Geology topics

Olav Orheim

Publications and source records attributed to Olav Orheim.

4 recordsLinked to original sources

USGS2017

Snow and ice studies by thematic mapper and multispectral scanner Landsat images

Digitally enhanced Landsat Thematic Mapper (TM) images of Antarctica reveal snow and ice features to a detail never seen before in satellite images. The six TM reflective spectral bands have a nominal spatial resolution of 30 m, compared to 80 m for the Multispectral Scanner (MSS). TM bands 2–4 are similar to the MSS bands. TM infra-red bands 5 and 7 discriminate better between clouds and snow than MSS or the lower TM bands. They also reveal snow features related to grain-size and possibly other snow properties. These features are not observed in the visible wavelengths. Large features such as flow lines show best in the MSS and lower TM bands. Their visibility is due to photometric effects on slopes. TM thermal band 6 has a resolution of 120 m. It shows ground radiation temperatures and may serve to detect liquid water and to discriminate between features having similar reflectivities in the other bands, such as blue ice.

Annals of Glaciology↗

USGS2017

Numerical analysis of Landsat Thematic Mapper images of Antarctica

Landsat-5 Thematic Mapper (TM) data from Dronning [Queen] Maud Land, Antarctica, have been analysed to provide insights into physical properties of the ice sheet. Brightness (at-satellite) temperatures calculated from digital numbers of the thermal band (TM band 6), using state-of-the-art equations and constants ( Markham and Barker 1986 ), are 8° to 20°C lower than temperatures measured on the surface. Such differences cannot be ascribed to atmospheric absorption or to emissivity variations; instead, they suggest errors in either the sensor or instrument calibration for the temperature range 0° to −20°C. The results indicate an excess gain factor of about 1.63. The TM band 6 data seem to reproduce faithfully the relative temperature variations across the surface. Principal components (PCs) calculated for TM bands 2, 3, 4, 5, and 7 are presented for a region of the interior ice sheet. PCs are superior to individual bands or combinations of bands for analysing the main characteristics of an image, such as rendition of surface topography (mostly given in PCl), and for distinguishing between different surface materials (mostly given in PCs 2 and 3). Band ratioing was most useful for enhancing subtle albedo variations, such as those caused by changes in surface properties due to melting. TM data of the region, collected 18 d apart, show large changes on the snow surface; strong patterns shown in PC2 and TM bands 5 and 7 of the earlier image were nearly faded 18 d later. These strong patterns are not present at visual wavelengths or in the thermal band, and we believe they reflect wind-related variations in the physical properties of the snow.

Annals of Glaciology↗

USGS2017

Investigating climate change by digital analysis of blue-ice extent on satellite images of Antarctica

Landsat-5 Thematic Mapper (TM) and SPOT data collected two years apart from an identical area of Dronning (Queen) Maud Land, Antarctica, have been analyzed to detect variations in surface features that may signal climatic change, and to establish a technique that readily identifies such changes. We found that selective principal component analysis (Chavez and Kwarteng 1989 ), on band ratios of near-IR/green, highlights changes in blue ice areas. The formation and preservation of blue ice is poorly understood, but we suggest that it generally takes longer to increase a blue ice area than to decrease it, and that blue ice extent is most sensitive to changes in accumulation rate. The investigated blue ice area shows a decrease in extent over the two-year period caused by incursion of snow that probably resulted from an increase in accumulation rate. Comparison of two TM images collected 18 days apart shows that transitory snow drifts have little effect on blue ice extent.

Annals of Glaciology↗

USGS1993

Glaciers of Europe

This chapter, consisting of six independently authored subchapters, including one subchapter, Glaciers of the Alps, that has four independently authored sections, is the fourth to be released in U.S. Geological Survey Professional Paper 1386, Satellite Image Atlas of Glaciers of the World, a series of 11 chapters. In each chapter, remotely sensed images, primarily from the Landsat 1, 2, and 3 series of spacecraft, are used to study the glacierized regions of our planet and monitor glacier changes. Landsat images, acquired primarily during the middle to late 1970’s, were used by an international team of glaciologists and other scientists to study various geographic areas or discuss glaciological topics. In each geographic area the present areal distribution of glaciers was compared, where possible, with historical information about their past extent. The atlas provides an accurate regional inventory of the areal extent of glacier ice on our planet during the 1970’s as part of a growing international scientific effort to measure global environmental change on the Earth’s surface.

Professional Paper↗