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Search Publications by: John T. Woodward IV (Fed)

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Displaying 26 - 50 of 123

Precise Measurement of Lunar Spectral Irradiance at Visible Wavelengths

November 12, 2013
Author(s)
Keith R. Lykke, John T. Woodward IV, Allan W. Smith, Claire E. Cramer
We report a measurement of lunar spectral irradiance with an uncertainty below 1 % from 420 nm to 1000 nm. This measurement uncertainty meets the stability requirement for many climate data records derived from satellite images, including those for

A novel apparatus to measure reflected sunlight from the Moon

September 19, 2013
Author(s)
Claire E. Cramer, Gerald T. Fraser, Keith R. Lykke, John T. Woodward IV, Alan W. Smith
We describe a new apparatus for measuring the spectral irradiance of the Moon at visible wavelengths. Our effort builds upon the United States Geological Survey’s highly successful Robotic Lunar Observatory (ROLO), which determined a precise model for the

New Instruments to Calibrate Atmospheric Transmission

September 17, 2012
Author(s)
Claire E. Cramer, Keith R. Lykke, John T. Woodward IV, Peter Zimmer, John T. McGraw, Daniel C. Zirzow
Changing atmospheric transmission accounts for the largest systematic errors limiting photometric measurement precision and accuracy for ground-based telescopes. While considerable resources have been devoted to correcting the effects of the atmosphere on

Near-field Calibration of an Objective Spectrophotometer to NIST Radiometric Standards for the Creation and Maintenance of Standard Stars for Ground- and Space-Based Applications

September 13, 2012
Author(s)
John T. Woodward IV, Keith R. Lykke, Claire E. Cramer, John T. McGraw, Peter Zimmer, Daniel C. Zirzow, Susana Deustua, Dean Hines
NIST-calibrated detectors will be used by the ground-based 100mm diameter Astronomical Extinction Spectrophotometer (AESoP) to calibrate the spectral energy distributions of bright stars to sub-1% per 1nm spectral resolution element accuracy. AESoP will

Tunable Laser Techniques for Improving the Precision of Optical Astronomy

September 13, 2012
Author(s)
Keith R. Lykke, Claire E. Cramer, John T. Woodward IV, Steven W. Brown, Ping-Shine Shaw
Improving the precision of optical astronomy requires not only new telescopes and instrumentation, but also advances in observing protocols, calibrations and data analysis. The Laser Applications Group at the National Institute of Standards and Technology

Precise Throughput Determination of the PanSTARRS Telescope and the Gigapixel Imager using a Calibrated Silicon Photodiode and a Tunable Laser: Initial Results

December 2, 2010
Author(s)
Christopher W. Stubbs, Peter Doherty, Claire Cramer, Gautham Narayan, Yorke Brown, Ned Henry, Keith R. Lykke, John T. Woodward IV, John L. Tinry
We have used a precision calibrated photodiode as the fundamental metrology reference in order to determine the relative throughput of the PanSTARRS telescope and the Gigapixel imager, from 400 nm to 1050 nm. Our technique uses a tunable laser as a source

Ground-based observatory operations optimized and enhanced by direct atmospheric measurements

July 22, 2010
Author(s)
John T. McGraw, Peter C. Zimmer, Azzam Mansour, Dean C. Hines, Anthony B. Hull, Lisa Rossmann, Daniel C. Zirzow, Steven W. Brown, Gerald T. Fraser, Keith R. Lykke, Allan W. Smith, John T. Woodward IV, Christopher W. Stubbs
Earth's atmosphere represents a turbulent, turbid refractive element for every ground-based telescope. We describe the significantly enhanced and optimized operation of observatories supported by the combination of a lidar and spectrophotometer that allows

Spectroradiometric Calibration of Telescopes using Laser Illumination of Flat Field Screens

July 15, 2010
Author(s)
Steven W. Brown, Claire E. Cramer, Keith R. Lykke, Allan W. Smith, John T. Woodward IV, Peter Doherty, Emilio Falco, Christopher W. Stubbs
It is standard practice at many telescopes to take a series of flat field images prior to an observation run. Typically the flat field consists of a screen mounted inside the telescope dome that is uniformly illuminated with a broadband light source. These

Space-based photometric precision from ground-based telescopes

July 1, 2010
Author(s)
Peter C. Zimmer, John T. McGraw, Anthony B. Hull, Daniel C. Zirzow, Steven W. Brown, Claire E. Cramer, Gerald T. Fraser, Keith R. Lykke, Allan W. Smith, John T. Woodward IV, Christopher W. Stubbs, Mark R. Ackermann, Dean C. Hines
Ground-based telescopes supported by lidar and spectrophotometric auxiliary instrumentation can attain space-based precision for all-sky photometry, with uncertainties dominated by fundamental photon counting statistics. Earth‟s atmosphere is a wavelength-

Internal quantum efficiency modeling of silicon photodiodes

April 1, 2010
Author(s)
Thomas R. Gentile, Steven W. Brown, Keith R. Lykke, Ping-Shine Shaw, John T. Woodward IV
Results are presented for modeling of the internal quantum efficiency (IQE) of silicon photodiodes in the 400 nm to 900 nm wavelength range. The IQE data are based on measurements of the external quantum efficiencies of three transmission trap detectors

Hyperspectral Imager Characterization and Calibration

December 1, 2009
Author(s)
John T. Woodward IV, Steven W. Brown, Allan W. Smith, Keith R. Lykke
Current radiometric calibration standards, specifically blackbody and lamp-based optical radiation sources, produce spatially, spectrally, and temporally simple scenes. Hyperspectral imaging instruments, which in-practice view spatially, spectrally, and

A proposed global atmospheric monitoring networkbased on standard stars

November 2, 2009
Author(s)
Gerald T. Fraser, Steven W. Brown, Keith R. Lykke, John T. McGraw, Allan W. Smith, John T. Woodward IV, Peter C. Zimmer, Christopher W. Stubbs
The feasibility of developing a network of telescopes to monitor the composition of the nighttime atmosphere using stellar spectrophotometry is explored. Spectral measurements of the extinction of starlight by the atmosphere would allow, for instance

Multimodal, Nanoscale, Hyperspectral Imaging Demonstrated on Heterostructures of Quantum Dots and DNA-Wrapped Single-Wall Carbon Nanotubes

October 21, 2009
Author(s)
Hyeong G. Kang, Matthew L. Clarke, Jianyong Tang, John T. Woodward IV, Shin G. Chou, Zhenping Zhou, Angela R. Hight Walker, Tinh Nguyen, Jeeseong Hwang
A multimodality imaging technique integrating atomic force, polarized Raman, and fluorescence lifetime microscopy and a 2D autocorrelation image analysis is applied to study the properties of a mesoscopic heterostucture of nanoscale materials. This