Xiulin Lou

Coastally trapped atmospheric gravity waves on SAR, AVHRR and MODIS images

Alternative dark–bright patterns on two ENVISAT Advanced Synthetic Aperture Radar (ASAR) images of the east coast of the Korean Peninsula acquired on 18 and 19 May 2004 are interpreted as atmospheric gravity waves (AGWs) on the basis of simultaneous multi‐satellite observations and atmospheric gravity wave theory. The AGWs appeared in the form of a wave packet containing several waves located between 50 and 200 km offshore. The wavelengths were ranging from 13 to 20 km. The lengths of AGW crests were from 20 to 150 km. An NOAA‐17 pass was received about 30 min after the ASAR pass. Its channel 4 infrared (IR) image clearly shows wave‐like moisture patterns. However, the sea surface temperature (SST) image derived after applying nonlinear calibration and split‐window atmospheric correction shows no wave patterns. A daytime true‐colour MODIS image taken about 14 h later still shows a cloud band of same AGWs, indicating the lifespan of the standing AGWs can be over half a day. Although oceanic internal waves (IWs) may also cause similar wave patterns imaged by spaceborne SAR as they modulate the ocean surface roughness, we provide evidence to eliminate this possibility in this case. The characteristics of satellite observed AGWs are in good agreement with these simulated by a linear coastal AGW model.

An Improved Local Gradient Method for Sea Surface Wind Direction Retrieval from SAR Imagery

Sea surface wind affects the fluxes of energy, mass and momentum between the atmosphere and ocean, and therefore regional and global weather and climate. With various satellite microwave sensors, sea surface wind can be measured with large spatial coverage in almost all-weather conditions, day or night. Like any other remote sensing measurements, sea surface wind measurement is also indirect. Therefore, it is important to develop appropriate wind speed and direction retrieval models for different types of microwave instruments. In this paper, a new sea surface wind direction retrieval method from synthetic aperture radar (SAR) imagery is developed. In the method, local gradients are computed in frequency domain by combining the operation of smoothing and computing local gradients in one step to simplify the process and avoid the difference approximation. This improved local gradients (ILG) method is compared with the traditional two-dimensional fast Fourier transform (2D FFT) method and local gradients (LG) method, using interpolating wind directions from the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis data and the Cross-Calibrated Multi-Platform (CCMP) wind vector product. The sensitivities to the salt-and-pepper noise, the additive noise and the multiplicative noise are analyzed. The ILG method shows a better performance of retrieval wind directions than the other two methods.

Satellite remote sensing of the oceanic environment in China

Satellite remote sensing technique has been used to monitor the oceanic environment. This paper presents the technique development and applications of satellite remote sensing to the oceanic environment in China. The technique development includes the development of algorithms and of methodology for extracting oceanographic parameters from satellite data. Applications of satellite remote sensing range from environmental monitoring to oceanographic research.

Remote sensing reflectance simulation of coastal optical complex water in the East China Sea

In this work, remote sensing reflectance (Rrs) spectra of the Zhejiang coastal water in the East China Sea (ECS) were simulated by using the Hydrolight software with field data as input parameters. The seawater along the Zhejiang coast is typical Case II water with complex optical properties. A field observation was conducted in the Zhejiang coastal region in late May of 2016, and the concentration of ocean color constituents (pigment, SPM and CDOM), IOPs (absorption and backscattering coefficients) and Rrs were measured at 24 stations of 3 sections covering the turbid to clear inshore coastal waters. Referring to these ocean color field data, an ocean color model suitable for the Zhejiang coastal water was setup and applied in the Hydrolight. A set of 11 remote sensing reflectance spectra above water surface were modeled and calculated. Then, the simulated spectra were compared with the filed measurements. Finally, the spectral shape and characteristics of the remote sensing reflectance spectra were analyzed and discussed.

Remote sensing monitoring of coastal change in Tangshan with Landsat imagery

Coastal zone is the interaction area between the ocean and the land, and it is one of the most important residential areas of human. Coastal area management and planning is necessary in utilizing coastal space and resources. Coastal zone changed rapidly in recent decades in Tangshan, China. In this research, a total of 11 Landsat images were selected for studying the coastal change in Tangshan during the last 35 years. Results showed that the coastline length increased by 114.05 km, while land area increased by 449.76km2 from 1975 to 2010. The main period of coastal increasing in Tangshan occurred during 2005–2010, and the primary area changes happened in Caofeidian District and Jingtang Port. The main reason of the rapid coastal changes in Tangshan was the human activities of industrial and commercial district construction and harbor construction.

