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

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

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

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)

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

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

Getting data

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!

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!

TES albedo consistency

Using individual TES stamps