Wetlands classification and assessment of Ramsar sites in China based on time series Moderate Resolution Imaging Spectroradiometer (MODIS) imagery
Liwei Xing A B , Zhenguo Niu A C , Panpan Xu A and Dachong Li A
+ Author Affiliations
- Author Affiliations
A State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, 20 Datun Road, Chaoyang District, Beijing, 100101, P.R. China.
B Satellite Surveying and Mapping Application Center, National Administration of Surveying, Mapping and Geoinformation, 1 Baishengcun, Zizhuyuan Road, Haidian District, Beijing, 100048, P.R. China.
C Corresponding author. Email: niuzg@radi.ac.cn
Marine and Freshwater Research 69(5) 658-668 https://doi.org/10.1071/MF17119
Submitted: 1 May 2017 Accepted: 1 September 2017 Published: 14 November 2017
Abstract
Globally, wetland loss and degradation have become serious environmental and ecological issues. Wetland monitoring of Ramsar sites in China is important for developing reasonable strategies to protect wetlands. Satellite image time series may be used for the long-term monitoring of wetland ecosystems. The present study used moderate-resolution imaging spectroradiometer (MODIS) time series data collected in 2001 and 2013 for 20 Ramsar sites in China and assessed the environmental status of these reserves using landscape metrics. The results showed that specific seasonal wetland classes, such as flooded mud, permanent water and seasonal marshes, can be identified using MODIS time series data with acceptable accuracy. In addition to wetland area, we suggest using other landscape metrics, including landscape integrity and landscape disturbance or degradation indices, to assess wetland environmental quality. The slight wetland loss (0.8%) noted in the 20 reserves evaluated herein could indicate the effectiveness of efforts of the Chinese government and local government agencies to protect Ramsar sites. The existing unfavourable environmental conditions, which were manifested by low landscape integrity and high landscape disturbance or degradation for some reserves, were caused primarily by increasing water requirements outside the reserves and by agricultural development within reserves. Therefore, determining how to balance relationships between economic development and ecological protection of the reserves will be important in the future.
Additional keywords: landscape metric, wetland remote sensing.
References
Alonso, M., and Malpica, J. A. (2010). Satellite imagery classification with LiDAR data. Trees – International Archives of the Photogrammetry, Remote Sensing and Spatial Information Science 38, 730–735.Bai, J., Ouyang, H., Cui, B., Wang, Q., and Chen, H. (2008). Changes in landscape pattern of alpine wetlands on the Zoige Plateau in the past four decades. Acta Ecologica Sinica 28, 2245–2252.
| Changes in landscape pattern of alpine wetlands on the Zoige Plateau in the past four decades.Crossref | GoogleScholarGoogle Scholar |
Brinson, M. M., and Malvárez, A. I. (2002). Temperate freshwater wetlands: types, status, and threats. Environmental Conservation 29, 115–133.
| Temperate freshwater wetlands: types, status, and threats.Crossref | GoogleScholarGoogle Scholar |
Bwangoy, J.-R. B., Hansen, M. C., Roy, D. P., De Grandi, G., and Justice, C. O. (2010). Wetland mapping in the Congo Basin using optical and radar remotely sensed data and derived topographical indices. Remote Sensing of Environment 114, 73–86.
| Wetland mapping in the Congo Basin using optical and radar remotely sensed data and derived topographical indices.Crossref | GoogleScholarGoogle Scholar |
Campos, J. C., Sillero, N., and Brito, J. C. (2012). Normalized difference water indexes have dissimilar performances in detecting seasonal and permanent water in the Sahara–Sahel transition zone. Journal of Hydrology 464–465, 438–446.
| Normalized difference water indexes have dissimilar performances in detecting seasonal and permanent water in the Sahara–Sahel transition zone.Crossref | GoogleScholarGoogle Scholar |
Ceccato, P., Flasse, S., and Gregoire, J.-M. (2002). Designing a spectral index to estimate vegetation water content from remote sensing data: part 2. Validation and applications. Remote Sensing of Environment 82, 198–207.
| Designing a spectral index to estimate vegetation water content from remote sensing data: part 2. Validation and applications.Crossref | GoogleScholarGoogle Scholar |
Chen, J., and Huang, G. (1995). Discussion on China wetland classification system and classification index. Forest Resources Management 5, 65–71.
