Project Selections for IIP-21

17 Projects Awarded Under the Instrument Incubator Program (IIP)

11/08/2021 – NASA’s Science Mission Directorate, NASA Headquarters, Washington, DC, has selected proposals through the 2021 solicitation of the Instrument Incubator Program (NNH121ZDA001N-IIP, element A.41 of the ROSES-21 omnibus announcement) in support of the Earth Science Division (ESD). The IIP-21 will provide instruments and instrument subsystems technology developments that will enable future Earth science measurements and visionary Earth-observing concepts.

The ESD is awarding 17 proposals, for a total dollar value over a three-year period of approximately $50 million, through the Earth Science Technology Office (ESTO).

The Instrument Incubator Program (IIP) supports the development of innovative technologies for new Earth observing instruments, sensors, and systems in support of Earth science. The technologies and measurement concepts developed under the IIP may extend through to field demonstrations, with a longer-term aim for infusion into future ESD research, applications, and flight programs.

The goal of the IIP is to promote innovation in the research, development, and demonstration of new measurement technologies that:
– Enable new or greatly enhanced Earth observation measurements; and
– Reduce the risk, cost, size, mass, and development time of Earth observing instruments.

56 proposals were evaluated of which 17 have been selected for award. The awards are as follows:



Separated Thinned Array for Sensing of Ice Sheets (STASIS)
Alexander Akins, Jet Propulsion Laboratory

The key objective of the Separated Thinned Array for Sensing of Ice Sheets (STASIS) concept study is to demonstrate feasibility of a constellation microwave interferometer approach to derive high resolution 3D maps of ice sheet temperature. Ice sheet temperature with depth is a fundamental parameter for ice process models and important to studies of ice mass balance and rheology. Accurate measurements of ice sheet temperature can benefit efforts to predict changes in ice mass balance and sea level over time, a high priority for NASA. However, only limited observations of these parameters exist due to the practical difficulty of in situ sampling. Passive microwave instruments are uniquely sensitive to thermal emission from deep within ice sheets. Observations at these wavelengths require up to 10-100m diameter antenna apertures to resolve variations in subsurface properties at 10km resolution, which is impractical for a real-aperture system. Interferometric aperture synthesis, or the correlation of measured intensity from several independent radiometer instruments, within a satellite constellation could be used to obtain high spatial resolution measurements of ice sheet state while bypassing the challenges associated with a single, large antenna. We propose a ICD modeling and feasibility study of disconnected interferometric radiometric techniques for long-wavelength remote sensing of polar ice sheets. In this concept, signals from 2 or more small satellites with broadband antennas are correlated to form interferometric baselines. Given a relatively time invariant target like the deep ice temperature of Antarctica, the complete set of interferometric baselines can be measured over many weeks to months, making a distributed array formation a feasible solution. We will develop a simulation to generate synthetic interferometric images of polar ice structure for a given constellation geometry and instrument design. This simulation will then be used to 1) parameterize the relationship between constellation design and the spatial/temporal resolution for ice sheet observations; 2) assess the contribution of systematic uncertainties to the absolute accuracy and precision of the derived polar images; and 3) study mission systems engineering trades. The measurement method discussed above represents an order of magnitude improvement in the spatial resolution of long wavelength passive remote sensing of the Antarctica ice sheet. The emergence of small satellites and low-cost ride-share options to space make this approach an attractive alternative to a 10-100m deployable real-aperture that would otherwise be needed. Measurements of deep ice sheet thermal structure at this enhanced spatial resolution would significantly improve estimates of geophysical parameters relevant to ice sheet modeling (e.g. deformation/sliding contributions to ice flow, geothermal heat flux). The proposed concept has the potential to provide a novel data product that will significantly improve the predictive power of ice sheet modeling by reducing uncertainties in ice flow parameterizations and is therefore relevant to the NASA Earth Science Focus Area of Climate Variability and Change. The duration of the proposed study is 18 months, and the entry and exit TRL of the concept are TRL 1 and TRL 2, respectively.

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Rydberg Radar: A quantum architecture covering the radio window for multi-science signal of opportunity remote sensing with focus on land surface hydrology
Darmindra Arumugam, Jet Propulsion Laboratory

We propose a concept for a high sensitivity, dynamically tunable, and ultra-broad-band radar system, named Rydberg Radar, that dramatically improves over the state-of-art radar using quantum Rydberg atomic sensing. The Rydberg Radar instrument concept vastly improves the existing radar capability to study dynamics and transients of the Earth system by enabling a single-detector-based measurement covering the entire ‘radio window’ (0-30 GHz) in a small form-factor deployable-free architecture. This fundamentally novel technology has the potential to enable multi-science applications covering various bands and applications on a single platform, including in focus areas of planetary boundary layer (PBL), surface topography and vegetation (STV), surface deformation and change (SDC), and sub-surface structure and change (SSC). The high sensitivity and very low-noise (ultimately limited by quantum-projection noise), ultra-broadband (10kHz-1THz), quantum down-conversation of radio signaling (no antenna, RF front-end, or mixers), and compact form-factor of the quantum Rydberg atomic detector (detection volume <1cubic-cm) makes the Rydberg Radar a vast improvement over traditional radars with potential for high-impact in all radar missions of the future.

