Haiqing Huang

Automatic registration of SeaWiFS and AVHRR imagery

An automatic approach for integrating images from multitemporal and multisensor remote sensing is outlined based on coastlines derived from satellite images. One point on a coastline is taken as a candidate point of ground control points (GCPs). A correlation-relaxation (CR) technique is used to search for the corresponding point in the second image. A decision rule is used to guarantee the correctness of GCPs which are used to compute a polynomial equation for registering two images. The relationship between the accuracy of registration and the number of GCPs indicates that a large number of GCPs will lead to more accurate image registration. The correctness of GCPs can also improve the accuracy of geometric registration. The approach can be used particularly well to register images of coastal areas. Examples are given for registration of SeaWiFS and AVHRR imagery.

Evaluation of Coastline Changes under Human Intervention Using Multi-Temporal High-Resolution Images: A Case Study of the Zhoushan Islands, China

Continued sea-level rise and coastal development have led to considerable concerns on coastline changes along inhabited islands. Analysis of long-term coastline changes of islands is however limited due to unavailable data and the cost of field work. In this study, high-resolution images taken from 1970–2011 at an interval of about 10 years and topographic maps were collected to determine coastline changes and their drivers in the Zhoushan Islands, China. Results show that nearly all inhabited islands appeared to have noteworthy seaward expansion during the past four decades. Coastline change rates varied among islands, and the annual change rate of Zhoushan Island (the main island) reached 12.83 ± 0.17 m/year during the same period. Since 2003, the study area has been dominated by artificial coast. The proportion of harbor/port and urban/industrial coast has significantly increased, while rocky coasts and shelter-farm coasts have shrunk greatly. Preliminary analysis of drivers for these coastline changes across the Zhoushan Islands highlights the roles of human policies during different periods as well as location, which were the dominant factors controlling the great spatial and temporal complexity of coastline changes of the major islands. Sediment supply from the Yangtze River decreased after the completion of the Three Gorges Dam in 2003; however, the Zhoushan coast rapidly accreted seaward during the last decade and the artificial siltation, coastal engineering, and harbor dredging materials could be responsible for the observed coastline changes. Pressured by rapid development of the port industry, the Zhoushan coast may face unprecedented challenges in coastal use in the near future. This research provides the basic background information for future studies on coastal protection and management.

A dynamic sediment model based on satellite‐measured concentration of the surface suspended matter in the East China Sea

The concentration of total suspended matter (TSM) at the sea surface is derived from satellite data using a complex proxy TSM model in East China Sea from 1997 to 2008. The structure of the mean TSM image is similar to that of the topography, indicating that the distribution of the surface concentration is strongly related to the water depth. A dynamic sediment model (DSM) is constructed to relate the TSM concentration at the sea surface with suspended sediment at the benthic boundary layer, the Rouse number, and the water depth. The DSM model is improved through iteration with a convergence identified by the mean relative difference between two adjacent bottom TSM images which becomes smaller with the more iterations and the value is less than 1% after 50 iterations. The performance of the DSM model is validated by satellite-measured concentration with a mean relative error of 5.2% for the monthly mean images. The DSM model is used to deduce the bottom TSM concentration at the benthic boundary layer and the distribution of the Rouse number. The spatial distribution of the sea surface TSM concentration is determined predominately by both the bottom suspended sediment concentration and water depth. The temporal variation of the sea surface concentration mainly depends upon the Rouse number in the water column. Our result shows that the discharge of the Changjiang River can change the distribution of the Rouse number to form a band-shaped region in the Changjiang Estuary. The DSM model provides a framework for understanding some of the mechanisms of the formation and variation of the primary TSM plume and the secondary plume in the ECS. The primary TSM plume corresponds approximately to the region with depth shallower than 20 m and the secondary plume corresponds to the region with depths between 20 and 50 m.

