University of Twente Student Theses

Assessment of the Normalized Difference Vegetation Index (NDVI) tool : Impact of environmental factors and precipitation in Overijssel on the reliability of the NDVI tool to determine impervious surfaces as input for water run-off models

Smeenk, S.R. (2023) Assessment of the Normalized Difference Vegetation Index (NDVI) tool : Impact of environmental factors and precipitation in Overijssel on the reliability of the NDVI tool to determine impervious surfaces as input for water run-off models.

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Abstract:	This thesis examines the effect of precipitation deficit and environmental factors on the determination of impervious surfaces by the FME NDVI tool in private gardens. This FME NDVI tool is used to determine the amount of impervious surface as input for water run-off models. The goal of this research is to get the output of the NDVI tool as reliable as possible in private areas. This is achieved in this thesis by first answering the question: What is the impact of precipitation deficit on the colour differences of small vegetation in the infrared picture? The impact on the colour difference of infrared pictures is assessed since the NDVI is calculated based on the colour values of these infrared pictures. The impact is determined by developing an FME mean infrared and red value calculator used on the small vegetation areas. The second question is: In which type of environment can the reliability of the NDVI tool be optimized? Here, the impact of environmental factors, like soil type is assessed. First, the interesting environmental factors are determined based on literature. Of these factors, the impact of soil type and tree crowns on the reliability of the tool is further assessed. This is done, by adding a reliability part to the existing tool which expresses the reliability of the outcome in a percentage. The third question is: In what way can the use of the tool be improved concerning the NDVI threshold value in the specific environments found in the questions above? Below the NDVI threshold value, the area is considered impervious surface and above vegetation. It is found that the relation between precipitation deficit and the colour values of the infrared picture is not realistic. It is assumed that this is partly due to the spread in the dates of the pictures used and consequently the temperature difference. Therefore, it is decided that the tool is not being optimized for the precipitation classes in the third question. There is also no clear relationship between the NDVI threshold value, and the environmental factors researched. No relationship between the soil type and the influence on the reliability of the tool is found. However, it has been found that the presence of leaves on the trees influences the reliability of the tool. These two environmental factors have nothing to do with the NDVI threshold value and because of this, these factors are not addressed in the third research question. As a result, in the third research question, a calibration tool for the NDVI threshold value is developed which can be used to optimize the NDVI threshold value for an area of interest. This calibration tool picks a small part of the study area and calibrates the optimal NDVI threshold value for this part. Then it is assumed that this relationship holds for the rest of the study area. To check if this relation holds a validation of the calibration tool is done. This study concludes that there is no optimal NDVI threshold value to get the highest reliability in combination with precipitation deficit, soil type and tree crowns. However, leaves on the trees negatively affect the reliability of the tool. Therefore, for a study area with a lot of trees, it is better to pick a picture without leaves on the trees to reach higher reliability. Furthermore, the calibration tool can help with getting the optimal NDVI threshold value for a certain study location resulting in optimized reliability.
Item Type:	Essay (Bachelor)
Faculty:	ET: Engineering Technology
Programme:	Civil Engineering BSc (56952)
Link to this item:	https://purl.utwente.nl/essays/95684
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