Initial results from a GIS-based unsupervised classification study of the Martian surface

Maps of thermal inertia-albedo units and thermal inertia-elevation units on Mars’ surface have been generated by choosing thresholds that fit the strongest peaks in the histograms of these datasets. The units thus defined were then interpreted as distinct mixtures of materials on the surface, such as: bright fines, rock + bedrock and ice. We have conducted an initial classification of Thermal Emission Spectrometer (TES) night-time thermal inertia and TES albedo using a hard classifier. The methods used here are largely unsupervised and differ from those of previous studies. The aim of our study is to investigate what information can be obtained by utilising unsupervised classification algorithms to investigate the distribution of thermal materials on the surface of Mars. We find that unsupervised classification reveals additional structure in the clustering and spatial distribution of surface materials with moderate-low albedo and moderate-high thermal inertia. We highlight a number of regions such as Acidalia and Valles Marineris for future detailed studies of this type.National Committee for Space Science (NCSS), National Space Society of Australia (NSSA

Epidemiology and geographical distribution of enteric protozoan infections in Sydney, Australia

Background. Enteric protozoa are associated with diarrhoeal illnesses in humans; however there are no recent studies on their epidemiology and geographical distribution in Australia. This study describes the epidemiology of enteric protozoa in the state of New South Wales and incorporates spatial analysis to describe their distribution. Design and methods. Laboratory and clinical records from four public hospitals in Sydney for 910 patients, who tested positive for enteric protozoa over the period January 2007-December 2010, were identified, examined and analysed. We selected 580 cases which had residence post code data available, enabling us to examine the geographic distribution of patients, and reviewed the clinical data of 252 patients to examine possible links between protozoa, demographic and clinical features. Results. Frequently detected protozoa were Blastocystis spp. (57%), Giardia intestinalis (27%) and Dientamoeba fragilis (12%). The age distribution showed that the prevalence of protozoa decreased with age up to 24 years but increasing with age from 25 years onwards. The geographic provenance of the patients indicates that the majority of cases of Blastocystis (53.1%) are clustered in and around the Sydney City Business District, while pockets of giardiasis were identified in regional/rural areas. The distribution of cases suggests higher risk of protozoan infection may exist for some communities. Conclusions. These findings provide useful information for policy makers to design and tailor interventions to target high risk communities. Follow-up investigation into the risk factors for giardiasis in regional/rural area is needed

Subsurface properties of Lucus Planum, Mars, as seen by MARSIS

Lucus Planum, extending for a radius of approximately 500 km around 181°E, 5°S, is part of the Medusae Fossae Formation (MFF), a set of several discontinuous deposits of fine-grained, friable material straddling across the Martian highland-lowland boundary. Parts of the MFF have been probed through radar sounding by MARSIS and SHARAD, synthetic-aperture, low-frequency radars carried respectively by ESA's Mars Express and NASA's Mars Reconnaissance Orbiter. They transmit low-frequency radar pulses that are capable of penetrating below the surface, and are reflected by any dielectric discontinuity present in the subsurface. The dielectric permittivity of the MFF material, estimated from data of both radars, is consistent with either a substantial component of water ice or a low-density, ice-poor material. There is no evidence for internal layering in SHARAD data, despite the fact that layering at scales of tens of meters has been reported in many parts of the MFF. This lack of detection can be the result of one or more factors, such as high interface roughness, low dielectric contrast between materials, or discontinuity of the layers. After more than 10 years of observations, MARSIS has acquired about 240 orbits across Lucus Planum, making it possible to map the presence and depth of subsurface interfaces to a much greater detail than in previous works. The positions and strengths of subsurface echoes were extracted manually from radargrams and mapped across Lucus Planum, converting echo time delay to apparent depth. The strongest subsurface echoes, resulting from weak internal attenuation, strong subsurface reflectivity, or both, are found within the deposits located NW of Apollinaris Patera, while no subsurface echoes could be detected in the central section of Lucus Planum, in spite of several high-SNR observations. Subsurface reflections are common in the Eastern and Northwestern sectors, in some cases to depths of more than 2000 m assuming a dielectric permittivity of about 3. The lack of subsurface reflections in the central part of Lucus Planum can be the result of several factors, some of which depend on surface properties. A high topographic roughness at scales comparable to the radar wavelength causes scattering of the impinging pulse, resulting in weaker surface and subsurface echoes. However, surface roughness estimated from MOLA data is higher in the Eastern part of Lucus Planum. Another possibility is that roughness at the base of the deposit is higher in its central part, although there is no indication of such kind of trend in the older surrounding terrains. Because subsurface echoes appear to be closely associated with areas of distinct surface morphology, it is possible that Lucus Planum is in fact laterally inhomogeneous and that the central part consists of denser, more radar-attenuating material. This work was supported by the Italian Space Agency (ASI) through contract no. I/032/12/1

