A new prototype thermal imaging system developed by a team from the CSIRO is showing promise as a reliable method of monitoring grapevine water status.
Called ProxiCrop, the proximal sensing device uses a low-cost, low-resolution thermal camera with a digital camera and adaptive image analysis in a bespoke device.
‘Monitoring grapevine canopy temperatures is a valuable tool for growers, because it allows them to identify when vines are experiencing water stress – and schedule their irrigation accordingly’, said CSIRO Research Team Leader, Dr Everard Edwards.
ProxiCrop, is a prototype thermal imaging system that is showing promise as a reliable method of monitoring grapevine water status
Existing canopy monitoring systems use infra-red thermometers to measure a specific ‘spot’ on a grapevine, often a leaf or a small section of the canopy. However, Dr Edwards said, this method had its drawbacks.
‘In the case of a leaf, you are effectively measuring vine stress across an entire vineyard on the basis of one leaf alone. And when you measure a ‘section’ of the vine you are also including its background in your data, whether that be soil, sky or trellis – which will likely have a very different temperature from the canopy and thus affect the measurement.’
Dr Edwards said another alternative was the use of high resolution hand-held thermal cameras to image the canopy, ‘but you only get a very few points in time and you still need to analyse the resulting images. They also tend to be expensive, so you aren’t likely to buy a pile of them and leave them around the vineyard.’
The ProxiCrop device instead scans the entire canopy of one or two vines continuously rather than just a few leaves at one point in time. It uses a low-cost, low-resolution thermal camera device that could be incorporated into a custom-built box.
‘By combining the low-resolution thermal image with a traditional RGB [truecolour] image (such as is taken by a phone camera), we can use a computing algorithm to automatically select out the canopy in the RGB image, overlay it accurately on the thermal image and select only the pixels in the thermal image that correspond to canopy’, Dr Edwards explained. ‘That way we get an accurate canopy temperature measurement that is adaptive to changes in the canopy size during the season.’
Dr Everard said the system wasn’t expected to replace soil moisture monitoring but be used as an additional tool to assist decision-making by grapegrowers.
‘It’s not as simple as saying thermal imaging is better than soil monitoring. They are complementary tools, and growers can use both. Thermal data can tell us the status of a vine in real time, whereas measuring soil moisture can tell us the water potentially available to the vine.’
Ten ProxiCrop sensors are currently being trialled across two vineyards to test their reliability and identify any issues that normal vineyard management might reveal. Dr Edwards and his team are also investigating the optimal way to assess the degree of vine stress using the canopy temperature data.
‘For example, we can combine it with local weather data, or we can use wet and/or dry references.’ He said the latter was suitable for a single time point measurement but was impractical for monitoring.
‘We can potentially also make use of the fact that the device creates measurements every few minutes and use the change in these, compared with the environmental changes, to estimate vine water status’, Dr Edwards said.
In the face of growing climate change, Dr Edwards said the ProxiCrop system could prove a valuable tool for growers.
‘Monitoring canopy temperature allows growers to determine vine water status from the vine itself, rather than guessing based on the soil moisture content. This is just a more reliable method of monitoring that canopy temperature.’
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, in partnership with CSIRO.