@article{MielkeBoescheRogassetal.2015, author = {Mielke, Christian and B{\"o}sche, Nina Kristine and Rogass, Christian and Kaufmann, Hermann and Gauert, Christoph}, title = {New geometric hull continuum removal algorithm for automatic absorption band detection from spectroscopic data}, series = {Remote sensing letters : an official journal of the Remote Sensing and Photogrammetry Society}, volume = {6}, journal = {Remote sensing letters : an official journal of the Remote Sensing and Photogrammetry Society}, number = {2}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {2150-704X}, doi = {10.1080/2150704X.2015.1007246}, pages = {97 -- 105}, year = {2015}, abstract = {Modern imaging spectrometers produce an ever-growing amount of data, which increases the need for automated analysis techniques. The algorithms employed, such as the United States Geological Survey (USGS) Tetracorder and the Mineral Identification and Characterization Algorithm (MICA), use a standardized spectral library and expert knowledge for the detection of surface cover types. Correct absorption feature definition and isolation are key to successful material identification using these algorithms. Here, a new continuum removal and feature isolation technique is presented, named the 'Geometric Hull Technique'. It is compared to the well-established, knowledge-based Tetracorder feature database together with the adapted state of the art techniques scale-space filtering, alpha shapes and convex hull. The results show that the geometric hull technique yields the smallest deviations from the feature definitions of the MICA Group 2 library with a median difference of only 8nm for the position of the features and a median difference of only 15\% for the feature shapes. The modified scale-space filtering hull technique performs second best with a median feature position difference of 16nm and a median difference of 25\% for the feature shapes. The scale-space alpha hull technique shows a 23nm median position difference and a median deviation of 77\% for the feature shapes. The geometric hull technique proposed here performs best amongst the four feature isolation techniques and may be an important building block for next generation automatic mapping algorithms.}, language = {en} } @article{BoescheRogassLubitzetal.2015, author = {B{\"o}sche, Nina Kristine and Rogass, Christian and Lubitz, Christin and Brell, Maximilian and Herrmann, Sabrina and Mielke, Christian and Tonn, Sabine and Appelt, Oona and Altenberger, Uwe and Kaufmann, Hermann}, title = {Hyperspectral REE (Rare Earth Element) Mapping of Outcrops-Applications for Neodymium Detection}, series = {Remote sensing}, volume = {7}, journal = {Remote sensing}, number = {5}, publisher = {MDPI}, address = {Basel}, issn = {2072-4292}, doi = {10.3390/rs70505160}, pages = {5160 -- 5186}, year = {2015}, abstract = {In this study, an in situ application for identifying neodymium (Nd) enriched surface materials that uses multitemporal hyperspectral images is presented (HySpex sensor). Because of the narrow shape and shallow absorption depth of the neodymium absorption feature, a method was developed for enhancing and extracting the necessary information for neodymium from image spectra, even under illumination conditions that are not optimal. For this purpose, the two following approaches were developed: (1) reducing noise and analyzing changing illumination conditions by averaging multitemporal image scenes and (2) enhancing the depth of the desired absorption band by deconvolving every image spectrum with a Gaussian curve while the rest of the spectrum remains unchanged (Richardson-Lucy deconvolution). To evaluate these findings, nine field samples from the Fen complex in Norway were analyzed using handheld X-ray fluorescence devices and by conducting detailed laboratory-based geochemical rare earth element determinations. The result is a qualitative outcrop map that highlights zones that are enriched in neodymium. To reduce the influences of non-optimal illumination, particularly at the studied site, a minimum of seven single acquisitions is required. Sharpening the neodymium absorption band allows for robust mapping, even at the outer zones of enrichment. From the geochemical investigations, we found that iron oxides decrease the applicability of the method. However, iron-related absorption bands can be used as secondary indicators for sulfidic ore zones that are mainly enriched with rare earth elements. In summary, we found that hyperspectral spectroscopy is a noninvasive, fast and cost-saving method for determining neodymium at outcrop surfaces.}, language = {en} }