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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Ocean Remote Sensing".

Deadline for manuscript submissions: closed (31 December 2019) | Viewed by 50776

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Special Issue Editors

Dr. Xiaofeng Li

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Guest Editor

NCWCP - E/RA3, 5830 University Research Court, College Park, MD 20740, USA
Interests: AI oceanography; big data; ocean remote sensing; physical oceanography; boundary layer meteorology; synthetic aperture radar imaging mechanism; multiple-polarization radar applications; satellite image classification and segmentation
Special Issues, Collections and Topics in MDPI journals

Dr. Gang Zheng

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Guest Editor

State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, No.36 Baochubei Road, Xihu District, Hangzhou 310012, China
Interests: AI oceanography; satellite oceanography; microwave remote sensing; image processing; tropical cyclone remote sensing
Special Issues, Collections and Topics in MDPI journals

Dr. Bin Liu

E-Mail Website
Guest Editor

Shanghai Ocean University, 999 Hucheng Ring Rd, Pudong Xinqu, Shanghai 201306, China
Interests: AI oceanography; data science and machine learning; SAR image processing and information retrieval; target detection and classification; image segmentation and classification

Special Issue Information

Dear Colleagues,

Ocean remote sensing is a research area that has undergone tremendous development in the past few decades. Much research has led to the operational implementation of many scientific algorithms to generate geoscience products that support the general public. The rapid development of satellites and sensors has caused a dramatic increase in both the amount and diversity of ocean remote sensing data, and such data requires extensive analysis and powerful technology to be understood. In the past few years, artificial intelligent (AI) technology has been widely used in many research fields for big data information mining and shown great potential in computer vision, natural language processing, and bioinformatics, among others. The number of AI-related papers has increased exponentially.

In order to consolidate the papers within the scope of AI applications in oceanography, this Special Issue on “AI-Based Remote Sensing Oceanography” will focus on the following four major disciplines:

AI-based remote sensing image CLASSIFCATION (oil, ship, coastal zone, inundation, harmful algal bloom, cloud, eddy, internal wave, etc.)
AI-based remote sensing data FUSION (altimeter, scatterometer, radiometer, hyperspectral, aerial photos, etc.)
AI-based remote sensing ALGORITHM development (sea surface temperature, ocean color, wind, wave, dynamic topography, sea ice, etc.)
AI-based ocean and marine meteorology FORECAST (sea surface temperature, storm, etc.)

We would like to invite articles on ocean-related studies using state-of-the-art AI techniques.

All submitted manuscripts will go through a peer review process. We look forward to receiving your submissions in this booming area of research.

Dr. Xiaofeng Li
Dr. Gang Zheng
Dr. Bin Liu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

AI
Remote sensing
Oceanography
Coastal zone
Marine meteorology

Published Papers (9 papers)

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21 pages, 8795 KiB

Open AccessArticle

Application of DINCAE to Reconstruct the Gaps in Chlorophyll-a Satellite Observations in the South China Sea and West Philippine Sea

by Zhaohui Han, Yijun He, Guoqiang Liu and William Perrie

Remote Sens. 2020, 12(3), 480; https://0-doi-org.brum.beds.ac.uk/10.3390/rs12030480 - 03 Feb 2020

Cited by 25 | Viewed by 5000

Abstract

The Data Interpolating Empirical Orthogonal Functions (DINEOF) method has demonstrated usability and accuracy for filling spatial gaps in remote sensing datasets. In this study, we conducted the reconstruction of the chlorophyll-a concentration (Chl-a) data using a convolutional neural networks model called Data-Interpolating Convolutional Auto-Encoder (DINCAE), and we compared its performance with that of DINEOF. Furthermore, the cloud-free sea surface temperature (SST) was used as a phytoplankton dynamics predictor for the Chl-a reconstruction. Finally, four reconstruction schemes were implemented: DINCAE (Chl-a only), DINCAE (Chl-a and SST), DINEOF (Chl-a only), and DINEOF (Chl-a and SST), denoted rec1, rec2, rec3, and rec4 respectively. To quantitatively evaluate the accuracy of these reconstruction schemes, both the cross-validation and in situ data were used. The study domain was chosen to be the Northern South China Sea (SCS) and West Philippine Sea (WPS), bounded by 115–125°E and 16–24°N to test the model performance for the reconstruction of Chl-a under different Chl-a controlling mechanisms. The in situ validation showed that rec1 performs best among the four reconstruction schemes, and that adding SST into the Chl-a reconstruction cannot improve the reconstruction results. However, for cross validation, adding SST can slightly improve spatial distributions of the root mean square error (RMSE) between the reconstructed data and the original data, especially over the SCS continental shelf. Furthermore, the potential of DINCAE prediction is confirmed in this paper; thus, the trained DINCAE model can be re-applied to reconstruct other missing data, and more importantly, it can also be re-trained using the reconstructed data, thereby further improving reconstruction results. Another consideration is efficiency; with similar reconstruction conditions, DINCAE is 5–10 times faster than DINEOF. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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23 pages, 4545 KiB

