Estimating Pasture Biomass and Canopy Height in Brazilian Savanna Using UAV Photogrammetry

Jonathan Li,Thales Akiyama,Bianca Oliveira,Veraldo Liesenberg,José Marcato Junior,Alexandre Dias,Wesley Gonçalves,Henrique Siqueira,Juliana Batistoti,Geison Salgado Filho,Eva Gomes,Maurício Souza,Edson Matsubara,Luís Ítavo

doi:10.3390/rs11202447

Abstract

The Brazilian territory contains approximately 160 million hectares of pastures, and it is necessary to develop techniques to automate their management and increase their production. This technical note has two objectives: First, to estimate the canopy height using unmanned aerial vehicle (UAV) photogrammetry; second, to propose an equation for the estimation of biomass of Brazilian savanna (Cerrado) pastures based on UAV canopy height. Four experimental units of Panicum maximum cv. BRS Tamani were evaluated. Herbage mass sampling, height measurements, and UAV image collection were simultaneously performed. The UAVs were flown at a height of 50 m, and images were generated with a mean ground sample distance (GSD) of approximately 1.55 cm. The forage canopy height estimated by UAVs was calculated as the difference between the digital surface model (DSM) and the digital terrain model (DTM). The R2 between ruler height and UAV height was 0.80; between biomass (kg ha−1 GB—green biomass) and ruler height, 0.81; and between biomass (kg ha−1 GB) and UAV height, 0.74. UAV photogrammetry proved to be a potential technique to estimate height and biomass in Brazilian Panicum maximum cv. BRS Tamani pastures located in the endangered Brazilian savanna (Cerrado) biome.

Highlights

The Brazilian territory contains nearly 160 million hectares of pastures which are located mainly in the North, Southeast, and Center-West regions [1]
In view of the scarcity of scientific data using unmanned aerial vehicle (UAV) to estimate height and biomass in Brazilian pastures, the present study investigates the use of UAV photogrammetry to estimate the pasture height and biomass of Panicum maximum cv
The normalized root mean square error (NRMSE) estimated using the leave-one-out method was around 10.99% when considering the height measured with the ruler and by the UAV (Figure 3)

Summary

Introduction

The Brazilian territory contains nearly 160 million hectares of pastures which are located mainly in the North, Southeast, and Center-West regions [1]. Though involves simple techniques that can be performed in small areas, manual measurements require time and extensive labor. For this reason, research involving automated and non-destructive measuring approaches is still necessary [6]. Cost–benefit values, and the miniaturization of technologies such as computer processors and the global navigation satellite system (GNSS) has made the UAV a versatile platform, resulting in a tool capable of performing well in a wide range of applications [7,8], including soybean yield estimation, plant maturity prediction [9], and wheat plant density estimation [10]. In view of the scarcity of scientific data using UAVs to estimate height and biomass in Brazilian pastures, the present study investigates the use of UAV photogrammetry to estimate the pasture height and biomass of Panicum maximum cv. The use of soil conservation techniques and the management of the pastures contribute to the sustainability of the ecosystem

Material and Methods

Experimental Area

Image Collection and Processing

Statistical Analysis

Results and Discussion