Mapping Urban Tree Cover Changes Using Object-Based Convolution Neural Network (OB-CNN)

Shirisa Timilsina,Jamie B Kirkpatrick,Jagannath Aryal

doi:10.3390/rs12183017

Shirisa Timilsina, Jamie B Kirkpatrick + Show 1 more

Open Access

https://doi.org/10.3390/rs12183017

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Journal: Remote Sensing	Publication Date: Sep 16, 2020
Citations: 47	License type: CC BY 4.0

Affiliation: University of Tasmania, University of Melbourne

Abstract

Urban trees provide social, economic, environmental and ecosystem services benefits that improve the liveability of cities and contribute to individual and community wellbeing. There is thus a need for effective mapping, monitoring and maintenance of urban trees. Remote sensing technologies can effectively map and monitor urban tree coverage and changes over time as an efficient and low-cost alternative to field-based measurements, which are time consuming and costly. Automatic extraction of urban land cover features with high accuracy is a challenging task, and it demands object based artificial intelligence workflows for efficiency and thematic accuracy. The aim of this research is to effectively map urban tree cover changes and model the relationship of such changes with socioeconomic variables. The object-based convolutional neural network (CNN) method is illustrated by mapping urban tree cover changes between 2005 and 2015/16 using satellite, Google Earth imageries and Light Detection and Ranging (LiDAR) datasets. The training sample for CNN model was generated by Object Based Image Analysis (OBIA) using thresholds in a Canopy Height Model (CHM) and the Normalised Difference Vegetation Index (NDVI). The tree heatmap produced from the CNN model was further refined using OBIA. Tree cover loss, gain and persistence was extracted, and multiple regression analysis was applied to model the relationship with socioeconomic variables. The overall accuracy and kappa coefficient of tree cover extraction was 96% and 0.77 for 2005 images and 98% and 0.93 for 2015/16 images, indicating that the object-based CNN technique can be effectively implemented for urban tree coverage mapping and monitoring. There was a decline in tree coverage in all suburbs. Mean parcel size and median household income were significantly related to tree cover loss (R2 = 58.5%). Tree cover gain and persistence had positive relationship with tertiary education, parcel size and ownership change (gain: R2 = 67.8% and persistence: R2 = 75.3%). The research findings demonstrated that remote sensing data with intelligent processing can contribute to the development of policy input for management of tree coverage in cities.

Highlights

Trees are an important element of the city and suburbs, benefiting and inconveniencing other urbanites in manifold ways [1,2,3,4,5]
The Intersection Over Union (IOU) values ranged from 62% to 88%
Mapping urban tree cover changes with high thematic accuracy in an automated way is a challenging task, and various attempts have been made in the past

Summary

Introduction

Trees are an important element of the city and suburbs, benefiting and inconveniencing other urbanites in manifold ways [1,2,3,4,5]. The heterogenous nature of natural and built environments in urban landscapes makes it difficult to quantify and monitor the spatial extent of urban tree canopies [19,20]. These assessments are typically achieved through conventional field-based methods that involve ground-based data collection activities [21,22]. Field-based tree cover data collection in cities may be limited by access to private lands. As an alternative to field-based methods, visual interpretation of aerial photography has been used extensively in tree detection since the early 1960s. The visual interpretation method is labour and cost-intensive [21,22]

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