Open AccessArticle

Hyperspectral Sea Ice Image Classification Based on the Spectral-Spatial-Joint Feature with Deep Learning

by Yanling Han, Yi Gao, Yun Zhang, Jing Wang and Shuhu Yang

Remote Sens. 2019, 11(18), 2170; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11182170 - 18 Sep 2019

Cited by 30 | Viewed by 3500

Abstract

Sea ice is one of the causes of marine disasters. The classification of sea ice images is an important part of sea ice detection. The labeled samples in hyperspectral sea ice image classification are difficult to acquire, which causes minor sample problems. In addition, most of the current sea ice classification methods mainly use spectral features for shallow learning, which also limits further improvement of the sea ice classification accuracy. Therefore, this paper proposes a hyperspectral sea ice image classification method based on the spectral-spatial-joint feature with deep learning. The proposed method first extracts sea ice texture information by the gray-level co-occurrence matrix (GLCM). Then, it performs dimensionality reduction and a correlation analysis of the spectral information and spatial information of the unlabeled samples, respectively. It eliminates redundant information by extracting the spectral-spatial information of the neighboring unlabeled samples of the labeled sample and integrating the information with the spectral and texture data of the labeled sample to further enhance the quality of the labeled sample. Lastly, the three-dimensional convolutional neural network (3D-CNN) model is designed to extract the deep spectral-spatial features of sea ice. The proposed method combines relevant textural features and performs spectral-spatial feature extraction based on the 3D-CNN model by using a large amount of unlabeled sample information. In order to verify the effectiveness of the proposed method, sea ice classification experiments are carried out on two hyperspectral data sets: Baffin Bay and Bohai Bay. Compared with the CNN algorithm based on a single feature (spectral or spatial) and other CNN algorithms based on spectral-spatial features, the experimental results show that the proposed method achieves better sea ice classification (98.52% and 97.91%) with small samples. Therefore, it is more suitable for classifying hyperspectral sea ice images. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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22 pages, 29508 KiB

Open AccessArticle

Estimating Subsurface Thermohaline Structure of the Global Ocean Using Surface Remote Sensing Observations

by Hua Su, Xin Yang, Wenfang Lu and Xiao-Hai Yan

Remote Sens. 2019, 11(13), 1598; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11131598 - 05 Jul 2019

Cited by 51 | Viewed by 3939

Abstract

Retrieving multi-temporal and large-scale thermohaline structure information of the interior of the global ocean based on surface satellite observations is important for understanding the complex and multidimensional dynamic processes within the ocean. This study proposes a new ensemble learning algorithm, extreme gradient boosting (XGBoost), for retrieving subsurface thermohaline anomalies, including the subsurface temperature anomaly (STA) and the subsurface salinity anomaly (SSA), in the upper 2000 m of the global ocean. The model combines surface satellite observations and in situ Argo data for estimation, and uses root-mean-square error (RMSE), normalized root-mean-square error (NRMSE), and R² as accuracy evaluations. The results show that the proposed XGBoost model can easily retrieve subsurface thermohaline anomalies and outperforms the gradient boosting decision tree (GBDT) model. The XGBoost model had good performance with average R² values of 0.69 and 0.54, and average NRMSE values of 0.035 and 0.042, for STA and SSA estimations, respectively. The thermohaline anomaly patterns presented obvious seasonal variation signals in the upper layers (the upper 500 m); however, these signals became weaker as the depth increased. The model performance fluctuated, with the best performance in October (autumn) for both STA and SSA, and the lowest accuracy occurred in January (winter) for STA and April (spring) for SSA. The STA estimation error mainly occurred in the El Niño-Southern Oscillation (ENSO) region in the upper ocean and the boundary of the ocean basins in the deeper ocean; meanwhile, the SSA estimation error presented a relatively even distribution. The wind speed anomalies, including the u and v components, contributed more to the XGBoost model for both STA and SSA estimations than the other surface parameters; however, its importance at deeper layers decreased and the contributions of the other parameters increased. This study provides an effective remote sensing technique for subsurface thermohaline estimations and further promotes long-term remote sensing reconstructions of internal ocean parameters. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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12 pages, 4615 KiB

Open AccessArticle

Oceanic Eddy Identification Using an AI Scheme

by Guangjun Xu, Cheng Cheng, Wenxian Yang, Wenhong Xie, Lingmei Kong, Renlong Hang, Furong Ma, Changming Dong and Jingsong Yang

