title: Quantitative characterisation of near and subsurface defects using active thermographic techniques

authors: Kopf, Larissa

subjects: line scanning thermography

abstract: A mobile Line Scanning Thermography (LST) setup combined with a novel post-processing method that can autonomously characterise different defect types across different materials has been developed and validated. This newly developed system facilitates a more complete inspection of large structures than currently available by removing subjectivity from data analysis, minimising operator input and reducing cost.
Inspection of large structures for defects is increasingly challenging due to the demand for complete evaluation. While a more complete evaluation is possible although likely time consuming, many non-destructive evaluation techniques and their data analysis require highly trained operators, making large scale inspecting costly. Automation is critical to improve inspection speed and reliability while reducing human error. Active thermography relies on a difference in thermal properties between defective and non-defective areas to locate defects by monitoring the surface temperature of the sample with an infrared camera after thermal excitation. Particularly LST is promising as it offers rapid, non-contact inspection, however, typically uses lasers, leading to bulky equipment and increased safety measures.
An elliptical reflector was designed using optical simulation to provide a compromise between maximum intensity, line width and acceptable variations for out of focus measurements. A thermal model, validated with experimental data, investigated the effect of different scanning parameters on defect visibility and can be used to tailor inspection parameters for the experimental setup. A polished aluminium reflector and halogen light were used which greatly reduced safety requirements compared to traditional laser based systems and demonstrating applicability towards real world inspection scenarios. Using the developed LST system and a proposed novel processing method, flat bottom holes in acrylic were autonomously detected and characterised with a minimum detected diameter to depth ratio of 3.2. The processing estimated depths with an accuracy of 0.1 mm for near and subsurface defects and lateral sizing had a median error of less than 4%. The Fourier-based filtering was introduced as an additional term to the post-processing method to allow accurate defect identification in composite samples, such as carbon fibre reinforced polymers. Artificial delamination defects were successfully identified at a maximum depth of 1.97 mm with diameter to depth ratios ranging from 10 to 3.8. Limitations were observed for deeper defects and in areas with surface non-uniformities, highlighting opportunities for further work to fully understand the detection limits of LST.
When combined with the post-processing method the developed LST system allowed for a more complete inspection of large areas by reducing subjectivity and operator time thereby lowering costs. This work extends the applicability of LST with an elliptical reflector to a variety of materials and defect types, while the rule based post-processing enables reliable defect characterisation across multiple scenarios without extensive training datasets, advancing the technique for a wide range of industrial applications.

text: Quantitative characterisation of near and subsurface defects using active thermographic techniques A mobile Line Scanning Thermography (LST) setup combined with a novel post-processing method that can autonomously characterise different defect types across different materials has been developed and validated. This newly developed system facilitates a more complete inspection of large structures than currently available by removing subjectivity from data analysis, minimising operator input and reducing cost.
Inspection of large structures for defects is increasingly challenging due to the demand for complete evaluation. While a more complete evaluation is possible although likely time consuming, many non-destructive evaluation techniques and their data analysis require highly trained operators, making large scale inspecting costly. Automation is critical to improve inspection speed and reliability while reducing human error. Active thermography relies on a difference in thermal properties between defective and non-defective areas to locate defects by monitoring the surface temperature of the sample with an infrared camera after thermal excitation. Particularly LST is promising as it offers rapid, non-contact inspection, however, typically uses lasers, leading to bulky equipment and increased safety measures.
An elliptical reflector was designed using optical simulation to provide a compromise between maximum intensity, line width and acceptable variations for out of focus measurements. A thermal model, validated with experimental data, investigated the effect of different scanning parameters on defect visibility and can be used to tailor inspection parameters for the experimental setup. A polished aluminium reflector and halogen light were used which greatly reduced safety requirements compared to traditional laser based systems and demonstrating applicability towards real world inspection scenarios. Using the developed LST system and a proposed novel processing method, flat bottom holes in acrylic were autonomously detected and characterised with a minimum detected diameter to depth ratio of 3.2. The processing estimated depths with an accuracy of 0.1 mm for near and subsurface defects and lateral sizing had a median error of less than 4%. The Fourier-based filtering was introduced as an additional term to the post-processing method to allow accurate defect identification in composite samples, such as carbon fibre reinforced polymers. Artificial delamination defects were successfully identified at a maximum depth of 1.97 mm with diameter to depth ratios ranging from 10 to 3.8. Limitations were observed for deeper defects and in areas with surface non-uniformities, highlighting opportunities for further work to fully understand the detection limits of LST.
When combined with the post-processing method the developed LST system allowed for a more complete inspection of large areas by reducing subjectivity and operator time thereby lowering costs. This work extends the applicability of LST with an elliptical reflector to a variety of materials and defect types, while the rule based post-processing enables reliable defect characterisation across multiple scenarios without extensive training datasets, advancing the technique for a wide range of industrial applications.

