EPJ Web Conferences 237, 01011 (2020) https://do i.org/10.1051/epjconf/202023701011 ILRC 29

LASER REMOTE SENSORS FOR NASA’S FUTURE EARTH AND SPACE SCIENCE MISSIONS Upendra N. Singh NASA Engineering Safety Center, NASA Langley Research Center, Hampton, Virginia 23681, USA *Email: [email protected] ABSTRACT $3M), and the desired maturities to begin an Earth Active optical (Laser/Lidar) measurement System Science Pathfinder (ESSP) flight projects (~ $300M). Too often, the laser and lidar technologies techniques are critical for the future National were still being developed during the flight projects, Aeronautics and Space Administration (NASA) leading to schedule delays and large labor bills from Earth, Planetary Science, Exploration, and the project personnel. These concerns led to NASA Aeronautics measurements. The latest science commissioning an Earth Science Independent Laser decadal surveys recommend a number of missions Review Panel during the early part of 2000. The Panel requiring active optical systems to meet the report cited critical deficiencies in NASA’s laser science measurement objectives and the strategy and recommended that NASA should address aeronautics community continues to use the cited deficiencies and put together a Laser Risk Laser/Lidar technologies to meet the aeronautics Reduction Program [1]. Through the Panel report, it measurement objectives. This presentation will was clear that development teams needed to mature laser and lidar technologies before the approval of provide an overview of NASA efforts in flight projects. For this reason, NASA approved the developing and maturing state-of-the-art advanced Laser Risk Reduction Program (LRRP), which began solid-state flight laser/lidar systems for airborne in 2002, had enjoyed many successes, and ended and space-borne remote sensing measurements. during 2010 [2-3]. The presentation will also provide details of a strategic approach for active optical technologies 2. RATIONALE FOR ACTIVE OPTICAL and techniques to meet the NASA’s future Earth SENSING and Space Science measurements/missions needs Many physical phenomena critical to improving our and requirements for space-based applications. understanding of Earth and planetary systems can only be measured practically using lidar techniques. Lidar 1. OVERVIEW remote sensing is analogous to radar remote sensing, NASA’s Strategic Plan calls for NASA “to improve except lidar employs electromagnetic radiation with prediction of climate, weather, and natural hazards,” wavelengths 4 to 5 orders of magnitude shorter than and to provide services to the Nation including radar. This wavelength difference causes “weather forecasting; climate prediction; natural hazard proportionally less beam divergence; profound assessment, prediction, and response; and differences in usable targets, atmospheric transmission, environmental management, including air quality and attainable resolution. Lidar also requires different forecasting and land use assessment.” These beam generation, handling, and detection technologies. assignments will require the use of Light Detection Therefore, lidar sensors maintain the advantages of And Ranging (lidar) (or laser radar) remote sensing active radar sensors with the self-contained light source, systems. Lidar sensors provide the excellent vertical choice and knowledge of exciting signal properties, resolution needed to do these jobs. NASA also is pointing at desired target, and range-resolved return working to advance radar, laser, and light detection and signal, while providing greatly improved horizontal ranging technologies to enable monitoring of such key and vertical spatial resolution, and access to new Earth system parameters as land surface, oceans, ice atmospheric and surface targets. In summary, lidar sheet topography, and global tropospheric winds that sensors offer: could lead to advances in weather and severe storm • Excellent vertical and horizontal spatial resolution prediction. After 35 years of passive and then • Relative independence from natural light sources, microwave radar remote sensing, NASA began to their angles, and time of day utilize lidar sensors in the 1990’s. However, many • Choice of optical wavelength, pulse duration, pulse difficulties were encountered with the lidar missions. shape, and polarization to optimize science return (i.e., Part of the cause of these difficulties arose from the the ability to target specific chemical and physical large gap between the technology maturities after phenomena by choosing the appropriate wavelength) Instrument Incubator Program (IIP) completion (~ • Choice of pointing direction

