Effect of halite and calcite coatings on thermal infrared spectra wih implications for Mars exploration

Knowing the occurrence and distribution of soluble ionic salts allows us to model the aqueous history and geochemical conditions of surface solutions on Mars. Salts deposited as coatings are particularly important for attaining this knowledge because the thermal infrared (TIR) remote sensing method for determining mineral abundance is limited to the top few hundred micrometers of the surface. To better understand the TIR properties of salt coatings, we investigated the effects of coating thickness and texture on the TIR reflectance spectra of halite- and calcite-coated glasses. We evaluated salt coating textures that could occur on Mars: 1) continuous, uniformly thick layers of salt without exposed substrate; 2) discontinuous particulate salt coatings with variable thickness and exposed substrate. Salt-coated glasses have spectral features attributable to the substrate and the coating. Partially transmissive coatings decrease the intensity of substrate absorption bands as thickness increases. This decrease in intensity is exponential for continuous and coarse particulate (< 50 μm) halite coatings and linear for fine particulate halite coatings (< 2 μm). All halite coating textures and continuous calcite v coatings have spectral features indicating nonlinear mixing of the coating and substrate spectra. Therefore, coatings may result in significant challenges to modeling mineral abundances on Mars using a linear deconvolution algorithm for TIR spectra. An exception is fine particulate calcite coatings (< 8 μm), which are effectively optically thick and display linear spectral mixing. We find that halite coatings can cause an increase in a reflectance minimum (emissivity maximum) found previously to be useful for identifying chloride deposits on Mars. Continuous and coarse particulate halite coatings that are thicker and cover more substrate increase the reflectance minimum and are easier to detect in remotely sensed TIR spectra. Fine particulate halite does not increase the reflectance minimum and is not detectable by the method.

Name thesis:degree_name

Earth and Planetary Sciences

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Department of Earth and Planetary Sciences

Year

2012

Author dc:creator

• Berger, Jeffrey A.

Contributors dc:contributor

• King, Penelope
• King, Penelope L.
• Agee, Carl B.
• Jones, Rhian H.
• Scuderi, Louis A.

• Mars
• Infrared
• Salts
• Remote sensing
• Rock coatings

Language dc:language

English

Identifier

https://digitalrepository.unm.edu/eps_etds/4

OAI identifier oai:identifier

oai:digitalrepository.unm.edu:eps_etds-1003