A Comparative Analysis of Phytovolume Estimation Methods Based on UAV-Photogrammetry and Multispectral Imagery in a Mediterranean Forest

Management and control operations are crucial for preventing forest fires, especially in Mediterranean forest areas with dry climatic periods. One of them is prescribed fires, in which the biomass fuel present in the controlled plot area must be accurately estimated. The most used methods for estimating biomass are time-consuming and demand too much manpower. Unmanned aerial vehicles (UAVs) carrying multispectral sensors can be used to carry out accurate indirect measurements of terrain and vegetation morphology and their radiometric characteristics. Based on the UAV-photogrammetric project products, four estimators of phytovolume were compared in a Mediterranean forest area, all obtained using the difference between a digital surface model (DSM) and a digital terrain model (DTM). The DSM was derived from a UAV-photogrammetric project based on the structure from a motion algorithm. Four different methods for obtaining a DTM were used based on an unclassified dense point cloud produced through a UAV-photogrammetric project (FFU), an unsupervised classified dense point cloud (FFC), a multispectral vegetation index (FMI), and a cloth simulation filter (FCS). Qualitative and quantitative comparisons determined the ability of the phytovolume estimators for vegetation detection and occupied volume. The results show that there are no significant differences in surface vegetation detection between all the pairwise possible comparisons of the four estimators at a 95% confidence level, but FMI presented the best kappa value (0.678) in an error matrix analysis with reference data obtained from photointerpretation and supervised classification. Concerning the accuracy of phytovolume estimation, only FFU and FFC presented differences higher than two standard deviations in a pairwise comparison, and FMI presented the best RMSE (12.3 m) when the estimators were compared to 768 observed data points grouped in four 500 m2 sample plots. The FMI was the best phytovolume estimator of the four compared for low vegetation height in a Mediterranean forest. The use of FMI based on UAV data provides accurate phytovolume estimations that can be applied on several environment management activities, including wildfire prevention. Multitemporal phytovolume estimations based on FMI could help to model the forest resources evolution in a very realistic way

Editorial for Special Issue “UAV Photogrammetry and Remote Sensing”

The concept of Remote Sensing as a way of capturing information from an object without making contact with it has, until recently, been exclusively focused on the use of earth observation satellites [...

Evaluation of Electrostatic Spraying Equipment in a Greenhouse Pepper Crop

Greenhouse vegetable production is of great importance in southern Europe. It is a cultivation system characterised by a high planting density and environmental conditions that favour the development of pests and diseases. Although alternatives to chemical pest and disease control have been used over recent years in greenhouse crops, it is still mostly plant protection products that are used to protect crops and prevent crop losses. Hand-held spraying equipment is mainly used to apply plant protection products to this type of crop. This equipment is technologically basic, offering low deposition efficiency in the plant canopy, high losses to the ground, and a high risk of worker exposure. In this context, it is important to utilise technologies that reduce the problems associated with using the conventional hand-held sprayers in greenhouses. This study evaluated the deposition and uniformity in the plant canopy and the losses to the ground when applying plant protection products with an electrostatic hand-held sprayer; the results were then compared with applications carried out using a conventional hand-held sprayer. For this purpose, a colorimetric method has been used based on the application of a tartrazine solution. The tests showed that the electrostatic spraying equipment increased the plant canopy deposition by 1.48 times that of the hand-held spray gun, resulting in a 48% reduction in the application rate. There was also a 1.78-times increase in deposition on the underside of the leaves and a 36.36% reduction in losses to the ground. In general, the electrostatic hand-held sprayer improves the effectiveness of the plant canopy deposition and reduces losses to the ground compared to the hand-held spray gun commonly used in pest and disease control