Angular Dependence and Spatial Distribution of Jupiter’s Centimeter-Wave Thermal Emission from Juno’s Microwave Radiometer

NASA’s Juno spacecraft has been monitoring Jupiter in 53-day orbits since 2016. Its six-frequency microwave radiometer (MWR) is designed to measure black body emission from Jupiter over a range of pressures from a few tenths of a bar to several kilobars in order to retrieve details of the planet’s atmospheric composition, in particular its ammonia and water abundances. A key step toward achieving this goal is the determination of the latitudinal dependendence of the nadir brightness temperature and limb darkening of Jupiter’s thermal emission through a deconvolution of the measured antenna temperatures. We present a formulation of the deconvolution as an optimal estimation problem. It is demonstrated that a quadratic expression is sufficient to model the angular dependence of thethermal emission for the data set used to perform the deconvolution. Validation of themodel and results from a subset of orbits favorable for MWR measurements are presented over a range of latitudes that cover up to 60° from the equator. A heuristic algorithm to mitigate the effects of nonthermal emission is also described.