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Performances of conventional fusion methods evaluated for inland water body observation using GF-1 image

Acta Oceanologica Sinica 2019年第1期38卷 172-179页

作者： Yong Du Xiaoyu Zhang zhihua mao Jianyu Chen School of Earth Sciences Zhejiang University School of Biology and the Environment Jiyang College of Zhejiang A&F University State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of Oceanography Ministry of Natural Resources

Satellite remote sensing of inland water body requires a high spatial resolution and a multiband narrow spectral resolution, which makes the fusion between panchromatic(PAN) and multi-spectral(MS) images particularly important. Taking the Daquekou section of the Qiantang River as an observation target, four conventional fusion methods widely accepted in satellite image processing, including pan sharpening(PS), principal component analysis(PCA), Gram-Schmidt(GS), and wavelet fusion(WF), are utilized to fuse MS and PAN images of *** results of subjective and objective evaluation methods application indicate that GS performs the best,followed by the PCA, the WF and the PS in the order of descending. The existence of a large area of the water body is a dominant factor impacting the fusion performance. Meanwhile, the ability of retaining spatial and spectral informations is an important factor affecting the fusion performance of different fusion methods. The fundamental difference of reflectivity information acquisition between water and land is the reason for the failure of conventional fusion methods for land observation such as the PS to be used in the presence of the large water body. It is suggested that the adoption of the conventional fusion methods in the observing water body as the main target should be taken with caution. The performances of the fusion methods need re-assessment when the large-scale water body is present in the remote sensing image or when the research aims for the water body observation.

关键词： GF-1 satellite image fusion methods fusion evaluation inland water body

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The algorithms of chlorophyll-a concentration for CMODIS

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Acta Oceanologica Sinica 2007年第5期26卷 25-33页

作者： mao zhihua ZHU Qiankun GONG Fang PAN Delu Second Institute of Oceanography State Oceanic Administration Hangzhou 310012 China State Key Laboratory of Satellite Ocean Environment Dynamics Hangzhou 310012 China

The algorithms of extracting chlorophyll-a （Chl-a） concentration have been established for Chinese moderate resolution imaging spectrometer （CMODIS） mounted on Shenzhou-3 spaceship launched on 25 March 2002. The CMODIS is an ocean color sensor with 30 visible channels and 4 infrared channels, much different from other ocean color satellites and needs new algorithms to process data. Three models of Chl-a concentration were established based on Chl-a data retrieved from sea-viewing wide field-ofview sensor （SeaWiFS）, with the average relative errors of 26. 6%, 24%. 0% and 33.5%, respectively. This practical and economic approach can be used for developing the algorithms of Chinese ocean color and temperature sensor （COCTS） on the satellite Haiyang-1 to derive the Chl-a concentration concentration distribution. The applicability of the algorithms was analyzed using some in situ measurements. Suspended sediment is the main factor influencing the accuracy of the spectral ratio algorithms of Chl-a concentration. The algorithms are suitable to using in the regions where suspended sediment concentrations （ SSC ） are less than 5 g/m^3 under the condition of relative error of Chl-a concentration retrieval within 35%. High concentration of suspended sediment leads to the overestimate remote sensing retrieval of concentration of Chl-a, while low-middle SSCs lead to the low Chl-a concentration values using the spectral ratio algorithms. Since the accuracy of Chl-a concentration by the spectral ratio algorithms is limited to waters of Case 2, it is necessary to develop semi-analytical models to improve the performance of satellite ocean color remote sensing in turbid coastal waters.

关键词： CMODIS chlorophyll-a concentration suspended sediment concentration

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A new algorithm based on the background field for red tide monitoring in the East China Sea

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Acta Oceanologica Sinica 2014年第5期33卷 62-71页

作者： XU Xiaohui PAN Delu mao zhihua TAO Bangyi South China Sea Institute of Oceanology Chinese Academy of Sciences State Key Laboratory of Satellite Ocean Environment Dynamics the Second Institute of Oceanography State Oceanic Administration University of Chinese Academy of Sciences

Remote sensing has been proven to be an effective means of monitoring red tides. The spectral information is an important basis for establishing a model to monitor red tides. The spectral curves of red tide events are analyzed and compared with multiyear monthly averaged spectral curves based on MODIS data from July 2002 to June 2012, as well as spectral differences at the same location during red tide presence and absence. A red tide monitoring algorithm is developed based on the background field to extract the red tide information of the East China Sea （ECS）. With the application of the algorithm in the ECS, the results reveal that the developed model can effectively determine the location of red tides, with good correspondence to the results from an official bulletin. This demonstrates that the algorithm can effectively extract the red tide information.

