Glimpsing vineyard microclimates at the micro-scale

A University of South Australia research team is developing a prototype it hopes will one day be able to measure a whole vineyard microclimate in 3-D and in real-time.

Professor Anthony Finn and his team are pioneering a technology known as AAT (acoustic atmospheric tomography), which observes the temperature and wind flow in the atmosphere above a vineyard and combines it with observations of the vineyard obtained using miniaturised long wave infrared cameras. This creates an accurate temperature mosaic of the vineyard infrastructure (vines, posts, inter-row ground, etc).

‘Together these two sets of measurements allow the user to compute the heat transfer between the vineyard and the atmosphere – and properties such as evapotranspiration rates, which vary spatially over the vineyard’, explained Professor Finn, Director of the University’s Defence and Systems Institute.

‘This, in turn, allows the user to estimate factors such as crop water stress index.’

Professor Finn said as the technology was still in its infancy, the full value of the information it offered was still being assessed. However, he said the technology had many potential benefits for growers.

‘It will allow growers to assess differences in microclimatic conditions within a region or vineyard and optimise irrigation – thus delivering water and energy savings.

‘Similarly, during frost events, the technology can provide high resolution thermal maps of the surface and air temperatures surrounding the vineyards as a function of height above the ground, as well as geographic and temporal variation.

‘This permits evaluation of the effectiveness and/or need for different frost mitigation strategies, such as frost fans or sprinklers.

However, he said initial conclusions suggest frost mitigation strategies based on air temperature measurements alone may be sub-optimal.

Other potential uses of the technology include:

• Estimation of seasonal crop coefficients: the spatial and temporal patterns of vine canopy development at key phenological stages from flowering to harvest would be determined using high resolution cameras flown onboard a UAV (unmanned aerial vehicle). Canopy width and height extracted from aerial images could then be used to estimate the crop coefficient (which is related to the area of exposed leaves).
• Estimating reference evapotranspiration (known as ET_o) via temperature and wind speed measurements, with relative humidity and solar radiation provided by an on-site weather station. Using these environmental parameters, high spatial resolution ET_o would then be calculated for the vineyard. ET_o and crop coefficients could then be used to calculate water use across a vineyard block and over the course of the growing season. 
• The thermal images obtained from the UAV-mounted infrared camera could be used to characterise patterns of water stress across the block.

Professor Finn said the developing technology could give growers knowledge of vineyard microclimates.

‘It gives them an opportunity to visualise their vineyard and fruit temperatures at the micro-scale with great precision and in near real time.’

‘This allows decisions to be based on micro-climate information that has been gathered safely, efficiently, and non-destructively.’

How it works

The AAT approach is very similar to the way in which MRI or CAT scans observe human tissue.

AAT synchronously measures the acoustic signature (noise) generated by a propeller-driven unmanned aerial vehicle^[1] (UAV), both onboard the aircraft and at a set of strategically located ground microphones.

‘This allows us to determine the propagation delay caused by the intervening atmosphere and hence the speed of sound’, Professor Finn said.

‘As sound speed is related to temperature and wind velocity, and we have multiple intersecting rays propagating from the UAV to the ground microphones, we can then use tomography to reconstruct and visualise a spatial representation of the intervening atmosphere at very high resolution.’

This project was funded by the Australian Government Department of Agriculture, Water and the Environment as part of its Rural R&D for Profit program and Wine Australia.