Precipitation Estimation from the Microwave Integrated Retrieval System (MiRS)

The Microwave Integrated Retrieval System (MiRS) has been the NOAA official operational microwave retrieval algorithm since 2007 and is run operationally on multiple microwave satellite/sensor systems. The algorithm is based on a 1-dimensional variational (1-DVAR) methodology, in which the fundamental physical attributes affecting the microwave observations are retrieved physically, including the profile of atmospheric temperature, water vapor, hydrometeors, as well as surface emissivity and temperature. A description of the mathematical basis and algorithm components are presented here, followed by examples of retrieved hydrometeorological parameters. Examples presented show that global estimates of surface rain rate from different satellites are generally consistent, and that the explicit treatment of both surface (e.g., emissivity) and atmospheric parameters in the forward radiative transfer model allows for accurate and consistent estimates over a variety of surfaces (e.g., ocean, land with different vegetation types, coastal regions). Validation and performance metrics using independent reference data indicate that the rainfall rates meet most NOAA operational requirements. Suggested avenues for future development and enhancements are also presented including an example of one planned operational enhancement that has led to improved light rain detection over land.