Intro for technical report
1 Introduction
This proposal has been developed in response to the request for proposals made for the National Parks Board (Nparks) to introduce an effective measure in monitoring the health of trees.
1.1 Background information
NParks, which stands for National Parks, is a national board which focuses on greenery, biodiversity conservation, and wildfire and animal health, welfare and management in Singapore. There are currently more than 350 parks, 33470 hectares of nature reserves such as Singapore Botanical Gardens and Jurong Lake Gardens.To ensure that the trees in the parks are well managed, NParks recruits tree specialists named as the arborists.
In general, arborists are in charge of ensuring that the condition of the trees in the park are in good condition. According to Julian (n.d), he states that the profession of arboriculture has advanced over the years, which makes it easier to understand the knowledge of trees better. Practices such as pruning, stress responses, good and bad retention and plant care practises. This shows that the role of arborist is pivotal to the health of the tree.
NParks have seen a sharp decrease of incidents from 3000 cases in 2001 to 400 cases in 2019. Despite the rapid decline of treefall in Singapore, incidents that threaten the lives of visitors in the parks were still occurring. An example of such an incident involves the loss of life of a woman trapped under a fallen tree which occurred on 18 February 2021. The tree was reported to be healthy during its inspection in April 2020. This shows that tree maintenance management of trees in the parks should not be taken for granted as the repercussions can be deadly.
NParks currently adopts a two-step process in assessing a tree. The first step is a basic tree assessment. Arborists will conduct a visual assessment such as looking out for dead branches and completing the checklist for this process. This process will take an approximate of 15 to 20 minutes. The next scheduled check for trees that passed the checklist requirements will be in 1 to 2 years. The second step will be for trees that need further inspection. Advanced assessment tools such as the resistograph and sound wave tomography on the tree trunk will be used for further assessment on the trees. The resistograph will drill into the tree trunk and measure the resistance of the tree. Less dense wood is usually a result of decay. Sound wave tomography will check for cavities in the tree trunk. Sound waves will travel through the trunk. The denser the trunk, the faster the sound waves will travel. From the speed taken by the sound waves, arborists can detect cavities in the trunk. Drones are also used to check for abnormalities in hard to reach places of the trees. Another alternative to tree assessment is infrared thermography.
Infrared thermography (IRT) is the conversion of infrared energy emitted from objects into apparent temperature. The thermal camera then captures and displays the thermal pattern, also known as an infrared image. In tree context, it illustrates the temperature pattern on the bark surface of a tree. This measure displays cavities or wood decay in different colours to represent that it is cooler than its surroundings. Infrared thermography is also non-invasive. Tree assessments usually involve invasive or destructive measures but infrared thermography does not disturb the tree as it requires no physical contact with trees. In addition, this process can be carried out at a distance. The absence of physical contact aids in investigation and accurate monitoring while saving the user from possible risks, inconvenience and ultimately time.
1.2 Problem Statement
The current approach by NParks is not effective enough in determining and monitoring the health of trees. By implementing infrared thermography technology, NParks can detect deteriorating trees early resulting in the reduced risk of treefall.
1.3 Purpose Statement
The report proposes the use of infrared thermography to the NParks to monitor the health of the trees, so that necessary precautions can be carried out to prevent deadfall and harm to people.
2 Proposed Solution
The team proposes using infrared thermography as an effective measure in detecting the health of trees. This measure is non-invasive, non-contact and non-destructive, which means it is safe for trees to be examined. It is an equipment that detects radiated heat energy from objects in the infrared range, converts it to a temperature, and it shows the image of the temperature field. The internal structure of a tree displays different thermal behaviour depending on its health. The difference in thermal behaviour results in differences in the colour pattern of the body surface image.
In Figure 1, the diagram depicts the process of heat transfers using infrared thermography. The camera receives radiation from the object, ambient between the object’s surface and the camera, and from the atmosphere.
Figure 1: Schematic diagram of infrared thermography on trees
2.1 Thermographic Procedures
The two main thermographic procedures are passive and active modes. The method of obtaining the thermal contrast using an external source of energy is called active procedures. During this procedure, there will be interference from other heat sources such as lamps and heaters. The defects and damages near the object surface cause thermal discontinuities producing thermal contrast. It is usually detected during thermographic inspection. In the passive procedure, thermal contrast is generated by sunlight. It is necessary to introduce an emissivity factor to calibrate the camera temperature measurement.
