IR mapping commenced
A common response of plants to water limitation is to reduce transpiration. Transpiration helps to cool leaves and when transpiration is reduced, leaves get warmer. SIMPaCT aims to have all plants in the park transpiring at full capacity in summer to provide us with the maximum level of cooling. This requires that we provide the plants with optimal soil moisture levels every day, and especially when it is really hot. But the threshold when plants begin to reduce transpiration differs from species to species. Because we can regulate soil moisture at a relatively fine scale in the park, we can ‘tune’ the soil moisture conditions to make all plants happy without overwatering them (and losing water).
We define the thresholds by simultaneously measuring soil moisture and checking the temperature of the plants. For the latter, we use drone-based infrared (IR) technology that can tell us how hot or cool tree crowns, shrubs and lawns are at a range of soil moisture levels. The work has started in the cooler months of the year where we now plan our IR imaging missions, including finding the best take-off and landing locations and flight paths.
We use a DJI Matrice 210 quadcopter (the aircraft) with real time kinetic GPS and the XT2 dual (RGB/IR) camera system. Aircraft safety is enhanced by using a parachute system from AVSS that was especially designed to fit the Matrice 200 series. The parachute pod sits on top of the aircraft and can be deployed automatically or manually if a critical failure of the aircraft occurs. A 3 square meter parachute will guarantee a soft landing.
Image: Matrice 210 RTK V2 aircraft with AVSS parachute system. Image © Sebastian Pfautsch
With the added weight of the parachute system, a typical flight mission lasts about 20 minutes in calm conditions. As engines have to work harder to keep the aircraft stable when windspeed increases, flight times will be shorter when it is windy. Although the M210 can be operated in all weather conditions, we only use it when it is not raining, and visibility is good.
Image: A range of pre-flight checks are done to ensure safety of the aircraft. Our take-off and landing zones are clearly marked with traffic cones. Operating in open space allows optimal control of the flightpath in relation to park visitors. Image © David Martin
Bicentennial Park has an undulating landscape and visibility of people can be obstructed by tree crowns and other obstacles. For that reason, we decided to increase the number of take-off and landing zones, which will keep operational zones relatively confined and much easier to monitor for park visitors. We never operate over or less than 30m away from people – it is a strict requirement from Civil Aviation Safety Authority (CASA) that regulates how air space in Australia can be used. We do have permission from Sydney Olympic Park Authority (SOPA) to operate the drone in the park for the project. Our pilots have a Remote Pilot License and an Aeronautical Radio Operator Certificate.
Image: Vertical take-off in a large carpark. The RTK GPS unit is visible in the foreground. This device gives us highly accurate location information about the aircraft. It also improves the safety of the operation as communication is not solely dependent on access to the global GPS satellite network. Image © David Martin
While the IR mapping of vegetation will become very important in spring and summer, the principle we are using is visible even in the cooler months. The image below shows an example. Clearly visible are differences in surface temperatures among the crowns of the figs (right row), eucalypts (middle row) and deciduous trees (left row). As one would expect, the deciduous trees have stopped transpiring and their leaves are senescing or have already dropped. This leaves the darker stems, branches and twigs exposed which warm up quickly in the morning sun. The warmest surfaces (white spots) can be seen under the eucalyptus trees where unshaded dark mulch absorbs solar radiation and surface temperatures rise quickly.
We continue refining our flight management in the park and look forward to the warmer (and hopefully drier) months later to roll out the program.
Image: Normal (left) and infrared view (right) of rows of different tree species and turf in the northern section of Bicentennial Park. Image © Sebastian Pfautsch