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The Geoscience Laser Altimeter System (GLAS) is the sole instrument on the Ice, Cloud, and land Elevation Satellite (ICESat) to be launched December 19, 2002. The main objective of the ICESat mission is to provide accurate, high-resolution elevation data that will enable researchers to better understand ice sheet mass balance in the polar regions. ICESat will have a near circular and near polar orbit with an altitude of approximately 600 km and global coverage to 86 degrees latitude. The ground track will repeat every eight days during the first 120 days following launch, to provide multiple overflights of ground verification and validation sites. The primary mission will use a 183-day repeat track.
The GLAS instrument is an integral part of the NASA Earth Science Enterprise. It is designed to measure temporal changes associated with ice sheet topography, as well as cloud and atmospheric properties.
The satellite position, altimeter measurement, and laser pointing direction determine the location on the Earth's surface illuminated by the laser pulse. The GLAS instrument will transmit 40 pulses per second to the surface. The spots produced on the Earth's surface by the laser pulses will each have a 60 m diameter footprint, and the spacing between spots will be 175 m.
|The Ice, Cloud, and land Elevation Satellite (ICESat) is slated to launch in 2002 with a mission to help scientists understand global warming. Image courtesy of Ball Aerospace & Technologies Corp.|
The ICESat mission has two sets of objectives. The primary objectives relate to the cryosphere and rely on altimetry: to provide accurate, high-resolution elevation measurements of the Greenland and Antarctic Ice Sheets. Time series of elevation changes determine the present-day mass balance of the ice sheets and help estimate present and future contributions of the ice sheets to global sea level rise. These data will also increase our understanding of the way that changes in the ice sheets affect changes in polar climate, such as precipitation, temperature, and cloudiness. The secondary objectives relate to the atmosphere (measurements of which rely on Light Detection and Ranging [LIDAR]), as well as to land and oceans (measurements of which rely on altimetry): to measure cloud heights and the vertical structure of clouds and aerosols in the atmosphere, land topography and vegetation canopy heights, sea ice roughness and thickness, ocean surface elevations, and surface reflectivity. GLAS data are expected to be an improvement over past ice sheet altimeter data. Seasat data collected in 1978 provided scientists with 20-km elevation grids that resolved only the largest surface undulations. Geosat (1985-86) was designed to track more precisely over variable surfaces, with 10-km gridded elevations plotted over the ice sheets. Initial ERS-1 satellite altimeter data sets (with 35-day repeat cycles), collected from April 1994 to March 1995, provided less dense coverage than Geosat, but better spatial coverage of the polar ice sheets - up to 81.5 degrees north and south latitudes. ERS-1 and ERS-2 data (with 168-day repeat cycles) were eventually combined with previous Geosat data to create a more dense gridding of elevation data for the ice sheets.
The laser altimeter on the GLAS instrument is expected to improve on this progression by measuring height from the spacecraft to the ice sheet with an intrinsic precision of better than 10 cm with a 60 m surface spot size, thereby providing the capability to measure subdecadal changes in ice sheet thickness of only a few tens of centimeters. Mass balance models and topographic detail of the ice sheets should be greatly improved. The accuracy of height determinations over land is yet to be determined, but will be assessed using ground slope and roughness.
GLAS data products will be in a flat binary format, except for at least one higher-level product that is a composite of many altimetric and atmospheric parameters, which will be in Hierarchical Data Format-Earth Observing System (HDF-EOS). NSIDC will archive and distribute all GLAS standard data products, including Levels 1A, 1B, and 2 laser altimeter and atmospheric lidar data.
Data are expected to be available in September 2003.
NSIDC now provides Moderate Resolution Imaging Spectroradiometer (MODIS) data users with an easy way to view daily snow cover data. Climate Modeling Grid (CMG) Browse images show the global snow cover derived from daily MODIS snow products. This helps users narrow their choices for finding the data they need to order from the EOS Data Gateway (EDG). The image below is a CMG Browse image from October 9, 2002.
To learn more about MODIS and to view further MODIS CMG Browse images, please
visit the MODIS Data at
NSIDC Web site.
NSIDC is pleased to announce a new version of the Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent product. Since the first release of this data set, Dave Robinson has issued updated snow charts that extend the available record back from 1971 to 1966, forward from 1995 to 2001, and include extensive reanalysis of the original time series that NSIDC used from 1971 to 1995. The newest snow charts represent the latest improvements and extension of Robinson's research. NSIDC has also made significant improvements to the ice climatology derived from SMMR and SSM/I data from 1978 to 1999.