2.2 Analysing of tree health
The thermal contrast captured by the camera represents the temperature of the surface of the tree. Applying infrared thermography will differentiate damaged and deteriorated tissue from healthy tissues. There are several factors affecting the health of trees such as diseases, pest attack and water stress.
For insect pest attacks, infrared thermography would be able to detect tunnels, that were built by insects, in the tree branches. Insects such as white pine cone beetle and Australian “Fire” beetle are easily detected by using infrared thermography.
Infrared thermography can also be applied for water stress assessment. The tree uses surplus energy to transform water into water vapour via the leaves to cool it. When there is a shortage of water, the leaves will be warmer and as a result, the tree will be dehydrated. Water stress is an important indicator as it provides information for the adequate water supply of each tree species.
2.3 Summary of Proposed Solution
The table below shows the summary of the proposed solution, infrared thermography.
3 Benefits
As compared to the current monitoring methods adopted by NParks, IRT is a technology that is safer for the trees. This technology is able to detect deterioration and abnormalities that weakens the structure in trees. IRT does not require physical contact with the trees thus allowing arborists to conduct tree assessment at a safe distance. This also means less stress on the trees as there is no need in harming the trees. Trees that are stressed will tend to be weaker resulting in the higher risk of treefall. IRT is also an efficient monitoring system that allows real time detection. As IRT screens the tree, real time monitoring can be recorded. IRT will be able to detect unseen cracks using its thermogram.
The current methods adopted by NParks mainly observe one part of the trees. For example, the resistograph and sound wave tomography is used on the tree trunk of the trees to detect deterioration. These equipment cannot be used on other parts of the trees such as the roots of canopy of trees. To check abnormalities on tree canopies, arborists have to implement the use of drones. IRT is not only capable of detecting internal damage in tree barks through temperature difference, it is also capable of detecting thermal changes in the branches and roots. IRT will also be equipped in recognising some of the factors that contributed to these changes. These factors include "diseases,pest attack,water stress and formation of new functional tissue". For tree water stress assessment, IRT detects the tree canopy temperature. Through the overall canopy temperature, arborists can take note of the water consumption by the trees and provide or reduce the water supplied to the trees.
4 Evaluation and limitations
Every technology has its limitations and this includes IRT. Despite the benefits that have been discussed in the previous section, IRT has its own disadvantages. Firstly, IRT is unable to "identify whether the damage detected is a void or deteriorated tissue". Secondly, it is incapable in providing the details on the magnitude of damage. Lastly, as it detects temperature, it is heavily affected by sunlight and water. Due to this reason, arborists are required to avoid tree assessment with IRT after the rain or after the trees are watered. Arborists are also advised to conduct these assessments at night so that to obtain more accurate data on the tree assessment.
IRT is considerably an expensive technology to adopt. Despite its cost, IRT is a good investment to be considered. There is an added value to this technology as it is able to take into account the different factors that affect the health of a tree.
5 Methodology
In this section, the method and resources that the team have utilized will be explained.
5.1 Primary research
For the team’s primary research, a 40-minute Zoom interview was conducted on 8th March 2021, 0930 hrs, with Mr Daryl Lee Tsen-Tieng, who is a senior researcher in Tree Mechanics from National Parks Board. Mr Daryl provided the team with detailed information about the role of an arborist and how they maintained the health of every tree.
5.2 Secondary research
The main source of secondary research is Agriculture [2019]. The review article by Agriculture details an in-depth assessment of infrared thermography used on trees which gave the team a better understanding of that equipment. Other sources of secondary resources include online websites which support this technical report.
6 Conclusion
To conclude, IRT provides effective measures that saves time and effort compared to other measures such as resistograph and sound wave tomography. Unlike current measures that NParks are currently using, IRT can be used to detect abnormalities on other parts of the tree that the current monitoring methods are able only to attain to a certain extent. Furthermore, with the investment of IRT, NParks will be able to save cost by the implementation of just one technology instead of two.
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