A low-cost integrated sensor for measuring tree diameter at breast height (DBH).

• DBH can be measured accurately in a noncontact mode, at low cost and portability. • Various factors are considered to improve the generalizability of the measurement. • Performance of DBH measurement was improved by the DBH calculation model. The measurement of tree diameter at breast height (DBH) is the basis for estimating forest timber volume, biomass, and carbon fluxes. The traditional contact methods of measuring DBH are time-consuming and labor-intensive. Thus, it is important to realize a low-cost and rapid method for measuring DBH. In this paper, a non-contact method was proposed by integrating passive (a smartphone) and active optical sensors (a laser ranger). With this device, the horizontal distance from the sensor to the tree trunk acquired by the laser ranger and the image of the target tree acquired by the smartphone were collected simultaneously. An autodetection algorithm was employed to identify the tree trunk within the image, and the diameter of the tree was then measured in combination with the horizontal distance based on the photogrammetry principle. The performance of the proposed method was validated using measuring tapes across 371 trees, the main species of which were Italian Poplar (Populus euramevicana) and Pine (Pinus tabuliformis) with diameters ranging from 6 to 51 cm. To investigate the factors that might affect the method, the results were further analyzed under four different conditions, i.e., varied illumination conditions, urban and natural forest conditions and different tree species with varied surface texture features. The results suggested that the measurements using the proposed device were in good agreement with those of the traditional contact method, with an absolute mean error (MAE) of 1.12 cm and RMSE of 1.55 cm. The attraction of the proposed method is that it is low-cost, portable, easy to use and sufficiently accurate. It is also expected that the proposed method can facilitate the measurement of DBH-related canopy structure parameters, such as tree volume, and other parameters, such as tree height, with little adaptation to the current version. [ABSTRACT FROM AUTHOR]