Browsing by Author "Stone, Tom"
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Item 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 Nighttime Aerosol Optical Depth Measurements Using a Ground-based Lunar Photometer(2015-06-26) Berkoff, Tim; Omar, Ali; Haggard, Charles; Pippin, Margaret; Tasaddaq, Aasam; Stone, Tom; Rodriguez, Jon; Slutsker, Ilya; Eck, Thomas; Holben, Brent; Welton, Judd; Silva, Arlindo da; Colarco, Pete; Trepte, Charles; Winker, DavidIn recent years it was proposed to combine AERONET network photometer capabilities with a high precision lunar model used for satellite calibration to retrieve columnar nighttime AODs. The USGS lunar model can continuously provide pre-atmosphere high precision lunar irradiance determinations for multiple wavelengths at ground sensor locations. When combined with measured irradiances from a ground-based AERONET photometer, atmospheric column transmissions can determined yielding nighttime column aerosol AOD and Angstrom coefficients. Additional demonstrations have utilized this approach to further develop calibration methods and to obtain data in polar regions where extended periods of darkness occur. This new capability enables more complete studies of the diurnal behavior of aerosols, and feedback for models and satellite retrievals for the nighttime behavior of aerosols. It is anticipated that the nighttime capability of these sensors will be useful for comparisons with satellite lidars such as CALIOP and CATS in additional to ground-based lidars in MPLNET at night, when the signal-to-noise ratio is higher than daytime and more precise AOD comparisons can be made.Item Nocturnal Aerosol Optical Depth Measurements with a Small-Aperture Automated Photometer Using the Moon as a Light Source(AMS, 2011-10-01) Berkoff, Timothy A.; Sorokin, Mikail; Stone, Tom; Eck, Thomas; Hoff, Raymond; Welton, Ellsworth; Holben, BrentA method is described that enables the use of lunar irradiance to obtain nighttime aerosol optical depth (AOD) measurements using a small-aperture photometer. In this approach, the U.S. Geological Survey lunar calibration system was utilized to provide high-precision lunar exoatmospheric spectral irradiance predictions for a ground-based sensor location, and when combined with ground measurement viewing geometry, provided the column optical transmittance for retrievals of AOD. Automated multiwavelength lunar measurements were obtained using an unmodified Cimel-318 sunphotometer sensor to assess existing capabilities and enhancements needed for day/night operation in NASA’s Aerosol Robotic Network (AERONET). Results show that even existing photometers can provide the ability for retrievals of aerosol optical depths at night near full moon. With an additional photodetector signal-to-noise improvement of 10–100, routine use over the bright half of the lunar phase and a much wider range of wavelengths and conditions can be achieved. Although the lunar cycle is expected to limit the frequency of observations to 30%–40% compared to solar measurements, nevertheless this is an attractive extension of AERONET capabilities.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.