Modeling the Response of Black Walnut -dominant Mixed Hardwoods to Seasonal Climate Effects with UAV-based Hyperspectral Sensor and Aerial Photogrammetry

The development of compact sensors in recent years has inspired the use of UAS-based hyperspectral and aerial imaging techniques for small-scale remote sensing applications. With increasing concerns about climate change, spectrally-derived vegetation indices (VIs) have proven useful for quantifying stress-induced vegetation response. The goal of this study was to develop predictive models and assess methodology for modeling the biological response of a black walnut -dominant mixed hardwood stand to seasonal climate events using UAV-based hyperspectral remote-sensing. The derived VIs were evaluated against the means of four seasonal measures of climate calculated for a two-week period prior to the flight date. A best subsets regression was used to create best fitting linear regression models according to Bayesian Information Criterion (BIC). The highest-ranked model for total precipitation had an AdjR² of 0.0839 and RMSE of 0.0827 inches. The highest-ranked model for maximum air temperature had an AdjR² of 0.9922 and RMSE of 0.5485 °F. The highest-ranked model for average air temperature had an AdjR² of 0.9987 and RMSE of 0.2256 °F. The highest-ranked model for total solar radiation had an AdjR² of 0.9961 and RMSE of 0.06405 MJ/M². The results indicate that select VIs measured at the canopy level may be useful in estimating the response to at least some measures seasonal climate. The proposed regression models could help local researchers and landowners in making short-term management decisions, as well as further our understanding of climate-induced tree stress for maintaining sustainable forests in Missouri

Individual tree-based forest species diversity estimation by classification and clustering methods using UAV data

Monitoring forest species diversity is essential for biodiversity conservation and ecological management. Currently, unmanned aerial vehicle (UAV) remote sensing technology has been increasingly used in biodiversity monitoring due to its flexibility and low cost. In this study, we compared two methods for estimating forest species diversity indices, namely the spectral angle mapper (SAM) classification approach based on the established species-spectral library, and the self-adaptive Fuzzy C-Means (FCM) clustering algorithm by selected biochemical and structural features. We conducted this study in two complex subtropical forest areas, Mazongling (MZL) and Gonggashan (GGS) National Nature Forest Reserves using UAV-borne hyperspectral and LiDAR data. The results showed that the classification method performed better with higher values of R2 than the clustering algorithm for predicting both species richness (0.62 > 0.46 for MZL and 0.55 > 0.46 for GGS) and Shannon-Wiener index (0.64 > 0.58 for MZL, 0.52 > 0.47 for GGS). However, the Simpson index estimated by the classification method correlated less with the field measurements than the clustering algorithm (R2 = 0.44 and 0.83 for MZL and R2 = 0.44 and 0.62 for GGS). Our study demonstrated that the classification method could provide more accurate monitoring of forest diversity indices but requires spectral information of all dominant tree species at individual canopy scale. By comparison, the clustering method might introduce uncertainties due to the amounts of biochemical and structural inputs derived from the hyperspectral and LiDAR data, but it could acquire forest diversity patterns rapidly without distinguishing the specific tree species. Our findings underlined the advantages of UAV remote sensing for monitoring the species diversity in complex forest ecosystems and discussed the applicability of classification and clustering methods for estimating different individual tree-based species diversity indices

Densidade de nuvens pontos UAV-Lidar na estimativa da altura de eucalipto em diferentes sistemas de manejo