The objective of this proposal is to develop the Rydberg Radar instrument concept for a CubeSat platform as part of a coordinated multi-satellite signal of opportunity (SoOp) concept to address dynamics and transients in land surface hydrology (LSH) science. The benefit of this concept is that it dynamically retrieves soil moisture content (SMC) from canopy to deep-root-zone using collocated detection from C- to I-band, which are sensitive to variables including canopy water content, vegetation water content, as well as near-surface and deeper root-zone soil moisture. The proposed work develops integrated models to study the performance of Rydberg Radar in LSH science and conducts a proof-of-concept SoOp detection. In addition, specific component level requirements for the Rydberg Radar system is developed.

The concept studied is composed of multiple coordinated CubeSats, where each CubeSat instrument concept architecture is composed of a dual-polarization fiber-coupled-laser Rydberg detector node with excitation, detection, and digital systems. Specific bands addressed for the LSH science in this concept are SoOps at 137MHz/260MHz/360MHz/1.5GHz/2.3GHz/3.9GHz (I/P/L/S/C bands), although the technology can be tuned to higher frequencies for other science applications. The concept has an entry level TRL of 2, with many critical components and subsystems at a considerably higher TRL. We will raise to TRL 3 over the 18-month effort.

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Quantum Gravity Gradiometry In Hybrid Architectures with Satellite-to-Satellite Tracking for Spaceborne Earth System Mass Change Measurements
Srinivas Bettadpur, University Of Texas, Austin

A hybrid architecture is envisaged for obtaining high-spatial-frequency mass change data from cross-track gradiometers in conjunction with the twin constellation of GRACE-like satellite to satellite tracking mission. A JPL/SURP-sponsored effort has shown the benefits of the cross-track gradient configuration at 10 micro Eotvos precision.

Quantum gravity gradiometry (QGG) uses ultracold atoms as test masses for absolute gradient measurement. However, the accuracy of baseline for gradient measurements, i.e., the separation of atomic clouds, has not been demonstrated to meet the demand of future QGG sensitivity requirements. Specifically, for a nominal 1500 Eotvos cross-track gravity gradient in GRACE orbit, a 10 micro Eotvos resolution requires a baseline stability of <10^-8, which is < 10 nm for a 1-m baseline.

Through this IIP-ICD effort, we propose to develop observation mathematical modeling for the hybrid architecture, address challenges such as spacecraft pointing, and technically demonstrate the feasibility to obtain baseline resolution to support the measurement concept. Through the results of this effort, a TRL-1 to TRL-3 transition is anticipated. The period of performance is expected to be between Feb 1, 2022 and September 30, 2023.

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Configurable Reflectarray for Electronic Wideband Scanning Radiometry (CREWSR)
William Blackwell, Massachusetts Institute of Technology/Lincoln Lab

Recent advances in deployable, rigid, panelized antennas and low-noise RF silicon-on-insulator (RFSOI) integrated circuits now make possible a new class of instruments that offer low-power, low-mass, low-cost, high-performance, and compatibility with ESPA-class small satellite systems. In this proposal, we demonstrate system-level technologies supporting a Configurable Reflectarray for Electronic Wideband Scanning Radiometry (CREWSR), and we develop a complete ProtoType (PT) of this instrument (PT-CREWSR) that demonstrates all the needed core technologies of a large-aperture CREWSR instrument that would benefit many earth science focus areas that rely on microwave imaging and sounding.

The PT-CREWSR instrument that we propose to build and test will operate at 23.8, 31.4, and 50-58 GHz and will include a 0.6 m x 0.9 m lightweight thin-panel configurable reflectarray that can electronically scan the antenna beam over a 45-degree field of view in two dimensions. The PT-CREWSR instrument will demonstrate all the core technologies needed to realize a very-large-aperture (1.8 m x 1.8 m) system comprising six of these panels, which can be folded up into an ESPA-class small satellite and deployed to achieve a factor of ten improvement over current state-of-the-art microwave temperature sounder spatial resolution. The single panel to be built as part of the PT-CREWSR instrument will consume less than 3W of average power with a mass less than 3 kg and will provide the performance of a phased array system with a factor of 100 reduction in power consumption, as no amplifiers are needed in the reflectarray surface – only low-power FET switches are used in each of approximately 20,000 elements in the panel to select one of 16 different phase states. Simulations of the antenna feed, reflectarray antenna elements, and the custom 45RFSOI beamformer radio frequency integrated circuits (RFICs) developed as part of this work yield excellent performance with antenna beam efficiencies of approximately 95 percent over the entire scanned field of view. The ultracompact feed module at the focus of the reflectarray comprises an entire tri-band radiometer with antenna feeds, calibration network, filter bank, and digital processing and control electronics. A computer board operates the radiometer and controls the reflectarray surface to permit switching of the antenna beam state on the order of a microsecond. The noise performance of the PT-CREWSR demonstration instrument proposed here will be at least as good as current state-of-the-art sensors such as the Advanced Technology Microwave Sounder, as the losses in the reflectarray surface (approximately 3 dB) are completely counteracted by the fact that PT-CREWSR can observe the field of view four times as long as a constant-velocity, mechanically cross-track-scanned system with a +/-45-degree field of view.