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• Choice of several lidar techniques: basic, altimetry, Earth can only be obtained through the use of Doppler, DIfferential Absorption Lidar (DIAL), and differential absorption lidar (DIAL) lidar techniques. polarization • Measurement of the global distributions of An active optical remote sensing technology tropospheric ozone and aerosols using a space-based development and maturation strategic approach DIAL system will help address the causes and impacts will mitigate lidar system technology of long-term climate variability and will distinguish development risks by coordinating activities with natural from human-induced drivers. This multiple NASA Centers and government agencies. measurement is essential to the modeling and assessment of chemical, radiative, convective, This will move NASA into the next logical era of dynamical, and transport processes in the troposphere. lidar remote sensing by enabling such critical Again, precise, vertical measurements (1 to 2 km space-based measurements as winds, ozone, CO2, vertical) are only available through the use of lidar moisture, clouds, aerosols, surface topography, ice techniques. thickness, vegetation, trace atmospheric species, • Lidar is the only method for measuring particle biogenic traces gases and materials, and oceanic profiles in the oceans’ mixing layer, necessary to properties. understand how oceanic carbon storage and fluxes contribute to the global carbon cycle Lidar is also crucial to improving the safety, • DIAL lidar is the only technique for global moisture reliability, and affordability of solar system profiles at high resolution (0.5 km vertical by 50 km exploration by providing atmospheric information horizontal) in the boundary layer. This is an essential for spacecraft aerocapture, entry and descent; and need for understanding the convective processes and guidance and hazard avoidance data to the severe storm development, and to improve our Planetary Landers. Furthermore, lidar techniques understanding of the global hydrological and energy are also regarded as enabling for a variety of cycle. homeland security, aviation, and environmental • Backscatter lidar is the only method for high vertical resolution (30 m) measurements of optical properties of pollution applications. NASA’s leadership in this clouds and aerosols including planetary boundary area would further cement its public perception as height, cloud base, cloud top, cloud amount, cloud a national asset and “crossover” entity depolarization, and aerosol microphysical properties encompassing both civil and DoD functions. This needed in climate modeling and research. effort will bring all lidar remote sensing • Altimetry lidar is the only technique for directly technologies together, including planetary, earth profiling a surface level changes of less than 1 cm/year, viewing, aerospace, and aeronautics. essential for studying terrestrial land cover vegetation, land surface topography, volcano monitoring, global 3. KEY MEASUREMENTS ENABLED sea level, and polar ice sheet level changes caused by An active optical strategic approach enables several climatic changes. key measurements that are likely to open new frontiers Especially critical measurements from the Space of research that practitioners cannot obtain in any other Science measurement roadmaps include: way. Especially critical measurements from the Earth • Lidar techniques offer versatile planetary surface Science measurement roadmaps include: topography measurements and other planetary surface • Global tropospheric winds, which are acknowledged deformation information with sub-meter vertical as the greatest unmet observational need for improving accuracy laser altimetry to study geological, volcanic, global weather forecasts on anything more than an climatic, and tidal effects in planetary bodies including incremental basis. Doppler lidar techniques are Mars, the Moon, Venus, Titan, and Jupiter’s Icy Moons. recognized as the only means for acquiring such data • As with terrestrial applications, backscatter lidar is with the required precision (1 m/s, 25-100-km the only method for determining detailed vertical horizontal resolution). profiles of the Martian and Jovian atmospheres • Similarly, the location, quantification, and extent of including dust storms and surface eddies that can CO2 sources and sinks; and their variability are prima provide information about their aerosol and clouds facie requirements for balancing the carbon budget in needed to study the structure, dynamical, and radiative global climate models. High precision profiling of properties of the atmospheres of these planetary bodies. tropospheric CO2 (0.3% mixing ratio, 2-km vertical • DIAL lidar enables measurement of the variability of scale) is essential to understanding the global carbon water vapor, ozone, CO2, and other trace gas species in cycle, greenhouse warming and sustainability of life on planetary atmospheres (e.g., Mars) to study the chemical and radiative properties and obtain

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information about water and water vapor that are of and Aeronautics, a strategic approach is needed to keen interest as an indispensable ingredient for life. identify areas where NASA should “lead, leverage • Doppler wind lidar is the only technique to study the or collaborate” with existing national and three-dimensional dynamical and transport properties, international industries to meet its future needs. dust storms, and turbulence in the atmospheres of Mars, An essential part of the assessment strategy was to Jupiter, Venus, Titan, and other planetary systems that can shed new insight into knowledge about the state of engage with other US Government entities, as these atmospheres well as industry and academia, to leverage • Surface-based lidar is ideal for measuring common Active Optical interests and tropospheric winds on Mars as a boundary condition in complementary skills/expertise resident in those global climate models, but also to ensure design safety sectors. To seek the input from broader national of next-generation entry, descent, and landing systems. entities, such as NASA, industry, academia, • Lidar with high power lasers can be used as remote Federally Funded Research and Development sensing mass spectrometers by performing laser Centers (FFRDC) and Other Government ablation of distant planetary bodies including Jupiter’s Agencies (OGA), the S&I CLT organized a Icy Moons, as well as direct compositional information Technical Interchange Meeting (TIM) during July about primitive objects including asteroids and comet nuclei. 31 through August 2, 2018 in Columbia, • Lidar Raman Spectroscopy for detection of organic Maryland, USA. Participants in the TIM phases at local and remote scales (e.g., on Mars) exchanged perspectives on the current state of the • Lidar spectroscopy for Biogenic Trace Gas sensing discipline’s technologies and the direction NASA (i.e., detection of methane and other species) in the needs to take in the future to raise the TRL of the Martian atmosphere. measurement technologies to meet these measurement needs in the applications domains. 4. ACTIVE OPTICAL CAPABILITY The TIM aimed at focusing NASA’s directions to ASSESSMENT AND STRATEGY attain the necessary technology TRL levels to NASA Sensors and Instrumentation (S&I) meet the Agency-level priority Active Optical Capability Leadership Team (CLT) was recently measurements in Space and Aeronautics. tasked by the NASA Agency Program 5. PRIORITY ACTIVE OPTICAL BASED Management Council (APMC) to determine if the MEASUREMENT AREAS Agency has the necessary expertise and capabilities to execute successfully the active The NASA TIM organized focused technical optical-based systems necessary to make the sessions in the priority active-optical based required measurements for Science, Exploration, measurements area for NASA critical needs in and Aeronautics. Given the charter from the Science, Exploration, and Aeronautics. These APMC, the S&I CLT leadership assembled a core sessions were: team to realize the assessment. The Active Optical 5.1 Mission Area I: Earth Science Focused assessment process utilized a multi-directorate Measurement Topic Areas teaming with representatives of the Science, Human Exploration and Operations, Aeronautics Atmospheric Composition sounding Research, and Space Technology Mission measurements in the troposphere including Directorates to provide guidance and list the aerosol and cloud properties and profiling, water priority measurements requirements to meet their vapor profiling, and Planetary Boundary Layer critical future needs. height • Earth’s Surface & Interior via geodetic imaging An Active Optical Tiger team consisting of including wide-swath laser altimetry mission directorate representatives, S&I capability • Climate Effect Monitoring including ice mass and technical leads/co-leads, and an external changes, global ice characterization, snow depth, assessment team worked together to seek national and snow-water equivalent measurements and international community inputs to formulate • Weather including global tropospheric Lidar an integrated Agency level strategy. Given the wind measurements for planetary boundary layer cross-cutting synergies in critical Active Optical energy, momentum, and mass exchanges; measurements for NASA Science, Exploration forecasting; convection; fluxes of heat,

