Browsing by Author "Turpie, Kevin"
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Item Air-LUSI: an autonomous robotic telescope for high-altitude lunar spectral irradiance measurements(SPIE, 2022-05-27) Newton, Andrew; Maxwell, Stephen E.; Gadsden, S. Andrew; Turpie, KevinThe airborne lunar spectral irradiance (air-LUSI) mission is an inter-agency partnership between the US National Aeronautics and Space Administration and the US National Institute of Standards and Technology. Air-LUSI aims to make SI-traceable measurements of lunar spectral irradiance at visible to near-infrared wavelengths with unprecedented accuracy. To minimize uncertainty, lunar spectra are acquired above 90 % of the Earth’s atmosphere aboard NASA’s Earth Resources aircraft, a civilian descendant of the U-2 spy plane. The data collected by the air-LUSI instrument is poised to improve upon current lunar calibrations of Earth observing satellites. The air-LUSI team recently completed their Operational Flight Campaign in Palmdale, California in March 2022. In addition to the Engineering Flight Campaign of August 2018 and the Demonstration Flight Campaign of November 2019, the air-LUSI instrument has been successfully deployed on over ten lunar spectral measurement flights at altitudes of roughly 21 km. This paper presents the simplified double gimbal design that was capable of recently tracking the Moon with a root mean square tracking error of less than 0.1°.Item Air-LUSI: Supporting Advancement [STC1] of the Moon as a Reference for Earth Observations from Space Air-LUSI: Supporting Advancement of the Moon as a Reference for Earth Observations from Space(EGU Publications) Turpie, Kevin; Brown, Steven; Woodward, John; Stone, Thomas; Gadsden, Andrew; Grantham, Steven; Larason, Thomas; Maxwell, Stephen; Cataford, Andrew; Newton, AndrewTo monitor global environments from space, satellites must be calibrated accurately and consistently across time, missions and instruments. This requires the use of a stable, common reference that is continuously accessible to Earth observing satellites, whether they make up series of missions spanning long periods of time or comprise constellations acquiring many simultaneous observations across the planetItem Airborne Lunar Spectral Irradiance (air-LUSI) Missioni Capability Demonstration(Calcon, 2020-09-21) Turpie, Kevin; Brown, Steve; Woodward, John; Gadsden, Andrew; Stone, Tom; Grantham, Steve; Maxwell, Stephen; Larason, Tom; Newton, Andrew; Rice, JoeThe Moon is a very useful calibration target for Earth-observing sensors in orbit because its surface is radiometrically stable and it has a radiant flux comparable to Earth scenes. To predict the lunar irradiance given an illumination and viewing geometry, the United States Geological Survey (USGS) has developed the Robotic Lunar Observatory (ROLO) Model of exo-atmospheric lunar spectral irradiance. The USGS ROLO model represents the current most precise knowledge of lunar spectral irradiance and is used frequently as a relative calibration standard by space-borne Earth-observing sensors. However, instrument calibration teams have expressed the need for an absolute lunar reference with higher accuracy.Item Calibration and Validation for the Surface Biology and Geology (SBG) Mission Concept: Recommendations for a Multi-Sensor System for Imaging Spectroscopy and Thermal Imagery(AGU, 2023-08-23) Turpie, Kevin; Casey, Kimberly A.; Crawford, Christopher J.; Guild, Liane S.; Kieffer, Hugh; Lin, Guoqing Gary; Kokaly, Raymond; Shrestha, Alok K.; Anderson, Cody; Chandra, Shankar N. Ramaseri; Green, Robert; Hook, Simon; Lukashin, Constantine; Thome, KurtThe primary objective of the NASA Surface Biology and Geology (SBG) mission is to measure biological, physical, chemical, and mineralogical features of the Earth’s surface, realizing a key conceptual component of the envisioned NASA Earth System Observatory (ESO). SBG is planned to launch as a two-platform mission in the late 2020s, the first of the ESO satellites. Targeted science and applications objectives based on observations of the Earth’s surface biology and geology helped to define the mission architecture and instrument capabilities for the SBG mission concept. These objectives further drove the need for enabling change detection and trending of surface