Equivalence relations for Mueller matrix symmetries of laboratory, LIDAR and planetary scattering geometries

Symmetry relationships for optical observations of matter generally fall into several common scattering geometries. The 'planetary' configuration is preferred among a group of observers of extraterrestrial planets, 'laboratory' observations are performed in the biomedical research field and the LIDAR configuration is preferred among those using lasers to probe optical properties of horizontal surfaces with mirror or axial symmetry. This paper starts with the Stokes matrix formalism and uses symmetries of Mueller matrix scattering to establishes links between the mathematical symmetries of each geometric configuration.Comment: 13 pages, 3 figure

Observations of a new stabilizing effect for polar water ice on Mars

Using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), we map the temporal variability of water ice absorption bands over the near-polar ice mound in Louth crater, Mars. The absorption band depth of water ice at 1.5 microns can be used as a proxy for ice grain size and so sudden reductions can time any switches from ablation to condensation. A short period of deposition on the outer edge of the ice mound during late spring coincides with the disappearance of seasonal water frost from the surrounding regolith suggesting that this deposition is locally sourced. The outer unit at Louth ice mound differs from its central regions by being rough, finely layered, and lacking wind-blown sastrugi. This suggests we are observing a new stabilizing effect wherein the outer unit is being seasonally replenished with water ice from the surrounding regolith during spring. We observe the transport distance for water migration at Louth crater to be ~4km, and we use this new finding to address why no water ice mounds are observed in craters <9km in diameter.Comment: 26 pages, 8 figure

SWIR Investigation of sites of astrobiological interest

Rover missions to the rocky bodies of the Solar System and especially to Mars require light- weight, portable instruments that use minimal power, require no sample preparation, and provide suitably diagnostic mineralogical information to an Earth-based exploration team. Short-wave infrared (SWIR) spectroscopic instruments such as the Portable Infrared Mineral Analyser (PIMA, Integrated Spectronics Pty Ltd., Baulkham Hills, NSW, Australia) fulfill all these requirements. We describe an investigation of a possible Mars analogue site using a PIMA instrument. A survey was carried out on the Strelley Pool Chert, an outcrop of stro- matolitic, silicified Archean carbonate and clastic succession in the Pilbara Craton, interpreted as being modified by hydrothermal processes. The results of this study demonstrate the ca- pability of SWIR techniques to add significantly to the geological interpretation of such hy- drothermally altered outcrops. Minerals identified include dolomite, white micas such as il- lite-muscovite, and chlorite. In addition, the detection of pyrophyllite in a bleached and altered unit directly beneath the succession suggests acidic, sulfur-rich hydrothermal activity may have interacted with the silicified sediments of the Strelley Pool Chert.Comment: Key Words: Pilbara, Short-wave infrared, spectroscopy, Mars, Stromatolites, Archea

Hydrothermal alteration at the Panorama Formation, North Pole Dome, Pilbara Craton, Western Australia

An airborne hyperspectral remote sensing dataset was obtained of the North Pole Dome region of the Pilbara Craton in October 2002. It has been analyzed for indications of hydrothermal minerals. Here we report on the identification and mapping of hydrothermal minerals in the 3.459 Ga Panorama Formation and surrounding strata. The spatial distribution of a pattern of subvertical pyrophyllite rich veins connected to a pyrophyllite rich palaeohorizontal layer is interpreted to represent the base of an acid-sulfate epithermal system that is unconformably overlain by the stromatolitic 3.42 Ga Strelley Pool Chert.Comment: 29 pages, 9 figures, 2 table

Correlations of atmospheric water ice and dust in the Martian Polar regions

We report on the interannual variability of the atmospheric ice/dust cycle in the Martian polar regions for Mars Years 28-30. We used CRISM emission phase function measurements to derive atmospheric dust optical depths and data from the MARCI instrument to derive atmospheric water ice optical depths. We have used autocorrelation and cross correlation functions in order to quantify the degree to which dust and ice are correlated throughout both polar regions during Mars Years 28-29. We find that in the south polar region, dust has the tendency to "self clear", demonstrated by negative autocorrelation around the central peak. This does not occur in the north polar region. In the south polar region, dust and ice are temporally and spatially anti correlated. In the north polar region, this relationship is reversed, however temporal correlation of northern dust and ice clouds is weak - 6 times weaker than the anticorrelation in the south polar region. Our latitudinal autocorrelation functions allow us to put average spatial sizes of event cores and halos. Dust events in the south are largest, affecting almost the entire pole, whereas dust storms are smaller in the north. Ice clouds in north are similar in latitudinal extent to those in the south (both have halos < 10{\deg}). Using cross-correlation functions of water ice and dust, we find that dust events temporally lag ice events by 35-80 degrees of solar longitude in the north and south poles, which is likely due to seasonality of dust and ice events.Comment: 29 pages, 7 figure

Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) (Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap (Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a 'minimum apparent' amount of deposition corresponding to a thin H2O ice layer of 0.2mm (with 70 percent porosity). This amount of H2O ice deposition is 0.6-6 percent of the total Martian atmospheric water budget. We compare our 'minimal apparent' quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.Comment: 35 pages, 5 figures, 2 tables and supplementary information of 2 table

Ultramafic talc-carbonate unit -- The North Pole Dome and Dresser Formation

Here we describe the ultramafic talc-carbonate unit of the North Pole Dome. The North Pole Dome (NPD) is located in the centre of the East Pilbara Terrane (Van Kranendonk et al., 2007). The NPD is a structural dome of bedded, dominantly mafic volcanic rocks of the Warrawoona and Kelly Groups that dip gently away from the North Pole Monzogranite exposed in the core of the dome (Figure 1) (Van Kranendonk, 1999, 2000). Average dips vary from 30 to 60 degrees in the inner part of the dome to about 60 to 80 degrees in the outer part of the dome (Van Kranendonk, 2000). The North Pole Monzogranite is interpreted to represent a syn-volcanic laccolith to the Panorama Formation (Thorpe et al., 1992) and has been estimated to extend approximately 1.5km below the surface, based on gravity surveys (Blewett et al., 2004). Felsic volcanic formations are interbedded with the greenstones (Hickman, 1983), and these are capped by cherts that indicate hiatuses in volcanism (Barley, 1993; Van Kranendonk, 2006). An overall arc-related model for hydrothermal activity is favored by Barley (1993), whereas more recent studies have indicated a mantle-plume model for igneous and hydrothermal activity at the North Pole Dome (Van Kranendonk et al., 2002, 2007; Smithies et al., 2003; Van Kranendonk and Pirajno, 2004).Comment: 8 pages, 4 Figures, chapter 10 of The North Pole Dome and Dresser Formation Field Guide by M. van Kranendon

On the effects of size factor on albedo versus wavelength for light scattered by small particles under Mie and Rayleigh regimes

Scattering by particles significantly smaller than the wavelength is an important physical process in the rocky bodies in our solar system and beyond. A number of observations of spectral bluing (referred to in those papers as "Rayleigh scattering") on planetary surfaces have been recently reported, however, the necessary mathematical modeling of this phenomenon has not yet achieved maturity. This paper is a first step to this effect, by examining the effect of grain size and optical index on the albedo of small conservative and absorbing particles as a function of wavelength. The basic conditions necessary for spectral bluing or reddening to be observed in real-world situations are identified. We find that any sufficiently monomodal size distribution of scattering particles will cause spectral bluing in some part of the EM spectrum regardless of its optical index.Comment: 28 pages, 6 figure

Circular Polarization and Coherent Backscattering

We extend the work of Mishchenko et al. (2000) regarding the exact results of the polarization effect, using the theory of Amic et al. (1997) to derive a model prediction for the polarization coherent opposition effect at small angles. Our extension is to assess the effect of circular polarized light, thus completing exact derivation of the full M\"uller matrix for the semi infinite slab of Rayleigh sized particles. We find the circular polarization peak is narrower than the coherent backscattering intensity peak, and weaker in intensity.Comment: 13 pages, 5 figure

Spectral Curve Fitting for Automatic Hyperspectral Data Analysis

Automatic discovery and curve fitting of absorption bands in hyperspectral data can enable the analyst to identify materials present in a scene by comparison with library spectra. This procedure is common in laboratory spectra, but is challenging for sparse hyperspectral data. A procedure for robust discovery of overlapping bands in hyperspectral data is described in this paper. The method is capable of automatically discovering and fitting symmetric absorption bands, can separate overlapping absorption bands in a stable manner, and has relatively low sensitivity to noise. A comparison with techniques already available in the literature is presented using simulated spectra. An application is demonstrated utilizing the shortwave infrared (2.0-2.5 micron or 5000-4000 cm-1) region. A small hyperspectral scene is processed to demonstrate the ability of the method to detect small shifts in absorption wavelength caused by varying white mica chemistry in a natural setting.Comment: 18 pages, 2 figures, 6 table