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LOLA Laser Radiometry and LCROSS Impact Site Selection

LOLA Laser Radiometry and LCROSS Impact Site Selection. Maria T. Zuber 1 , David E. Smith 2 , Ian Garrick-Bethell 1 1 Massachusetts Institute of Technology 2 NASA/Goddard Space Flight Center LCROSS Site Selection Workshop NASA/Ames Research Center October, 2006. Question:.

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LOLA Laser Radiometry and LCROSS Impact Site Selection

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  1. LOLA Laser Radiometry and LCROSS Impact Site Selection Maria T. Zuber1, David E. Smith2, Ian Garrick-Bethell1 1Massachusetts Institute of Technology 2NASA/Goddard Space Flight Center LCROSS Site Selection Workshop NASA/Ames Research Center October, 2006

  2. Question: • Can the effect of the LCROSS impact be detected by LOLA radiometry?

  3. Example from Mars North Polar Region South Polar Region Ls=0 Ls=180 Ls=284 Ls=104 Passive 1064-nm reflectance of Mars from MOLA. Zuber et al. [2004]

  4. Schematic & Instrument Parameters Beam Expander Radiator Rx Telescope Earth Ranging Port Lunar Altimetry Port Laser Detectors (5) 2 more on far side Sun et al. [2005]

  5. LOLA Sampling Pattern Pattern Clock Angle = 26° S/C Velocity 1.6 km/s 5 m • Spot pattern is clocked 26° wrt s/c velocity vector and provides: • 5 profiles ~ 10 to 15 m apart • 140 measurements/s • LOLA pulse rate = 28 Hz ±0.1 Hz; • maintains nominal shot spacing • D such that peak deviation < 0.5 m 25 m D~ 56 m ds • Each 5-m diameter spot contains a measurement of: • elevation; 10-cm precision • surface roughness (rock heights); 30-cm resolution • surface brightness; 10% ~65 m LOLA Measurement Team

  6. Surface Reflectance Measurement • LOLA will measure surface reflectance of LOLA laser light via ratio of transmitted (Tx) and echo pulse energies (Rx) to search for ice in permanently shadowed regions. • Mixtures of ice crystals in regolith (4% ice) will exhibit higher surface reflectance (b = 80% ice, b = 20% regolith) than surrounding areas. Simulated regolith-ice mixture detection assuming 2% random noise in Tx and 12% in Rx. LOLA Measurement Team

  7. Discriminating young ejecta from ejecta of a different composition • To determine which bright, young craters have ejecta that is bright due to immaturity (and not composition) compare iron content [Lucey et al. 2000a] and optical maturity (OMAT) [Lucey et al., 200b]. • Both iron and maturity maps use ratios of the band strength at 750 and 950 nm. • Select craters that appear bright in OMAT, but do not show up in iron. Lucey, P.G., et al., Lunar iron and titanium abundance algorithms based on final processing of Clementine ultraviolet-visible images, J. Geophys. Res., 105, 20,297, 2000a. Lucey, P.G., et al., Imaging of lunar surface maturity, J. Geophys. Res., 105, 20,377-20,386, 2000b.

  8. Average highlands reflectance at 1000 nm • Analyze large section of farside highlands with few mare units. • Average reflectance of all pixels to obtain estimate of average highlands reflectance: 0.241. • good agreement with laboratory reflectance spectra of highland soils from Apollo 16 at 950 nm [Lucey et al., 2000b].

  9. Data set and regions analyzed • Use calibrated Clementine images at wavelengths of 750, 950 and 1000 nm. • LOLA detects 1064 nm but spectrum of most lunar materials monotonically increases in region between 1000 -1100 nm [Hawke, B.R., et al., Origin of lunar crater rays, Icarus, 170, 1-16, 2004]. • Can detect brightness variations in craters down to 1-km diameter (bigger than expected LCROSS crater but best resolvable from Clementine.)

  10. “Double” region (0oN, 160oE) 750 nm 1000 nm

  11. “Double” region (0oN, 160oE) -- north crater

  12. “Double” region (0oN, 160oE) -- south crater • Reflectance of ejecta is significantly higher than surrounding highlands, by as much as 0.1.

  13. “Far west” region (-1.5oN, 188oE) 750 nm 1000 nm

  14. “Far west” region (-1.5oN, 188oE) -- A & C Crater A Crater C

  15. “Far west” region (-1.5oN, 188oE) -- Crater B • Reflectance is higher over craters by as much as 0.1.

  16. “Far east” region (0oN, 236oE) 750 nm 1000 nm

  17. “Far east” region (0oN, 236oE) -- -- A & C Crater A Crater C

  18. “Far east” region (0oN, 236oE) -- Crater B

  19. “Far east” region (0oN, 236oE) -- Crater D • Crater reflectance ranges from 0.03 to 0.08 above surrounding highlands.

  20. Summary • LOLA will measure 1064-nm reflectance of lunar surface to ~10% in each 5-m spot (0.02, 3 sigma); smaller variations detectable by averaging. • Results from Clementine image analysis: • highland reflectance at 1000 nm is ~0.24. • reflectance of fresh, young craters is almost always greater than 10% above surrounding highlands; in some cases reflectance is 50% greater. • LOLA has a chance of detecting a change in brightness of the lunar surface associated with the LCROSS impact, even in a permanently shadowed crater.

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