year: 2025

title: The effects of irrigation on soil carbon and nitrogen stocks of pumice soils

authors: Millar, Jamie Alexandra

subjects: Carbon

abstract: The use of irrigation has become important for sustaining the production of food, fibre and biofuel. In New Zealand (NZ), irrigation of pastures is increasing in areas with seasonal water deficits, such as the Central North Island. Nationally, there was an estimated 794,443 ha of land under irrigation in 2017. A synthesis of the literature showed that soil C and N stocks response to irrigation was dependent on the initial soil organic matter content and climatic zone. However, most of the literature focused on arid/semiarid climate regimes where cereals and other crops were grown, with few studies conducted on pastoral land in temperate climates. However Mudge et al. (2017), measured a decrease in soil carbon (C) (6.99 t C ha⁻¹) and nitrogen (N) (0.58 t N ha⁻¹) to 0.3 m depth in irrigated grazed pastures relative to adjacent non-irrigated grazed pastures. Of their 34 paired sites across NZ, only seven were sampled from the Pumice Soil order, which was insufficient to determine whether this soil order was vulnerable to soil C and N loss.
The main objective of this thesis was to compare the total soil C and N stocks of irrigated and non-irrigated Pumice Soils. A second objective was to determine where there were any trends in changes in soil C and N in relation to irrigation duration.
Fourteen paired irrigated and adjacent non-irrigated sites were sampled in the Reporoa Basin, north of Taupo and soil C and N stocks were measured accounting for differences in soil bulk density. Most sites where sampled to 0.6 m depth, however, due to high water tables and buried soils, some sites were only sampled to 0.4 m or 0.5 m depth. One site was omitted from statistical analysis due to high residuals (F11-35) and was considered an outlier that potentially represented a poorly matched pair of sites. On average, for the remaining 13 paired sites, irrigated soils had significantly (P < 0.05) lower soil C stocks (5.93 t C ha⁻¹) to 0.2 m depth and lower N stocks (0.24 t N ha⁻¹) to 0.1 m depth in comparison to adjacent non-irrigated soils. When considering the full depth of the sampled soils (0-0.6 m), there were no significant changes in soil C and N stocks (P > 0.05). Using this coring method, I was able to detect a change of about 6.9 % in soil C stocks and a 4.8 % in soil N stocks. This study also found no evidence of a relationship between soil response to irrigation and duration of irrigation.
With the loss of soil C and N under irrigation comes potential release of CO₂ to the atmosphere and N leaching into surrounding water bodies. Based on the findings in this thesis, there is a need for further investigation on the effects of irrigation for different Soil Orders. This research will aid farmers in understanding their land management on-farm and inform them of their potential effects on greenhouse gas emissions on a national scale.

