Estimating tree height using low-cost UAV

Precision agriculture (PA) is defined as an agricultural management based on the observation, measurement, and response of a set of quantitative and qualitative variables that affects agricultural production. The first step in the approach to precision agriculture is, therefore, the acquisition and collection of data from optical, multispectral, geophysical sensors, etc. aimed at obtaining knowledge and monitoring of the crop. In recent years UAVs are assuming an important role in precision agriculture. The possibility of mounting RGB, multispectral, LiDAR sensors on them make these systems fast, accurate, and usability compared other geomatic methods. In this study, we focus on a very low-cost UAV system to assess individual tree height and generate 3D Model and orthophoto of the study area. We used the DJI Mini2, a low-cost UAV that can be used without a flight rating and without restrictions due to its light weight of only 250 grams. The case study where the survey was performed is an agricultural area of about 1 hectare, where are some fruit trees and a small vineyard. The area was selected because it contained both tall and small trees. The study concerned the influence of the relative flight altitude and therefore of the GSD of the images on the extraction of the dimensional data of the trees. From the results obtained, it can be stated that the flight altitude has certainly more influence on the measurement of small tree (around one meter tall) compared to tall ones (around 4 m).