Chen, D., Huang, J., and Jackson, T. J. (2005). Vegetation water content estimation for corn and soybeans using spectral indices derived from MODIS near-and short-wave infrared bands. Remote Sensing of Environment 98, 225–236.
| Vegetation water content estimation for corn and soybeans using spectral indices derived from MODIS near-and short-wave infrared bands.Crossref | GoogleScholarGoogle Scholar |
Chen, Y., Huang, C., Ticehurst, C., Merrin, L., and Thew, P. (2013). An evaluation of MODIS daily and 8-day composite products for floodplain and wetland inundation mapping. Wetlands 33, 823–835.
| An evaluation of MODIS daily and 8-day composite products for floodplain and wetland inundation mapping.Crossref | GoogleScholarGoogle Scholar |
Chen, Y., Niu, Z., Hu, S., and Zhang, H. (2016). Dynamic monitoring of Dongting Lake wetland using time-series MODIS imagery. Journal of Hydraulic Engineering 47, 1093–1104.
| Dynamic monitoring of Dongting Lake wetland using time-series MODIS imagery.Crossref | GoogleScholarGoogle Scholar |
Cheng, Y., and Zhang, P. (2005). Regional patterns changes of Chinese grain production and response of commodity grain base in northeast China. Dili Kexue 25, 513–520.
Cheng, Y., Wang, X., Guo, J., Zhao, Y., and Huang, J. (2012). The temporal–spatial dynamic analysis of China rice production. Zhongguo Nong Ye Ke Xue 45, 3473–3485.
| The temporal–spatial dynamic analysis of China rice production.Crossref | GoogleScholarGoogle Scholar |
Ding, S., and Liang, G. (2004). Landscape pattern change of regional wetland along the Yellow River in Henan Province in the last two decades. Acta Geographica Sinica 59, 653–661.
Fan, D., Wang, X., Li, E., Cai, X., Huang, J., Hu, Y., and Jiang, L. (2012). Dynamics of Lake Dongting wetland from 1993 to 2010. Hupo Kexue 24, 571–576.
| Dynamics of Lake Dongting wetland from 1993 to 2010.Crossref | GoogleScholarGoogle Scholar |
Foody, G. M. (2002). Status of land cover classification accuracy assessment. Remote Sensing of Environment 80, 185–201.
| Status of land cover classification accuracy assessment.Crossref | GoogleScholarGoogle Scholar |
Galford, G. L., Mustard, J. F., Melillo, J., Gendrin, A., Cerri, C. C., and Cerri, C. E. P. (2008). Wavelet analysis of MODIS time series to detect expansion and intensification of row-crop agriculture in Brazil. Remote Sensing of Environment 112, 576–587.
| Wavelet analysis of MODIS time series to detect expansion and intensification of row-crop agriculture in Brazil.Crossref | GoogleScholarGoogle Scholar |
Gao, B. (1996). NDWI – a normalized difference water index for remote sensing of vegetation liquid water from space. Remote Sensing of Environment 58, 257–266.
| NDWI – a normalized difference water index for remote sensing of vegetation liquid water from space.Crossref | GoogleScholarGoogle Scholar |
Gao, F., Masek, J., Schwaller, M., and Hall, F. (2006). On the blending of the Landsat and MODIS surface reflectance: predicting daily Landsat surface reflectance. IEEE Transactions on Geoscience and Remote Sensing 44, 2207–2218.
| On the blending of the Landsat and MODIS surface reflectance: predicting daily Landsat surface reflectance.Crossref | GoogleScholarGoogle Scholar |
Gong, P., Niu, Z., Cheng, X., Zhao, K., Zhou, D., Guo, J., Liang, L., Wang, X., Li, D., and Huang, H. (2010). China’s wetland change (1990–2000) determined by remote sensing. Science China. Earth Sciences 53, 1036–1042.
| China’s wetland change (1990–2000) determined by remote sensing.Crossref | GoogleScholarGoogle Scholar |
Guo, Q., Kelly, M., and Graham, C. H. (2005). Support vector machines for predicting distribution of Sudden Oak Death in California. Ecological Modelling 182, 75–90.
