ResearchValidation study
Sample: phone-photo canopy closure against a spherical densiometer
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Summary
We compared canopy closure measured with the sample app against a spherical densiometer at 40 forest plots. The two agreed closely: 38 of the 40 paired readings were within ten points of each other. The app read about two points higher than the densiometer on average, and it met the pass threshold.
- App tested
- Sample app, version 1.2
- Compared against
- Spherical densiometer, four readings per plot
- Full study
- Full study (PDF placeholder)
What counts as a pass
The app passes if at least 95% of paired readings fall within ±10 percentage points of the densiometer, and the mean difference is under 3 points.
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Method
Forty plots were placed at random within a second-growth stand of Tsuga heterophylla and Thuja plicata near 49°19′12″N. At each plot centre, one observer took four densiometer readings, one facing each cardinal direction, and averaged them. A second observer then took four upward photos with the sample app at 1.3 m, in the same four directions, within 15 minutes of the densiometer readings.
Agreement was assessed with Bland–Altman analysis: the mean difference between the two methods, and the range within which 95% of differences fall.
Results
| Measure | Value |
|---|---|
| Paired readings | 40 |
| Mean difference, app minus densiometer | +2.1 points |
| 95% limits of agreement | −5.9 to +10.1 points |
| Readings within ±10 points | 38 of 40 (95%) |
The app read slightly higher than the densiometer across the full range of closure, from 41% to 88%. Both parts of the pass threshold were met.
Limitations
All plots were in one stand type under overcast skies, so the results say nothing yet about open woodland or bright sun. The densiometer is itself an estimate, not a true value; agreement with it shows the app reproduces the reference method, not that either is correct.
Sources
- Bland, J. M., & Altman, D. G. (1986). Statistical methods for assessing agreement between two methods of clinical measurement. The Lancet, 327(8476), 307–310.
- Lemmon, P. E. (1956). A spherical densiometer for estimating forest overstory density. Forest Science, 2(4), 314–320.
How to cite
Author, S., & Author, T. (2026). Sample: phone-photo canopy closure against a spherical densiometer [Validation study]. fun.limited. http://fun.limited/research/sample-validation-study/