Dongling Li

Observation of sand waves in the Taiwan Banks using HJ-1A/1B sun glitter imagery

Abstract This study focuses on the large sand waves in the Taiwan Banks. Our goals are to observe the sand waves as completely as possible, to obtain their direction, wavelength, density, and ridge length, to analyze their spatial distributions, and to understand the effects of the current field and water depth on the sand waves. This study demonstrates the possibility of using HJ-1A/1B sun glitter imagery with a large swath width and rapid coverage in studying sand waves. Six cloud-free HJ-1A/1B optical images with sun glitter signals received during 2009 to 2011 were processed. The sand waves were mapped based on their features in the images; their direction, wavelength, density, and ridge length were measured and analyzed. We identified 4604 sand waves distributed in an area of 16,400     km 2 . The distributions of sand waves and their characteristics were analyzed, and the differences of sand waves between the northwestern subregion and the southeastern subregion are reported. Further analysis and discussion of the relationships between spatial distribution of the sand waves and both the tidal current field from a numerical simulation and water depth led to some interesting conclusions. The current field determines the orientation of the sand wave, while the hydrodynamic conditions and water depth influence the shape, size, and density of sand waves to a certain degree.

Observation of submarine sand waves using ASTER stereo sun glitter imagery

Signatures of sun glitter images strongly depend on the viewing angle. Stereo observation can provide more valuable information than observation from one angle. In this work, the sun glitter patterns caused by submarine sand waves were studied using stereo images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which operates a high spatial resolution (15 m) optical and near-infrared sensor on board the Terra satellite. The previous imaging geometrical model has been improved, and the difference in the viewing angle among pixels is considered. We found that brightness reversal occurs in some stereo imagery of submarine sand waves. Based on the imaging geometry model, an interaction model of current topography, and a sun glitter radiance transfer model, a simulation model was developed for sun glitter from submarine sand waves at multiple viewing angles. The cases of nadir-looking and backward-looking were simulated with the model. The results show the following differences between the two viewing angles, which have also been observed in the ASTER images. Both tendency and extent of the simulated radiance are in good agreement with those in actual images. In the nadir-looking view, obvious differences have been observed between the normalized significant radiance from smooth and rough facets. This difference increases with increasing viewing angle, to a peak, and then decreases. However, in most cases, the difference in the back view is smaller and shows an opposite tendency regarding the viewing angle from the nadir-looking view. Thus, the sand-wave characteristics in the nadir-looking images seem to be more enhanced than that in the backward-looking images.

Bathymetric mapping of submarine sand waves using multiangle sun glitter imagery: a case of the Taiwan Banks with ASTER stereo imagery

Abstract. Submarine sand waves are visible in optical sun glitter remote sensing images and multiangle observations can provide valuable information. We present a method for bathymetric mapping of submarine sand waves using multiangle sun glitter information from Advanced Spaceborne Thermal Emission and Reflection Radiometer stereo imagery. Based on a multiangle image geometry model and a sun glitter radiance transfer model, sea surface roughness is derived using multiangle sun glitter images. These results are then used for water depth inversions based on the Alpers–Hennings model, supported by a few true depth data points (sounding data). Case study results show that the inversion and true depths match well, with high-correlation coefficients and root-mean-square errors from 1.45 to 2.46 m, and relative errors from 5.48% to 8.12%. The proposed method has some advantages over previous methods in that it requires fewer true depth data points, it does not require environmental parameters or knowledge of sand-wave morphology, and it is relatively simple to operate. On this basis, we conclude that this method is effective in mapping submarine sand waves and we anticipate that it will also be applicable to other similar topography types.

Shallow water bathymetric surveys by spaceborne synthetic aperture radar

A numerical model for shallow water bathymetric surveys by spaceborne synthetic aperture radar (SAR) and its calculation procedure have been developed based on the SAR imaging mechanism of sea bottom topography. Water depths of the Xiaoyinsha sandwave off the east coast of Jingsu province have been calculated from the ERS-1 SAR imagery. The results have been compared with the sea chart. It is shown that the agreement between the image-calculated bathymetric pattern and that in the chart is excellent. A root mean square difference accuracy of 0.42 m has been achieved.

