HALE InSAR for Continual and Precise Measurement of Earth's Changing Surface

Interferometric synthetic aperture radar (InSAR) is a proven technique for observing wide-area surface deformation and topographic change at sub-cm vertical scales. However, the limited temporal resolutions of current InSAR techniques preclude the detailed study of dynamics that occur on timescales of days or hours. Substantially improved revisit times and long durations for InSAR are achievable at low cost from high-altitude long-endurance (HALE) platforms such as solar-powered aircraft and stratospheric airships. Aloft Sensing proposes to develop a high-performance compact InSAR instrument that, when hosted on these platforms, offers continual and precise collection of surface deformations and topographic changes that are unattainable with any other existing method. Objective and Benefits: Aloft will develop and demonstrate a low-SWaP InSAR payload (<7 kg and <250 W) that enables continuous and accurate surface deformation (millimeter) and topographic measurements (centimeter) from HALE platforms. Operation from these platforms present three key challenges for InSAR: 1) limited payload size, weight, and power, 2) low platform velocities, and 3) coarse trajectory control. As a result, existing InSAR instruments and algorithms are incompatible with HALE-based operations. This work addresses all three challenges and enables new science by extending the benefits of InSAR to the stratosphere. Revisit times improved from weekly to sub-hourly (a 100x benefit), coupled with flight durations of months to years, enables the thorough capture of geophysical and topographic processes (e.g., glacier dynamics, earthquakes, volcanoes, landscape erosion), as well as real-time responsiveness to events on the ground. Outline and Methodology: Newly available RF system-on-a-chip (RFSoC) and front-end module RF integrated circuit (RFIC) components enables a breakthrough level of integration and power efficiency for a software defined radar (SDRr) with an active electronically steered array (AESA). Once developed, the tightly integrated prototype instrument is hosted on the nimble, low-cost Swift Ultra Long Endurance (SULE) aircraft for stratospheric demonstration. Innovative processing algorithms that achieve micron-level position and milli-degree orientation overcome the challenges associated with stratospheric InSAR operation. In the first year of the program, the RFIC-based AESA is redesigned and prototyped, the payload bay of SULE is modified to accommodate the AESA, the interfaces of the RFSoC-based SDRr are verified, and the processing algorithms are defined and tested. In the second year, the SULE, SDRr, AESA, and onboard algorithms are fully integrated and verified at low altitude before initial stratospheric flight testing. In the third year, additional payload system units are manufactured for continued HALE InSAR testing and demonstration in the stratosphere, and the algorithms are efficiently embedded into a GPU/FPGA-based onboard processing solution for future operations. Period of Performance: A three-year effort: 1 Jan 2022 to 31 Dec 2024. Entry and Exit TRL: (Entry TRL: 3, Exit TRL: 6) Aloft has previously demonstrated SAR from HALE platforms, but the concept of InSAR from HALE is new and unproven. We have identified the hardware challenges and formulated the algorithmic approaches for InSAR, but they have not been applied experimentally. Hardware components exist at TRLs ranging from 2 to 8, but as a complete ultra-low SWaP instrument, the composite HALE-InSAR system has yet to be developed and tested. Therefore, the instrument system has Entry TRL 3. This work provides the analytical and experimental critical functioning, as well as performance validation of the tightly integrated low-SWaP hardware required for operation in a stratospheric environment. This establishes the instrument system Exit TRL at level 6.

Enabling lower cost innovative remote sensing instrument development from concept through breadboard and demonstration

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