Shannon Brown (NASA Jet Propulsion Laboratory, United States)

The advanced microwave radiometer (AMR) is a critical payload on the series of ocean altimetry missions, including Jason-2 and recently launched Jason-3 mission, designed to provide the electrical range delay of the radar altimeter signal due to tropospheric water vapor and cloud liquid water. The errors in the wet tropospheric path delay measurements have a direct impact on the record of global mean sea level (GMSL) and could lead to uncertainty in derived trends if spurious drifts in the radiometer are not accounted for. Therefore, it is imperative to quantify and correct radiometer calibration drift, enabling producing of a high-quality stable record of wet tropospheric path delay for use in the development of GMSL.

Over the course of the Jason mission series, various calibration methodologies have been applied to maintain the long-term calibration of the microwave radiometer, that includes, vicarious cold calibration, amazon hot reference, and inter-satellite calibration. In this work, we demonstrate a new methodology for monitoring radiometer calibration of the AMR using MERRA-2 reanalysis and radiative transfer simulation fields. In comparison to inter-satellite calibration and other ground-based calibration methods, the advantage of using reanalysis fields is that monitoring on-orbit calibration over the entire globe and of daily time scales is possible. We employ radiative transfer simulation in conjunction with emissivity models to identify calibration drift in the three AMR channels (18.7, 23.8, and 34.0 GHz). Over the ocean, the FASTEM emissivity model is used, while, over land, we employ the TELSEM emissivity database for the radiative transfer simulation. The long-term temporal and regional calibration of the Jason-2 radiometer and preliminary calibration results from the initial cal/val phase of Jason-3 mission will be presented. While, the reanalysis fields may have seasonal and region dependent biases, some other traditional calibration methodologies will also be investigated, including, vicarious cold and warm calibration. In addition, we will compare the results to the data from the cold sky calibration maneuver in supporting the Jason-2 and Jason-3 AMR on-orbit calibration.