Laser rangefinder-based measuring of crop biomass under field conditions

Abstract

Knowledge of site-specific crop parameters such as plant height, coverage and biomass density is important for optimising crop management and harvesting processes. Sensors for measuring crop parameters are essential pre-requisites to gather this information. In recent years, laser rangefinder sensors have been adopted in many industrial applications. In agricultural engineering, the potential of laser rangefinders for measuring crop parameters has been little exploited. This paper reports the design and the performance of a measuring system based on a triangulation and a time-of-flight laser rangefinder for estimating crop biomass density in representative crops under field conditions. It was shown that the mean height of reflection point is a suitable parameter for non-contact indirect measurement of crop biomass by laser rangefinder sensors. The main parameters for potential assessment were the coefficient of determination (R 2 ) and the standard error (RMSE) for the relation between crop biomass density and the mean height of the reflection point in crop stands from oilseed rape, winter rye, winter wheat and grassland during the vegetation period in 2006. For the triangulation sensor, R 2 was in the range from 0.87 to 0.98 and for the time-of-flight sensor in the range from 0.75 to 0.99 for both fresh matter and dry matter density. The triangulation sensor had a reduced suitability caused by masking effects of the reflected beam and because of limited measuring range. Based on the results of experiments and technical data, it was concluded that the time-of-flight principle has good potential for site-specific crop management.

A Combination of Plant NDVI and LiDAR Measurements Improve the Estimation of Pasture Biomass in Tall Fescue (Festuca arundinacea var. Fletcher)

“…The solid line of best fit (in relation to the 1:1 line) suggests that the combined sensor index tended to underestimate the actual GDM and this is consistent with the observations of other workers. It has been reported that the morphology of the vegetation canopy greatly influences the accuracy of some laser rangefinders [33]. In particular, vegetation with an erectophile morphology (typical in grasslands and pastures) produce higher uncertainties in height measurements and tends to underestimate the mean reflection height [33,34], due to the outgoing laser beam typically glancing off the erectophile vegetation rather than reflecting back towards the sensor.…”

“…It has been reported that the morphology of the vegetation canopy greatly influences the accuracy of some laser rangefinders [33]. In particular, vegetation with an erectophile morphology (typical in grasslands and pastures) produce higher uncertainties in height measurements and tends to underestimate the mean reflection height [33,34], due to the outgoing laser beam typically glancing off the erectophile vegetation rather than reflecting back towards the sensor. For this study, the NDVI was the only SRI that was examined as a predictor of biomass, the reason for this being that is it a commonly used index as well as the fact that NDVI is one of the standard outputs from the Raptor™ sensor.…”

Crop height determination with UAS point clouds

“…dust, vibration, and sun. Ehlert et al, 2009 have generally shown that laser scanners are able to meet these requirements. However, tractorbased systems are bound to the tramlines to measure the plant height.…”

Terrestrial laser scanning for plant height measurement and biomass estimation of maize

“…By contrast, studies show that terrestrial laser scanning (TLS), as an active system, can be applied for agricultural purposes. Investigated plant parameters are plant height (Zhang and Grift, 2012), biomass (Keightley and Bawden, 2010;Ehlert et al, 2009;2008), crop density (Hosoi and Omasa, * Corresponding author: nora.tilly@uni-koeln.de 2012;Saeys et al, 2009), and leaf area index (Gebbers et al, 2011). As mentioned the large height of maize plants causes difficulties for ground based system.…”