In addition to the realization of very large apertures from an ESPA-class small satellite platform, the electronic beam steering capability opens up a broad new trade space of how satellite-borne radiometers can be operated, both in low-earth and geostationary orbits. The beam can be pointed at any point in the field of regard at any time, and this permits much more sophisticated spatial and angular sampling of the scene to be achieved. The spatial sampling could be dynamically optimized based on the characteristics of the scene being viewed, and super-resolution techniques could be used to focus on a region of interest to further improve spatial resolution by a factor of two with no increase in noise.

The project is led by MIT Lincoln Laboratory, who will provide the reflectarray and system integration and test in collaboration with U. California-San Diego, who will provide the phase shifter and beam forming RFICs. Entry TRL is 2 and exit TRL is projected to reach 5.

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Simplified Gravitational Reference Sensors for Future Earth Constellations
John Conklin, University of Florida, Gainesville

Our team led by the University of Florida, in collaboration with Caltech/JPL, Ball Aerospace, and Embry-Riddle Aeronautical University propose to elevate a Simplified Gravitational Reference Sensor (S-GRS), an ultra-precise inertial sensor for future Earth geodesy missions, from TRL 3 to TRL 5. These sensors are used to measure or compensate for all non-gravitational accelerations of the host spacecraft so that they can be removed in the data analysis to recover spacecraft motion due to Earth’s gravity field, the main science observable. They consist of a dense metallic test mass that is free-falling inside an electrode housing. When operated as an accelerometer, small electrostatic forces are applied to the test mass to keep it centered in its housing. The applied force provides information about spacecraft acceleration. In a drag-compensated scheme, spacecraft propulsion is used to directly compensate for atmospheric drag, reducing the electrostatic force needed to keep the test mass centered and also the force noise on the test mass. Low-low satellite-to-satellite tracking missions like GRACE-FO that utilize laser ranging interferometers are technologically limited by the acceleration noise performance of their electrostatic accelerometers, as well as by temporal aliasing associated with Earth’s dynamic gravity field. The current accelerometers, used in GRACE and GRACE-FO have a limited sensitivity of ~1E–10 m/s^2 Hz^1/2 around 1 mHz. The S-GRS is estimated to be at least 40 times more sensitive than the GRACE accelerometers if operated on a GRACE-like spacecraft bus and more than 500 times more sensitive if operated on a drag-compensated platform. The improved performance is primarily enabled by (a) removing the small test mass grounding wire used in the GRACE accelerometers and replacing it with a non-contact UV photoemission-based charge management system, (b) increasing the mass of the sensor’s test mass, and (c) increasing the gap between the test mass and its electrode housing.

The S-GRS concept, as well as two candidate mission architectures, were developed in our current IIP Instrument Concept Demonstration (ICD) project. During our ICD effort we have shown that this level of improvement allows future missions to fully take advantage of the sensitivity of the GRACE-FO Laser Ranging Interferometer (LRI) in the gravity recovery analysis. The S-GRS concept is a simplified version of the flight-proven LISA Pathfinder GRS. Our performance estimates are based on models vetted during the LISA Pathfinder flight and the expected low Earth orbit spacecraft environment based on flight data from GRACE-FO. The relatively low volume (~5,000 cm^3), mass (<13 kg), and power consumption (<20 W) enables use of the S-GRS on ESPA-class microsatellites, reducing launch costs or enabling larger numbers of satellite pairs to be utilized to improve the temporal resolution of Earth gravity field maps.

Our approach to advancing the technology readiness will follow two primary paths. The first will be to develop a Metrology and Charge Management Testbed at the University of Florida that will be used to demonstrate S-GRS readout sensitivity, charge management performance, and test mass and drag-compensation control system performance in a hardware-in-the-loop configuration. These tests will first be done on a bench-top in air (TRL 4), then a higher fidelity unit will be tested in the UF thermal vacuum chamber (TRL 5). The second path will be to produce a Structural, Thermal, and Optical prototype and test it in the relevant environment through shock and vibration testing and thermal vacuum chamber testing. This TRL 5 prototype will be designed and fabricated by Ball Aerospace with oversight from UF. This programmatic choice expedites technology transfer to industry allowing earlier flight readiness. The success of this project will allow the S-GRS to be ready for a flight demonstration in the second half of this decade.

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Multi-Functional Lidar Measurements to Identify and Characterize Marine Debris using Time-Resolved Fluorescence
Madeline Cowell, Ball Aerospace & Technologies Corporation

Current remote sensing systems are not optimized to monitor the exponential increase of marine debris pollution, nor quantify its impact to ocean health. While passive imaging spectrometers with near infrared (NIR) and shortwave infrared (SWIR) bands provide some limited utility in identifying debris floating on the surface, most debris is submerged and these systems cannot “see” below the water’s surface. Building on the near/below surface studies of phytoplankton using CALIPSO, we propose to investigate the capability of a fluorescent lidar system, to both identify and characterize near-surface and submerged marine debris.