关键词： red tide remote sensing background field East China Sea

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Optical detection of Prorocentrum donghaiense blooms based on multispectral reflectance

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Acta Oceanologica Sinica 2013年第10期32卷 48-56页

作者： TAO Bangyi PAN Delu mao zhihua SHEN Yuzhang ZHU Qiankun CHEN Jianyu State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of OceanographyState Oceanic Administration

Prorocentrum donghaiense is one of the most common red tide causative dinoflagellates in the Changjiang （Yangtze） River Estuary and the adjacent area of the East China Sea. It causes large-scale blooms in late spring and early summer that lead to widespread ecologic and economic damage. A means for distinguish- ing dinoflagellate blooms from diatom （Skeletonema costatum） blooms is desired. On the basis of measure- ments of remote sensing refectance [Rrs（λ）] and inherent optical parameters, the potential of using a mul- tispectral approach is assessed for discriminating the algal blooms due to P. donghaiense from those due to S. costatum. The behavior of two reflectance ratios [R1 = Rrs（560）/Rrs（532） and Re = Rrs（708）/Rrs（665）], suggests that differentiation of P. donghaiense blooms from diatom bloom types is possible from the current band setup of ocean color sensors. It is found that there are two reflectance ratio regimes that indicate a bloom is dominated by P. donghaiense; （1） R1 〉 1.55 and R2 〈 1.0 or （2） R1 〉 1.75 and R2 ≥ 1.0. Various sensitivity analyses are conducted to investigate the effects of the variation in varying levels of chlorophyll concentration and colored dissolved organic matter （CDOM） as well as changes in the backscattering ratio （bbp/bp） on the efficacy of this muitispectral approach. Results indicate that the intensity and inherent op- tical properties of the algal species explain much of the behavior of the two ratios. Although backscattering influences the amplitude of Rrs（λ）, especially in the 530 and 560 nm bands, the discrimination between P. donghaiense and diatoms is not significantly affected by the variation of bbp/bp. Since aCDOM （440） in coastal areas of the ECS is typically lower than 1.0 m-1 in most situations, the presence of CDOM does not interfere with this discrimination, even as SCDOM varies from 0.01 to 0.026 nm-1. Despite all of these effects, the dis- crimination of P. donghaiense blooms from diatom blooms based on mul

关键词： multispectral reflectance harmful algal blooms Prorocentrum donghaiense Skeletonerna costatum discrimination

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Latitudinal and interannual variations of the spring phytoplankton bloom peak in the East Asian marginal seas

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Acta Oceanologica Sinica 2016年第12期35卷 81-88页

作者： CHEN Cheng mao zhihua HAN Guoqi ZHU Qiankun GONG Fang WANG Tianyu State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of OceanographyState Oceanic Administration Biological and Physical Oceanography Section Fisheries and Oceans CanadaNorthwest Atlantic Fisheries CentreNewfoundland and Labrador

Combined studies of latitudinal and interannual variations of annual phytoplankton bloom peak in East Asian marginal seas(17°–58°N, including the northern South China Sea(SCS), Kuroshio waters, the Sea of Japan and the Okhotsk Sea) are rarely. Based on satellite-retrieved ten-year(2003–2012) median timing of the annual Chlorophyll a concentration(Chl a) climax, here we report that this annual spring bloom peak generally delays from the SCS in January to the Okhotsk Sea in June at a rate of(21.20±2.86) km/d(decadal median±SD). Spring bloom is dominant feature of the phytoplankton annual cycle over these regions, except for the SCS which features winter bloom. The fluctuation of the annual peak timing is mainly within ±48 d departured from the decadal median peak date, therefore this period(the decadal median peak date ±48 d) is defined as annual spring bloom period. As sea surface temperature rises, earlier spring bloom peak timing but decreasing averaged Chl a biomass in the spring bloom period due to insufficient light is evident in the Okhotsk Sea from 2003 to 2012. For the rest of three study domains, there are no significant interannual variance trend of the peak timing and the averaged Chl a biomass. Furthermore this change of spring phytoplankton bloom timing and magnitude in the Okhotsk Sea challenges previous prediction that ocean warming would enhance algal productivity at high latitudes.

