Instrument Overview
===================
The Microwave Radiometer (MWR) is one of a suite of instruments on Juno.
The Juno mission has the overall goal of answering the outstanding questionsoutstanding about Jupiter's structure and origin. Specifically, the MWR was designed to characterize Jupiter's atmosphere as following:
- Determine the global O/H ratio (water abundance) in Jupiter'satmosphere- Measure latitudinal variations in Jupiter's deep atmosphere(composition, temperature, cloud opacity, and dynamics) - Measure the microwave brightness temperatures of Jupiter over alllatitudes at wavelengths that fully sample the atmospheric thermalemission at all altitude levels from the ammonia cloud-formingregion to below the water cloud-forming region
To achieve this the MWR experiment uses a microwave sounding approach described in Janssen et al., 2005. The MWR instrument measures the atmospheric thermal emission at six frequencies. Thermal emission from an atmosphere arises because of the presence of absorbing constituents in the atmosphere, and the measured emission contains information on both the concentration and temperature of these constituents. The information content changes with frequency, and the determination of the spectrum of atmospheric thermal emission can be used to infer key parameters of both the temperature and compositional structure of the atmosphere. Water and ammonia are the only significant sources of microwave opacity in Jupiter's atmosphere, so their concentrations are the unique target of any microwave sounding approach.

The MWR instrument comprises what are essentially six independent radiometers, each of which measures the microwave emission viewed through its own independent antenna. The six antennas are distributed around the spacecraft body and view in a direction perpendicular to the spin axis of the spacecraft. Since the spin axis of the spacecraft is oriented approximately perpendicular to the orbit plane, the beam of each antenna sweeps through a great circle on the sky that passes along the sub-spacecraft track on Jupiter and through the nadir direction. Each point along this track is thus observed numerous times, at different emission angles, as the spacecraft spins and moves along its orbit. The accumulated data at each such point and its dependence on emission angle an frequency is then analyzed to obtain vertical atmospheric composition and structure using a radiative transfer model.

Each receiver makes contiguous radiometric measurements, or integrations, of fixed 100-ms duration. In a typical sequence of such integrations an internal switch is cycled from the antenna input to periodically view an internal load, and three independent internal reference noise sources are periodically switched on and off for calibration. The cycle for such switching is synchronous for all receivers and is set by selecting from a table contained in the flight software. The table may be changed by an uplink command. The choice of specific sequences depends on instrument performance and optimization of the calibration algorithm.

For the key observations to be made in the nine-hour window around Jupiterperijove, the MWR is desiged to downlink all contiguous 100-ms observations.
Outside this window, however, not all of this data is essential and in most cases the resulting data would quickly fill the MWR's partition on the spacecraft. To avoid this, a command is sent to downlink only a fraction of the data obtained. The instrument organizes its data stream into time-contiguous units of ten 100-ms observations, each thus corresponding to one second's worth of observation. Successive units may be contiguous in time (full data rate) or separated by n seconds each (reduced data rate). A different on-board switching sequence is typically commanded in order to optimize the calibration for reduced sampling rates.

Documents that describe the major components of the MWR instrument and its operation will be found in the DOCUMENTS folder and include:1. The MWR volume SIS2. The MWR instrument paper (Janssen et al., 2017)3. The MWR Operations Guide (not yet available)4. The MWR Instrument Users Guide5. The MWR Flight Software Users Guide6. The MWR Algorithm and Theoretical Basis Document and Error Analysis
The canonical paper that describes the design, operation, calibration, and analysis of the MWR data to achieve the scientific objectives of the MWR experiment is Janssen et al., 2017.