J. Saastamoinen is known for his significant contributions to the field of geodesy, particularly in the area of atmospheric science. His work has focused on improving the accuracy of satellite positioning systems by accounting for atmospheric effects, which is crucial for precise measurements in various applications. Additionally, Saastamoinen developed models that help in understanding the impact of the atmosphere on geodetic measurements. These models are widely used in GPS technology and have enhanced the reliability of data collected for both scientific research and practical applications in navigation and mapping.