biological and geological features. These needs implied fundamental calibration goals to achieve the necessary science data quality characteristics. To meet those goals, calibration and validation pre-launch and on-orbit methods formed a basis of the calibration and validation concept, including the combined use of on-board references, vicarious techniques, and routine lunar imaging. International collaboration with space agencies in other countries, an important feature of the recommended SBG mission architecture, uncovered and emphasized the need for inter-calibration techniques that underscored the importance of collaborative instrument characterization data sharing and the use of common calibration references that are International System of Units (SI) traceable in pre-launch and post-launch on orbit calibration mission phases. International collaboration through the use of terrestrial and aquatic networks on six continents for vicarious calibration and validation activities will further assure necessary science data quality while in orbit.Item Evaluation of air-LUSI Measurements to Advance Lunar Modeling and the ROLO Lunar Calibration Reference(2021-10-20) Stone, Thomas C.; Turpie, Kevin; Brown, Steven; Maxwell, Stephen; Woodward, JohnThe airborne Lunar Spectral Irradiance (air-LUSI) project is dedicated to acquiring high-accuracy, spectrally resolved measurements of the Moon from the NASA ER-2 high-altitude aircraft, flying above more than 90% of Earth's atmosphere. The air-LUSI instrument is a non-imaging system designed specifically for measuring spectral irradiance of the Moon at wavelengths from ~350 nm to 1100 nm. The project aims to achieve absolute measurement uncertainty approaching 0.5% (k=1) with traceability to NIST radiometric standards and SI. These measurements can advance lunar calibration by constraining absolute scale of models that constitute the lunar radiometric reference, such as the USGS ROLO model. A 5-night flight campaign in November 2019 collected lunar measurements at phase angles ranging from 9.4 to 58.5 degrees after Full Moon. ROLO model outputs have been generated for the times and aircraft locations of each night's observations. Inter-night comparisons after normalizing by ROLO show inter-consistency of the measurements within 1.5%, despite a factor of 3.34 difference in lunar irradiance at 500 nm over the 5-night span. These results give no indication of an appreciable phase angle dependence in the ROLO model within the observed range. This talk will highlight implications of the high-accuracy air-LUSI measurements with regard to lunar calibration using irradiance measurements derived from lunar images acquired by space-based sensors.Item Improving the ROLO Lunar Calibration Reference with New Measurements of the Moon(2023-06-12) Stone, Thomas C.; Turpie, Kevin; Woodward, John; Maxwell, StephenThe Moon provides a calibration target that can serve as a common reference for all space-based Earth observing sensors. Lunar calibration has the potential to achieve very high accuracy, leading to important capabilities for Earth remote sensing such as inter-calibration of instruments in satellite constellations and building climate data records. Practical use of the Moon for radiometric calibration requires a model to account for the continuously changing lunar brightness and that can accommodate the various viewing geometries of sensors’ Moon observations. The USGS ROLO lunar calibration system operates with a model for the disk-integrated irradiance at reflected solar wavelengths, developed from an extensive set of ground-based observations. Although the ROLO model is widely used, to reach the full accuracy potential of lunar calibration requires collecting new characterization measurements of the Moon to apply toward refining and ultimately reformulating the analytic model that provides the lunar reference. The airborne Lunar Spectral Irradiance (air-LUSI) project is a currently operational system to acquire spectrally resolved measurements of the Moon from the NASA ER-2 high-altitude aircraft, flying above ~95% of the atmosphere.Item Measurements of Absolute, SI Traceable Lunar Irradiance with the Airborne LUnar Spectral Irradiance (air LUSI) Instrument(2021-10-20) Woodward, John T.; Brown, Steven W.; Grantham, Steve; Larason, Thomas