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momentum, water vapor and other gases; and • Quantification of flow field and surface model validation and improvement parameters in ground-based wind tunnel testing of • Carbon, Ecosystems, & Biogeochemistry aero vehicle including measurements of CO2 and CH4 fluxes To include the international active optical and trends, vegetation 3D structure, biomass, and capability as a part of the NASA strategy, the S&I disturbance, ocean mixing layer CLT coordinated efforts with other space agencies 5.2 Mission Area II: Space Science and and organized an International IEEE-GRSS Exploration Focused Measurement Topic Workshop on Space-based Lidar Remote Sensing Areas Techniques and Emerging Technologies during June 4-8, 2018 at Milos Conference Center, • Lunar Exploration including landing navigation Adamas, Milos Island, Cyclades, Greece. The and hazard avoidance, and surface exploration and NASA and ESA leadership jointly organized characterization similar technical sessions as in the TIM. This • Jovian Moons including surface features and Workshop brought together Active Optical characterization, and tidal signatures experts and policy makers from NASA, ESA, • Jovian Environment including atmospheric JAXA, CNES, and DLR engaged in advancing cloud and wind structure, atmospheric space missions/measurements in the Active composition Optical area for Science and Exploration. • Mars Exploration including atmospheric winds, density, and dust profiling, surface topography, 6. CONCLUSIONS surface exploration and characterization, search To address the critical Agency needs in the area of for organic signatures, moisture distribution, and active optical measurements, the NASA Sensors cloud characterization and Instrumentation Capability Leadership Team • Martian Mission Support including precision worked with experts and leaders from NASA, landing, navigation, and hazard avoidance, sample industry, academia, FFRDCs, OGAs, and return rendezvous and capture, atmospheric international Space Agencies to assess existing characterization to support entry, descent, and active optical capabilities and opportunities for landing leveraging and collaboration for addressing • Titan and Venus including balloon-borne active NASA’s critical needs for Science, Exploration, optical instrumentation and Aeronautics. The S&I CLT hosted TIM and • Situational awareness of space weather international workshop to capture national and phenomena international technical inputs from experts. Inputs • Laser interferometry, active –optical sensing of gathered were provided to an independent and telescope and satellite swarm elements to enable external Active Optical Assessment and observations Recommendation Team (AOART). In coming 5.2 Mission Area III: Aeronautics Focused months, AOART team will complete a final report Measurement Topic Areas and present its findings, observation, and • Turbulence detection on flight vehicles recommendation to the APMC, including a • Situational awareness detection of atmospheric suggested strategy to address the Agency’s needs hazards including volcanic ash, ice, and snow in a crosscutting, synergistic and cost effective • Sense and avoidance for autonomous UAVs and manner. The conference presentation will future autonomous urban mobility aircraft summarize these results and recommendations. • Airport ground control management for taxiing, REFERENCES takeoff, and landing including wake vortex detection [1] S. Alejandro, et al., NASA Internal Report, • UAV-based target imaging November 2000. • Sensing and avoiding hazards in the National Air [2] U. Singh, et al., Proc. of SPIE 4882-81 (2002). Space including miniaturized, low-power active [3] F. Peri, et al., Proc. of SPIE 4893-24 (2002).

optical sensors and instrumentation for UAV and

personal air vehicles

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