Our goal is to characterize the laser induced fluorescence (LIF) return of marine debris both in the spectral and time domain. We will include measurements from naturally occurring targets, such as phytoplankton, to demonstrate sufficient differentiation in aquatic scenes between biogenic and anthropogenic material. Time-correlated single photon counting (TCSPC) will provide a measure of fluorescence lifetime of the various targets. After having success measuring fluorescence spectra and fluorescence lifetime independently, we propose to expand upon this research to feed into this study. The laboratory measurements will consist of a tunable pulsed laser as the excitation source, a photon-sensitive fast detector, and spectral filters tuned to the target’s peak emission wavelength. To ensure high probability of classification, machine learning algorithms will be developed and tested. The results of this study will define the sensitivity of the fluorescence return for future performance modeling necessary for developing an effective space-based lidar system. Ultimately, this will inform a mission architecture to achieve global coverage for marine debris identification, characterization, and monitoring.

Our team includes leading lidar technologists from both industry and NASA and research and application scientists from Academia and NOAA, all focused on addressing the marine debris problem. The PI and technology team are from Ball Aerospace, with participation from NASA LARC. Research and applications support is provided by collaborators from Woods Hole Oceanographic Institution (material experts studying the change in plastic characteristics as they decay in the ocean) and NOAA (application scientists who target and remove marine debris).

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Photonic Integrated Circuits (PICs) in Space: The Hyperspectral Microwave Photonic Instrument (HyMPI)
Antonia Gambacorta, NASA Goddard Space Flight Center

Our Team’s Hyperspectral Microwave Photonic Instrument (HyMPI) breaks away from 40-year old microwave sounding technology and breaks through to a new era of advanced measurements of Earth’s atmospheric temperature and water vapor profiles.

Hyperspectral (a few hundred to a few thousand channels) microwave sensors have been strongly advocated by numerous space and meteorological agencies worldwide, to augment Earth atmosphere sounding capability of temperature and water vapor from space. In general, the strength of a microwave sensor rests in its high cloud penetrability, which enables retrieval of temperature and water vapor under all sky conditions. However, the current Program of Record (POR), (e.g., the Advanced Technology Microwave Sounder (ATMS), the Time Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS)) only have a couple dozen sparsely sampled channels. This hinders vertical resolution and accuracy in the retrieved temperature and water vapor soundings, limiting data utilization. The Earth’s planetary boundary layer (PBL) is the most affected region, due to the opacity introduced by the overlaying atmospheric layers.

The reason for stalled progress in hyperspectral microwave technology rests in the numerous technological challenges associated with simultaneously processing an ultra-wide bandwidth (20-200 GHz) at hyperspectral resolution (< 1 GHz), while maintaining a feasible instrument size, weight and power consumption, and cost (SWaP-C). Traditional microwave radiometers are based on radio-frequency (RF) technology whose constraints limit the capabilities of current spectrometers. However, SWaP-C can be improved by means of photonic signal processing techniques, enabled by up-conversion of a microwave signal to an optical carrier.

This proposal aims to solve the SWaP-C challenge of current RF technology by combining Photonic Integrated Circuits (PICs) and Application Specific Integrated Circuits (ASICs) into a “PICASIC” module, the heart of the hyperspectral microwave spectrometer. The results will yield a low mass, low power, high spectral resolution and wide band instrument. The PICASIC modular approach enables full-spectrum (20 – 200 GHz) and contiguous spectral coverage with a tunable capability to measure the spectrum with higher resolution where higher structure in the signal is exhibited.

The proposed PICASIC is the missing puzzle piece, the critical technology element, needed to realize HyMPI, a first of a kind combined hyperspectral microwave imager and sounder.

The NASA Planetary Boundary Layer (PBL) Incubation Study Team Report lists hyperspectral microwave sensors as an “Essential Component” of the future global PBL observing system, to provide “accurate PBL and free tropospheric 3D temperature and water vapor structure context”. We studied a Hyperspectral Microwave Photonic Instrument (HyMPI) design configured to respond to the requirements outlined in the PBL Study Team Report. One of the primary goals of this proposal is to finalize instrument design trade studies and derive a final optimal configuration ready for follow-on airborne flight demonstrations.

Key to improved retrieval thermodynamic structure are the HyMPI’s enhanced spectral coverage and resolution, uniquely enabled by the PICASIC technology. Thanks to the reduced SWaP-C also enabled by the PICASIC technology, HyMPI can meet the 5km spatial resolution requested by the PBL Study Team Report and achieve a Smallsat/Cubesat deployable capability, key to provide high temporal refresh for weather applications.

Following the proposed research effort, the PICASIC can be proposal-ready for the first in-space demonstration of an integrated hyperspectral microwave photonic system with science-grade performance.

The period of performance is February 1, 2022 to January 31, 2025. The entry TRL is 2, the exit TRL is 5.