| Support vector machines for predicting distribution of Sudden Oak Death in California.Crossref | GoogleScholarGoogle Scholar |
Han, X., Chen, X., and Feng, L. (2015). Four decades of winter wetland changes in Poyang Lake based on Landsat observations between 1973 and 2013. Remote Sensing of Environment 156, 426–437.
| Four decades of winter wetland changes in Poyang Lake based on Landsat observations between 1973 and 2013.Crossref | GoogleScholarGoogle Scholar |
Hoang, T. H., Lock, K., Mouton, A., and Goethals, P. L. M. (2010). Application of classification trees and support vector machines to model the presence of macroinvertebrates in rivers in Vietnam. Ecological Informatics 5, 140–146.
| Application of classification trees and support vector machines to model the presence of macroinvertebrates in rivers in Vietnam.Crossref | GoogleScholarGoogle Scholar |
Jackson, T. J., Chen, D., Cosh, M., Li, F., Anderson, M., Walthall, C., Doriaswamy, P., and Hunt, E. R. (2004). Vegetation water content mapping using Landsat data derived normalized difference water index for corn and soybeans. Remote Sensing of Environment 92, 475–482.
| Vegetation water content mapping using Landsat data derived normalized difference water index for corn and soybeans.Crossref | GoogleScholarGoogle Scholar |
Ji, L., Zhang, L., and Wylie, B. (2009). Analysis of dynamic thresholds for the normalized difference water index. Photogrammetric Engineering and Remote Sensing 75, 1307–1317.
| Analysis of dynamic thresholds for the normalized difference water index.Crossref | GoogleScholarGoogle Scholar |
Jones, T. G., Coops, N. C., and Sharma, T. (2010). Assessing the utility of airborne hyperspectral and LiDAR data for species distribution mapping in the coastal Pacific Northwest, Canada. Remote Sensing of Environment 114, 2841–2852.
| Assessing the utility of airborne hyperspectral and LiDAR data for species distribution mapping in the coastal Pacific Northwest, Canada.Crossref | GoogleScholarGoogle Scholar |
Kashaigili, J. J., Mbilinyi, B. P., Mccartney, M., and Mwanuzi, F. L. (2006). Dynamics of Usangu Plains wetlands: use of remote sensing and GIS as management decision tools. Physics and Chemistry of the Earth 31, 967–975.
| Dynamics of Usangu Plains wetlands: use of remote sensing and GIS as management decision tools.Crossref | GoogleScholarGoogle Scholar |
Kavzoglu, T., and Colkesen, I. (2009). A kernel functions analysis for support vector machines for land cover classification. International Journal of Applied Earth Observation and Geoinformation 11, 352–359.
| A kernel functions analysis for support vector machines for land cover classification.Crossref | GoogleScholarGoogle Scholar |
Klein, I., Dietz, A. J., Gessner, U., Galayeva, A., Myrzakhmetov, A., and Kuenzer, C. (2014). Evaluation of seasonal water body extents in Central Asia over the past 27 years derived from medium-resolution remote sensing data. International Journal of Applied Earth Observation and Geoinformation 26, 335–349.
| Evaluation of seasonal water body extents in Central Asia over the past 27 years derived from medium-resolution remote sensing data.Crossref | GoogleScholarGoogle Scholar |
Knight, A. W., Tindall, D. R., and Wilson, B. A. (2009). A multitemporal multiple density slice method for wetland mapping across the state of Queensland, Australia. International Journal of Remote Sensing 30, 3365–3392.
| A multitemporal multiple density slice method for wetland mapping across the state of Queensland, Australia.Crossref | GoogleScholarGoogle Scholar |
Landmann, T., Dietz, A., and Dech, S. (2009). Large scale wetland mapping in semi-arid Africa using 250-meter MODIS phenology metrics and topographic variables. In ‘Geoscience and Remote Sensing Symposium: IGARSS 2009’, 12–17 July 2009, Cape Town, South Africa. (Ed. H. Annegarn.) Paper 11246466. (IEEE International: Cape Town, South Africa.)