Remote Sens. 2019, 11(11), 1349; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11111349 - 05 Jun 2019

Cited by 62 | Viewed by 5300

Abstract

Oceanic eddies play an important role in global energy and material transport, and contribute greatly to nutrient and phytoplankton distribution. Deep learning is employed to identify oceanic eddies from sea surface height anomalies data. In order to adapt to segmentation problems for multi-scale oceanic eddies, the pyramid scene parsing network (PSPNet), which is able to satisfy the fusion of semantics and details, is applied as the core algorithm in the eddy detection methods. The results of eddies identified from this artificial intelligence (AI) method are well compared with those from a traditional vector geometry-based (VG) method. More oceanic eddies are detected by the AI algorithm than the VG method, especially for small-scale eddies. Therefore, the present study demonstrates that the AI algorithm is applicable of oceanic eddy detection. It is one of the first few of efforts to bridge AI techniques and oceanography research. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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19 pages, 8699 KiB

Open AccessArticle

Assimilation of SMOS Sea Surface Salinity in the Regional Ocean Model for South China Sea

by Ziyao Mu, Weimin Zhang, Pinqiang Wang, Huizan Wang and Xiaofeng Yang

Remote Sens. 2019, 11(8), 919; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11080919 - 16 Apr 2019

Cited by 10 | Viewed by 4098

Abstract

Ocean salinity has an important impact on marine environment simulations. The Soil Moisture and Ocean Salinity (SMOS) mission is the first satellite in the world to provide large-scale global salinity observations of the oceans. Salinity remote sensing observations in the open ocean have been successfully applied in data assimilations, while SMOS salinity observations contain large errors in the coastal ocean (including the South China Sea (SCS)) and high latitudes and cannot be effectively applied in ocean data assimilations. In this paper, the SMOS salinity observation data are corrected with the Generalized Regression Neural Network (GRNN) in data assimilation preprocessing, which shows that after correction, the bias and root mean square error (RMSE) of the SMOS sea surface salinity (SSS) compared with the Argo observations can be reduced from 0.155 PSU and 0.415 PSU to −0.003 PSU and 0.112 PSU, respectively, in the South China Sea. The effect is equally significant in the northwestern Pacific region. The preprocessed salinity data were applied to an assimilation in a coastal region for the first time. The six groups of assimilation experiments set in the South China Sea showed that the assimilation of corrected SMOS SSS can effectively improve the upper ocean salinity simulation. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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23 pages, 4806 KiB

Open AccessArticle

Comparison of Machine Learning Algorithms for Retrieval of Water Quality Indicators in Case-II Waters: A Case Study of Hong Kong

by Sidrah Hafeez, Man Sing Wong, Hung Chak Ho, Majid Nazeer, Janet Nichol, Sawaid Abbas, Danling Tang, Kwon Ho Lee and Lilian Pun

Remote Sens. 2019, 11(6), 617; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11060617 - 13 Mar 2019

Cited by 135 | Viewed by 10864

Abstract

Anthropogenic activities in coastal regions are endangering marine ecosystems. Coastal waters classified as case-II waters are especially complex due to the presence of different constituents. Recent advances in remote sensing technology have enabled to capture the spatiotemporal variability of the constituents in coastal waters. The present study evaluates the potential of remote sensing using machine learning techniques, for improving water quality estimation over the coastal waters of Hong Kong. Concentrations of suspended solids (SS), chlorophyll-a (Chl-a), and turbidity were estimated with several machine learning techniques including Artificial Neural Network (ANN), Random Forest (RF), Cubist regression (CB), and Support Vector Regression (SVR). Landsat (5,7,8) reflectance data were compared with in situ reflectance data to evaluate the performance of machine learning models. The highest accuracies of the water quality indicators were achieved by ANN for both, in situ reflectance data (89%-Chl-a, 93%-SS, and 82%-turbidity) and satellite data (91%-Chl-a, 92%-SS, and 85%-turbidity. The water quality parameters retrieved by the ANN model was further compared to those retrieved by “standard Case-2 Regional/Coast Colour” (C2RCC) processing chain model C2RCC-Nets. The root mean square errors (RMSEs) for estimating SS and Chl-a were 3.3 mg/L and 2.7 µg/L, respectively, using ANN, whereas RMSEs were 12.7 mg/L and 12.9 µg/L for suspended particulate matter (SPM) and Chl-a concentrations, respectively, when C2RCC was applied on Landsat-8 data. Relative variable importance was also conducted to investigate the consistency between in situ reflectance data and satellite data, and results show that both datasets are similar. The red band (wavelength ≈ 0.665 µm) and the product of red and green band (wavelength ≈ 0.560 µm) were influential inputs in both reflectance data sets for estimating SS and turbidity, and the ratio between red and blue band (wavelength ≈ 0.490 µm) as well as the ratio between infrared (wavelength ≈ 0.865 µm) and blue band and green band proved to be more useful for the estimation of Chl-a concentration, due to their sensitivity to high turbidity in the coastal waters. The results indicate that the NN based machine learning approaches perform better and, thus, can be used for improved water quality monitoring with satellite data in optically complex coastal waters. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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21 pages, 4821 KiB

