Xianwen Ding

Coastline Extraction Using Dual-Polarimetric COSMO-SkyMed PingPong Mode SAR Data

A two-step physically consistent procedure is proposed to exploit COSMO-SkyMed (CSK) synthetic aperture radar (SAR) data acquired in the incoherent dual-polarization PingPong mode. The first step, which deals with land/sea discrimination, is accomplished in a robust and effective way by exploiting the inherent peculiarities of the CSK PingPong mode. Hence, a dual-polarization scattering model that relates the correlation between the HH and VV CSK polarimetric channels to the coherence time of the observed scene is first proposed. The second step, which deals with the extraction of the continuous coastline, is accomplished by a simple image processing that consists of extracting intermediate frequency components using two Gaussian-shaped filters. Experiments undertaken over actual CSK single-look slant range complex PingPong HH/VV SAR data show the physical soundness of the proposed rationale and the processing effectiveness.

Monitoring of Oil Spill Trajectories With COSMO-SkyMed X-Band SAR Images and Model Simulation

The Shell North Sea Gannet Alpha platform oil spill accident occurred on August 10, 2011. This was the largest oil spill accident in United Kingdom waters in the last decade. The spills were observed on four COSMO-SkyMed (CSK) X-band synthetic aperture radar (SAR) images acquired between August 17 and 22, 2011, with revisit time from 11 h to 3 days between the SAR acquisitions. The areas of oil slicks were extracted from SAR images using an existing image classification and segmentation algorithm. It was found that the oil slicks moved toward the southwest with slick size enlarging from 3.69 to 62.01 km2 in the first 24 h between the first and second SAR acquisitions. We tracked the oil spill trajectories using the General NOAA Operational Modeling Environment (GNOME) oil-drifting model. The 6-hourly surface wind fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA) Interim products and the 3-hourly ocean surface current fields from the Navy Coastal Ocean Model (NCOM) global operational model were used to drive the GNOME model. The simulated oil slick movement was in good agreement with that observed by the CSK SAR images. Moreover, the simulation showed that the movement of oil spills was dominated by the surface winds in the North Sea.

Performance Analysis and Validation of Waterline Extraction Approaches Using Single- and Dual-Polarimetric SAR Data

In this study, the performance of two waterline extraction approaches is analyzed using dual-polarization Cosmo-SkyMed (CSK) Synthetic Aperture Radar (SAR) data and ancillary ground truth information. The single-polarization approach is based on multiscale normalized cuts segmentation; while, the dual-polarization one exploits the inherent peculiarities of the CSK PING PONG incoherent dual-polarimetric imaging mode together with a tailored scattering model to perform land/sea discrimination. The two approaches are applied to the actual CSK SAR data collected over the coastal area of Shanghai, China. To provide a detailed and complete validation of the two approaches, we carried out several field surveys collecting in situ ancillary information including Global Positioning System (GPS) data and tidal information. Experimental results show that 1) both approaches provide satisfactory results in extracting waterline from CSK SAR data in the intertidal flat under low-to-moderate wind conditions and under a very broad range of incidence angles; 2) the accuracy of the waterline extracted by both approaches decreases in case of water within the intertidal flat; 3) the single-polarization approach is unsupervised when the land/sea contrast ratio is high. However, it needs manual supervision to correct the extracted waterline when the land/sea contrast is low or in complex areas. A typical CSK scene is processed in about 25 min; 4) the dual-polarization approach is unsupervised and very effective: a typical CSK SAR scene is processed in seconds.

Tracking the internal waves in the South China Sea with environmental satellite sun glint images

The propagation of internal solitary waves (ISWs) in the South China Sea (SCS) was tracked using National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) sun glint image pairs. The acquisition times of the two images comprising the same pair is usually separated by about 2 hours. Four pairs of images in May and August 2013 were analysed. The ISW phase speeds were derived using the horizontal displacement of the ISW patterns and the time difference between the 2 satellite images. The phase speeds were in good agreement with the theoretical calculations using the Sturm–Louisville (S − L) equation with a non-linear term. Monthly ocean stratification data and bathymetry were used in the theoretical calculations. The ISW phase speeds are mainly affected by bottom depth, with seasonal variations. The ISWs propagated faster in August than in May. Our results also show that the ISW propagation in northern SCS can be mapped using environmental satellite sun glint images in short period of time with the advantage of large scale.