Lee, T. M., and Yeh, H. C. (2009). Applying remote sensing techniques to monitor shifting wetland vegetation: a case study of Danshui River estuary mangrove communities, Taiwan. Ecological Engineering 35, 487–496.
| Applying remote sensing techniques to monitor shifting wetland vegetation: a case study of Danshui River estuary mangrove communities, Taiwan.Crossref | GoogleScholarGoogle Scholar |
Lhermitte, S., Verbesselt, J., Verstraeten, W. W., and Coppin, P. (2011). A comparison of time series similarity measures for classification and change detection of ecosystem dynamics. Remote Sensing of Environment 115, 3129–3152.
| A comparison of time series similarity measures for classification and change detection of ecosystem dynamics.Crossref | GoogleScholarGoogle Scholar |
Liu, Z., and Ma, X. (2006). Wetland classification. Wetland Science & Management 2, 60–63.
Liu, H., Zhang, S., and Lu, X. (2002). Processes of wetland landscape changes in Naoli River Basin since 1980s. Journal of Natural Resources 17, 698–705.
Löw, F., Michel, U., Dech, S., and Conrad, C. (2013). Impact of feature selection on the accuracy and spatial uncertainty of per-field crop classification using support vector machines. ISPRS Journal of Photogrammetry and Remote Sensing 85, 102–119.
| Impact of feature selection on the accuracy and spatial uncertainty of per-field crop classification using support vector machines.Crossref | GoogleScholarGoogle Scholar |
McFeeters, S. (1996). The use of the normalized difference water index (NDWI) in the delineation of open water features. International Journal of Remote Sensing 17, 1425–1432.
| The use of the normalized difference water index (NDWI) in the delineation of open water features.Crossref | GoogleScholarGoogle Scholar |
Moser, L., Voigt, S., Schoepfer, E., and Palmer, S. (2014). Multitemporal wetland monitoring in Sub-Saharan West-Africa using medium resolution optical satellite data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 7, 3402–3415.
| Multitemporal wetland monitoring in Sub-Saharan West-Africa using medium resolution optical satellite data.Crossref | GoogleScholarGoogle Scholar |
Na, X., and Zang, S. (2011). Classifying wetland vegetation type from MODIS NDVI time series using Fourier analysis. In ‘Applied Informatics and Communication: International Conference on Applied Informatics and Communication, ICAIC 2011, Proceedings, Part I’, 20–21 August 2011, Xi’an, China. (Ed. Z. Dehuai.) pp. 66–73. (Springer: Xi’an, China.)
Nguyen, T. T. H., De Bie, C. A. J. M., Ali, A., Smaling, E. M. A., and Chu, T. H. (2012). Mapping the irrigated rice cropping patterns of the Mekong Delta, Vietnam, through hyper-temporal SPOT NDVI image analysis. International Journal of Remote Sensing 33, 415–434.
| Mapping the irrigated rice cropping patterns of the Mekong Delta, Vietnam, through hyper-temporal SPOT NDVI image analysis.Crossref | GoogleScholarGoogle Scholar |
Ni, J., Yin, K., and Zhao, Z. (1998). Comprehensive classification for wetlands I: Classification. Journal of Natural Resources 13, 214–220.
Niu, Z., Gong, P., Cheng, X., Guo, J., Wang, L., Huang, H., Shen, S., Wu, Y., Wang, X., and Wang, X. (2009). Geographical characteristics of China’s wetlands derived from remotely sensed data. Science in China – D. Earth Science 52, 723–738.
| Geographical characteristics of China’s wetlands derived from remotely sensed data. Science in China – D.Crossref | GoogleScholarGoogle Scholar |
Niu, Z., Zhang, H., Wang, X., Yao, W., Zhou, D., Zhao, K., Zhao, H., Li, N., Huang, H., and Li, C. (2012). Mapping wetland changes in China between 1978 and 2008. Chinese Science Bulletin 57, 2813–2823.
| Mapping wetland changes in China between 1978 and 2008.Crossref | GoogleScholarGoogle Scholar |
Ordoyne, C., and Friedl, M. A. (2008). Using MODIS data to characterize seasonal inundation patterns in the Florida Everglades. Remote Sensing of Environment 112, 4107–4119.
| Using MODIS data to characterize seasonal inundation patterns in the Florida Everglades.Crossref | GoogleScholarGoogle Scholar |
Ouma, Y. O., and Tateishi, R. (2006). A water index for rapid mapping of shoreline changes of five East African Rift Valley lakes: an empirical analysis using Landsat TM and ETM+ data. International Journal of Remote Sensing 27, 3153–3181.
