Abstract

In this work, a semantic segmentation-based deep learning method, DeepLabV3+, is applied to classify three vegetation land covers, which are tree, shrub, and grass using only three band color (RGB) images. DeepLabV3+’s detection performance has been studied on low and high resolution datasets that both contain tree, shrub, and grass and some other land cover types. The two datasets are heavily imbalanced where shrub pixels are much fewer than tree and grass pixels. A simple weighting strategy known as median frequency weighting was incorporated into DeepLabV3+ to mitigate the data imbalance issue, which originally used uniform weights. The tree, shrub, grass classification performances are compared when all land cover types are included in the classification and also when classification is limited to the three vegetation classes with both uniform and median frequency weights. Among the three vegetation types, shrub is found to be the most challenging one to classify correctly whereas correct classification accuracy was highest for tree. It is observed that even though the median frequency weighting did not improve the overall accuracy, it resulted in better classification accuracy for the underrepresented classes such as shrub in our case and it also significantly increased the average class accuracy. The classification performance and computation time comparison of DeepLabV3+ with two other pixel-based classification methods on sampled pixels of the three vegetation classes showed that DeepLabV3+ achieves significantly higher accuracy than these methods with a trade-off for longer model training time.

Highlights

  • Land cover classification has been used in change monitoring [1], construction surveying [2], agricultural management [3], digital terrain model (DTM) generation [4], and identifying emergency landing sites for unmanned air vehicles (UAVs) during engine failures [5,6]

  • Two DeepLabV3+ models are trained for two cases: (a) Uniform weights for the 8 classes in model training, (b) median frequency weights for the 8 classes

  • We provided screenshots of two images in the Slovenia test dataset

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Summary

Introduction

Land cover classification has been used in change monitoring [1], construction surveying [2], agricultural management [3], digital terrain model (DTM) generation [4], and identifying emergency landing sites for UAVs during engine failures [5,6]. Shrub, and grass are three of the vegetation-type land covers and classification of them using remote sensing data has several important applications. In emergency landing of unmanned air vehicles (UAVs), it is critical to land on grassland rather than on trees or shrubs [5,6]. Removing tall vegetation from the digital surface model (DSM) such as trees and shrub is an important step in developing an accurate digital terrain model (DTM) [2]. NDVI cannot differentiate tree, shrub, and grass because of their similar spectral characteristics. NDVI requires near infrared (NIR) band, which may not be available sometimes

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