Seasonal variation of absorption spectral characteristics of CDOM and De-pigmented Particles in East China Sea

The Colored Dissolved Organic Materials (CDOM) and the de-pigmented particles are the main components affecting the ocean colors in China coastal waters (which are commonly considered as the Case II waters). Understanding of their spectral characteristics is very important to develop the regional bio-optical algorithms for ocean color remote sensing. The coastal water in East China Sea (ECS) is influenced by the terrestrial materials especially the Yangtze River outflow, which has high dissolved organic and suspended materials concentration and complex particles composition. In this paper, we analyze the in situ datasets collected in four seasons between 2006 and 2007 in ECS, and get the spectral absorption models of CDOM and de-pigmented particles. The distributions of absorption coefficients of CDOM ( ) and de-pigmented particles ( ) show a decreasing trend from coastal water to the off-shore waters, which is influenced mainly by the Yangtze River outflow and coastal currents with remarkable seasonal variation in ESC. The maxima of adp CDOM a dp a dp is very high and even up to 90 m-1 level in estuary waters that it will apparently influence the retrieval of CDOM. The frequency of slops of the exponential spectrum of de-pigmented particles obeys the Gaussian distribution and it has good relationships with the absorption coefficient especially in the near-shore areas. The optical characteristics in ECS will give feasible reference to the further development of regional bio-optical algorithms.

Analysis of the characters of chromophoric dissolved organic matter in water using laser induced fluorescence and spectral fluorescence signature

A sort of analytical method of fast diagnosis of chromophoric dissolved matter (CDOM) in water is discussed. The total luminescence spectra (TLS) of CDOM in several types of water samples with laser-induced fluorescence (LIF) measurements using a 405 nm wavelength excitation source were measured in the laboratory, and the spectra of CDOM were pointed out and obtained with spectral fluorescence signature (SFS) technique. The spectrum of water Raman scattering and fluorescence of CDOM were separated from TLS with fitting Gaussian of the least squares method, and the curve of fluorescence peak intensity of CDOM against corresponding concentration of CDOM is showed. High correlation (R2 = 0.93) was observed between concentration of CDOM and fluorescence normalized to water Raman scattering. The results have presented the capability of the LIF technique as an integrated tool for research and observations.

Relationship between the colored dissolved organic matter and dissolved organic carbon and the application on remote sensing in East China Sea

A cruise was conducted in the East China Sea (ECS) in autumn 2010 to collect Dissolved Organic Carbon (DOC) and Colored Dissolved Organic Matter (CDOM) samples. The distribution of DOC mainly controlled by the hydrography since the relationship between DOC and salinity was significant in both East China Sea. The biological activity had a significant influence on the concentration of DOC with a close correlation between DOC and Chl a. The absorption coefficient of CDOM (a355) decreased with the salinity increasing in the shelf of East China Sea (R2=0.9045). CDOM and DOC were significantly correlated in ECS where DOC distribution was dominated largely by the Changjiang diluted water. Based on the relationship of CDOM and DOC, we estimated the DOC concentration of the surface in ECS from satellite-derived CDOM images. Some deviations induced by the biological effect and related marine DOC accumulations were discussed.

The use of MERIS fluorescence bands for red tides monitoring in the East China Sea

The development of algorithm for the detection and monitoring of red tides, using data from Medium Resolution Imaging Spectrometer (MERIS), is discussed. The interpretation of in-situ measured remote-sensing reflectance spectra above both waters is presented in this paper. And a radiative transfer model based on Matrix Operator techniques is used to study feature of the reflectance peak near 700nm. Based on the analysis of measured and modeled spectrums, the redshift phenomenon is obviously observed above the red tide water. The reflectance peak is observed to shift progressively from a centre wavelength of 683nm (clear and green water) to longer wavelengths (red tide waters). By using MERIS fluorescence bands, the line height at 681 nm (LH681) and 709 nm (LH709) above a baseline through the measurements at 665 nm and 753 nm are calculated. It is found that due to the red-shift phenomenon the LH709 is much higher than LH681 in red tide waters. So in this paper, the ratio of LH709 to LH681 is used as an index to detect the red tides. The results of operational red tide detection in the East China Sea have been presented.