Multiple subglacial water bodies below the south pole of Mars unveiled by new MARSIS data

The detection of liquid water by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) at the base of the south polar layered deposits in Ultimi Scopuli has reinvigorated the debate about the origin and stability of liquid water under present-day Martian conditions. To establish the extent of subglacial water in this region, we acquired new data, achieving extended radar coverage over the study area. Here, we present and discuss the results obtained by a new method of analysis of the complete MARSIS dataset, based on signal processing procedures usually applied to terrestrial polar ice sheets. Our results strengthen the claim of the detection of a liquid water body at Ultimi Scopuli and indicate the presence of other wet areas nearby. We suggest that the waters are hypersaline perchlorate brines, known to form at Martian polar regions and thought to survive for an extended period of time on a geological scale at below-eutectic temperatures

Assessing the role of clay and salts on the origin of MARSIS basal bright reflections

Anomalously bright basal reflections detected by MARSIS at Ultimi Scopuli have been interpreted to indicate the presence of water-saturated materials or ponded liquid water at the base of the South Polar Layered Deposits (SPLD). Because conventional models assume basal temperatures (≤200 K) much lower than the melting point of water, this interpretation has been questioned and other explanations for the source of the bright basal reflections have been proposed, involving clay, hydrated salts, and saline ices. Combining previous published data, simulations, and new laboratory measurements, we demonstrate that the dielectric properties of these materials do not generate strong basal reflections at MARSIS frequencies and Martian temperatures. Plausible candidates remain perchlorates and chlorides brines that exhibit a strong dielectric response at much lower temperatures than other materials. This explanation might require that metastability could be maintained for a long period of time on a geological scale

Reply to: Explaining bright radar reflections below the south pole of Mars without liquid water

In their Matter Arising Lalich et al.1 simulate MARSIS echoes at the base of the South Polar Layered Deposits (SPLD) assuming three different layering scenarios (Fig. 1 in ref.1): (a) dusty water ice overlaying bedrock; (b) one CO2 ice layer between dusty water ice and bedrock; and, (c) two basal CO2 ice layers interbedded with one layer of dusty water ice. A surficial layer of CO2 ice ranging from 0 m (no layer) to 2 m in thickness is also considered. The first layer in each simulation is a semi-infinite half space assigned the permittivity of free space, and the bedrock is a semi-infinite half space with pure basaltic rock permittivity. These authors argue that constructive interference generated by some layered configurations produce waveforms (Fig. 2 in ref.1) with local maxima corresponding to the bright basal reflections observed by MARSIS at Ultimi Scopuli 2,3. They conclude that this explanation is more plausible than liquid brines being the source of the bright reflections, as posited instead by Orosei et al.2 and Lauro et al.3. In an earlier paper, however, Orosei et al.4 explored the same model and mathematics covering the entire range of possible parameters for two and three basal CO2 ice layers. Through the quantitative analysis of 3.45 x 108 simulation results, these authors demonstrated that local maxima at one of the MARSIS operating frequencies are not matched by local maxima at the other operating frequencies: that is, a layer stack producing constructive interference at one frequency, does not produce the same effect at the other frequencies, which is inconsistent with MARSIS real data. Thus, constructive interference by basal layers is not a viable mechanism to explain the bright basal reflections at Ultimi Scopuli. Because most of the points in Lalich et al.1 are superseded by Orosei et al.’s4 work, we refer interested readers to that earlier paper for a full discussion of the models and results. Here, we focus on three critical aspects: electromagnetic model; dielectric values used in the simulations; and materials and geology

Probing the Hidden Geology of Isidis Planitia (Mars) with Impact Craters

In this study we investigated Isidis Planitia, a 1325 km diameter multi-ring impact basin intersecting the Martian hemispheric dichotomy, located in the eastern hemisphere, between Syrtis Major and Utopia Planitia. From Mars Orbiter Laser Altimeter gridded data we observed that in the center of Isidis the −3700 m and −3800 m isolines strike NW-SE, being quasi-parallel to the diameter of the basin. We interpreted this as evidence that the basement of Isidis Planitia was faulted prior to being completely covered by layers of sediments and volcanic rocks. Plotting the morphometric data of impact craters located on the floor of the basin in a measured depths vs. predicted depths diagram (MPD), we concluded that the fault planes should dip SW, which is consistent with the location of the most topographically depressed sector of Isidis Planitia. We also estimated a minimum vertical displacement of ~1–2 km. Considering that the crust under Isidis Planitia is only a few km thick, our estimate implies brittle behavior of the lithosphere under the basin, suggesting that a low geothermal gradient and rheologically strong material characterize this Martian location

