Identification of multi-style hydrothermal alteration using integrated compositional and topographic remote sensing datasets

The western part of the island of Milos, Greece has undergone widespread, intense alteration associated with a range of mineralization, including seafloor Mn-Fe-Ba, sub seafloor Pb-Zn-Ag, and epithermal Au-Ag. The surrounding country rocks are a mixture of submarine and subaerial calc-alkaline volcanic rocks ranging from basaltic andesite to rhyolite in composition, but are predominantly andesites and dacites. The current surface spatial distribution of the alteration mineralogy is a function not only of the original hydrothermal, but also subsequent tectonic and erosional processes. The high relief and the excellent rock exposure provide ideal conditions to evaluate the potential of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite remote sensing data to identify and differentiate the different styles of alteration mineralisation. Laboratory spectral reflectance and calculated emittance measurements of field samples, supported by XRD analysis and field mapping, were used to support the analysis. Band ratio and spectral matching techniques were applied to the shortwave-infrared (SWIR) reflectance and thermal-infrared (TIR) emissivity imagery separately and were then integrated with topographic data. The band ratio and spectral matching approaches produced similar results in both the SWIR and TIR imagery. In the SWIR imagery, the advanced argillic, argillic and hydrous silica alteration zones were clearly identifiable, while in the TIR imagery, the silicic and advanced argillic alteration zones, along with the country rock, were differentiable. The integrated mineralogical–topographic datasets provided an enhanced understanding of the spatial and altitude distribution of the alteration zones when combined with conceptual models of their genesis, which provides a methodology for the differentiation of the multiple styles of alteration.Natural Environment Research Council (GA/09F/139) Greece-UK bilateral research project - Mapping Epithermal Alteration zones associated with Gold Mineralisation using ASTER satellite data

Contribution of Alaskan glaciers to sea level rise derived from satellite imagery

International audienceOver the last 50 years, retreating glaciers and ice caps (GIC) contributed 0.5 mm/yr to sea level rises (SLR), and one third is believed to originate from ice masses bordering the Gulf of Alaska. However, these estimates of ice wastage in Alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others. How these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear. Here, combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models (DEMs), we found that, between 1962 and 2006, Alaskan glaciers lost 41.9 ± 8.6 km**3/yr water equivalent (w.e.) and contributed 0.12±0.02 mm/yr to SLR. Our ice loss is 34% lower than previous estimates. Reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work. Estimates of mass loss from GIC in other mountain regions could be subject to similar revisions

Assessing the potential of multispectral remote sensing for lithologic mapping on the Antarctic Peninsula: case study from eastern Adelaide Island, Graham Land

The results of lithological mapping using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for the Wright Peninsula region of Adelaide Island, Antarctic Peninsula are compared with existing geological maps and recent field observations to assess the potential of multispectral remote sensing to undertake lithological mapping on the Antarctic Peninsula. The Wright Peninsula comprises calc-alkaline intrusive rocks ranging from granite to gabbro, volcanic rocks of acidic to intermediate composition, and arc-related sediments. The reflective and thermal bands of a single ASTER image were analysed with reference to reflectance spectra of rock samples from the study area. Assessment of the ASTER mapping outcomes was undertaken with a newly compiled geological map of Adelaide Island and observations made during recent fieldwork. The results demonstrate that ASTER can uniquely discriminate granitoid intrusive rocks and altered rhyolitic volcanic rocks that display distinctive spectral properties. The results are more ambiguous at discriminating more intermediate/mafic rocks such as diorite/gabbro, andesite/basalt and chlorite-bearing sediments due to the similarity in spectral properties. These results demonstrate that although ASTER data are limited in their ability to uniquely discriminate lithologies they can provide important lithological information in support of geological mapping on the Antarctic Peninsula

DATA ACQUISITION STRATEGIES FOR ASTER GLOBAL DEM GENERATION

The ASTER Global DEM (GDEM) version 1, is a global digital elevation model with one arc-second grid, generated using the ASTER stereo image archive 2000 to August 2008, and was released on June 29, 2009. The GDEM-1 had some bad elevation data. The most simple and effective way to reduce bad elevation data in the GDEM-1 is to add new ASTER observation data and re-generate the GDEM. An ASTER Data Acquisition Request was defined, based on the number of good pixels and the number of observations at each observation area, for the GDEM version 2 that was released on October 17, 2011. Using more input data and an improved algorithm, GDEM version 2 reduced the amount of the bad pixel by 4.5% to 7.5% and increased the amount of good tiles by 10.7% to 54.3% over the GDEM-1, except for Antarctica. Another ASTER data set is being collected for GDEM version 3, scheduled for 2013. The ASTER data collection scheme, however, has some constraints. This study sought for techniques to optimize the GDEM data collection balancing the overall ASTER operations and reduction of bad pixels in the GDEM data

Technical Methodology for ASTER Global Water Body Data Base

A waterbody detection technique is an essential part of a digital elevation model (DEM) generation to delineate land⁻water boundaries and set flattened elevations. This paper describes the technical methodology for improving the initial tile-based waterbody data that are created during production of the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) GDEM, because without improvement such tile-based waterbodies data are not suitable for incorporating into the new ASTER GDEM Version 3. Waterbodies are classified into three categories: sea, lake, and river. For sea-waterbodies, the effect of sea ice is removed to better delineate sea shorelines in high latitude areas: sea ice prevents accurate delineation of sea shorelines. For lake-waterbodies, the major part of the processing is to set the unique elevation value for each lake using a mosaic image that covers the entire lake area. Rivers present a unique challenge, because their elevations gradually step down from upstream to downstream. Initially, visual inspection is required to separate rivers from lakes. A stepwise elevation assignment, with a step of one meter, is carried out by manual or automated methods, depending on the situation. The ASTER global water database (GWBD) product consists of a global set of 1° latitude-by-1° longitude tiles containing water body attribute and elevation data files in geographic latitude and longitude coordinates and with one arc second posting. Each tile contains 3601-by-3601 data points. All improved waterbody elevation data are incorporated into the ASTER GDEM to reflect the improved results

A Highly Sensitive Ammonia Gas Sensor Using Micrometer-Sized Core–Shell-Type Spherical Polyaniline Particles

A highly sensitive NH3 gas sensor based on micrometer-sized polyaniline (PANI) spheres was successfully fabricated. The PANI microspheres were prepared via a facile in situ chemical oxidation polymerization in a polystyrene microsphere dispersion solution, resulting in a core–shell structure. The sensor response increased as the diameter of the microspheres increased. The PSt@PANI(4.5) sensor, which had microspheres with a 4.5 μm average diameter, showed the largest response value of 77 for 100 ppm dry NH3 gas at 30 °C, which was 20 times that of the PANI-deposited film-based sensor. Even considering measurement error, the calculated detection limit was 46 ppb. A possible reason for why high sensitivity was achieved is simply the use of micrometer-sized PANI spherical particles. This research succeeded in providing a new and simple technology for developing a high-sensitivity NH3 gas sensor that operates at room temperature