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Combining Distributed RF and Multi-spectral Optical Observations for a Spaceborne 3-D Lightning Measurement Concept
Patrick Gatlin, NASA Marshall Space Flight Center

The goal of this proposal is to advance key components of the CubeSpark measurement concept to prepare it future satellite demonstration or Earth Venture opportunities for obtaining novel, global 3D measurements of lightning. The CubeSpark concept is to use a constellation of small satellites with combined optical and RF lightning instruments to retrieve the 3D location (latitude, longitude, and altitude) of lightning flashes within thunderstorms around the globe with a spatial resolution of at least 1- to 2-km. This will make use of fast, high-resolution bispectral lightning imagers, which can be assembled using commercial-off-the-shelf (COTS) CMOS-based detectors, and a recent ESTO-funded ACT project to design a CubeSat-based RF antenna/receiver, which has a planned exit TRL of 4-5, for detecting lightning. The organizations involved in this proposal have a long heritage of developing space-based lightning instruments and missions and have demonstrated success obtaining novel and impactful measurements of lightning on a global scale.

The objectives of this work are as follows: 1) establish that a bispectral lightning imager can enhance the performance and science return of space-based optical detection of lightning for CubeSpark; 2) demonstrate a space-based time-of-arrival approach capable of measuring the 3D location to address CubeSpark science questions; 3) determine a baseline concept of operations for CubeSpark. The tasks we are proposing to meet these objectives will be completed within the time frame of 18 months. The entry TRL is 2 with an expected exit TRL of 4.

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Compact Fire Infrared Radiance Spectral Tracker (c-FIRST)
Sarath Gunapala, Jet Propulsion Laboratory

Remote sensing and characterization of high temperature targets on the Earth’s surface is required for many cross-disciplinary science investigations and applications including fire and volcano impacts on ecology, the carbon cycle, and atmospheric composition. For decades this research has been hindered by insufficient spatial resolution and/or detector saturation of satellite sensors operating at short and mid-infrared wavelengths (1-5 μm) where the spectral radiance from high temperature (>800 K) surfaces is most significant.

To address this critical need, the Jet Propulsion Laboratory and partnering institutions propose to develop and validate a compact modular high dynamic range (HDR) multispectral imager concept, with the flexibility to operate in the short, mid- or long-wavelength infrared spectral bands. The goal of this IIP project is to demonstrate this novel technology through the maturation of a mid-wavelength infrared (MWIR) imager, the Compact Fire Infrared Radiance Spectral Tracker (c-FIRST), which leverages digital focal plane array (DFPA) development from the Advanced Component Technology (ACT) Program. The DFPA is hybridized from a state-of-the-art high operating temperature barrier infrared detector (HOT-BIRD) and a digital readout integrated circuit (D-ROIC), which features an in-pixel digital counter to prevent current saturation, and thereby provides very high dynamic range (>100 dB). The DFPA will thus enable unsaturated, high-resolution imaging and quantitative retrievals of targets with a large variation in temperatures, ranging from 300 K (background) to >1600 K (hot flaming fires). With the resolution to resolve 50 m-scale thermal features on the Earth’s surface from a nominal orbital altitude of 400 km, the full temperature and area distribution of fires and active volcanic eruptions and the cool background are captured in a single observation, increasing science content per returned byte. The use of a non-saturating detector is novel, overcomes previous problems where high radiance values saturate detectors (which diminishes the science content and usefulness of the data), and demonstrates a breakthrough capability in remote sensing – one with broad applicability in both terrestrial and planetary settings. By incorporating this technology, c-FIRST is suitable for quantifying emissions from fires and volcanic eruptions of different temperatures and intensities, which is critical for establishing their impact on ecosystems, carbon fluxes, and air-quality at local scales and climate at global scales. c-FIRST will incorporate artificial intelligence (AI) approaches to identify events of high scientific value (e.g., wildfires and volcanic eruptions) while limiting the need for significant onboard storage or high bandwidths for data downlink, which is a particular handicap for high-spatial resolution satellite sensors. When deployed in a future constellation (not proposed as part of this work), multiple instruments could communicate directly with one another to perform continuous tracking and focused quantitative characterization of the thermal emissions from fires and volcanoes. This modular, AI-enhanced instrument design will enable and accelerate the development of constellations of intelligent, interacting Cube- or SmallSats. The period of performance of the project is 3 years, with an entry TLR of 3 and a planned exit TRL of 5.

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Compact Optomechanical Accelerometers for Space Geodesy
Felipe Guzman, Texas A&M Engineering Experiment Station

GRACE has fundamentally improved our understanding of the surface anomalies in Earth’s gravitational field and its dynamics. However, GRACE has shown that certain technologies, such as low-frequency high-sensitivity accelerometers, require improvements in both sensitivity and reliability to ensure future high quality science outputs. Significant progress in the development of optomechanical sensing technologies has been achieved by the scientific community over the past decade. Building upon these advancements, we target the development of compact optomechanical low-frequency acceleration sensors with sensitivity levels that enable mass change and geodesy observations.

Monolithic inertially-sensitive optomechanical sensors yield high mechanical quality factors and, therefore, high acceleration sensitivities. Readout of these sensors is performed by laser interferometry. Careful selection of materials is necessary to ensure low internal mechanical losses. Furthermore, these materials are non-magnetic resulting in a measurement system that is less sensitive to external electromagnetic fields that typically affect electrostatically readout sensors.