Satellite study of the influence of coastal upwelling on a red tide in the Zhejiang Coastal Waters

In this article, EOS MODIS ocean color and sea-surface temperature data were used to study the influence of coastal upwelling on a red tide in the Zhejiang Coastal Waters in the summer of 2007. Several cloud-free and date-continued ocean color and sea-surface temperature images during the red tide event were selected and processed in this study. According to the field observations of the red tide, pixels with chlorophyll concentration higher than a certain value were considered as the red tide waters in the ocean color images. And the coastal upwelling in the Zhejiang Coastal Waters was measured by applying a temperature threshold approach from the sea-surface temperature images. Then, the temporal and spatial distributions of the red tide and the coastal upwelling were contrastively analyzed. Results show that there exists a high degree of correlation in spatial distribution between the coastal upwelling and the red tide. The coastal upwelling affects the spatial cover of the red tide according to their spatial correlation and the upwelling plays a crucial role in the development of the red tide in term of water temperature. The upwelling in the Zhejiang Coastal Waters is an important dynamic factor for the formation of red tides there.

An extracting process of the retrieval coefficients for three frequency channel microwave radiometer

This paper focuses on the coefficients in the retrieval model of wet troposphere path delay. The kind of microwave radiometers with three frequency channels, such as TOPEX/Poseidon microwave radiometer (TMR) and Jason-1 microwave radiometer (JMR), is discussed. A process of extracting these retrieval coefficients from the data of bright temperature and relevant physical quantities is presented. The data of JMR are used to extract the retrieval coefficients and validate this extracting process. A good agreement is shown between the data retrieved with the retrieval coefficients and the data of JMR.

Detection studies of the ship targets on sea-surface based on fusion of multi-parameter satellite SAR images

Recently, the developments of multi-parameter SAR systems are so fast. Those images are of multi-bands, multi-polarizations, multi-look-angles, multi-resolutions and multi-swaths and so on respectively in order to meet the different needs from ocean, atmosphere and land users. The safeties and operations for the ships over sea surface offer important supports based on real detection from satellite SAR. So, Satellite SAR remote sensing methodology is of great potential for monitoring ships. The research areas of the paper include satellite SAR developing states and its progresses, SAR imaging mechanisms and studied techniques for ship detection, example research and compare their results by the approach and tradition. The studies indicate that the monitoring technology for ship provided by the studies is of important application values and develop potential.

Characteristics of merchant vessels in spaceborne SAR imagery

Ship features in high-resolution spaceborne Synthetic Aperture Radar (SAR) imagery has crucial significance for ship classification from satellite. In this paper, we discuss the features of merchant Ships including oil tanker, container ship and bulk carrier in SAR imagery, which is comprised of geometrical feature, scattering feature, tonnage information with Radar Cross Section (RCS) and wake. The study show that the ship lengths measured from SAR imagery has a good correlation with the real lengths, but the correlation of ship beam is worse. Ship scattering feature has positive correlation with the ship structure, which maybe is a feature to distinguish container ship from other vessels. A new equation about ship length and its displacement in tons is presented in this paper. The relation suggested by Skolnik M.I between ship tonnage and RCS is tested but not validated. We also validate the means of extracting ship speed by ship turbulence wake in SAR imagery.

Remote sensing detection of complex oceanic features by using multi-parameter synthetic aperture radar (SAR)

The dynamic and random processes of ocean features and their multi-element mixs make the detections of ocean phenomena and information seperations so much complicated. The multi-parameter synthetic aperture radar (SAR), including multi-frequencies, multi-polarizations, multi-incident angles multi-resolutions and multi-swaths etc., are quite significant approaches in order to obtain a lot of oceanic multi-elements and the parameter estimations of these elementss according to SAR images. In the paper, the complication of the ocean processes and their application needs as well as multi-parameter SAR remote sensing abilities are briefly introduced at the first. The remote sensing principles and methodologies of multi-parameter SAR studying on complicated oceanic dynamic features are described. Multi-parameter SAR simulations and detections of sea surface waves, internal waves, currents and sea surface winds etc. are studied in detail. The further development of multi-parameter SAR systems and their potential in ocean applications is discussed and concluded at the final.