关键词： latitudinal and interannual variation spring bloom peak phytoplankton phenology East Asian marginal seas climate change

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Analysis on coral reefs mapping using SPOT5 data at the Dongsha Atoll

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Acta Oceanologica Sinica 2007年第2期26卷 26-35页

作者： CHEN Jianyu mao zhihua ZHANG Huaguo WU Junping CHEN Xiaodong PAN Delu State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of Oceanography State Oceanic Administration Hangzhou 310012 China

Coral reefs are an sensitive-to-environment complex marine ecosystem. The ecosystem of corals is rich in biodiversity. Remote sensing offers a powerful tool for categorizing coral reefs and is the most cost - effective approach for the large - scale reef survey. The Dongsha Atoll, more than 300 km2 with an average depth of 10 m, is located at the northern continental margin of the South China Sea. It has been abused by destructive fishing during recent decades. Three satellite imageries （Quickbird2, ETM ＋ and SPOTS） are used to evaluate the capabilities of SPOT5 imagery to provide data that are useful for categorizing the current distribution of coral reefs therein. During the data processing, unsupervised classification functions are adopted for ETM ＋ and SPOT5 data, while the supervised classification method is used for Quickbird2. The classes are （or not） merged into coral reef, and then will be operated by vectorization, simplification, and topological analysis. There are 1 331 coral reefs larger than 100 m2 with a detection limit of 3 × 3 pixels at the multi - band data of Quickbird2, which is taken as the comparison baseline. The results extracted from SPOT5 and ETM images are less in number and area than those from the Quickbird2 image, whereas the results from SPOT5 data are better than those of ETM data at the silty lagoon due to its higher resolution. SPOT5 XS band 2 fails to distinguish the deep substrate inside the atoll compared with ETM data because of its poor penetration capability. Only SPOT XS band 1 cannot be used to differentiate coral reef from sand bottom. Merging the SPOT5 multi - bands data with the spatial resolution of SPOT5 pan - data and referring to ETM imagery are expected to provide an optimal satellite - based approach for mapping of coral reefs.

关键词： coral reef Dongsha Atoll SPOT5 Quickbird2

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Measurements of ocean wave spectrum from airborne radar at small incidence angles

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Acta Oceanologica Sinica 2011年第1期30卷 40-46页

作者： REN Lin PAN Delu mao zhihua Department of Electromagnetic Fields and Microwave Theory Nanjing University of Science andTechnology Nanjing 210094 China State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of OceanographyState Oceanic Administration Hangzhou 310012 China

This paper proposes the retrieval method of ocean wave spectrum for airborne radar observations at small incidence angles, which is slightly modified from the method developed by Hauser. Firstly, it makes use of integration method to estimate total mean square slope instead of fitting method, which aims to reduce the affects of fluctuations superposed on normalized radar cross-section by integration. Secondly, for eliminating the noise spectrum contained in signal spectrum, the method considers the signal spectrum in certain look direction without any long wave components as the assumed noise spectrum, which would be subtracted from signal spectrum in any look direction for linear wave spectrum retrieval. Estimated v from the integration method are lower than the one from fitting method and have a standard deviation of 0.004 between them approximately. The assumed noise spectrum energy almost has no big variations along with the wave number and is slightly lower to the high wave number part of signal spectrum in any look direction, which follows that the assumption makes sense. The retrieved directional spectra are compared with the buoy records in terms of peak wavelength, peak direction and the significant wave height. Comparisons show that the retrieved peak wavelength and significant wave height are slightly higher than the buoy records but don＇t differs significantly （error less than 10%）. For peak direction, the swell waves in first case basically propagate in the wind direction 6 hours ago and the wind-generated waves in second case also propagate in the wind direction, but the 180° ambiguity remains. Results show that the modified method can carry out the retrieval of directional wave spectrum.