Open AccessArticle

Ship Classification Based on Multifeature Ensemble with Convolutional Neural Network

by Qiaoqiao Shi, Wei Li, Ran Tao, Xu Sun and Lianru Gao

Remote Sens. 2019, 11(4), 419; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11040419 - 18 Feb 2019

Cited by 48 | Viewed by 5066

Abstract

As an important part of maritime traffic, ships play an important role in military and civilian applications. However, ships’ appearances are susceptible to some factors such as lighting, occlusion, and sea state, making ship classification more challenging. This is of great importance when exploring global and detailed information for ship classification in optical remote sensing images. In this paper, a novel method to obtain discriminative feature representation of a ship image is proposed. The proposed classification framework consists of a multifeature ensemble based on convolutional neural network (ME-CNN). Specifically, two-dimensional discrete fractional Fourier transform (2D-DFrFT) is employed to extract multi-order amplitude and phase information, which contains such important information as profiles, edges, and corners; completed local binary pattern (CLBP) is used to obtain local information about ship images; Gabor filter is used to gain the global information about ship images. Then, deep convolutional neural network (CNN) is applied to extract more abstract features based on the above information. CNN, extracting high-level features automatically, has performed well for object classification tasks. After high-feature learning, as the one of fusion strategies, decision-level fusion is investigated for the final classification result. The average accuracy of the proposed approach is 98.75% on the BCCT200-resize data, 92.50% on the original BCCT200 data, and 87.33% on the challenging VAIS data, which validates the effectiveness of the proposed method when compared to the existing state-of-art algorithms. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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14 pages, 5533 KiB

Open AccessLetter

Oceanic Mesoscale Eddy Detection Method Based on Deep Learning

by Zijun Duo, Wenke Wang and Huizan Wang

Remote Sens. 2019, 11(16), 1921; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11161921 - 17 Aug 2019

Cited by 48 | Viewed by 6012

Abstract

Oceanic mesoscale eddies greatly influence energy and matter transport and acoustic propagation. However, the traditional detection method for oceanic mesoscale eddies relies too much on the threshold value and has significant subjectivity. The existing machine learning methods are not mature or purposeful enough, as their train set lacks authority. In view of the above problems, this paper constructs a mesoscale eddy automatic identification and positioning network—OEDNet—based on an object detection network. Firstly, 2D image processing technology is used to enhance the data of a small number of accurate eddy samples annotated by marine experts to generate the train set. Then, the object detection model with a deep residual network, and a feature pyramid network as the main structure, is designed and optimized for small samples and complex regions in the mesoscale eddies of the ocean. Experimental results show that the model achieves better recognition compared to the traditional detection method and exhibits a good generalization ability in different sea areas. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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10 pages, 7070 KiB

Open AccessLetter

A Data-Driven Approach to Classifying Wave Breaking in Infrared Imagery

by Daniel Buscombe and Roxanne J. Carini

Remote Sens. 2019, 11(7), 859; https://0-doi-org.brum.beds.ac.uk/10.3390/rs11070859 - 10 Apr 2019

Cited by 26 | Viewed by 4651

Abstract

We apply deep convolutional neural networks (CNNs) to estimate wave breaking type (e.g., non-breaking, spilling, plunging) from close-range monochrome infrared imagery of the surf zone. Image features are extracted using six popular CNN architectures developed for generic image feature extraction. Logistic regression on these features is then used to classify breaker type. The six CNN-based models are compared without and with augmentation, a process that creates larger training datasets using random image transformations. The simplest model performs optimally, achieving average classification accuracies of 89% and 93%, without and with image augmentation respectively. Without augmentation, average classification accuracies vary substantially with CNN model. With augmentation, sensitivity to model choice is minimized. A class activation analysis reveals the relative importance of image features to a given classification. During its passage, the front face and crest of a spilling breaker are more important than the back face. For a plunging breaker, the crest and back face of the wave are most important, which suggests that CNN-based models utilize the distinctive ‘streak’ temperature patterns observed on the back face of plunging breakers for classification. Full article

(This article belongs to the Special Issue AI-based Remote Sensing Oceanography)

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