Earth Surface Processes
LI Shuang, ZHANG Zu-lu, ZHOU De-min
Wetland vegetation is an important component of wetland. The biomass of vegetation is an essential index to describe the wetland ecosystem and reflects its health status. Therefore, the investigation of wetland vegetation biomass has important practical significance.In this paper, the Honghe National Natural Reserve (HNNR) was selected as the study area. The TM images on August 19th, 2008, August 30th, 2006, August 1st, 2004 and 29 samples of biomass data in the same period were used as the data source to establish the estimation models. The correlations between the remote information (reflectivity, vegetation index) and measured biomass were analyzed in this paper. The estimation models were established based on the method of regress model and artificial neural network (ANN). The models included the linear regression models, the curve regression models, the stepwise regression models, and ANN models (BP network and RBF network). In comparison of all the models, the best estimation models were obtained. The accuracy of the dry biomass models and the humid biomass models were compared. Then, the total biomass of meadow and marsh in HNNR were estimated. Finally, the total biomass spatial distribution maps of 2004, 2006 and 2008 were made, and the trend of the biomass was analyzed in this paper. The conclusions of the research were as follows. (1) The correlations between the wetland vegetation aboveground biomass and RS information were good, and the correlation between the dry biomass and RS information was better than that between the humid biomass and RS information. The estimation models based on the RS information can estimate the wetland vegetation aboveground biomass relatively well.(2) The performance of the models based on RBF network was better than that based on regression models and BP network. With the method of RBF, the mean relative error (MRE) of estimated dry biomass was 2.795% and the MRE of estimated humid biomass was 3.399%. The dry biomass models were better than the humid biomass models in comparison with them.(3) In this study area, dry biomass was mainly between 300 g/m2 and 900 g/m2 and the humid biomass was mainly between 600 g/m2 and 1800 g/m2. By analyzing the total biomass of the three years, the total dry biomass showed an upward trend, and the total humid biomass showed a downward trend. There was little extreme high or low biomass, which was mainly distributed in the places where a lot of mixed-pixels existed, such as the edge of the forest and bush, or the marsh with a lot of water.