Fully-polarimetric Millimeter-wave Spectrometers for Measurement of Earth's Magnetic Field

We propose to develop an array of 12 fully-polarimetric millimeter-wave radiometer/spectrometers operating near 118 GHz. The digital spectrometer for these receivers was funded in HTiDS 2017 (PI Dr. Yee/ Johns Hopkins University) and with this proposal we will develop the low cost, low power, low mass polarimetric 118 GHz millimeter-wave array receivers that will not require cooling to meet the sensitivity requirements. As Dr. Yee's digital spectrometer project will be finalized in 2019, we will be able to integrate the complete end-to-end system in 2020. This work will enable a second generation small satellite mission with an off-nadir viewing instrument comprised of 120 such receivers that will globally map the magnetic field in the mesosphere at a horizontal resolution ~50 km with 1-sigma error of 50-90 nT. Earth's ionosphere responds dynamically over a wide range of temporal and spatial scales to changes in the magnetosphere and solar wind from above, and to neutral atmospheric dynamics from below. The atmosphere-ionosphere-magnetosphere (AIM) system is a complex and active element of space weather. The Decadal Survey (DS) prioritized "Determining the dynamics and coupling of Earth's magnetosphere, ionosphere, and atmosphere..." and the DS and the Heliophysics Roadmap both deem vector magnetic field measurements at all altitudes to be essential, as the field plays a major role in controlling the distribution of ionospheric plasma. It is difficult to measure the B-field, either locally or globally, at the altitudes of the upper mesosphere and lower thermosphere (UMLT) where the transfer of energy and momentum between the plasma and neutral components of the system occur. This region is too high for balloons and too low for spacecraft; we need a substitute for in-situ measurements. The 118-GHz imaging magnetometer will measure all four Stokes parameters as a function of frequency about the Zeeman-split center of the 118-GHz molecular oxygen line. From these measurements, the magnitude and direction of the magnetic field imposed upon oxygen molecules near the peak of the receiver's vertical weighting function in the upper mesosphere will be inferred. One potential application of the proposed measurement technique is to provide further understanding of Geomagnetic Induced Currents (GICs) during strong geomagnetic storms. Another important science application is mapping of the horizontal structure and magnitude of magnetic field disturbances associated with the auroral electrojet. High horizontal spatial resolution of the proposed instrument will give a unique opportunity to evaluate spatial variability of storm-time magnetic fields due to variations both in ground conductivity and in the structure of the ionospheric current drivers. Development of this measurement capability will be an important step towards the global monitoring of magnetic field disturbances during strong storms from orbit, which is a potential extension of ground-based networks of extreme-event magnetic observatories. This project will advance the TRL of the large receiver array for the second generation small satellite mission from 4 to 5. The duration of the project is 24 months.

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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