Material selections include low-loss glass ceramics – such as fused-silica – and crystalline silicon or silicon-nitride, among others. The materials used to fabricate the mechanical oscillators and the built-in optical components – which constitute the compact test mass sensing interferometers – are inherently compatible with vacuum operations and show low susceptibility to radiation and magnetic effects. Moreover, the materials selected typically exhibit very low coefficients of thermal expansion (CTE), in the order of 10^-7 K^-1. The design of mechanical oscillators and laser interferometer topologies are designed such that the impact of thermal effects and temperature fluctuations can be minimal. Laboratory optical sensor prototypes have demonstrated displacement sensitivities of the order of 10^-13 – 10^-15 m/rtHz over measurement frequencies of 2 mHz up to 100 Hz, respectively. Also, micro-fabricated oscillators with natural frequencies around 10 Hz and below demonstrated mechanical quality factors above 270,000; indicating acceleration noise floors at levels below 10^-10 m s^-2/√Hz, within the observation bandwidth of interest for mass change.

The Mass Change Designated Observable has identified strategic value in this technology and has funded a Category 3 effort to advance it to a level where it can be more vigorously supported by a NASA technology development program. Furthermore, it is worth mentioning the value in the realization of a US-sourced low-SWaP low-frequency accelerometer that enables Earth science applications. Presently, no similar US-sourced alternatives exist.

The Laboratory of Space Systems and Optomechanics (LASSO) research group at Texas A&M University, led by Dr. F. Guzman, will develop this instrument. LASSO will collaborate with Dr. Christopher McCullough at JPL, who will assist the research program by providing scientific expertise to help steer the technology development in a direction that maximizes scientific output, as well as by conducting gravity field recovery simulations using our experimentally determined instrument performance as determined at progressive stages in the development process.

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Compact Total and Spectral Solar Irradiance Sensor (CTSIS) Mission Concept Study
David Harber, University Of Colorado, Boulder

We intend to propose an Instrument/Measurement Concept Demonstration (IIP-ICD) to develop a detailed mission concept for a next-generation solar irradiance observation system that employs a robust and affordable mission architecture to provide future continuity of the measurement of total solar irradiance (TSI) and spectral solar irradiance (SSI). Solar irradiance, along with Earth reflected and emitted radiance, is one of the longest and most fundamental of all climate data records derived from space-based observations. Measurement of TSI and SSI, and the monitoring of small long-term changes, is necessary for the understanding of Earth’s climate.

The LASP-built Total and Spectral Solar Irradiance Sensor (TSIS-1) instrument has been operating on the ISS since 2018, and LASP is currently building the TSIS-2 instrument with an anticipated launch in late 2023. With the understanding of the need to make these measurements in perpetuity, and the advent of advanced technologies which allow for equivalent and better measurement accuracy on CubeSats and SmallSats, LASP and ESTO have embarked on the design and launch of pathfinder missions which have and will prove the ability to provide solar irradiance measurements using smaller, low cost, reliable platforms. The first demonstration was the launch of Compact Solar Irradiance Monitor (CSIM) which demonstrated the ability to make equivalent measurements with a CubeSat form factor. The next demonstration will be the ESTO-funded Compact Total Irradiance Monitor (CTIM) mission with a planned launch in 2022.

The natural technical evolution is to develop a single, compact system, which includes both the Total and Spectral Irradiance sensors. This new platform, which LASP is calling the Compact Total and Spectral Solar Irradiance Sensor (CTSIS) will enable robust, long term, low cost, resilient measurements. During the first phase of the planned 12-month study two to three distinct mission architectures will be identified, such as a small constellation of 12U CTSIS CubeSats with a two-channel CSIM and a four-channel CTIM versus a 50 kg class CTSIS SmallSat with a three- channel CSIM and a four-channel CTIM. In parallel, we will summarize desired modifications to future CSIM and CTIM instruments based on lessons learned during the CSIM flight and the CTIM I&T, and the estimated impact of these modifications on the cost and performance of future CSIM and CTIM instruments. Next, the team will work through a manufacturing, build, calibration and storage plan of the different mission architectures, followed by the development of a mission timeline for each architecture. Finally, these inputs will allow us to estimate the lifecycle cost, and the resiliency of each architecture. These results will be compared directly against the estimated cost and resiliency of a “build to print” implementation using the heritage TSIS-1 instrument designs, similar to TSIS-2. These results will be summarized in a final report at the conclusion of the study. The ultimate goal of this study is to identify and document a new mission architecture, leveraging the CSIM and CTIM instruments, which will provide solar irradiance measurement continuity at a significantly lower cost, and greater or equal resiliency, than a TSIS-1 rebuild. Entry TRL at the CTSIS system level is TRLin = 2 with a planned exit TRLout = 3.

