Ingunn Burud

Classification of crystal defects in multicrystalline silicon solar cells and wafer using spectrally and spatially resolved photoluminescence

In this contribution, spectral photoluminescence (SPL) imaging detecting both the spectral distribution and the lateral position is applied on recombination active defects in multicrystalline silicon solar cells and wafers. The result is analysed by a Multivariate Curve Resolution (MCR) algorithm using the spectral photoluminescence response and their positions. (i) Without any pre-assumptions made, the algorithm distinguishes four different recombination active defect types. Looking at the spatial distribution, it is shown that two of these defect types coincide with two defect types that have been distinguished on solar cell level using an analysis of forward and reverse biased electroluminescence (denoted as Type-A and -B) previously. (ii) Using SPL, all previously classified defects can also be distinguished at the wafer level. Therefore, the defects limiting the solar cell efficiency are already present in the wafer material and not introduced by the solar cell process. This is of particular interest...

Weathering kinetics of thin wood veneers assessed with near infrared spectroscopy

Wooden elements may be subjected to mechanical, environmental or biological alterations during their service life. The most susceptible parts of wood structural members are the exposed surfaces since they are subjected to ageing, weathering and/or decay. Knowledge of the influence of weathering factors and polymer degradation mechanisms is essential for understanding the weathering process of wood. The goal of this study was to investigate the degradation of thin wooden samples exposed to short-term weathering. Tests were performed through the European summer (July), which according to previous research is considered as the most severe period for weathering of wood micro-sections. Fourier transform near infrared spectroscopy was used for evaluation of chemical changes of wood samples. Three approaches for data evaluation are presented in this paper: (1) direct spectral interpretation, (2) a concept for calculation of a weathering index Wind and (3) kinetics of lignin changes in relation to the exposure direction for selected wavelengths. Observation of the effects of weathering will allow better understanding of the degradation process. The southern exposure site was slightly more affected by weathering than other sites. Results of this research will be used for future determination of the weather-dose response model and could be essential for predicting the future performance of timber facade elements.

Near Infrared Hyperspectral Imaging in Transmission Mode: Assessing the Weathering of Thin Wood Samples:

Untreated wooden surfaces degrade when exposed to natural weathering. In this study thin wood samples were studied for weather degradation effects utilising a hyperspectral camera in the near infrared wavelength range in transmission mode. Several sets of samples were exposed outdoors for time intervals from 0 days to 21 days, and one set of samples was exposed to ultraviolet (UV) radiation in a laboratory chamber. Spectra of earlywood and latewood were extracted from the hyperspectral image cubes using a principal component analysis-based masking algorithm. The degradation was modelled as a function of UV solar radiation with four regression techniques, partial least squares, principal component regression, Ridge regression and Tikhonov regression. It was found that all the techniques yielded robust prediction models on this dataset. The result from the study is a first step towards a weather dose model determined by temperature and moisture content on the wooden surface in addition to the solar radiation.

Hyperspectral imaging of weathered wood samples in transmission mode

Surfaces are the most vulnerable part of structures due to continuous exposure to variable climatic conditions. Even if weathering mainly affects the aestethic appearance of wooden facades it may lead to more advanced degradation such as wood cracking, checks and consequently penetration of the wood-decaying agents into the material. The goal of this research was to investigate the kinetics of the degradation rate of wooden samples. The experimental specimens were weathered at 15 locations in Europe for a period of 1 month. Hyperspectal imaging was used for evaluation of earlywood and latewood degradation. Two approaches for image analysis were presented highlighting their advantages and constraints regarding the evaluation of weathered samples. The proposed technique was able to scrutinise differences in degradation of earlywood and latewood, therefore provided new understanding for the kinetic of the weathering process.

Hyperspectral near Infrared Imaging of Wooden Surfaces Performed Outdoors and Indoors

Hyperspectral near infrared imaging has been applied in a field study of fungal growth on a variety of wood substrates exposed in an outdoor environment over a six-month period. This study was performed as a follow up to a hyperspectral examination study of fungal growth on wood surfaces in a laboratory setting. Hyperspectral measurements were carried out both outdoors and indoors in order to explore the influence of the different light conditions. Segmentation of the mould growth on the wood surfaces was carried out using principal component analysis, spectral angle mapper and partial least squares-discriminant analysis. Growth curves showing the fungal growth over time were obtained for all the samples from the measurements performed outdoors. However, there are some challenges connected to studies of wood surfaces due to structures caused by growth rings, knots and sometimes cracks. These wood properties will cause a great variation in the spectra from the wood and also cause natural variation in the fungal growth. Determining specific classes in a classification model such as partial least squares-discriminant analysis is proposed as a way to overcome these issues. Moreover, the wood substrates exposed in an outdoor environment will have a colour change due to photodegradation of lignin, wetting/leaching of the upper layer of the wood surface and growth of a variety of wood discolouring fungi. Hyperspectral technology is a promising technique to study wood properties and we plan to carry out a study to be able to separate and model the different effects on colour degradation on wood surfaces.

Spatially and spectrally resolved temperature dependence of defect related luminescence using hyperspectral imaging

Spatially and spectrally resolved defect related photoluminescence of multicrystalline Silicon wafers has been obtained through hyperspectral photoluminescence imaging. The defect related emissions has been studied as a function of temperature, between 300 K (room temperature) and 87 K. The emissions D1, 0.72 eV, VID3 (0.93 eV) and BB (1,1 eV) emissions are detectable at all temperatures and their peak intensities seem to shift to higher energies with decreasing temperatures. A similar shift in the peak energy for the D2 signal is measured, however, the D2 signal is not visible at room temperature and becomes detectable at 127 K. The D3 and D4 transitions do not exhibit a shift in photon energy with temperature.

