Evaluating the use of ALOS data (microwave and optical) for mapping geomorphological features of selected areas in Livingston Island, South Shetland Islands (West Antarctica)
Magaly Koch(1), Jeronimo Lopez Martinez(2), Thomas Schmid(3), Enrique Serrano(4) and Jose Gumuzzio(2)
(1) Boston University, 725 Commonwealth Ave., Boston, MA 02215, United States
(2) Autonomous University of Madrid, Campus Cantoblanco, 28049 Madrid, Spain
(3) CIEMAT, Avda. Complutense 22, 28040 Madrid, Spain
(4) Valladolid University, Paseo Prado de la Magdalena s/n, 47011 Valladolid, Spain
Livingston Island is the second largest island of the South Shetland archipelago, an island arc located to the northwest of the Antarctic Peninsula. Its climate is cold maritime and its geomorphology is characterized by the presence of glacial and periglacial landforms, as well as numerous raised beaches, erosive platforms and volcanic plugs. Most of the island is covered by snow and ice; however, about 10 % remains snow free during the Antarctic summer season. Glacial free areas are mainly located in three parts of the island, namely Byers Peninsula, Hurd Peninsula and Barnard Point area, and are the main focus of this work.
The reasons for selecting Livingston Island as a test site for evaluating the suitability of ALOS microwave (PALSAR) and optical (PRISM) data for geomorphological mapping is due to: 1) the existing landscape variability on this island, and 2) the existence of detailed geomorphological information from field work and aerial photo-interpretation. This means that within a short distance, a variety of landforms can be found belonging mainly to glacial, periglacial and coastal environments. Some parts of the island are ice free (especially Byers Peninsula, which is the largest ice free area in the archipelago) and are, therefore, ideal for the detection of erosional and depositional glacial landforms by remote sensing. Periglacial features include patterned ground (resulting from frost action related to active layer), cryoturbation, gelifraction in the bedrock, stone fields and rock glaciers. Marine related landforms include several raised erosive marine platforms at different altitude as well as a series of Holocene raised beaches.
Since the aim of this paper is to determine from Earth Observation (EO) data various types of periglacial and other geomorphological features and the characteristics of their occurrence and associated processes, e.g. those occurring predominantly on platforms and those occurring on slopes; a well-studied area was selected with extensive field information and maps obtained from several field trips carried out by our group in the last years (López-Martínez et al., 1992a, 1992b, 1995, 1996; Serrano and López-Martínez, 2000) . Geomorphological and topographic maps at a scale of 1:25,000 are used as a ground truth reference in all image processing tasks. These maps were compiled from information obtained in the field, and the interpretation of aerial photographs (from 1956/57).
The EO data set consists of a PALSAR fine beam dual-pol image (15 October 2006) obtained with a processing level of 1.5, a panchromatic high-resolution PRISM image (9 October 2006) with a processing level of 1B2, and a Landsat7 ETM+ image (1 March 2004) with a processing level of 1G. The processing steps include: 1) co-registration of PALSAR, PRISM and ETM+, and subsequent georeferencing to topographic and geomorphological maps available at a scale of 1:25,000; 2) application of basic SAR procedures to enhance linear and textural features (i.e., edge detector, box car and lee refined filters, and texture analysis); 3) polarimetric SAR processing of the dual-pol image (multi-look incoherent averaging, partial polar supervised classification); and 4) spectral processing of ETM+ using standard transformation and (NDVI, tasseled cap, PCA) and supervised classification techniques (Spectral Angle Mapper).
In the case of the Landsat supervised classification, spectral curves were first extracted from the image and used together with the ground truth maps as references for the selection of training areas. Whereas in the case of the supervised classification of the PALSAR image a lee filter was first applied to both polarization modes (to reduce the speckle effect) before synthesizing them into a color composite (R = HH, G = HH-VH, B = VH) on which the geomorphological map was overlaid. The geomorphological map facilitated the selection of the training areas that correspond to periglacial landforms. In addition, the surface snow cover conditions at the time of PALSAR image acquisition were checked for selected areas (Hurd Peninsula and Barnard Point) using the high resolution PRISM image, since both image dates are only one week apart. This way the selection of training sites representing periglacial features in snow-free areas could be confirmed as well as the L-band penetration capacity in snow covered areas could be determined.
Results show that the fine beam resolution (12.5 m) and the dual polarization (HH, HV) of PALSAR enables the identification and mapping of complex and relatively small scale geomorphological features such as raised beaches, scarpments, volcanic plugs, moraines, and periglacial landforms and deposits such as stone fields, patterned ground and other features indicating the presence of permafrost. However, the multispectral ETM+ sensor performed better than the microwave PALSAR sensor in discriminating lithological units and their boundaries. This work shows the use of EO data for extracting and combining the textural and spectral information related to various periglacial features in order to facilitate their identification and mapping in similar but poorly studied polar regions.
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