Radar-derived rainfall estimation is one of the most significant recent advances in hydrologic engineering and practice. Rain gauges provide point values of rainfall depth and intensity but are not cost effective in providing information about the spatial distribution of rainfall, whereas radar-derived rainfall data provides a density of measurements that are not obtainable by rain gauges alone. Combining these two sensor systems produces better rainfall estimates that more accurately characterize rainfall across a watershed. MOP 139 will be a valuable resource for government agencies, a framework for engineering firms, practicing engineers, researchers, and students working in the hydrologic engineering field.