Design and Flight Results of the Airborne Microwave Barometric Radar and Sounder (MBARS)

The Microwave Barometric Radar and Sounder (MBARS) is a NASA-funded airborne instrument to demonstrate atmospheric marine surface pressure retrievals with a V-band (65.5-70 GHz) differential absorption radar (DAR). This technology represents a significant advancement in atmospheric pressure measurement, and if deployed from space promises to fill in the gaps between drifting buoys and improve global weather forecasts.

The MBARS instrument measures the surface attenuated radar cross section (ARCS) at three sets of frequencies along the oxygen absorption line. This multi-frequency approach allows for the estimation of the atmospheric attenuation due to oxygen while suppressing the impact of other sources of differential such as surface normalized cross section (NRCS), water vapor, and clouds. This, combined with temperature and water vapor retrievals enables estimation of the atmospheric column mass and thus the surface pressure.

The primary technical challenges to this type of DAR are achieving sufficient signal-to-noise ratio (SNR) in the presence of significant oxygen attenuation, and achieving the necessary precision and stability to retrieve small changes in the atmospheric column mass. MBARS addresses these challenges with a frequency-diversity waveform that enables as many as sixteen independent samples per pulse repetition interval (PRI), with subchannels optimized for the anticipated attenuation. It also includes a thermally-stabilized transceiver and internal calibration electronics.

MBARS flew for the first time on the NASA ER-2 high-altitude aircraft during summer and fall of 2024 for test flights and the Westcoast & Heartland Hyperspectral Microwave Sensor Intensive Experiment (WH2yMSIE) field campaign. During these flights it collected attenuated radar cross section (ARCS) data over a variety of atmospheric conditions including areas of constant pressure and a pronounced pressure gradient.

We will summarize the instrument design and performance, present current atmospheric pressure retrievals using MBARS data, and discuss future possibilities with the MBARS instrument and technology.