Soil moisture has been identified as a land surface parameter of great importance in various fields of application. Based on long-term time series data of various radar sensors, change detection methods for scatterometer and ScanSAR data are presented. After data processing and model parameter estimation, individual radar backscatter measurements are compared to references describing location specific backscatter conditions representing dry and wet surface soil moisture. Using exponential filtering, also profile soil moisture can be calculated. The method have been implemented in a fully automatic data processing chain for soil moisture retrieval for ERS-1/2 and MetOp ASCAT data and Envisat ASAR ScanSAR data. Various validation studies showed good agreement between the remotely sensed soil moisture products and reference data.