Satellite data is of high importance for ocean environment monitoring and protection. However, due to the missing values in satellite data, caused by various force majeure factors such as cloud cover, bad weather and sensor failure, the quality of satellite data is reduced greatly, which hinders the applications of satellite data in practice. Therefore, a variety of methods have been proposed to conduct missing data imputation for satellite data to improve its quality. However, these methods cannot well learn the short-term temporal dependence and dynamic spatial dependence in satellite data, resulting in bad imputation performance when the data missing rate is large. To address this issue, we propose the Spatio-Temporal Attention Generative Adversarial Network (STA-GAN) for missing value imputation in satellite data. First, we develop the Spatio-Temporal Attention (STA) mechanism based on Graph Attention Network (GAT) to learn features for capturing both short-term temporal dependence and dynamic spatial dependence in satellite data. Then, the learned features from STA are fused to enrich the spatio-temporal information for training the generator and discriminator of STA-GAN. Finally, we use the generated imputation data by the trained generator of STA-GAN to fill the missing values in satellite data. Experimental results on real datasets show that STA-GAN largely outperforms the baseline data imputation methods, especially for filling satellite data with large missing rates.

The ultra-dense network (UDN) based on mobile edge computing (MEC) is an important technology, which can achieve the low-latency of 5G communications and enhance the quality of user experience. However, how to improve the task offloading efficiency is a hot topic of UDN under the constraint on the limited wireless resources. In this article, we propose a heuristic task offloading algorithm HTOA to optimize the delay and energy consumption of offloading tasks in UDN. Firstly, a convex programming model for MEC resource allocation is established, which aims to obtain the optimal allocation set of resources for offloading tasks, and optimize the execution delay of offloading tasks. Followed by, the problem of joint channel allocation and user upload power control is solved by the greedy strategy and golden section method, which aims to optimization the delay and energy consumption of task upload data. Compared with the random task offloading algorithm, numerical simulations show that the algorithm HTOA can effectively reduce the delay and energy consumption of task offloading, and perform better as the number of users increases.

With the rapid amassing of spatial-temporal (ST) ocean data, many spatial-temporal data mining (STDM) studies have been conducted to address various oceanic issues, including climate forecasting and disaster warning. Compared with typical ST data (e.g., traffic data), ST ocean data presents some unique characteristics, e.g., diverse regionality and high sparsity. These characteristics make it difficult to design and train STDM models on ST ocean data. To the best of our knowledge, a comprehensive survey of existing studies remains missing in the literature, which hinders not only computer scientists from identifying the research issues in ocean data mining but also ocean scientists to apply advanced STDM techniques. In this article, we provide a comprehensive survey of existing STDM studies for ocean science. Concretely, we first review the widely used ST ocean datasets and highlight their unique characteristics. Then, typical ST ocean data quality enhancement techniques are discussed. Next, we classify existing STDM studies for ocean science into four types of tasks, i.e., prediction, event detection, pattern mining, and anomaly detection, and elaborate the techniques for these tasks. Finally, promising research opportunities are discussed. This survey can help scientists from both computer science and ocean science better understand the fundamental concepts, key techniques, and open challenges of STDM for ocean science.

Remote sensing data are of considerable significance for monitoring global climate, detecting harmful algae bloom, etc. However, due to sensor failures, cloud cover, and thick aerosols, the collected remote sensing data for various ocean factors, such as Chlorophyll-a (Chl-a) concentration and Sea Surface Temperature (SST), often have a high missing rate, which seriously hinders their applications. Existing data imputation models mostly ignore highly-sparse spatial locations or perform bad when the data missing rate is high due to the lack of available information. Large Language Models (LLMs) possess powerful representation learning capabilities and can effectively capture sequential correlations even with extremely limited information, thereby presenting promising potential for highly-sparse remote sensing data imputation. Therefore, we proposed a novel LLM-based spatio-temporal model for highly-sparse remote sensing data imputation, i.e., LLM4HRS. First, LLM4HRS develops a LLM-based bidirectional temporal representation learning module to learn forward and backward temporal dependencies in data sequences and fuses them together to obtain comprehensive temporal representations. Next, LLM4HRS constructs a LLM-based spatial representation learning module to learn spatial correlations with the learned temporal representation. Finally, a spatio-temporal representation fusion and data imputation module is developed to achieve data imputation. Experiments on the SST and Chl-a remote sensing datasets demonstrate that LLM4HRS significantly outperforms existing data imputation models, with its advantages becoming more pronounced as the masking rate increases. Furthermore, when extended to the remote sensing PAR data in a large region, LLM4HRS still achieves the best performance, further validating its broad applicability for remote sensing data imputation. The code of LLM4HRS is publicly available at https://github.com/ssyuwang/LLM4HRS-master.

Accurate prediction of ocean factors (e.g., temperature and salinity) is crucial for plenty of applications, including weather forecasting, storm tracking, and ecosystem protection. Meanwhile, it is well-known that the ocean is a unified system and various ocean factors usually influence each other. For example, the changes in temperature would affect the distribution of salinity in ocean. However, existing studies for ocean factor prediction mainly focus on designing individual models for predicting specific factors and ignore the correlations between different factors, thus having potentials to be further improved. Therefore, we propose a unified framework UniOcean to predict multiple ocean factors simultaneously, and capture the correlations between them to improve the prediction accuracy. First, considering that ocean factors are usually collected with different temporal scales, we develop the fine-grained multi-scale data fusion module to integrate multiple ocean factors with different temporal scales, and effectively learn their hierarchical patterns at different levels. Then, since the correlations between ocean factors may vary across different time periods, the multi-factor correlation learning module is constructed to adaptively learn the dynamic correlations between different factors. Finally, we utilize the factor-specific towers to predict multiple ocean factors simultaneously. Experimental results on five real-world remote-sensing datasets demonstrate that UniOcean significantly improves the prediction accuracy by 11%-53% in terms of MSD for different ocean factors.