| A water index for rapid mapping of shoreline changes of five East African Rift Valley lakes: an empirical analysis using Landsat TM and ETM+ data.Crossref | GoogleScholarGoogle Scholar |
Ozesmi, S. L., and Bauer, M. E. (2002). Satellite remote sensing of wetlands. Wetlands Ecology and Management 10, 381–402.
| Satellite remote sensing of wetlands.Crossref | GoogleScholarGoogle Scholar |
Petus, C., Lewis, M., and White, D. (2013). Monitoring temporal dynamics of Great Artesian Basin wetland vegetation, Australia, using MODIS NDVI. Ecological Indicators 34, 41–52.
| Monitoring temporal dynamics of Great Artesian Basin wetland vegetation, Australia, using MODIS NDVI.Crossref | GoogleScholarGoogle Scholar |
Qiu, P., Xu, S., Xie, G., and Fu, Y. (2010). Comparisons of natural wetland, semi-constructed wetland and engineered wetland. Journal of Hainan Normal University –Nature and Science 23, 209–231.
Rao, Y., Zhu, X., Chen, J., and Wang, J. (2015). An improved method for producing high spatial-resolution NDVI time series datasets with multi-temporal MODIS NDVI data and Landsat TM/ETM plus images. Remote Sensing 7, 7865–7891.
| An improved method for producing high spatial-resolution NDVI time series datasets with multi-temporal MODIS NDVI data and Landsat TM/ETM plus images.Crossref | GoogleScholarGoogle Scholar |
Rebelo, L. M., Finlayson, C. M., and Nagabhatla, N. (2009). Remote sensing and GIS for wetland inventory, mapping and change analysis. Journal of Environmental Management 90, 2144–2153.
| Remote sensing and GIS for wetland inventory, mapping and change analysis.Crossref | GoogleScholarGoogle Scholar |
Sakamoto, T., Van Nguyen, N., Kotera, A., Ohno, H., Ishitsuka, N., and Yokozawa, M. (2007). Detecting temporal changes in the extent of annual flooding within the Cambodia and the Vietnamese Mekong Delta from MODIS time-series imagery. Remote Sensing of Environment 109, 295–313.
| Detecting temporal changes in the extent of annual flooding within the Cambodia and the Vietnamese Mekong Delta from MODIS time-series imagery.Crossref | GoogleScholarGoogle Scholar |
Schroeder, M. A., Gorrell, J., Vander Haegen, M., Anthony, J., Duff, A., Foisy, J., Gibilisco, C., and Cosentino, B. (2013). Ecological integrity monitoring of wildlife areas in Washington State: pilot study for the 2011–2013 Biennium. Lands Division, Wildlife Program, Washington Department of Fish and Wildlife, Olympia, WA, USA.
Sims, N. C., and Colloff, M. J. (2012). Remote sensing of vegetation responses to flooding of a semi-arid floodplain: implications for monitoring ecological effects of environmental flows. Ecological Indicators 18, 387–391.
| Remote sensing of vegetation responses to flooding of a semi-arid floodplain: implications for monitoring ecological effects of environmental flows.Crossref | GoogleScholarGoogle Scholar |
Sun, F., Zhao, Y., Gong, P., Ma, R., and Dai, Y. (2014). Monitoring dynamic changes of global land cover types: fluctuations of major lakes in China every 8 days during 2000–2010. Chinese Science Bulletin 59, 171–189.
| Monitoring dynamic changes of global land cover types: fluctuations of major lakes in China every 8 days during 2000–2010.Crossref | GoogleScholarGoogle Scholar |
Tana, G., Letu, H., Cheng, Z., and Tateishi, R. (2013). Wetlands mapping in North America by decision rule classification using MODIS and ancillary data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 6, 2391–2401.
| Wetlands mapping in North America by decision rule classification using MODIS and ancillary data.Crossref | GoogleScholarGoogle Scholar |
Tang, X., and Huang, G. (2003). Study on classification system for wetland types in China. Forest Research 16, 531–539.
