Abstract : The thesis works have contributed to improve the surface soil moisture estimates and the root-zone soil moisture estimates on the Sahel band in West Africa. The first part was dedicated to assess the ability of different algorithms to estimate soil moisture based on satellite measurements in thermal infrared spectrum. In the second part, a method was developed in order to obtain a soil moisture mapping at high temporal resolution (< 3h) based on two satellite products: a satellite-based rainfall product and daily passive microwave measurements sensitive to soil moisture. In a third part, an assessment of the reliability and robustness of the methodology has been proposed. Finally, a semi-empirical method was used to produce root-zone soil moisture maps (0-1 m) over the Sahel region. Ground-based soil moisture measurements obtained at three sites in Mali, Niger and Benin during the AMMA program were used to assess the quality of estimates of near-surface and root-zone soil moisture at each stage of this work. The results show that an estimate of the surface soil moisture is possible with an accuracy of less than 3% vol. over the Sahel band. The error is about 5% vol. over the Sudanian zone (Benin). The accuracy is identical for the root-zone soil moisture estimate. Finally, the developed method allows at the same time to correct satellite-based rainfall products and notably the overestimation of the annual accumulation and the number of rain events of the three rainfall satellite products used in this work.