Multiclass Land Cover Mapping from Historical Orthophotos Using Domain Adaptation and Spatio-Temporal Transfer Learning

Abstract

Historical land cover (LC) maps are an essential instrument for studying long-term spatio-temporal changes of the landscape. However, manual labelling on low-quality monochromatic historical orthophotos for semantic segmentation (pixel-level classification) is particularly challenging and time consuming. Therefore, this paper proposes a methodology for the automated extraction of very-high-resolution (VHR) multi-class LC maps from historical orthophotos under the absence of target-specific ground truth annotations. The methodology builds on recent evolutions in deep learning, leveraging domain adaptation and transfer learning. First, an unpaired image-to-image (I2I) translation between a source domain (recent RGB image of high quality, annotations available) and the target domain (historical monochromatic image of low quality, no annotations available) is learned using a conditional generative adversarial network (GAN). Second, a state-of-the-art fully convolutional network (FCN) for semantic segmentation is pre-trained on a large annotated RGB earth observation (EO) dataset that is converted to the target domain using the I2I function. Third, the FCN is fine-tuned using self-annotated data on a recent RGB orthophoto of the study area under consideration, after conversion using again the I2I function. The methodology is tested on a new custom dataset: the ‘Sagalassos historical land cover dataset’, which consists of three historical monochromatic orthophotos (1971, 1981, 1992) and one recent RGB orthophoto (2015) of VHR (0.3–0.84 m GSD) all capturing the same greater area around Sagalassos archaeological site (Turkey), and corresponding manually created annotations (2.7 km² per orthophoto) distinguishing 14 different LC classes. Furthermore, a comprehensive overview of open-source annotated EO datasets for multiclass semantic segmentation is provided, based on which an appropriate pretraining dataset can be selected. Results indicate that the proposed methodology is effective, increasing the mean intersection over union by 27.2% when using domain adaptation, and by 13.0% when using domain pretraining, and that transferring weights from a model pretrained on a dataset closer to the target domain is preferred.

A Review and Meta-analysis of Semantic Segmentation Models in Land Use/ Land Cover Mapping

“…The model attained a comparable overall accuracy with DeepLabV3+ at various segmentation scale parameter on Vaihingen dataset and suboptimal overall accuracy to DeepLabV3+ on Potsdam dataset. Another approach identified is utilizing a Generative Adversarial Networkbased approach for domain adaptation, such as Full Space Domain Adaptation Network [106] as well as leveraging domain adaptation and transfer learning [129]. It has proven to enhance accuracy in scenarios where source and target images originate from distinct domains.…”

A Systematic Literature Review and Bibliometric Analysis of Semantic Segmentation Models in Land Cover Mapping

“…The model attained a comparable overall accuracy with DeepLabV3+ at various segmentation scale parameters on the Vaihingen dataset and suboptimal overall accuracy compared to DeepLabV3+ on the Potsdam dataset. Another approach identified is utilizing a Generative Adversarial Network-based approach for domain adaptation, such as the Full Space Domain Adaptation Network [103], as well as leveraging domain adaptation and transfer learning [126]. It has been proven to enhance accuracy in scenarios where source and target images originate from distinct domains.…”