Establishment of a hyperspectral evaluation model of ocean color satellite-measured reflectance

The accuracy of the satellite-measured reflectance is a key question for data processing and oceanographic applications. A hyperspectral satellite remote sensing reflectance evaluation model (HRSREM) was developed to evaluate the accuracy of the satellite measured reflectance. The model can compute the total reflectance at the top of the atmosphere (TOA) according to observation conditions of satellites, based on a radiative transfer model with the consideration of multiple scattering effects and atmospheric absorption effects. The performance of the HRSREM model was examined by Gordon’s algorithms, showing that the relative errors of the Rayleigh scattering reflectance and the aerosol scattering reflectance are less than 2%. The model can also compute the sky reflectance which can be validated by in-situ measurements. The two sky reflectances match well with a spectral average error of 5.4%. The relative error of the total reflectance of the model, verified by sea-viewing wide field-of-view sensor (SeaWiFS) data, is about 3.5%. Therefore, the total reflectances at TOA, computed by the model, can be taken as reference values to evaluate the accuracy of satellite reflectances. The model was used to evaluate the accuracy of the hypersptral satellite (Hyperion) remote sensing data. The Hyperion reflectance matches the total reflectance of HRSREM very well at visible and near-infrared bands with an average error of 7.3%, while the status of calibration coefficients at shortwave infrared bands are not stable with a large spectral average error of 63.5%. The reflectance evaluation of a moderate resolution imaging spectrometer (CMODIS) data indicated that relative errors are large, especially at near-infrared bands with relative errors more than 100%. The calibration coefficients of CMODIS, obtained from laboratory measurements, are not reliable. The CMODIS data should be recalibrated for oceanographic applications. The performance of the HRSREM model is effective in evaluating satellite data and its algorithms can be easily modified in order to evaluate the accuracy of other ocean color satellite sensors.

The second Chinese ocean color satellite HY-1B and future plans

Since China launched first marine satellite HY-1A in May 2002, the second Chinese ocean color satellite HY-1B sponsored by the State Oceanic Administration (SOA) was launched by the Long March rocket on April 11, 2007. There are two sensors in the satellite, one is the Chinese ocean color and temperature scanner (COCTS), and the other is the Coastal Zone Imager (CZI). So far, more than one thousand five hundred orbits data have been received and analysis for application study. In this paper, first the properties and characteristics of HY-1B are briefly introduced with comparing to the SeaWiFS. Second, the data processing technique of COCTS will be discussed in detail, such as satellite cross radiation calibration, atmospheric correction, etc. Third, the remote sensing products of ocean color and temperature are mapped by HY-1B to study its application potentiality. The results show that the HY-1B has its latent capability for the application of marine environment detection. Finally, some suggestion is proposed to modify the next ocean satellite and sensors, such as adding the properties of tilt scanning case, modification of CZI element uniform and future ocean color satellite development in China.

A study of predictability of SST at different time scales based on satellite time

Sea surface temperature (SST) is both an important variable for weather and ocean forecasting, but also a key indicator of climate change. Predicting future SST at different time scales constitutes an important scientific problem. The traditional approach to prediction is achieved through numerical simulation, but it is difficult to obtain a detailed knowledge of ocean initial conditions and forcing. This paper proposes a improved prediction system based on SOFT proposed by Alvarez et al and studies the predictability of SST at different time scales, i.e., 5 day, 10 day, 15 day, 20 day and month ahead. This method is used to forecast the SST in the Yangtze River estuary and its adjacent areas. The period of time ranging from Jan 1st 2000 to Dec 31st 2005 is employed to build the prediction system and the period of time ranging from Jan 1st 2006 to Dec 31st 2007 is employed to validate the performance of this prediction system. Results indicate: The prediction errors of 5 day,10 day,15 day, 20 day and monthly ahead are 0.78°C,0.86°C,0.90°C,1.00°C and 1.45°C respectively. The longer of time scales prediction, the worse of prediction capability. Compared with the SOFT system proposed by Alvarez et al, the improved prediction system is more robust. Merging more satellite data and trying to better reflect the real state of ocean variables, we can greatly improve the predictive precision of long time scale.