disk-integrated polarization of the moon in the ultraviolet from solstice m. snow, g. holsclaw, w....
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Disk-Integrated Polarization of the Moon in
the Ultraviolet from SOLSTICE
M. Snow, G. Holsclaw, W. McClintock, T. Woods
University of Colorado/LASP
Outline
• SOLSTICE Instrument• Lunar observing campaign• Observing geometry• Polarization observations
SOLSTICE Lunar Irradiance 3
SOLar STellar Irradiance Comparison Experiment
(SOLSTICE)• Measures irradiance in ultraviolet
– 115-180 nm Far Ultraviolet (FUV)– 180-300 nm Middle Ultraviolet (MUV)
• Measures stellar irradiance for tracking long term degradation.
• On board SORCE:– Low Earth Orbit
SOLSTICE Lunar Irradiance 4
Solar-Stellar Ratio
Need a large dynamic range to measure both sun and stars with same optics and detectors
SOLSTICE Lunar Irradiance 5
SOLSTICE Layout
Change entrance aperture 2x10^4Widen exit slit 10 or 20Lengthen integration 10^3
SOLSTICE Lunar Irradiance 6
Lunar Observing Campaign• June 2006 to December 2010• Added the Moon to the schedule of
eclipse calibration activities• On average, we observed one disk-
integrated spectrum per day in each channel
• NASA Grant: LASP Lunar Albedo Measurement and Analysis from SOLSTICE (LLAMAS)
Overview of Observations
ROLO
GOME
SSBUV (MESSENGER)
(Galileo)
(SNOE)
(Cassini)
(Mariner 10)
NOZOMI
(HUT)(Apollo 17)
SOLSTICE
Lunar Irradiance Spectra
Phase angle 2 degrees
SOLSTICE Lunar Irradiance 9
Phase Angle
Phase Curve (282 nm)
UV Disk-integrated Albedo
Phase angle 10 degrees
Instrument Sensitivity to Polarization
Measured at SURF before launch for both channels. Very little sensitivity to polarization in FUV channel.
Instrument Roll Angle
Calculating Polarization Fraction
= A + B cos 2
Using Mueller Matrices, we can express the measured signal in terms of the spacecraft roll angle, θ
The polarization of the lunar irradiance is then given by:
𝑃𝑚=𝐵𝐴×
1𝑃 𝐼
Extracting Pm
For each wavelength and phase angle, we can find A and B using least-squares fitting algorithm.
Polarization vs Phase
Polarization vs Wavelength
Summary
• SOLSTICE has observed the disk integrated albedo of the Moon from • -170 to 170 degrees phase • 130-300 nm
• Instrument is sensitive to polarization above 250 nm• Reasonable signal-to-noise measurement of
polarization from -90 to 90 degrees phase• Consistent with WUPPE measurements and trends
from visible region of the spectrum• Analysis of systematic errors in data processing
continues!
Acknowledgements &References
This work was supported by NASA grant NNX09AQ60G (LLAMAS) and NASA contract NAS5-97045 (SORCE) at the University of Colorado.
Snow, M., Holsclaw, G., McClintock, W. E., and Woods T. N. (2012) Absolute ultraviolet irradiance of the Moon from the LASP Lunar Albedo Measurement and Analysis from SOLSTICE (LLAMAS) project. In: Cross-calibration of Past and Present Far UV Spectra of Solar System Objects and the Heliosphere, E. Quemerais, M. Snow, and R. M. Bonnet (eds), ISSI Scientific Report No. 12 (in press)
Snow, M., Holsclaw, G., McClintock W. E., and Woods, T. N. (2007) Absolute ultraviolet irradiance of the Moon from SORCE SOLSTICE. Proc. SPIE 6677:66770D
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