关键词： airborne radar directional wave spectrum retrieval total mean square slope

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Data fusion in data scarce areas using a back-propagation artificial neural network model： a case study of the South China Sea

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Frontiers of Earth Science 2018年第2期12卷 280-298页

作者： Zheng WANG zhihua mao Junshi XIA Peijun DU Liangliang SHI Haiqing HUANG Tianyu WANG Fang GONG Qiankun ZHU School of Geographic and Oceanographic Sciences Nanjing University Nanjing 210023 China Collaborative Innovation Center for the South China Sea Studies Nanjing University Nanjing 210023 China States Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of Oceanography State Oceanic Administration Hangzhou 310012 China Research Center for Advanced Science and Technology The University of Tokyo Tokyo 153-8904 Japan Ocean College Zhejiang University Hangzhou 310058 China

The cloud cover for the South China Sea andits coastal area is relatively large throughout the year,which limits the potential application of optical remotesensing. A H J-charge-coupled device （HJ-CCD） has theadvantages of wide field, high temporal resolution, andshort repeat cycle. However, this instrument suffers fromits use of only four relatively low-quality bands whichcan＇t adequately resolve the features of long *** Landsat Enhanced Thematic Mapper-plus （ETM＋）provides high-quality data, however, the Scan LineCorrector （SLC） stopped working and caused striping ofremote sensed images, which dramatically reduced thecoverage of the ETM＋ data. In order to combine theadvantages of the HJ-CCD and Landsat ETM＋ data, weadopted a back-propagation artificial neural network （BP-ANN） to fuse these two data types for this study. Theresults showed that the fused output data not only have theadvantage of data intactness for the HJ-CCD, but also havethe advantages of the multi-spectral and high radiometricresolution of the ETM＋ data. Moreover, the fused datawere analyzed qualitatively, quantitatively and from apractical application point of view. Experimental studiesindicated that the fused data have a full spatial distribution,multi-spectral bands, high radiometric resolution, a smalldifference between the observed and fused output data, anda high correlation between the observed and fused *** excellent performance in its practical application is afurther demonstration that the fused data are of highquality.

关键词： data fusion South China Sea BP-ANN model

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Factors affecting spring bloom in the South of Cheju Island in the East China Sea

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Acta Oceanologica Sinica 2015年第3期34卷 51-58页

作者： FU Dongyang HUANG Zhaojun ZHANG Yuanzhi PAN Delu DING Youzhua LIU Dazhao ZHANG Ying mao zhihua CHEN Jianfang Laboratory of Remote Sensing and Information Technology Guangdong Ocean University Shenzhen Research Institute Chinese University of Hong Kong State Key Laboratory of Satellite Ocean Environment Dynamics Second Institute of Oceanography State Oceanic Administration

A soil circulation occurs in the south of Cheju Island in the spring. Nutrients and its influence on chloro-phyll a （Chla） around the circulations were studied from April 9 to May 6, 2007. Spring bloom with elevated concentrations of Chla was observed during the investigation. High concentrations of phosphate, nitrate and silicate at 0.6, 12, and 8 mmol/m3, respectively, were detected. A low water temperature prevented the growth of phytoplankton. Chla concentrations in the study area might be strongly associated with the high silicate concentration.

关键词： phosphate nitrate silicate phytoplankton circulation

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An alternative approach to determine critical angle of contrast reversal and surface roughness of oil slicks under sunglint

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International Journal of Digital Earth 2018年第9期11卷 972-979页

作者： Yansha Wen Mengqiu Wang Yingcheng Lu Shaojie Sunc Minwei Zhang zhihua mao Jing Shi Yongxue Liu International Institute for Earth System Science Nanjing UniversityNanjingPeople’s Republic of China State Key Laboratory of Satellite Ocean Environment Dynamics SOAHangzhouPeople’s Republic of China College of Marine Science University of South FloridaSt.PetersburgFLUSA

The critical angle is the angle at which the contrast of oil slicks reverse their contrasts against the surrounding oil-free seawater under *** determination of the critical angle can help estimate surface roughness and refractive index of the oil *** it’s difficult to determine a certain critical angle,the potential critical angle range help to improve the estimation *** this study,the angle between the viewing direction and the direction of mirror reflection is used as an indicator for quantifying the critical angle and could be calculated from the solar/viewing geometry from observations of the Moderate Resolution Imaging Spectroradiometer(MODIS).The natural seep oil slicks in the Gulf of Mexico were first delineated using a customized segmentation approach to remove noise and apply a morphological *** the basis of the histograms of the brightness values of the delineated oil slicks,the potential range of the critical angle was determined,and then an optimal critical angle between oil slicks and seawater was then determined from statistical and regression analyses in this *** critical angle corresponds to the best fitting between the modeled and observed surface roughness of seep oil slicks and seawater.

关键词： Sunglint critical angle natural seep oil slicks surface roughness MODIS

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