Estimation Approach of Chlorophyll-a Concentration in Baiyangdian Based on Semi-Supervised Optical Classification
CHEN Wen-yue1, 2, ZHAO Qi-chao1, 2*, YANG Xiu-feng1, 2, HAN Bao-hui1, 2, 3, ZHANG Yu-qing1, 2
1. North China Institute of Aerospace Engineering, Institute of Remote Sensing Information Engineering, Langfang 065000, China
2. Hebei Aerospace Remote Sensing Information Processing and Application Collaborative Innovation Center, Langfang 065000, China
3. Hebei Institute of Laser, Shijiazhuang 050000, China
Abstract:The estimation of Chlorophyll-a concentration (Chl-a) using remote sensing technology is considered an effective way to monitor eutrophication in water bodies. Due to the complexity of the optical properties of inland water bodies and the existence of large spatial and temporal variability, it is difficult for a single estimation model to accurately estimate Chl-a concentration, and targeted modelling estimation based on the results of the optical classification of water bodies is one of the most important technological approaches for inland water body Chl-a inversion. In this study, Baiyangdian is taken as the study area, and a semi-supervised optical classification-based estimation method is proposed using the measured reflectance spectra and Chl-a concentration as the data source. First, to ensure that the number of samples in each category after classification is sufficient to support the construction of the estimation model, this study divides the samples into modelling set and validation set according to the ratio of 7∶1. Representative labelled samples of Baiyangdian were selected by multiple spectral indices and Moore's voting algorithm. Secondly, the fuzzy C-mean clustering algorithm and random forest algorithm are selected to construct a semi-supervised classifier, based on the representative labelled samples obtained, to further explore the potential information in the unlabelled samples and improve the classification accuracy of the unlabelled samples. Finally, the estimation models were established for each water type, the centre-of-mass spectra of each water type were calculated, and the final estimation results were obtained by hybrid-weighting using distance weights. The results show that Baiyangdian water bodies can be classified into phytoplankton-dominated, intermediate and suspended matter-dominated according to the spectral characteristics, and different types of water bodies have obvious differences in optical properties, which can be used to select the optimal estimation model and improve the estimation accuracy according to the optical classification results. Compared with the traditional optical classification strategy, the method proposed in this study performed the best, with a decrease in the mean relative error, root mean square error and mean absolute error, and was able to estimate Chl-a concentration more accurately (MRE=0.10, RMSE=0.126 μg·L-1, MAE=0.106 μg·L-1). In addition, applying ZY01-02E image data for Chl-a estimation in this study can effectively reveal the spatial distribution of Chl-a concentration. This method demonstrates the potential for application in eutrophication monitoring of water bodies, and also provides a new idea for remote sensing estimation of Chl-a concentration in inland water bodies.
Key words:Semi-supervised classification;Optical type of water;Chlorophyll-a;Baiyangdian
陈雯玥,赵起超,杨秀峰,韩宝辉,张雨晴. 基于半监督光学分类的白洋淀叶绿素a浓度反演方法[J]. 光谱学与光谱分析, 2025, 45(07): 2068-2077.
CHEN Wen-yue, ZHAO Qi-chao, YANG Xiu-feng, HAN Bao-hui, ZHANG Yu-qing. Estimation Approach of Chlorophyll-a Concentration in Baiyangdian Based on Semi-Supervised Optical Classification. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(07): 2068-2077.