C.; Maxwell, Stephen E.; Turpie, Kevin; Gadsden, S. Andrew; Newton, Andrew; Stone, Thomas C.The Moon is a very useful calibration target for Earth-observing sensors in orbit because its surface is radiometrically stable and it has a radiant flux comparable to Earth scenes. To predict the lunar irradiance given an illumination and viewing geometry, the United States Geological Survey (USGS) has developed the Robotic Lunar Observatory (ROLO) Model of exo-atmospheric lunar spectral irradiance. The USGS ROLO model represents the current most precise knowledge of lunar spectral irradiance and is used frequently as a relative calibration standard by space-borne Earth-observing sensors. However, its accuracy as an absolute reference may be limited to several percent and it is not SI-traceable. Advancing the model to be a more accurate absolute lunar reference requires new measurements. The objective of the airborne LUnar Spectral Irradiance (Air-LUSI) mission is to make highly accurate, SI-traceable measurements of lunar spectral irradiance in the VNIR spectral region from NASA’s high-altitude ER-2 aircraft, above 95% of the atmosphere. To that end, the Air-LUSI system uses a non-imaging telescope system that robotically tracks the Moon in flight, fiber-optic coupled to a stable spectrometer housed in an enclosure providing a robustly controlled environment. The spectrometer measures about 350 to 1050 nm at 3.8 nm resolution, with 0.8 nm sampling. The instrument is reproducibly stable to 0.3% and rigorously calibrated before and after campaigns and flights using a similar transfer standard spectrograph. An on-board LED source is used to monitor the instrument response during flight ascent and descent. Air-LUSI successfully conducted a Demonstration Flight Campaign on five consecutive nights from 12 to 17 November 2019, corresponding to lunar phase angles of about 10°, 21°, 34°, 46° and 59°. Each night, the Air-LUSI system observed the Moon from above 68,000 feet altitude for 30 to 40 minutes. To reach a target uncertainty for lunar irradiance of 0.5% (k=1), processing the raw data to exo-atmospheric lunar spectral irradiance required accounting for various known behaviors of the instrument, such as thermal and stray light corrections. Additional measures were taken to address variances idiosyncratic to the campaign and were factored into the measurement error budget. The resulting error budget currently stands at less than 1% over most of the VNIR range. This paper reviews the steps taken towards high accuracy results for Demonstration Flight Campaign, how they factored in the error budget, and how our uncertainty target can be met in future campaigns.Item NASA's Surface Biology and Geology Concept Study: Status and Next Steps(IEEE, 2021-02-17) Thompson, David R.; Schimel, David S.; Poulter, Benjamin; Brosnan, Ian; Hook, Simon J.; Green, Robert O.; Glenn, Nancy; Guild, Liane; Henn, Christopher; Cawse-Nicholson, Kerry; Kokaly, Ray; Lee, Christine; Luvall, Jeffrey; Miller, Charles E.; Nastal, Jamie; Pavlick, Ryan; Phillips, Benjamin; Schneider, Fabian; Uz, Stephanie Schollaert; Serbin, Shawn; Stavros, Natasha; Townsend, Philip; Turner, Woody; Turpie, Kevin; Wang, WeileThe National Academies Decadal Survey for Earth Science recommended that NASA pursue global imaging spectroscopy and thermal infrared measurements in the coming decade [1]. Both measurements would offer repeat coverage on approximately five-day to biweekly cadence, with comprehensive coverage of the globe's coastal and terrestrial area. This would be an unprecedented volume of data with the potential to transform remote sensing practice. To address this recommendation, NASA has sponsored a concept study by NASA research centers and associated university partners (https://sbg.jpl.nasa.gov). This study is determining a family of architecture options - including launch vehicle, spacecraft, instrument, and suborbital components - that could address the Decadal Survey objectives. The architecture study is driven by science needs and builds on input of the research community. As of this writing, the study is entering a phase in which a large field of system possibilities is pared down to a representative handful for an ultimate decision by NASA.Item NASA's surface biology and geology designated