Töyrä, J., and Pietroniro, A. (2005). Towards operational monitoring of a northern wetland using geomatics-based techniques. Remote Sensing of Environment 97, 174–191.
| Towards operational monitoring of a northern wetland using geomatics-based techniques.Crossref | GoogleScholarGoogle Scholar |
Vermote, E., Kotchenova, S. Y., and Ray, J. P. (2011). MODIS Land Surface Reflectance Science Computing Facility user’s guide, ver. 1.4. National Aeronautics and Space Administration, Washington, DC, USA
Wang, A., Zhang, S., and Zhang, B. (2002). A study on the change of spatial pattern of wetland in the Sanjiang Plain. Acta Ecologica Sinica 23, 237–243.
Wang, L., Hu, L., Li, H., Liu, X., and Wei, C. (2014). Driving forces of landscape changes in Nanweng River Nature Reserve based on RS and GIS. Protection Forest Science and Technology 3, 16–18.
Xiao, D., Tian, B., Tian, K., and Yang, Y. (2010). Landscape patterns and their changes in Sichuan Ruoergai wetland national nature reserve. Acta Ecologica Sinica 30, 27–32.
| Landscape patterns and their changes in Sichuan Ruoergai wetland national nature reserve.Crossref | GoogleScholarGoogle Scholar |
Zarco-Tejada, P. J., Rueda, C. A., and Ustin, S. L. (2003). Water content estimation in vegetation with MODIS reflectance data and model inversion methods. Remote Sensing of Environment 85, 109–124.
| Water content estimation in vegetation with MODIS reflectance data and model inversion methods.Crossref | GoogleScholarGoogle Scholar |
Zhang, M., and Dong, Y. (2002). Study on changes of coastal wetland landscape in Shuangtaihekou Nature Reserve and its management measures. Dili Kexue 22, 119–122.
Zhang, W., Lu, Q., Gao, Z., and Peng, J. (2008). Response of remotely sensed normalized difference water deviation index to the 2006 drought of eastern Sichuan Basin. Science in China – D. Earth Science 51, 748–758.
| Response of remotely sensed normalized difference water deviation index to the 2006 drought of eastern Sichuan Basin.Crossref | GoogleScholarGoogle Scholar |
Zhang, S., Na, X., Kong, B., Wang, Z., Jiang, H., Yu, H., Zhao, Z., Li, X., Liu, C., and Dale, P. (2009). Identifying wetland change in China’s Sanjiang Plain using remote sensing. Wetlands 29, 302–313.
| Identifying wetland change in China’s Sanjiang Plain using remote sensing.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXlt12lsg%3D%3D&md5=5d394afb85123b24bd9d98913d681f36CAS |
Zhang, Y., Lu, D., Yang, B., Sun, C., and Sun, M. (2011). Coastal wetland vegetation classification with a Landsat Thematic Mapper image. International Journal of Remote Sensing 32, 545–561.
| Coastal wetland vegetation classification with a Landsat Thematic Mapper image.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhtlCqur3E&md5=e3c9bdafcd328f05790a0b225ddf6500CAS |
Zhao, B., Yan, Y., Guo, H., He, M., Gu, Y., and Li, B. (2009). Monitoring rapid vegetation succession in estuarine wetland using time series MODIS-based indicators: an application in the Yangtze River Delta area. Ecological Indicators 9, 346–356.
| Monitoring rapid vegetation succession in estuarine wetland using time series MODIS-based indicators: an application in the Yangtze River Delta area.Crossref | GoogleScholarGoogle Scholar |
Zhu, X., Chen, J., Gao, F., Chen, X., and Masek, J. G. (2010). An enhanced spatial and temporal adaptive reflectance fusion model for complex heterogeneous regions. Remote Sensing of Environment 114, 2610–2623.
| An enhanced spatial and temporal adaptive reflectance fusion model for complex heterogeneous regions.Crossref | GoogleScholarGoogle Scholar |
Zhu, C., Luo, J., Shen, Z., and Huang, C. (2011). Wetland mapping in the Balqash Lake Basin using multi-source remote sensing data and topographic features synergic retrieval. Procedia Environmental Sciences 10, 2718–2724.
| Wetland mapping in the Balqash Lake Basin using multi-source remote sensing data and topographic features synergic retrieval.Crossref | GoogleScholarGoogle Scholar |
