Browsing by Author "Woodward, John"
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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 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 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.