Crop water stress shows in canopy temperature before it shows in colour: stressed plants close stomata, stop evaporative cooling and warm up — making a thermal drone an irrigation auditor that sees trouble days before the eye does.
- 640×512Radiometric baseline
- MiddayFor stress and uniformity
- DawnFor drainage and standing water
- HighFull-canopy emissivity
Key takeaways
- Stressed plants close stomata, stop evaporative cooling and warm — canopy temperature is a leading indicator, not a lagging one.
- Blocked emitters, pressure loss and coverage gaps read as warm streaks across an otherwise evenly cooled canopy.
- Radiometric capture is what makes stress rankings comparable across weeks; without it you have images, not a trend.
- Full canopy has high, friendly emissivity. Bare soil mixed into the frame complicates readings considerably.
On this page
Irrigation Uniformity Audits
Blocked emitters, pressure loss and coverage gaps appear as warm streaks and patches across an otherwise evenly cooled canopy. The mechanism is direct: irrigated plants transpire and cool, under-watered ones do not, and the pattern of warmth maps the pattern of delivery.
Fly midday under irrigation-on conditions for maximum signal. This is the opposite of most thermal work, which avoids solar loading — here the solar load is what drives the evaporative cooling difference you are measuring, so you want it. A dawn flight over the same field shows almost nothing.
The finding translates directly into maintenance. A warm streak following a lateral is a pressure or blockage problem at a known location, and the deliverable is a map an irrigation technician can walk. That directness is why irrigation audits tend to be the fastest-payback thermal work on a farm.
Water Stress and Scheduling
Canopy temperature relative to air temperature is an established stress index. The relationship is physiological rather than empirical: a plant with adequate water transpires and runs cooler than the surrounding air, and one that has closed its stomata to conserve water loses that cooling and rises toward or above air temperature.
Repeated thermal passes rank blocks by stress and inform irrigation priority. The value is comparative — this block is more stressed than that one today — rather than absolute, which is fortunate because absolute canopy temperature depends on conditions that change hourly.
Radiometric capture makes the numbers comparable across weeks. Without calibrated temperature data, two surveys flown a fortnight apart produce images whose display scales have shifted independently, and the comparison is meaningless. Radiometric vs non-radiometric covers why the decision has to be made at purchase, and radiometric measurement on UAV payloads covers the calibration chain.
Record air temperature with every flight. The index is canopy temperature relative to air. A survey without an air temperature reading cannot be converted into a stress figure afterwards, and the flight has to be repeated.
Beyond the Crop
The same aircraft covers infrastructure that has nothing to do with canopies. Pump and motor hotspots read directly — a bearing running hot is the same finding on a farm as in a substation. Leaking mains show as cool wet ground, and clogged filters show as pressure-driven temperature differences across the assembly.
And the same payload covers livestock counts and night checks in mixed operations: one aircraft, two departments. Livestock monitoring with thermal drones covers night counts, stray search and calving checks, all of which run on the same 640×512 channel bought for irrigation work.
That dual use is often what justifies the purchase. An irrigation-only case has to compete with soil moisture sensors; an irrigation-plus-livestock case competes with sensors and hours of quad-bike time, which is a much easier argument. The precision agriculture application page covers the programme view.
Payload and Timing Notes
Radiometric 640×512 is the working baseline, and the thermometry version of the MV-2P fits most farm aircraft at 130 g with the most sensitive published NETD in the line.
| Task | Best window | Why |
|---|---|---|
| Irrigation uniformity | Clear-sky midday, irrigation on | Solar load drives the evaporative cooling difference |
| Crop water stress | Clear-sky midday | Stress index compares canopy against air temperature under load |
| Standing water and drainage | Dawn | Water’s thermal mass shows against cooled soil |
| Drainage tile lines | Early morning after rain | Moisture contrast is at its strongest |
| Pump and motor checks | Any time under load | Resistance and friction heating are load-driven, not solar |
| Livestock counts | After full dark | Animals settled, solar loading dissipated |
Emissivity of a full canopy is high and friendly — dense vegetation behaves close to a blackbody, which makes readings well-behaved. Bare soil mixed into the frame complicates matters, because soil has different emissivity and heats differently, so early-season fields with visible ground between rows are harder to interpret than closed canopies. Emissivity in drone thermography covers the correction.
What Thermal Does Not Tell You
Thermal reports water status. It does not report why the water status is what it is, and conflating the two produces bad agronomy.
A warm block might be under-irrigated, or it might be a different variety, a shallower soil, a root disease, or a compaction layer restricting uptake. The thermal survey narrows a field to the blocks worth investigating, and someone with a soil auger and agronomic judgement establishes the cause. That is a genuine and valuable narrowing — it is not a diagnosis.
Nor does thermal replace multispectral. The two answer different questions and the sensible programmes run both where budget allows. Where it does not, water-limited operations get faster payback from thermal because water is the binding constraint they can actually act on.
Related reading
- Radiometric Temperature Measurement on UAV Payloads
- The Thermal Image Processing Pipeline
- Livestock Monitoring with Thermal Drones
- Radiometric vs Non-Radiometric Thermal
- Emissivity in Drone Thermography
- 256×192 vs 640×512 Resolution
- What a Thermal Inspection Report Should Contain
- Drone Roof Moisture Surveys
- MV-2P — 640×512 thermal at 130 g
- MV-2M — 110 g dual-sensor micro pod
- OP-90A — zoom, thermal and ranging
- Precision Agriculture Thermal Drones
FAQ
Thermal or multispectral for agriculture?
Complementary rather than competing. Multispectral tracks chlorophyll and vigour; thermal tracks water status and physical irrigation faults. Water-limited operations get faster payback from thermal, because water is usually the constraint they can act on this week. Where budget allows both, they answer different questions and a programme running the two together sees more than either alone.
Can thermal find drainage tile lines?
Often, at the right moisture contrast — early morning after a rain event is the classic window. The lines show because soil above a drain dries and warms differently from the soil beside it. The contrast is transient, so the timing is narrow: too soon and everything is uniformly wet, too late and the difference has equalised.
Why fly irrigation surveys at midday when most thermal work avoids the sun?
Because here the solar load is the driver of the signal rather than a contaminant. Irrigated plants transpire and cool under sun; under-watered ones cannot, and the difference between them is what you are mapping. Fly the same field at dawn and the evaporative cooling difference has not developed, so the pattern you came for is simply absent.
Questions about the technology? Talk to our engineers — we reply within 2 business days.