Velocity Estimation of Ocean Surface Currents in along-Track InSAR System Based on Conditional Generative Adversarial Networks

Velocity estimation of ocean surface currents is of great significance in the fields of the fishery, shipping, sewage discharge, and military affairs. Over the last decade, along-track interferometric synthetic aperture radar (along-track InSAR) has been demonstrated to be one of the important instruments for large-area and high-resolution ocean surface current velocity estimation. The calculation method of the traditional ocean surface current velocity, as influenced by the large-scale wave orbital velocity and the Bragg wave phase velocity, cannot easily separate the current velocity, characterized by large error and low efficiency. In this paper, a novel velocity estimation method of ocean surface currents is proposed based on Conditional Generative Adversarial Networks (CGANs). The main processing steps are as follows: firstly, the known ocean surface current field diagrams and their corresponding interferometric phase diagrams are constructed as the training dataset; secondly, the estimation model of the ocean surface current field is constructed based on the pix2pix algorithm and trained by the training dataset; finally, the interferometric phase diagrams in the test dataset are input into the trained model. In the simulation experiment, processing results of the proposed method are compared with those of traditional ocean surface current velocity estimation methods, which demonstrate the efficiency and effectiveness of the novel method.

Measuring Ocean Surface Current in the Kuroshio Region Using Gaofen-3 SAR Data

The Kuroshio is the strongest warm current in the western North Pacific, which plays a crucial role in climate and human activities. In terms of this, the accurate acquisition of ocean surface current velocity and direction in the Kuroshio region is of great research value. Gaofen-3 synthetic aperture radar (SAR) provides data support for the study of ocean surface current measurements in the Kuroshio region, but no relevant experimental result has been published yet. In this paper, four available stripmap mode SARs’ data acquired by Gaofen-3 in the Kuroshio region are used for measuring the ocean surface current field. In general, the Doppler centroid anomaly (DCA) estimation is a common method to infer ocean surface currents from single-antenna stripmap data, but only the radial velocity component can be retrieved. In order to measure current vectors, a novel method combining the sub-aperture processing and the least squares (LS) technology is suggested and demonstrated by applying to the Gaofen-3 SAR data processing. The experiment’s results agree well with model-derived ocean current data, indicating that the Gaofen-3 SAR has the capability to accurately retrieve the ocean surface current field in the Kuroshio region and motivate further research by providing more data.

Evaluation of CFOSAT Scatterometer Wind Data in Global Oceans

The China-France Oceanography SATellite (CFOSAT), launched on 29 October 2018, is a joint mission developed by China and France. To evaluate the CFOSAT wind product, L2B swath data with a spatial resolution of 25 × 25 km were compared with in situ measurements between December 2018 and December 2020. The in situ measurements were collected from 217 buoys. All buoy winds were adjusted to 10 m height using a simple logarithmic correction method. The temporal and spatial separations between the CFOSAT and in situ measurements were restricted to less than 30 min and 0.25°. The results indicate that the CFOSAT wind retrievals agree well with the buoy measurements. The root mean square errors (RMSEs) of wind vectors were 1.39 m s−1 and 34.32° and negligible biases were found. In the near shore under rain-free conditions, the RMSEs were enhanced to 1.42 m s−1 and 33.43°. Similarly, the RMSEs were reduced to 1.16 m s−1 and 30.41° offshore after the rain effect was removed. After winds less than 4 m s−1 were removed, the RMSE of wind directions was reduced to 19.69°. The effects of significant wave height, air-sea temperature difference, sea surface temperature, atmospheric pressure and ocean surface current on the wind residuals were assessed. The performance of wind retrievals under the passage of tropical cyclones was evaluated. The evaluation results show that the CFOSAT wind retrievals satisfy the accuracy requirements of scientific research, although some improvements are needed to enhance the performance.

Tracing the Source of Ocean Trash

Ocean trash is an emerging environmental crisis causing plastic gyres and polluted beaches, but there are only a limited number of models available for ocean trash tracing. This project created a database from Ocean Surface Current Analysis Real-Time (OSCAR) third degree resolution data with data transformation, aggregation, calculation, and expansion, and developed a GIS model for tracing potential trash sources given a location where the trash is spotted on a beach or in an ocean. The GIS model was developed as an ocean trash tracing Python script tool in ArcGIS Pro, which was then published as a geoprocessing tool in ArcGIS Server. The geoprocessing service was embedded in a web application where users can input the starting locations and see potential travelling routes of ocean trash. This project also developed an intuitive web application for the public to trace possible trash sources and raises the awareness of the ocean trash crisis.

Influence of coastal upwelling on the surface current in the Bay of Bengal using HF radar and satellite observations

<p>Coastal Upwelling is a phenomenon in which cold and nutrient-enriched water from the Ekman layers reaches the surface enhancing the biological productivity of the upwelling region. In this work, an attempt is made to understand the influence of coastal upwelling on surface current variations during May 2018 to August 2018, when HF radar current observation (source: NIOT, India) is available. The wind-based Upwelling Index(UI<sub>wind</sub>) showed coastal upwelling throughout the study period. But the SST based upwelling index (UI<sub>sst</sub>) showed upwelling occurred only from May to the first week of June. Cross-shore components of HF radar-derived ocean surface current (CSSC)  showed strong similarity with UI<sub>sst</sub>. The first phase of upwelling from UI<sub>sst</sub> is observed to start on 5<sup>th</sup> May and lasts till 14<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km. Then, there is a break period for about three days and after that, the second phase of upwelling starts on 17<sup>th</sup> May and lasts till 25<sup>th</sup> May with a maximum peak on around 20<sup>th</sup> May, but this time the horizontal extension is ~100 km which is much larger than during the first phase. A strong positive (from coast to offshore) CSSC is observed to start on around 5<sup>th</sup> May and lasts till 13<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km, as observed from UIsst. A reversal of CSSC (towards coast) is noted on 14<sup>th</sup> May when the break of coastal upwelling is evident from UI<sub>sst</sub>. The CSSC then again started intensifying 15<sup>th</sup> May onwards and continued for ten days till 25<sup>th</sup> May, similar to UI<sub>sst</sub>.  The horizontal extension of the upwelling signature in the second phase of upwelling is ~70 km. Therefore, a 7-10 days of the coastal upwelling and its horizontal extension are identified in this study. This study suggests the use of high resolution (~6 km) HF radar current observation on the monitoring of coastal upwelling processes.</p>

Detection and analysis of surface currents in western Guangdong by compact surface wave radar

In order to study the detection performance of compact surface wave radar on ocean surface current in the west of Guangdong Province, firstly, the bistatic radar is set up to collect ocean echo data on the west coast of Guangdong Province. Then, by using the Multiple Signal Classification (MUSIC) algorithm, the comparative analysis results of ocean surface current information and the actual measurement results of DVS Current Meter are obtained. The root mean square error of flow velocity less than 10cm/s and the root mean square error of flow direction less than 25 degrees were obtained. It shows that compact surface wave radar can achieve good results and has good detection capability in the west of Guangdong, china.