Disk-Integrated Polarization of the Moon in the Ultraviolet from SOLSTICE M. Snow, G. Holsclaw, W. McClintock, T. Woods University of Colorado/LASP snow@lasp.colorado.edu.

Disk-Integrated Polarization of the Moon in

the Ultraviolet from SOLSTICE

M. Snow, G. Holsclaw, W. McClintock, T. Woods

University of Colorado/LASP

snow@lasp.colorado.edu

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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