The method
A calibration, start to finish.
Water-sensitive paper has been the field standard for decades. What has been missing is a way to read a whole card line consistently, keep the result, and compare it with the last time. That is the whole idea.
Step zero
What the card tells you.
Water-sensitive paper stains where a droplet lands. The size of each stain relates to the size of the droplet that made it, and the count and spread of stains across the card describe the deposit at that point in the swath.
Read one card and you know about one point. Read a line of cards across the swath and you have the pattern — which is what determines whether the field gets an even application.
Card line, two ways
Perpendicular to the wind
The standard pattern test. Shows lateral displacement — how far the wind moved your pattern sideways, and what that does to the swath you can actually use.
Parallel to the wind
Shows coverage flying into or with the wind — a different question, and the app keeps the two apart so a headwind pass is never compared with a crosswind pass.
Five steps, plus one
In the field.
- 01
Lay the cards
Water-sensitive paper across the swath, perpendicular or parallel to the wind. The app records the layout and which card sat where.
- 02
Fly the pass
Fly it the way you actually spray. Enter aircraft, delivery system, rate, speed, height and the weather at the time.
- 03
Photograph each card
Photograph the cards with a calibrated camera. Analysis runs on the device — full-resolution photos are never uploaded.
- 04
Read the pattern
Deposition profile, CV%, uniformity, droplet spectrum, coverage and drift risk — for the swath you actually flew.
- 05
Act on it
The optimiser shows the swath spacing that matches your pattern, and what the numbers would be if you flew it. Then save, print or share.
- 06
Truth-test the changeOptional
Prove it. Fly a second pass with exactly one variable changed and the report puts the two passes side by side — so you know whether the change earned its place.
Step 06 · optional
Change one variable. Measure what it did.
The analysis tells you what happened and the optimiser tells you what it expects to happen. A Truth Test closes the gap between the two: fly it again with a single setting changed and find out whether the change actually helped.
Save a pass, choose Conduct a Truth Test Pass, and select the variable to change. Everything else — aircraft, delivery system, card layout, every other setting — is locked to Pass 1, so whatever moves in the results moves because of your change and not because half a dozen variables shifted at once. The app takes you straight to the screen where that change is made, then you fly and photograph as normal.
The report comes back as a comparison — Pass 1 against Pass 2, with the setting you changed stated at the top — and the saved record stays linked to the pass it was tested against, so the pair still makes sense next season.
One variable per test
- Swath
- Rate
- Target droplet size (VMD)
- Flight speed
- Altitude
- Drift reduction agent
- Tank-mix products
Changing the tank mix or adding a drift-reduction agent counts as one change too — the app treats the whole mix as a single variable.
One honest caveat: the app locks your settings, not the weather. Each pass records its own conditions, so check those before you credit a result to the change rather than to a dropping wind.
Is a tighter swath really better?
The optimiser says 30 ft; you suspect 25. Fly it at 25 and compare the CV% you measure.
Is the DRA earning its place?
Identical pass, mixed with and without. Watch what it does to droplet size and drift risk.
Does slowing down fix the pattern?
Drop the speed by 5 and see whether uniformity moves enough to be worth the extra time in the air.
The part most tools skip
Calibrate the camera, not just the sprayer.
Phone cameras sharpen, denoise and adjust contrast. Left unchecked, that means two phones photographing the same card produce two different droplet readings — and neither one is wrong in a way you could spot by eye.
Aerial Cal has a one-time camera calibration against a printed reference sheet with known stain sizes. Once your phone is calibrated, its numbers are comparable with your own past passes and with everyone else's. It is also the reason the Community Library is worth reading: an uncalibrated device cannot contribute to it.
Why it matters
- Comparable over timeA pass in June and a pass in August measured the same way.
- Comparable between operatorsThe community pool only means something if everyone measured the same way.
- DefensibleA report you can hand to a customer with the method behind it.
Reading the report
What the numbers mean.
The full version of this lives inside the app, next to the figures themselves.
- VMDVolume median diameter
- The droplet size that splits your spray volume in half — half the volume is in droplets bigger than this, half in smaller. It is the single number that drives both drift risk and coverage, and it is why a drift-reduction agent changes your whole result.
- CV%Coefficient of variation
- How much the deposit varies across the swath. Lower is flatter. It is the number that decides your spacing: a pattern with a high CV needs more overlap to even out.
- UniformityPattern uniformity
- The same idea read the other way round — how consistent the composite pattern is once adjacent passes overlap.
- CoveragePercent area covered
- How much of the card the spray actually wetted. High coverage with large droplets and low coverage with fine droplets are very different situations, which is why it is never read alone.
- Effective swathThe spacing your pattern supports
- Not the boom width and not the brochure figure — the spacing at which your measured pattern overlaps into an even composite.
- Drift riskFines fraction against conditions
- Rated from your droplet spectrum together with the temperature, humidity and wind you entered for that pass.
All outputs are computed estimates. Accuracy depends on photo quality, camera calibration, card handling, weather, spray solution and equipment. Verify before you act on them.