Urban surfaces studied by VIS/NIR imaging from UAV: possibilities and limitations

The present research approach aims at analyzing the relation between material properties and their thermal behavior using airborne multispectral imaging in VIS/NIR and IR with sensors mounted on Unmanned Aerial Vehicle (UAV). As a follow up to a pilot study from spring 2016, a survey including several flights spanned over three days, from early morning before sunrise until late evening after sunset, was carried out in Athens in June 2017. The camera specifications for the survey in 2017 were different than the ones used in 2016. The performance of the cameras was evaluated, taking into account atmospheric correction. The images have been combined to form maps of surface temperature distribution and material physical properties. The VIS/NIR images were used to classify the different surface materials, to compute a map of estimated albedo, and to construct a 3D-model of the area. By combining thermal maps with material classification, albedo information and local weather data, thermal material properties could be characterized for the various materials. The derived properties from this dataset yield valuable information for improved simulation models of urban climate.

Phenotyping studies of wheat by multispectral image analysis

To meet an increasing demand for food production there is a need for faster genetic gains in Norwegian cereal breeding. Yield gains can be improved by use of High-Throughput Phenotyping (HTP) based on multispectral imaging and application of genomic selection. Several spectral indices have been tested to estimate grain yield, such as the Normalized Differential Vegetation Index (NDVI) and MERIS Terrestrial Chlorophyll Index (MTCI). For the present work, data was gathered from a field trial with 96 plots of 24 wheat cultivars laid out in an alpha-lattice split plot design. The design had two levels of nitrogen (N) fertilization, 75 and 150 kg N/ha, applied at sowing. Also, a larger field trial with 301 breeding lines with two reps of high N fertilization was used. Multispectral images where taken in the wavebands green (550 nm), red (660 nm), red edge (735 nm) and near infrared (NIR) (790 nm) with a Parrot Sequoia multispectral camera combined with a sunshine sensor. This allows vegetation indices to be calculated. In addition, 3D models and Digital Surface Models (DSM) are used to estimate plant height. All cameras and sensors were mounted on a light Unmanned Aerial Vehicle (UAV). Images were taken at regular intervals throughout the growth season. The time series of the vegetation indices showed high values during the period of grain filling for wheat plots that received higher dose of fertilization. The values reached their peak around the period of grain filling before declining when plants approached maturity. For site B, the historical cultivars showed significant differences in NDVI and MTCI, but the indices were weakly correlated with grain yield. On site B, however, the large field with breeding lines, both vegetation indices were associated with grain yield with MTCI showing the strongest correlation coefficient of 0.49. The plant heights computed from the DSM showed deviations of 0.1 to 0.2 meters from the manual measurements, indicating that more sophisticated models are needed for reliable prediction of plant height.

CLASSIFICATION OF URBAN BLUE GREEN STRUCTURES WITH AERIAL MEASUREMENTS

The development of climate-responsive design has social and environmental impacts, as the adverse effects of climate change are particularly relevant for urban areas. Green and blue infrastructure has been identified as best practice for achieving greater urban sustainability and resilience. The climatic improvements from use of blue-green infrastructure are generally related to the ability to moderate the impacts of extreme precipitation and temperature. However, the challenges and barriers to implementation of climate adaptation plans focusing on the use of blue-green spaces have not been analysed extensively to date. The present work describes a novel methodology to measure and classify urban surface parameters, which are important for the understanding and simulation of urban flooding. An aerial survey with multispectral sensors in VIS/NIR (Visible and Near Infrared) and IR (Infrared) wavelengths on a UAV (Unmanned Airborne Vehicle) has been carried out at the campus of the Norwegian University of Life Sciences in Ås, Norway. The area covers various types of surface such as asphalt, concrete, gravel, vegetation and water. The Normalized Difference Vegetation Index (NDVI) derived from the VIS/ NIR images have been used to study the spatial distribution and physical characteristics of the vegetation. Multivariate statistical tools have further been utilized to classify the different terrain materials according to their reflectance spectral properties from the multispectral VIS/NIR/IR data cubes. These materials have been linked to roughness and infiltration properties that are commonly used in water analysis simulation tools. Photogrammetry was applied to compute the Digital Surface Map (DSM), which was used to determine drainage lines and water accumulation areas in the surveyed area. The applied method provides data with high spatial resolution that can simplify and improve simulation of urban flooding.

Application of unmanned aerial vehicles in earth resources monitoring: focus on evaluating potentials for forest monitoring in Ethiopia

ABSTRACT Application of unmanned aerial systems was limited to the military until the last decade when we see dramatic growth of interest by civilian users. Among the many fields of application of unmanned aerial vehicles (UAVs), forestry has diverse uses ranging from forest cover assessment to species classification and real-time forest fire monitoring. Inspired by the potential uses of the technology, this study is a review of literature on the types and uses of UAVs, the challenges and opportunities, current experiences and the future prospects of using UAVs for forest resources monitoring in Ethiopia. The study has identified potential uses of UAVs for forestry applications. It has also shown that there is perceived need for accurate, demand-based and cost-effective tools for forest resources monitoring in developing countries including Ethiopia. Hence, the use of small UAVs in the forestry sector in Ethiopia is believed to be a supplementary method to the existing methods of spatial data capture for filling the gap of information and improving the quality of forest information that is needed to comply with international standards. The results of this study indicate that Ethiopia can make use of the technology and improve its forest information system. However, while doing so, rules and regulations must be put in place to avoid the challenges that come along with introducing the technology. If properly used, the technology will enhance the forest management decision-support system of the country.