Development of a Dual-Attention U-Net Model for Sea Ice and Open Water Classification on SAR Images

Yibin Ren,Xiaofeng Li,Xiaofeng Yang,Huan Xu

doi:10.1109/lgrs.2021.3058049

Abstract

This study develops a deep learning (DL) model to classify the sea ice and open water from synthetic aperture radar (SAR) images. We use the U-Net, a well-known fully convolutional network (FCN) for pixel-level segmentation, as the model backbone. We employ a DL-based feature extracting model, ResNet-34, as the encoder of the U-Net. To achieve high accuracy classifications, we integrate the dual-attention mechanism into the original U-Net to improve the feature representations, forming a dual-attention U-Net model (DAU-Net). The SAR images are obtained from Sentinel-1A. The dual-polarized information and the incident angle of SAR images are model inputs. We used 15 dual-polarized images acquired near the Bering Sea to train the model and employ the other three images to test the model. Experiments show that the DAU-Net could achieve pixel-level classification; the dual-attention mechanism can improve the classification accuracy. Compared with the original U-Net, DAU-Net improves the intersection over union (IoU) by 7.48.% points, 0.96.% points, and 0.83.% points on three test images. Compared with the recently published model DenseNet <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FCN</sub> , the three improvement IoU values of DAU-Net are 3.04.% points, 2.53.% points, and 2.26.% points, respectively.

Highlights

T HE changes in global sea ice volume, distribution, and movement reflect the interaction of the atmosphere– cryosphere–hydrosphere and the global climate change [1].Manuscript received November 13, 2020; revised January 6, 2021; accepted February 3, 2021
A series of studies have been devoted to classifying sea ice and open water on synthetic aperture radar (SAR) images, including threshold-based methods [4], expert systems [5], and machine learning (ML) methods
The main contributions of this study are: we propose fully convolutional network (FCN)-based sea ice and open water classification model dual-attention U-Net model (DAU-Net), and integrating the dual-attention mechanism into the original U-Net is helpful to improve the classification performance

Summary

INTRODUCTION

T HE changes in global sea ice volume, distribution, and movement reflect the interaction of the atmosphere– cryosphere–hydrosphere and the global climate change [1]. A series of studies have been devoted to classifying sea ice and open water on SAR images, including threshold-based methods [4], expert systems [5], and machine learning (ML) methods. Li et al [18] proposed a CNN-based model to classify sea ice and open water from Chinese Gaofen-3 SAR images. CNN-based models achieve end-to-end classification between sea ice and open water on SAR images. To solve the mentioned drawback, we proposed an FCN-based model to classify sea ice and open water on SAR images. The main contributions of this study are: we propose FCN-based sea ice and open water classification model DAU-Net, and integrating the dual-attention mechanism into the original U-Net is helpful to improve the classification performance.

Overall Structure of DAU-Net

Encoder

Attention

EXPERIMENTS

Comparison Experiments Against Other Models

CONCLUSION