Synergistic estimation of soil organic matter based on Sentinel-1 and Sentinel-2 data: a case study of the black soil region in Baoqing County, Sanjiang Plain - Jinbao He; Jian Zhao; Hongbo Liu; Yongxin Mao; Guanhong Dong; Yiyang Zheng; Chengcheng You; Fanpeng Kong (International Journal of Remote Sensing, 2026)