Converting THEMIS VIS to Albedo

1. Sean Marshall Advised by Phil Christensen Converting THEMIS VIS to Albedo

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

3. 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 Methods

4. Radiance of the Sun (W/m2/sr): Irradiance/flux from the Sun at 1 AU (W/m2): Calculating albedo 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. Radiance of Mars if it were a perfect reflector (W/m2/sr): Calculating albedo 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. 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

7. Getting data

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

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

10. TES albedo consistency

11. Using individual TES stamps