The new remote sensing derived Swiss glacier inventory: II. First results

Complete Swiss glacier inventories are available for 1850 (reconstructed) and 1973 (from aerial photography). Connected to the GLIMS project a new Swiss glacier inventory for approximately the year 2000 (SGI 2000) is compiled mainly based on satellite imagery. The developed and applied remote sensing and GIS methods are described in part I of the contribution. In part II, the inventory design, first result analyses and comparisons with former glacial conditions are presented. As basic entries SGI 2000 contains the individual glacier identification, planimetric glacier boundaries as derived from image analysis, digitised central flowlines and polygonal glacier basin maps. All other parameters are automatically deduced from the above entries and a DEM within a GIS. Here, we analyse a set of small Bernese and Valais glaciers of < 10 km. These glaciers lost about 21% of area from 1973 to 1998, in addition to ca. 80% during 1850–1973, both with respect to the 1973 area. In order to track the latest trend in more detail, an intermediate glacier condition has been compiled from satellite imagery of 1985. This analysis gave an increasing speed of area loss (19%) for 1985–1998. Kääb, A., et al.(2002):The new remote sensing derived Swiss glacier inventory: II. First results. Annals of Glaciology. 34. pp 362-366. INTRODUCTION Glacier changes are among the clearest signals of ongoing warming trends existing in nature. In view of today's rapid environmental changes, combined with the high thermal sensitivity of earth's mountain glaciers, detailed, repeated and up-to-date information of any glacierised region of the world is of growing interest. Spaceand airborne remote sensing and geo-informatics play an important role for such glacier inventorying and monitoring work. Steps are now being undertaken to make worldwide glacier monitoring part of the Global Terrestrial Observing System (GTOS) by WMO, ICSU, FAO, UNEP and UNESCO. Such a worldwide collection of standardised observations includes repeated compilation of statistical information on the distribution and topographic characteristics of perennial surface ice in space (glacier inventories). Glacier inventory work is repeated at time intervals comparable to characteristic dynamic response times of mountain glaciers (a few decades), and helps with analysing and assessing changes at a regional scale (e.g. Haeberli and Hoelzle, 1995; Haeberli and others, 2000). The highest information density and most complete historical record of glaciers exists in the European mountain ranges. In Switzerland, a complete glacier inventory was compiled from aerial photography taken in 1973 (Müller and others, 1976). This inventory was revised in detail and completed with a reconstruction of the 1850 glacierisation (Maisch and others, 1999). Comparison of the two data bases together with long-term observations at individual sites and regional studies using more recent imagery indicate major mass losses with an acceleration tendency in the last 20 years. Now the time has come to compile a new glacier inventory for the Swiss Alps. This task fits into the USGS-led GLIMS project (Global Land Ice Measurements from Space) for worldwide glacier mapping, using satellite imagery in combination with digital elevation information. GLIMS is about, for the first time, to compile a global remote sensing derived inventory of land ice masses. Connected to this project, a new Swiss glacier inventory for approximately the year 2000 (SGI 2000) is based on Landsat 5 TM. Later Landsat 7 ETM+, SPOT imagery , IRS (Indian Remote Sensing Satellite) and aerial imagery, and also ASTER images (Advanced Spaceborne Thermal Emission and Reflection Radiometer on board Terra) will be applied. This work continues the long Swiss tradition of glacier monitoring, but also serves as a GLIMS pilot study. In view of this global perspective, it was decided not to use aerial photogrammetric approaches (cf. Würländer and Eder, 1998) for SGI 2000, but to develop and apply remote sensing and GIS (Geographical Information System) technology suitable for glacier inventorying over large areas. Although of much greater spatial resolution, glacier inventories derived from aerial photogrammetry do not allow for a high degree of Kääb, A., et al.(2002):The new remote sensing derived Swiss glacier inventory: II. First results. Annals of Glaciology. 34. pp 362-366. automated glacier detection because of the panchromatic information. They are more costand time-consuming and substantially restricted by the availability of suitable aerial photography. Space-borne remote sensing, on the other hand, is the only technology suitable for standardised global glacier inventorying and monitoring. Part I of this contribution (Paul and others, this issue) describes the evaluation of remote sensing algorithms for automatic glacier detection, the selection of remote sensing procedures suitable for SGI 2000, and the fusion of the classification results with digital elevation models (DEM) using GIS technology towards the SGI 2000 data base. Here, in Part II we present regional examples of SGI 2000, and a first comparison of SGI 2000 with the 1973 inventory and an intermediate 1985 stage.