Wet Mars implications of revised scaling calculations for Evros Vallis

In this paper we report the results of our investigation of Evros Vallis, a martian late Noachian dendritic valley network centered at ~12°E, 12°S. The study area is located SSW of Schiaparelli and SE relative to Meridiani Planum. After establishment o

An Alternative Approach to Mapping Thermophysical Units from Martian Thermal Inertia and Albedo Data Using a Combination of Unsupervised Classification Techniques

Thermal inertia and albedo provide information on the distribution of surface materials on Mars. These parameters have been mapped globally on Mars by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor. Two-dimensional clusters of thermal inertia and albedo reflect the thermophysical attributes of the dominant materials on the surface. In this paper three automated, non-deterministic, algorithmic classification methods are employed for defining thermophysical units: Expectation Maximisation of a Gaussian Mixture Model; Iterative Self-Organizing Data Analysis Technique (ISODATA); and Maximum Likelihood. We analyse the behaviour of the thermophysical classes resulting from the three classifiers, operating on the 2007 TES thermal inertia and albedo datasets. Producing a rigorous mapping of thermophysical classes at ~3 km/pixel resolution remains important for constraining the geologic processes that have shaped the Martian surface on a regional scale, and for choosing appropriate landing sites. The results from applying these algorithms are compared to geologic maps, surface data from lander missions, features derived from imaging, and previous classifications of thermophysical units which utilized manual (and potentially more time consuming) classification methods. These comparisons comprise data suitable for validation of our classifications. Our work shows that a combination of the algorithms—ISODATA and Maximum Likelihood—optimises the sensitivity to the underlying dataspace, and that new information on Martian surface materials can be obtained by using these methods. We demonstrate that the algorithms used here can be applied to define a finer partitioning of albedo and thermal inertia for a more detailed mapping of surface materials, grain sizes and thermal behaviour of the Martian surface and shallow subsurface, at the ~3 km scale

Spatial partitioning and temporal evolution of Australia's total water storage under extreme hydroclimatic impacts

Australia experienced one of the worst droughts in history during the early 21st-century (termed the 'big dry'), exerting negative impacts on food production and water supply, with increased forest die-back and bushfires across large areas. Following the 'big dry', one of the largest La Nina events in the past century, in conjunction with an extreme positive excursion of the Southern Annular Mode (SAM), resulted in dramatic increased precipitation from 2010 to 2011 (termed the 'big wet'), causing widespread flooding and a recorded sea level drop. Despite these extreme hydroclimatic impacts, the spatial partitioning and temporal evolution of total water storage across Australia remains unknown. In this study we investigated the spatial-temporal impacts of the recent 'big dry' and 'big wet' events on Australia's water storage dynamics using the total water storage anomaly (TWSA) data derived from the Gravity Recovery and Climate Experiment (GRACE) satellites.Results showed widespread, continental-scale decreases in TWS during the 'big dry', resulting in a net loss of 3.89 +/- 0.47 cm (299 km(3)) total water, while the 'big wet' induced a sharp increase in TWS, equivalent to 11.68 +/- 0.52 cm (898 km(3)) of water, or three times the total water loss during the 'big dry'. We found highly variable continental patterns in water resources, involving differences in the direction, magnitude, and duration of TWS responses to drought and wet periods. These responses clustered into three distinct geographic zones that correlated well with the influences from multiple large-scale climate modes. Specifically, a persistent increasing trend in TWS was recorded over northern and northeastern Australia, where the climate is strongly influenced by El Nifio-Southern Oscillation (ENSO). By contrast, western Australia, a region predominantly controlled by the Indian Ocean Dipole (IOD), exhibited a continuous decline in TWS during the 'big dry' and only a subtle increase during the 'big wet', indicating a weak recovery of water storage. Southeastern Australia, influenced by combined ENSO, IOD and SAM interactions, exhibited a pronounced TWS drying trend during the 'big dry' followed by rapid TWS increases during the 'big wet', with complete water storage recoveries. A spatial intensification of the water cycle was further identified, with a wetting trend over wetter regions (northern and northeastern Australia) and a drying trend over drier regions (western Australia). Our results highlight the value of GRACE derived TWSA as an important indicator of hydrological system performance for improved water impact assessments and management of water resources across space and time. (C) 2016 Elsevier Inc. All rights reserved