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Flexible Configuration Distributed Synthetic Aperture Digital Beamforming Radar (FlexSAR)
Yunling Lou, Jet Propulsion Laboratory

We propose to develop technologies for a flexible, scalable, and adaptive distributed architecture for implementing synthetic aperture radar (SAR) systems, hereinafter referred to as “FlexSAR,” to address a number of targeted observables (TOs) identified by the 2017-2027 Decadal Survey. Considering the diversity of products needed to accommodate the Surface Topography and Vegetation (STV) TOs, and the resulting observational frequencies and modalities, a fundamentally new approach to realizing this vision must be developed. We therefore propose the FlexSAR technology such that multiple observational needs can be realized within the same unified architecture. The proposed technology hinges on digital beamforming electronics that are (1) flexible and scalable across a large frequency range including P-band, L-band, and beyond, (2) reconfigurable for different imaging modalities such as polarimetry, interferometry, ScanSAR, and spotlight mode SAR, (3) reconfigurable for resolution and spatial coverage. This architecture will be suitable for implementation on low cost distributed platforms such as CubeSats, achieving a large synthesized aperture via docking of multiple CubeSats that provides high signal-to-noise ratio, high effective spatial resolution, reduced overall system risks and potentially overall system costs, unprecedented flexibility and reconfigurability, and increased resilience compared to traditional one-off SAR systems.

We will demonstrate the FlexSAR architecture with L-band and P-band SAR. L-band is chosen due to its commonality amongst multiple STV and Surface Deformation and Change (SDC) observables. P-band is chosen due to its ability to penetrate dense vegetation, an advantage in solid Earth and vegetation structure observations as the majority of the land surface is covered by vegetation. Spaceborne P-band radar concepts have long been hindered by the lack of spectrum allocation for Earth exploration and the need for very large antennas. We plan to employ spread spectrum techniques to work around restricted bands, while this distributed aperture approach eliminates the need of very large deployable antenna structures.

New technologies are needed to enable digital beamforming across multi-platform elements of the distributed aperture. We propose to (i) design a distributed aperture architecture that will minimize grating lobes of the sparse array while optimizing radar performance, (ii) develop clock synchronization and calibration scheme for cross-platform antenna elements necessary to facilitate digital beamforming across the distributed aperture, (iii) conduct multi-frequency and imaging trade study, an incubation activity highlighted in the STV Incubation Study Report, to guide the FlexSAR design optimization and architecture, (iv) develop novel synthetic wideband waveforms to address fragmented spectrum availability in P-band, (v) develop a flexible simulation environment for multi-frequency radar retrieval of STV/SDC observables, followed by proof-of-concept science product development. To validate the multi-platform distributed aperture technology, we propose to develop Software Defined Radar electronics with clock synchronization, internal calibration, digital beamforming, and synthetic wideband waveform generation capabilities in a compact form factor. We will utilize UAVSAR’s L-band active array antenna front-end to conduct airborne demonstration to further test the proposed technologies in a relevant environment. By modifying UAVSAR, NASA/JPL’s airborne SAR testbed, we will simultaneously demonstrate FlexSAR’s feasibility and prepare UAVSAR to help mature technology and science algorithms in support of STV studies.

The proposed development is a 3-year effort. We will enter at TRL 2 and plan to exit at TRL 5.

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Metamaterial-based Super Spectral Filter Radiometers for Atmospheric Sounding of Temperature and Water Vapor
Richard Lynch, Atmospheric & Environmental Research, Inc.

Through metamaterial filter development, building and testing of a benchtop prototype sensor, and atmospheric retrieval studies, the concept of an ultra-compact IR sensor for measurements of temperature and water vapor in boundary layer will be built and its capabilities demonstrated. Metamaterial-based spectral filtering offers narrow passband spectral channels in a fast-optical system to provide performance matching that of a much larger spectrometer or interferometer-based systems.

Retrieval studies using measured prototype sensor characteristics and a sensor model determined from benchtop analysis offer a way to test the application of this technology to sounding of the boundary layer and free troposphere. Optical tests on a fabricated filter array with scores of spectral bands will quantify its spectral characteristics, stray light levels, and spectral sampling performance when paired with an appropriate focal plane array. Use of the device measurements in a sensor performance model then give high-fidelity predictions of a space-based sensor using a metamaterial based super spectral sensor. Development of retrievals for sounding with a super spectral sensor and sensitivity studies using the measured prototype sensor optical characteristics produce a verification of the measurement approach for atmospheric sounding and a quantitative picture of its capabilities.

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Microwave Barometric Radar and Sounder (MBARS)
Matthew McLinden, NASA Goddard Space Flight Center

Atmospheric surface pressure and pressure profiles are essential variables in weather modeling and forecasting. Pressure gradients generate atmospheric motion and are essential to the air-sea heat exchange feedbacks within the planetary boundary layer (PBL) that lead to convective storms and heavy precipitation. Despite the importance of pressure and pressure gradients on meso-, synoptic-, and global-scale weather patterns, current technology relies almost entirely on buoy measurements over the majority of the ocean. These measurements are too sparse to capture pressure gradients of even many synoptic scale events, and leave models starved of information.

Data assimilation studies have demonstrated that ocean surface pressure data contain a more useful information about the large-scale atmospheric circulations than observations of surface wind or temperature. Research at the NASA/GSFC Global Modeling and Assimilation Office (GMAO) shows that assimilation of a potential wide-swath satellite-based surface pressure retrieval product significantly impacts forecasts of ocean winds and temperature from the PBL through the mid troposphere.

