pivot, at the radius of the faulty emitter. On a mid-day thermal image the band is warmer than its neighbors; on multispectral, NDVI drops there.
• Leak. A puddle or dark patch at the foot of a tower, or a side jet visible in the RGB image while the pivot is running. On thermal, a cold spot.
• Pressure-related sprinkler failure. If pressure drops at the end of the line, the last span applies less water: the outer ring of the circle looks lighter than the rest.
• Misaligned or stopped tower. In the image, the pivot line is no longer straight; in the field, a wedge with a different irrigation depth where the machine sat longer or moved faster.
• Tires and wheel tracks. Deep ruts, flat tires or a stuck tower show up on low-altitude RGB.
• Control panel and cabling. Thermal over the control panel and the pivot center reveals hot connections.

The image doesn’t fix anything. It tells the mechanic where to go, which on a large pivot is half the job.

How often to fly

There is no single rule. What works in practice:

• At the start of the season, before switching on, as an inventory: nozzles, tires, alignment, visible leaks.
• After every significant repair, to confirm the dry band is gone.
• At peak demand, when the pivot runs almost every day and a failure costs more.
• When the sensors flag something, which is the most useful trigger (see below).

An inspection like this, with a light aircraft in visual line of sight, at low altitude and away from people, is usually the lowest-risk kind of operation under drone rules (the open category under EASA in the EU; FAA Part 107 covers commercial flights in the US). Registration and airspace authorization may still be required: check the current rules of your aviation authority.

What the pivot’s sensors tell you before the drone does

A monitored pivot has three numbers on the platform: pump hours (engine hours), flow (a meter on the supply main) and, usually, pressure at the center or at the end of the line. Cross-checking the three, a failure announces itself:

• Flow goes up at the same pressure and the same irrigation program: water is getting out where it shouldn’t. Probably a leak.
• Flow drops at normal pressure: clogged emitters or a partly closed valve.
• Pressure drops and flow goes up: a burst pipe or a large leak.
• The hour meter logs extra hours for the same programmed depth: the pivot is moving slower or has stopped at a tower.

Each of these combinations becomes an alert on the platform. The alert says a problem exists; the flight says where it is. Flying only when an alert fires saves flights and finds the failure while it is still small.

What you can automate

Three things, today, with what we integrate:

1. The route. A pivot flight plan is always the same: a circle at the chosen altitude with the camera pointing down, plus a low pass along the line. Once saved, it repeats without replanning.
2. The comparison. Two images of the same pivot, weeks apart, aligned, with the differences highlighted. A band that appeared is a candidate defect.
3. The link. Each detected anomaly enters the platform as a point with coordinates, tied to the pivot and to the alert that triggered the flight. When the mechanic closes the work order, the point closes with it.

What you can’t automate without a dedicated project: takeoff and landing without a pilot, flights beyond visual line of sight, and diagnosis without someone looking at the image. Drone-in-a-box systems exist for that, and it is the kind of thing we design to order, but it is not an off-the-shelf product, and it requires specific authorization from the aviation authority.

An example cycle

On Monday the flow meter reads 6% above normal for the same irrigation sector, at the same pressure. The platform opens an alert. On Tuesday, a 20-minute flight over the pivot; the thermal image shows a cold patch at the foot of tower 5. On Wednesday, the crew replaces the gasket. On Thursday, flow is back to normal and the alert closes, with the photo and the work order attached to the pivot’s history.

Without the meter, the leak would have been found when the ground at the foot of the tower turned into a mud hole. Without the drone, it would have meant hours of walking along the line.

What to do now

1. Install a flow meter and an hour meter on the pivot if it doesn’t have them. Inspections build on what those two instruments record.
2. Log a baseline flight with the pivot in good shape. That is what later flights are compared against.
3. Set the alert thresholds together with whoever runs the pivot. Flow 6% above normal may be fine in one sector and a defect in another.

If you’d like to discuss a project, talk to one of our engineers.

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Sources: FAO Irrigation and Drainage Paper 56 (application uniformity and efficiency).