Abstract
The profitability of agricultural industries that utilise pasture can be strongly affected by the ability to accurately measure pasture biomass. Pasture height measurement is one technique that has been used to estimate pasture biomass. However, pasture height measurement errors can occur if the sensor is mounted to a farm vehicle that experiences tilting or bouncing. This work describes the development of novel low ultrasonic frequency arrays for pasture biomass estimation. Rather than just measuring the distance to the top of the pasture, as previous ultrasonic studies have done, this hardware is designed to also allow ultrasonic measurements to be made vertically through the pasture to the ground. The hardware was mounted to a farm bike driving over pasture at speeds of up to 20 km/h. The analysed results show the ability of the hardware to measure the ground location through the grass. This allowed pasture height measurement to be independent of tilting and bouncing of the farm vehicle, leading to 20 to 25% improvement in the R 2 value obtained for biomass estimation compared with the traditional technique. This corresponded to a reduction in root mean squared error of predicted biomass from about 350 to 270 kg/ha, where the average biomass of the pasture was 1915 kg/ha.
Highlights
Accurate estimation of biomass can provide significant improvement in the productivity of agricultural industries that utilise pasture [1]
This meant that the array was directed in a single direction and was equivalent to a transducer with a directivity pattern given by the point spread function of the array
If the ultrasonic sensor is attached to a farm vehicle, tilting and bouncing of the vehicle can lead to height estimation errors
Summary
Accurate estimation of biomass can provide significant improvement in the productivity of agricultural industries that utilise pasture [1]. It has been reported that the accuracy of capacitance readings can be affected by moisture due to rain Optical sensors, such as the GreenSeeker (https://agriculture.trimble.com/product/ greenseeker-system/), have been used to measure a range of parameters of crops and pastures including biomass. A system that can be mounted directly to a farm vehicle and simultaneously measure both the top of the grass and the ground locations using non-contact (remote sensing) techniques would be desirable. In reference [31], the authors presented the first study to use ultrasonic echoes from throughout the vertical depth of the pasture to improve biomass estimation by including pasture density information This was able to be achieved due to novel ultrasonic hardware that was developed for this purpose.
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