Transcript Disk-Integrated Polarization of the Moon in the

Disk-Integrated Polarization
of the Moon in the
Ultraviolet from SOLSTICE
M. Snow, G. Holsclaw,
W. McClintock, T. Woods
University of Colorado/LASP
[email protected]
Outline
•
•
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SOLSTICE Instrument
Lunar observing campaign
Observing geometry
Polarization observations
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
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Solar-Stellar Ratio
Need a large dynamic
range to measure both sun and stars
with same optics and detectors
SOLSTICE Lunar Irradiance
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SOLSTICE Layout
Change entrance aperture 2x10^4
Widen exit slit 10 or 20
Lengthen integration 10^3
SOLSTICE Lunar Irradiance
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Lunar Observing Campaign
• June 2006 to December 2010
• Added the Moon to the schedule of
eclipse calibration activities
• On average, we observed one diskintegrated spectrum per day in each
channel
• NASA Grant: LASP Lunar Albedo
Measurement and Analysis from
SOLSTICE (LLAMAS)
SOLSTICE Lunar Irradiance
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Overview of Observations
SSBUV
(MESSENGER)
ROLO
GOME
SOLSTICE
(Galileo)
(SNOE)
(Cassini)
(HUT)
(Mariner 10)
(Apollo 17)
NOZOMI
Lunar Irradiance Spectra
Phase angle 2 degrees
Phase Angle
SOLSTICE Lunar Irradiance
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Phase Curve (282 nm)
UV Disk-integrated Albedo
Phase angle 10 degrees
Instrument Sensitivity to
Polarization
sensitivity
0.025
H
0.020
0.015
V
0.010
0.005
0.000
180
200
220
240
260
wavelength (nm)
280
300
240
260
wavelength (nm)
280
300
polarization
0.8
0.6
(H-V)/(H+V)
0.4
0.2
0.0
180
200
220
Measured at SURF before launch for both channels.
Very little sensitivity to polarization in FUV channel.
Instrument Roll Angle
roll angle (degrees)
180
135
90
45
0
-180 -135 -90 -45
0
45
90
phase angle (degrees)
135
180
Calculating Polarization
Fraction
Using Mueller Matrices, we can express the measured signal in terms
of the spacecraft roll angle, θ
𝐶(𝜆, 𝜃) = A + B cos 2𝜃
The polarization of the lunar irradiance is then given by:
𝐵 1
𝑃𝑚 = ×
𝐴 𝑃𝐼
Extracting Pm
For each wavelength and phase angle, we can find A and B using
least-squares fitting algorithm.
280nm, 10deg
280nm, 80deg
0.014
disk-equivalent albedo
disk-equivalent albedo
0.10
0.08
0.06
0.04
data
model fit
0.02
0.00
0
45
90
roll angle (deg)
135
0.012
0.010
0.008
0.006
0.004
data
model fit
0.002
180
0.000
0
45
90
roll angle (deg)
135
180
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
Questions?