text: The effects of irrigation on soil carbon and nitrogen stocks of pumice soils The use of irrigation has become important for sustaining the production of food, fibre and biofuel. In New Zealand (NZ), irrigation of pastures is increasing in areas with seasonal water deficits, such as the Central North Island. Nationally, there was an estimated 794,443 ha of land under irrigation in 2017. A synthesis of the literature showed that soil C and N stocks response to irrigation was dependent on the initial soil organic matter content and climatic zone. However, most of the literature focused on arid/semiarid climate regimes where cereals and other crops were grown, with few studies conducted on pastoral land in temperate climates. However Mudge et al. (2017), measured a decrease in soil carbon (C) (6.99 t C ha⁻¹) and nitrogen (N) (0.58 t N ha⁻¹) to 0.3 m depth in irrigated grazed pastures relative to adjacent non-irrigated grazed pastures. Of their 34 paired sites across NZ, only seven were sampled from the Pumice Soil order, which was insufficient to determine whether this soil order was vulnerable to soil C and N loss.
The main objective of this thesis was to compare the total soil C and N stocks of irrigated and non-irrigated Pumice Soils. A second objective was to determine where there were any trends in changes in soil C and N in relation to irrigation duration.
Fourteen paired irrigated and adjacent non-irrigated sites were sampled in the Reporoa Basin, north of Taupo and soil C and N stocks were measured accounting for differences in soil bulk density. Most sites where sampled to 0.6 m depth, however, due to high water tables and buried soils, some sites were only sampled to 0.4 m or 0.5 m depth. One site was omitted from statistical analysis due to high residuals (F11-35) and was considered an outlier that potentially represented a poorly matched pair of sites. On average, for the remaining 13 paired sites, irrigated soils had significantly (P < 0.05) lower soil C stocks (5.93 t C ha⁻¹) to 0.2 m depth and lower N stocks (0.24 t N ha⁻¹) to 0.1 m depth in comparison to adjacent non-irrigated soils. When considering the full depth of the sampled soils (0-0.6 m), there were no significant changes in soil C and N stocks (P > 0.05). Using this coring method, I was able to detect a change of about 6.9 % in soil C stocks and a 4.8 % in soil N stocks. This study also found no evidence of a relationship between soil response to irrigation and duration of irrigation.
With the loss of soil C and N under irrigation comes potential release of CO₂ to the atmosphere and N leaching into surrounding water bodies. Based on the findings in this thesis, there is a need for further investigation on the effects of irrigation for different Soil Orders. This research will aid farmers in understanding their land management on-farm and inform them of their potential effects on greenhouse gas emissions on a national scale.

year: 2018

title: A history of Māori literacy success

authors: Derby, Melissa

abstract: This article explores literacy in 19th century Māori society, and in particular, this work considers the initial interactions Māori tribal groups had with literacy following contact with British settlers. The overarching purpose of this article is to respond to the increasingly prevalent suggestion that literacy is a Western competency, and that to be concerned with ensuring Māori children are achieving well in reading and writing is an act of colonisation. This work illustrates that these narratives run counter to the history, behaviour, and values of many tribal groups in New Zealand. More specifically, the historical interactions Māori had with literacy illustrate that both the ability and the desire to succeed in reading and writing was a feature of Māori historical practices. Therefore, to ensure high levels of literacy achievement in contemporary times is not a colonising act but rather aligns with Māori history, behaviour, and values.

text: A history of Māori literacy success This article explores literacy in 19th century Māori society, and in particular, this work considers the initial interactions Māori tribal groups had with literacy following contact with British settlers. The overarching purpose of this article is to respond to the increasingly prevalent suggestion that literacy is a Western competency, and that to be concerned with ensuring Māori children are achieving well in reading and writing is an act of colonisation. This work illustrates that these narratives run counter to the history, behaviour, and values of many tribal groups in New Zealand. More specifically, the historical interactions Māori had with literacy illustrate that both the ability and the desire to succeed in reading and writing was a feature of Māori historical practices. Therefore, to ensure high levels of literacy achievement in contemporary times is not a colonising act but rather aligns with Māori history, behaviour, and values.

year: 2021