Biomass Density Distribution at Heading Stage of Early Rice in Sanya City from 2019 to 2024

Based on the planting area distribution of early rice in Sanya from 2019 to 2024, the biomass density at heading stage was estimated. Our team created a Dynamic Growth Period Unification (DGU) algorithm: Based on the objective law that NDVI of rice heading stage reaches the maximum value in the whole growth period, the change trend of rice NDVI in satellite remote sensing images of the study area is analyzed and the corresponding time range of rice heading stage is extracted. This method solves the problem of inaccurate prediction of large-scale spatial rice biomass due to the difference of crop rotation time in farmers' planting patterns and different growth stages of rice varieties. Then, Sentinel-1 radar data and Sentinel-2 optical data of the corresponding time period were obtained according to this time range, and the radar data, optical data and texture information were input into four machine learning algorithms, namely random forest, support vector machine, gradient lifting decision tree and BP neural network, to develop a rice biomass density estimation model. The results show that: The random forest algorithm performed best in the prediction task of rice biomass density. Its coefficient of determination R2 was 0.746, root mean square error (RMSE) was 290.531 g/m², Bias was 6.766 g/m², and relative root mean square error (RRMSE) was 23.84%. The Bias% was 0.555%. The results showed that the biomass density of rice in Sanya City fluctuated in different years and regions. The average biomass density fluctuated between 1142.218 g/m² and 1177.41 g/m², and the total biomass fluctuated between 21120.266 tons and 28696.107 tons. The average biomass density in Yazhou district fluctuated between 1143.687 g/m² and 1167.343 g/m², and the total biomass fluctuated between 7845.106 tons and 12082.792 tons. The average biomass density fluctuated between 1149.634 g/m² and 11944.17 g/m², and the total biomass fluctuated between 6710.375 tons and 10139.787 tons. The average biomass density in Jiyang District fluctuated between 1159.411 g/m² -1227.457 g/m², and the total biomass fluctuated between 1797.002 tons and 2757.501 tons. The average biomass density of Haitang district fluctuated between 1114.167 g/m² -1184.708 g/m², and the total biomass fluctuated between 3717.419 tons and 5421.217 tons.