The dynamic monitoring and infinite-scale management of coastal zone with remote sensing and fractal approach

The new needs for quantitative and precise detection for coastline dynamic changes and their environmental factors are addressed with the fast and more developing activities of coast areas. The magnitudes from satellite or airborne remote sensing and in-situ observed data, and different scale mapping as well as multi-dimension changes are increasingly important. So the problems on capture, store, process, display and management of an unprecedented amount of information have become a very important. Satellite remote sensing associated with fractal approaches presented here are new methodologies to solve related scientific problems. The situation and requirement of coast zone are briefly introduced in the paper at the first. The theories and models of fractal system and the examples of their application in coastline and the possibility of infinite scale managements of the coastline are described in detail. The potential of satellite remote sensing associated with fractal approach in detecting and manage of coast zone is discussed and concluded at the final of the paper.

Whitecap features induced by submarine sand waves in stereo optical imagery

Under high wind speed conditions, waves break on the sea surface producing whitecaps, which can be recorded in optical satellite images. However, the breaking of waves is also influenced by submarine topography. In this study, we investigate the whitecap features induced by submarine sand waves using optical stereo images. We determine the whitecap coverage in images, and estimate the probabilities of wave breaking. The observed and estimated results are in agreement with some previous investigation results. A physical model is used to discuss the mechanisms of wave breaking along sand wave crests. The physical model is able to qualitatively explain the differences between the observed whitecap coverage and the estimated probability of wave breaking between the sand wave area (SWA) and the background area (BGA). Further analysis shows that the periodic sand wave system may play the role of a frequency-control device, and may result in more broken waves in the SWA than in the BGA. This study demonstrates that it is possible to observe submarine topography under high-wind conditions by using whitecap features.

Wetland landscape pattern analysis with remote sensing images in Ximen Island special marine protected area

This paper focuses on the wetland of Ximen Island special marine protected areas in Yueqing Bay, Zhejiang, China. In this paper, four remote sensing images from Landsat-7, SPOT-4, SPOT-5 and WorldView-2 satellites are collected. These images are used for wetland investigation and analysis. Wetland information of island and tidal flat is derived from the remote sensing images. Wetland in island includes aquaculture water, pond water, paddy fields and reservoirs. Tide wetland includes vegetation areas, breeding areas, mud tide flat and water. The results mainly showed that the area of island wetland is 1,281,973.04 square meters, accounting for 18.09% of the whole island area, and that the mangroves communities distribute along the coast of Ximen Island.

The dynamic monitoring and management of coastal zone with SAR remote sensing and fractal approach

It is known that coastal zone and its environments are the complex and specialized areas. Synthetic aperture radar (SAR) with all weather is the powerful tools for monitoring the dynamic changes of those regions, and fractal approaches may be a good ideal technologies for managements on the unprecedented amount of information from the coastal spatial and temporal processes and remote sensing images etc. database. The needs of coastal dynamic monitoring are introduced at the first. The imaging mechanisms and the technologies as well as the example studies of SAR detecting coastal zone are described in detail.

Bathymetric mapping of shallow water surrounding Dongsha Island using QuickBird image

This article presents an experiment of water depth inversion using the band ratio method in Dongsha Island shallow water. The remote sensing data is from QuickBird satellite on April 19, 2004. The bathymetry result shows an extensive agreement with the charted depths. 129 points from the chart depth data were chosen to evaluate the accuracy of the inversion depth. The results show that when the water depth is less than 20m, the inversion depth is accord with the chart, while the water depth is more than 20m, the inversion depth is still among 15- 25m. Therefore, the remote sensing methods can only be effective with the inversion of 20m in Dongsha Island shallow water, rather than in deep water area. The total of 109 depth points less than 20m were used to evaluate the accuracy, the root mean square error is 2.2m.

Island topography measurement methods and test with satellite remote sensing

This paper focuses on the topography measurement of island with satellite remote sensing. In this paper, remote sensing stereo images from Cartosat-1 satellite are used to survey the topographic information of island. Ground control points (GCPs) data are collected through on-site measurement. Then, some distributed GCPs are selected for remote sensing image processing. The digital elevation information (DEM) is extracted from Cartosat-1 remote sensing data by DEM extraction processing. And then, contour, slope and aspect are calculated based on DEM information. Finally, some ground control points is selected to validate the accuracy of topographic information. The results show that the accuracy of topographic information obtained 4.32m at horizontal position and 6.24m at vertical elevation accuracy.