1. Converting THEMIS VIS to Albedo
Sean Marshall
Advised by
Phil Christensen
Note that the Space Grant banner at the bottom here has effectively 38.4 rows of colored horizontal streaks

2. Albedo M-W: “fraction of incident radiation… reflected by a surface”
Values from 0 to 1
Depends on wavelength, and on direction
Helps determine composition
Albedo data from Thermal Emission Spectrometer (TES) on Mars Global Surveyor

3. Methods
Visible Imaging Subsystem (VIS) of the Thermal Emission Imaging System (THEMIS) on 2001 Mars Odyssey
Visible camera – detects reflected sunlight
Five different bands
Very well calibrated (see McConnochie et al., 2006)
Calculate albedo from VIS

4. Calculating albedo Radiance of the Sun (W/m2/sr):
Irradiance/flux from the Sun at 1 AU
(W/m2):
Irradiance from the Sun at Mars
(W/m2):
= Sun’s luminosity (3.846e26 W)
= Sun’s radius (6.96e8 m)
= solid angle subtended by the Sun at 1 AU
= Sun-Mars distance (in AU)

5. Calculating albedo
Radiance of Mars if it were a perfect reflector (W/m2/sr):
Wavelength dependence – spectral radiance in W/m2/sr/μm
Calibrated spectral radiance (L) detected by THEMIS VIS: from RDR (simple conversion)
Lambert albedo:
= Sun’s solid angle at 1 AU
= Sun-Mars distance
= Sun’s radiance
= Sun’s flux at Mars
θ = solar incidence angle

6. Getting data Calculate spectral radiance of Sun
Load THEMIS VIS image in Davinci
Calculate average radiance from all or part of the image (in band 3)
Find region in JMARS and get TES albedo data
Copy relevant parameters to spreadsheet

7. Getting data

8. Analysis Albedo values are consistently high Using band 3 (red)
Typically by >50%
Using band 3 (red)
But Mars is mostly red…
Using other bands
Points color coded
Colors matter!

9. Acknowledgments Phil Christensen, Greg Mehall
Advising
Saadat Anwar, Chris Edwards, Kim Murray, Dale Noss
Consulting
McConnochie et al.
JMARS & Davinci teams
Everyone at Space Grant!

10. TES albedo consistency

11. Using individual TES stamps