Orientador: Prof. Dr. Carlos Roberto SanquettaCoorientadora: Profa. Dra. Ana Paula Dalla CorteDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Agrárias, Programa de Pós-Graduação em Engenharia Florestal. Defesa : Curitiba, 23/02/2021Inclui referências: p. 44-55Área de concentração: Manejo FlorestalResumo: O manejo florestal evoluiu para a fronteira 4.0, a qual utiliza tecnologias a seu favor, destas, destacam-se os Lasers scanners, os quais podem mensurar a floresta. Contudo, essa ferramenta é onerosa, de modo que uma alternativa mais barata e de alta densidade de pontos é a união destes sensores com veículos aéreos não tripulados (UAV-Lidar). Logo, deve-se verificar a influência da densidade de pontos na acurácia das métricas da floresta. Neste sentido, objetivou-se avaliar o desempenho de diferentes densidades de nuvens de pontos UAV-Lidar na estimativa da altura individual de Eucalyptus benthamii em sistemas agrosilvipastoris, implantados em 2012. O estudo foi conduzido na fazenda Canguiri, Pinhais, Paraná, na qual foi realizado o censo das árvores, medindo-se o diâmetro e altura. Os dados UAV-Lidar foram coletados com o sistema GatorEye. A nuvem de pontos foi pré-processada no LASTOOLS, onde foi unida e recortada para a área de estudo. Posteriormente, em linguagem de programação R, esta foi homogeneizada em nove diferentes densidades: 2.000, 1.500, 1.000, 500, 250, 100, 50, 25 e 5 pts/m². Estas nove nuvens de pontos foram classificadas quanto ao solo e normalizadas, favorecendo a determinação dos modelos digitais de terreno, superfície e copas. Foi extraído a altura máxima das árvores, com base no pixel mais alto presente no modelo digital de copas e na nuvem de pontos normalizada. As alturas derivadas foram avaliadas em relação as alturas medidas em campo pelo coeficiente de correlação de Pearson, raiz quadrada do erro médio, viés, análise gráfica e teste t pareado. A densidade de 2.000 pts/m² melhor representou o perfil da árvore e o solo, obtendo maior correlação (0,79) e menor RMSE (14,55 %). Em todas as densidades, as alturas derivadas e mensuradas foram estatisticamente semelhantes. A redução da densidade de pontos ocasionou divergências no perfil da árvore e modelo de copas, não havendo grandes diferenças no modelo digital do terreno. O sistema GatorEye foi acurado para derivar a altura total do Eucalyptus benthamii. Até 100 pts/m² não há perda de acurácia na derivação da altura.Abstract: The 4.0 frontier has arrived in the forest management, employing technologies in its benefit, among them, Lasers scanners, which measure the forest. However, this tool is expensive, so a cheaper and high point density alternative is the union of these sensors with unmanned aerial vehicles (UAV-Lidar). Therefore, the point density influence on the forest metrics' accuracy should be verified. We evaluate the performance of UAV-Lidar's different point cloud densities in the individual height of the Eucalyptus benthamii estimates on different Crop-Livestock-Forest systems, implemented in 2012. It was conducted at Canguiri Farm, Pinhais, Paraná, where the census of the trees was performed, measuring the diameter and height. The UAV-Lidar data were collected with the GatorEye system. The Point Cloud was pre-processing in the LASTOOLS software, where it was merged and clipped into the study area. Then in R programming language, it was thinned in nine densities: 2,000, 1,500, 1,000, 500, 250, 100, 50, 25 and 5 pts/m². The point clouds were classified in ground and normalized, improving the digital models of terrain, surface, and crown. The highest tree height was extracted, based on the highest pixel on the digital crown model and the normalized point cloud. Heights were evaluated by Pearson's correlation, rootsquare- mean error, bias, graphic analysis, and paired t-test. The processing was performed in R language. The tree's profile and the soil were better represented by 2,000 returns.m-², obtaining higher correlation (0.79) and lower RMSE (14.55 %). At all densities, the derived and measured heights were statistically similar. The point cloud density's reduction produced variances in tree profile and CHM, with few differences in DTM. The GatorEye system was accurate to derive the Eucalyptus benthamii's total height. There is no accuracy decrease in the height's derivation until 100 returns.m-²

An assessment of the repeatability of automatic forest inventory metrics derived from UAV-borne laser scanning data

We assessed the reproducibility of forest inventory metrics derived from an unmanned aerial vehicle (UAV) laser scanning (UAVLS) system. A total of 82 merged point clouds were captured over six 500-m2 plots within a Eucalyptus globulus plantation forest in Tasmania, Australia. Terrain and understory height, together with plot- and tree-level metrics, were extracted from the UAVLS point clouds using automated methods and compared across the multiple point clouds. The results show that measurements of terrain and understory height and plot-level metrics can be reproduced with adequate repeatability for change detection purposes. At the tree level, the high-density data collected by the UAV provided estimates of tree location (mean deviation (MD) of less than 0.48 m) and tree height (MD of 0.35 m) with high precision. This precision is comparable to that of ground-based field measurement techniques. The estimates of crown area and crown volume were found to be dependent on the segmentation routine and, as such, were measured with lower repeatability. The precision of the metrics found within this paper demonstrates the applicability of UAVs as a platform for performing sample-based forest inventories