observable: A perspective on surface imaging algorithms(Elsevier, 2021-05) Cawse-Nicholson, Kerry; Townsend, Philip A.; Schimel, David; Assiri, Ali M.; Campbell, Petya Entcheva; Huemmrich, Karl; Roberts, Dar; Turpie, Kevin; The SBG Algorithms Working Group; et al.The 2017–2027 National Academies' Decadal Survey, Thriving on Our Changing Planet, recommended Surface Biology and Geology (SBG) as a “Designated Targeted Observable” (DO). The SBG DO is based on the need for capabilities to acquire global, high spatial resolution, visible to shortwave infrared (VSWIR; 380–2500 nm; ~30 m pixel resolution) hyperspectral (imaging spectroscopy) and multispectral midwave and thermal infrared (MWIR: 3–5 μm; TIR: 8–12 μm; ~60 m pixel resolution) measurements with sub-monthly temporal revisits over terrestrial, freshwater, and coastal marine habitats. To address the various mission design needs, an SBG Algorithms Working Group of multidisciplinary researchers has been formed to review and evaluate the algorithms applicable to the SBG DO across a wide range of Earth science disciplines, including terrestrial and aquatic ecology, atmospheric science, geology, and hydrology. Here, we summarize current state-of-the-practice VSWIR and TIR algorithms that use airborne or orbital spectral imaging observations to address the SBG DO priorities identified by the Decadal Survey: (i) terrestrial vegetation physiology, functional traits, and health; (ii) inland and coastal aquatic ecosystems physiology, functional traits, and health; (iii) snow and ice accumulation, melting, and albedo; (iv) active surface composition (eruptions, landslides, evolving landscapes, hazard risks); (v) effects of changing land use on surface energy, water, momentum, and carbon fluxes; and (vi) managing agriculture, natural habitats, water use/quality, and urban development. We review existing algorithms in the following categories: snow/ice, aquatic environments, geology, and terrestrial vegetation, and summarize the community-state-of-practice in each category. This effort synthesizes the findings of more than 130 scientists.Item Producing Exo atmospheric Fiduciary Reference Measurements of Lunar Spectral Irradiance from the Airborne Lunar Spectral Irradiance (air LUSI) March 2022 Flight Campaign(2023-06-12) Woodward, John; Maxwell, Stephen; Larason, Thomas; Grantham, Steven; Stone, Tom; Turpie, Kevin; Gadsden, S. Andrew; Newton, AndrewIn March of 2022 air-LUSI made four flights aboard a NASA ER-2 high-altitude aircraft and measured the lunar spectral irradiance from above ~95% of the Earth’s atmosphere. Measurements were made at lunar phases of -60.3°, -37.0°, -25.0° and -12.9° with a flight scheduled for -48.8° canceled due to high winds. The measurements are traceable to the SI through artifacts calibrated at NIST and used to calibrate air-LUSI while on the aircraft. An LED-based monitoring system then verifies the calibration during flight. In addition to calibration, both the transfer spectrograph and the air-LUSI instrument were characterized for their linearity and change in response with temperature. A tunable laser was used to measure their bandpass and correct for stray light. We will discuss the calibration approach and the measurement chain that establishes the SI-traceability of these measurements. A pipeline developed in Python incorporates the characterization results with measurements taken at each stage of the calibration chain to obtain a series of at-sensor lunar irradiances for each flight. To achieve top-of-the atmosphere (TOA) irradiance the flight telemetry data was used to correct for the residual atmospheric losses using MODTRAN. The spectra were normalized to a single time point using the ROLO model to correct for the relative change in lunar irradiance during forty minutes of data collection. The result is an SI-traceable TOA lunar spectrum for each flight. Our approach to developing an uncertainty budget will also be discussed.Item SBG Applications: Aquatic Ecosystems Including Corals, Harmful Algal Blooms, Water Quality, Restoration(NASA Technical Reports Server, 2019-06-12) Uz, Stephanie; Tzortziou, Maria; Guild, Liane; Ortiz, Joe; Turpie, Kevin; Lee, Christine; Stravros, Natasha; Luvall, Jeff; Glenn, NancyItem Spectral Fidelity of Earth's Terrestrial and Aquatic Ecosystems(American