This joint team of NASA/GSFC, NASA/LaRC, and Remote Sensing Solutions proposes to develop a Microwave Barometric Radar and Sounder (MBARS) for surface air pressure and pressure profiles, especially over oceans. MBARS is a combined active/passive microwave sensor in the O2 absorption V-band (64-70 GHz). This instrument consists of an innovative scanning multi-channel differential absorption radar (DAR) to provide an estimation of total atmospheric column oxygen content and thus the surface air pressure. MBARS also provides radiometric temperature profiling that enables vertical pressure profiling based on the hypsometric relationship between pressure and temperature.

The proposed system leverages significant Small Business Innovation Research (SBIR) program investments, including a software-defined radar/radiometer (SDRr) and a highly efficient power amplifier. A future spaceflight instrument may also leverage one of several SBIR technologies advancing deployable antennas. Various cutting-edge communication and radar technologies used in the sensor development enable the exacting precision and stability requirements for pressure retrieval.

The proposed effort will develop and demonstrate the innovative MBARS sensor on the NASA ER-2 high-altitude aircraft. This three-year Instrument Incubator Program (IIP) Instrument Development and Demonstration (IDD) project will start on February 1, 2022, and end on January 31, 2025. The sensor development, laboratory experiment, and flight test will raise the Technology Readiness Level (TRL) of the pressure measurement concept from 3 to 5, paving the way for future spaceborne missions on SmallSat platforms.

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SNOWWI: Snow Water-equivalent Wide Swath Interferometer and Scatterometer
Paul Siqueira, University Of Massachusetts, Amherst

In this response to the 2021 ESTO Instrument Incubator Program research announcement, the University of Massachusetts (UMass), the University of Michigan (UMich), Boise State University, and Capella Space are partnering to create an advancement in using snow surface and volume scattering characteristics for estimating the snowpack characteristics of Snow Water Equivalent (SWE), snow density and snow depth, all Essential Climate Variables (ECVs) that are used to quantify water resources, land- and ice-surface albedo. The basis of the work is centered around four basic activities: 1.) airborne instrument development, 2.) ground calibration and validation campaigns, 3.) theoretical development, and 4.) the transition of these activities into a realizable spaceborne design. The fundamentals of the remote sensing technology development are the use of high-resolution volume and surface scattering signatures that occur in a dual-frequency Ku-band regime and can be expanded upon through the use of ancillary sensors, such as ESA’s Sentinel-1 C-band mission which has demonstrated a useful sensitivity to deep snow, and changes in snow cover in mountainous regions

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Quantum Parametric Mode Sorting (QPMS) Lidar
Carl Weimer, Ball Aerospace & Technologies Corporation

Lidars and laser altimeters have demonstrated that they can bring the third dimension to satellite remote sensing for Earth Science (ICESat, ICESat2, CALIPSO, GEDI, ADM Aeolus). For future lidars to increase scientific knowledge of our planet there will need to be new technologies and new techniques. Trending is important, but new understanding of our Earth using remote sensing requires new technologies. Some key lessons learned from these past lidars/altimeters are 1) solar background light always decreases their effectiveness during the day, and 2) scenes are easily obscured by cloud, blowing snow, or turbid water – again reducing measurement quality e.g., lowering detectability of objects below and introducing biases in the science products. With next generation systems in pre-phase A development, we need to look forward now to what will follow – development cycles are lengthy.

The Quantum Parametric Mode Sorting (QPMS) lidar technique draws from developments created for Quantum Information Science (QIS). The technique uses a laser system tailored to emit in a unique Temporal-Frequency mode, a laser pulse made up of many photons all phase coherent within a pulse. The lidar receiver uses a nonlinear crystal carefully chosen to have a phase matching bandwidth smaller than the laser pulse bandwidth. This effectively creates a temporal/spectral filter, only photons in the correct mode are converted all other photons are rejected. This creates the perfect filter against background light. It also identifies signal photons that have passed through dense obscurations and still carry the precise time-of-flight to Earth scenes to allow mapping under a wider range of conditions. This is because highly multiple scattered photons will lose their intrapulse coherence and thus not be detected by the QPMS receiver. This is similar to Low-Coherence Interferometry, the basis to Optical Coherence Tomography, that allows imaging and ranging into dense tissue for medical applications.

The system is currently at TRL 4 for 1550 nm having proven out the precise ranging even through optically dense obscuration and in the presence of strong background light. The most serious of limitations of traditional up-conversion technique have been addressed with funding from ESTO (ESTO ATI-QRS-20). For it to be useful for a broader range of Earth scenes the system must be adapted to the visible spectrum where there is much lower absorption, setting the entry of the proposed development to TRL 1 The proposed effort will extend the techniques to the visible and perform lab testing in snow and water scenes. For snow the objective is to precisely measure (mm resolution) snow depth up to 0.8 m and potentially characterize snowpack properties such as grain size/shape and snow water equivalent (SWE) a critical parameter as called out in the Decadal Survey. For water it is to increase the depth at which bathymetry can be performed in turbid water. The path to a packaged system for field demonstrations and eventual space application will be evaluated. This will advance the technique to TRL 3 and prepare it for actual Earth missions at NASA, e.g., for the future snow/hydrology missions and Surface Topography and Vegetation mission.

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HALE InSAR for Continual and Precise Measurement of Earth’s Changing Surface
Lauren Wye, Aloft Sensing, Inc.

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.


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