COASTLINE DETECTION IN SAR IMAGES USING MULTISCALE NORMALIZED CUT SEGMENTATION

The multiscale normalized cut technique is used to detect land/sea boundary in synthetic aperture radar (SAR) images. The proposed method is a region-based one, which is able to capture and utilize spatial information in the image. The real SAR images, e.g. ERS, ENVISAT and COSMO-SkyMed (CSK) SAR images, together with the Landsat-7 ETM+ optical data and in-situ GPS data were collected and used to validate the performance of the proposed method for coastline detection in SAR images.

Shoreline movement monitoring based on SAR images in Shanghai, China

In this article, a divide-and-combine approach and multiscale normalized cut techniques are combined to extract water–land boundaries from synthetic aperture radar (SAR) images. A validation study shows that waterline extraction from SAR using the proposed algorithm is consistent with that derived from Landsat optical remote-sensing imagery. Analysis of six European Remote Sensing-1/2 (ERS-1/2) satellite and Envisat SAR images acquired at spring tides in Lingang New City, a new land-reclamation city in the suburb of Shanghai, China, between 1993 and 2005 shows the shoreline movement of the study region. We find that the shoreline had minimum seaward movement in the region due to natural forces between 1993 and 1996. Between 1996 and 1999, the shoreline moved more in the eastern and slower in the western part due to artificial impelling siltation and deposition of silt in the Yangtze River. Later, between 1999 and 2005, the shoreline significantly changed following commencement of a tidal flat reclamation project.

Oil spill detection in SAR images using multiscale normalized cut segmentation

The multiscale normalized cut technique is used to detect oil spill in synthetic aperture radar (SAR) images. The proposed approach is a region-based one, which is able to capture and utilize spatial information in the image. Actual ENVISAT ASAR image was collected and used to validate the effectiveness and efficiency of the proposed approach for oil spill detection in SAR images.

Observation and simulation of 2010 ULVA prolifera bloom in the Yellow Sea

In this paper, the Ulva prolifera bloom event in the Yellow Sea in summer 2010 is investigated by MODIS (Moderate Resolution Imaging Spectroradiometer) images. We use the FAI (Floating Algae Index) method to detect the distribution of the floating macroalgae from the images. Then we apply the GNOME (General NOAA Operational Modeling Environment) model to simulate the trajectories of the Ulva prolifera in the Yellow Sea. The model results agree well with satellite observations, indicating that the occurrence and movement of the floating macroalgae can be investigated with the combination of GNOME model and satellite data.

Fusion of SAR and MODIS images for oceanic internal waves tracking in the South China Sea

South China Sea (SCS) is one of the most active areas for internal waves (IW) occurrences in the world. These waves generated at the Luzon Strait, propagate westward into the SCS, and dissipate on the continental shelf after persisting for more than 4 days. IW phase speed is an important parameter to study the evolution of IWs and the ocean interior characteristics. In this paper, we analyzed one pair of SAR/MODIS images containing same IW signatures in the SCS spanning from 19N to 23N and from 115E to 118E. The SAR and MODIS images were taken at 02:07:52 and 02:50:00 UTC on 22 April 2007, respectively. First, the SAR and MODIS images are calibrated and geo-referenced. By overlaying images in a GIS system, we are able to track the same wave-crest displacement between the time intervals of the image pair, and thus, derive the phase speeds of IWs at different locations. We show that the phase speeds of individual wave packets can be estimated accurately using this pair of MODIS/ASAR images separated in time by 42 minutes and 8 seconds. Furthermore, we find that there is an inseparable relationship between IW phase speed and water depth. The IW phase speeds are in proportion to the water depths along their pathways. In conclusion, we present a new multiple-sensor image fusion technique in a GIS environment to extract IW geolocation information and derive their propagation phase speeds.

A differential SAR interferometry (DInSAR) investigation of the deformation affecting the coastal reclaimed areas of the Shangai megacity

In this work we investigate the deformation signals affecting the coastal region of the megacity of Shangai (China) where, to satisfy the growing land demand for industrial and urban development, man-made lands reclaimed from the sea have been retrieved and used to build airports, harbors, and industrial areas. The presented analysis is carried out through the application of spaceborne Differential Synthetic Aperture Radar (SAR) Interferometry (DInSAR) techniques. A general picture of the ground deformation field is provided by applying the Small Baseline Subset (SBAS) as well as the Permanent Scattereres (PS) approaches to archives of SAR images collected by ENVISAT and COSMO-SkyMed sensors from 2007 to 2014 over the investigated area.