Geophysical Union, 2021-07-10) Thompson, David R.; Brodrick, Philip G.; Cawse-Nicholson, Kerry; Chadwick, K. Dana; Green, Robert O.; Poulter, Benjamin; Serbin, Shawn; Shiklomanov, Alexey; Townsend, Philip; Turpie, KevinAbstract The Surface Biology and Geology (SBG) investigation will create global maps of spectral surface reflectance and emissivity at a cadence of 16 days or better, with coverage to address global questions about Earth's geology, cryosphere and ecosystems. The revolutionary potential poses a commensurate challenge: creating contiguous maps free from regional biases induced by atmosphere, observation geometry, or inversion error. This will require an accurate calibration with precise knowledge of each channel's spectral response. Here we quantify the impact of spectral calibration on SBG's aquatic and terrestrial ecosystem objectives. We find that contemporary algorithms for ecosystem trait retrieval demand more accurate spectral calibration than historical missions. Errors due to drift or spatial nonuniformity in the wavelength calibration that have previously been considered acceptable can cause systematic errors larger than the instrument noise and of the same order as the variability SBG aims to measure. Moreover, their impact on atmospheric correction can induce climate-dependent systematic errors that thwart comparisons between ecosystems. These results underscore the importance of spectral response accuracy in SBG mission design. Plain Language Summary Remote imaging spectrometers operating in visible to shortwave infrared wavelengths of the electromagnetic spectrum measure the intensity of solar-reflected light as hundreds of distinct channels. This requires knowing the precise spectral range to which each channel is sensitive. The accurate association of wavelengths to instrument channels is known as the spectral calibration of the instrument, or simply spectral fidelity. Small errors in this calibration can have a significant impact on measurement accuracy. This study evaluates the sensitivity of a future global investigation of Earth's ecosystems to such errors. We find that small errors in spectral calibration can cause large inaccuracies in maps of ecosystem properties. This means that accurate spectral calibration will be critical for the success of these future investigations.Item Towards a second-generation robotic telescope mount for the air-LUSI instrument(SPIE, 2023-06-13) Newton, Andrew; McCafferty-Leroux, Alex; Gadsden, S. Andrew; Turpie, KevinEarth observation satellites, such as those responsible for monitoring the effects of climate change, require rigorous calibration protocols to account for on-orbit sensor degradation. An increasingly dependable method to address this issue uses the Moon as a reference light source for in-situ calibration. The airborne lunar spectral irradiance (air-LUSI) mission aims to improve the utility of the Moon as an on-orbit calibration target for remote sensing instruments, by tying the currently accepted lunar model to the SI and establishing lunar irradiance on an absolute scale. To this end, air-LUSI collects SI-traceable measurements of lunar irradiance at visible to nearinfrared wavelengths with unprecedented accuracy. A non-imaging telescope is flown at an altitude of 21 km, aboard NASA’s high-altitude ER-2 aircraft, which places the instrument above 95% of the Earth’s atmosphere for clean, minimally obstructed lunar spectra. To fix the optical axis on the Moon during flight, an autonomous control system is required to compensate for aircraft motion and track the Moon across its celestial transit. In this paper, we present an overview of the robotic subsystem used to track the Moon on more than ten high-altitude flights, and the valuable lessons learned from those campaigns. From this insight, a preliminary design for a second-generation robotic telescope mount is presented. Referred to as the HAAMR, it will supplant the current robotics system on future air-LUSI Operational Flight Campaigns, with the nearest field deployment slated for January 2024. We show how this new system is poised to offer a more reliable, accurate, and responsive platform for the air-LUSI instrument to continue collecting data that will ultimately help to improve our understanding of the Earth’s climate.