For more information about this product, please visit the EASE-Grid Web site.
NSIDCs Ted Scambos and Rob Bauer joined three other researchers in Antarctica in November to study large snow and ice features called "megadunes." NSIDC has launched a new Web site dedicated to this expedition, titled Antarctic Megadunes: Research at the Edge of the Earth.
Visit the Antarctic Megadunes Web site to learn how the researchers live and work in extreme field conditions, including constant wind and temperatures of -51°C (-60°F). The site explains how researchers get to the remote field site, how they are trained, what kind of research they are doing, and how the megadunes may have been formed.
In December 2002, in partnership with NOAA's National Geophysical Data Center, NSIDC released the NOAA/NSIDC Glacier Photograph Collection. This database consists of approximately 1000 digitized historic glacier photographs and their accompanying metadata. The images are part of the NSIDC archive of the American Geographical Society Collection of historical glacier photographs, dating from the 1880s to 1975, and includes both aerial and terrestrial photos.
The glacier record is an important part of the climate database. Over long periods of time, glacier extents fluctuate in response to changes in climate. Historic glacier photos can be used to determine changes in glacier terminus location and to estimate changes in mass balance. To obtain a complete picture of climate change as recorded by glacier fluctuations, information from many glaciers must be used. The historic glacier photo collections at NSIDC are the only source of this information for many glaciers, and they constitute an invaluable resource for the scientific community. Images in the database are retrievable by glacier name, photographer name, date, state, geographic coordinates, and subject keywords, using an interactive tool available online. Glaciers from Colorado, Wyoming, Montana, Washington, and Alaska are represented. Ideally, the database will grow as present-day photographs are paired with the existing photos to provide visual evidence of glacier fluctuations. NSIDC also hopes to expand the database in 2003 by including more images of glaciers outside the United States.
Funding for the project was provided by NOAA's Climate Database Modernization Program (CDMP), whose goal is to make major climate databases available over the internet.
|Variegated Glacier, Alaska. From the Glacier Photograph Collection at NSIDC.|
In July 2002, the ARCSS Data Coordination Center (ADCC) was alerted to errors in two files in the GISP2 core data, found on the Greenland Summit Ice Core CD-ROM, originally released in 1998. The corrected files can bedownloaded from NSIDC's FTP site.
The dust file, m1650.dat, was missing altogether from the product; the other corrected file is electrical conductivity measurement (ecm) data, d1000.dat. The original d1000.dat file had the same data as the d1100.dat (data for 1100-1149). If you have a copy of this product, please download the corrected files for your use. We apologize for any inconvenience.
Please contact NSIDC User Services if you have any questions.
NSIDCs theme Web site, All About Snow, was selected by the National Science Teachers Association as a recipient of the SciLinks Award. The award is based on a review using a stringent set of criteria that ensures selected materials have accurate content and effective teaching.
A three-day workshop will be convened at NSIDC, with the aim of evaluating current methods of determining the worldwide recession of mountain glaciers over the last half-century or longer. Recent evidence suggests an acceleration of glacier mass loss in several key regions, and a more comprehensive evaluation of glacier changes is imperative in order to assess ice contributions to global sea level rise and the future of water resources from glacierized basins. The inadequacy of conventional field surveys, the declining number of glaciers being routinely monitored, and the current status of the World Glacier Inventory (which describes barely 44 percent of world glaciers with, in most cases, few specifics as to their characteristics) indicate the necessity for a new coordinated approach.
The recent availability of high-resolution Landsat 7 and ASTER satellite images, along with new digital inventories of glaciers in the former Soviet Union and in China, combined with GIS techniques, offer one potential solution. The broader impacts of this workshop include bringing together experts from leading groups, as well as under-represented young and female scientists from North America and elsewhere. About 25-30 selected individuals will be funded, and the workshop will be open to other interested individuals. There is a training dimension in the planned demonstration of new GIS-based mapping techniques using ASTER imagery and digital databases. The publication of a workshop report in EOS, for example, will bring the ideas to a wide scientific audience, and recommendations will be fed into the Global Cryospheric Observing System (GCOS) strategy for terrestrial observations for climate that supports the U.N. Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC) assessments.
For more information about the workshop, please contact NSIDC User Services.
The Third Session of the Arctic Climate System/Climate and Cryosphere (ACSYS/CliC) Scientific Steering Group (SSG) was held at the China Meterological Administration (CMA) in Beijing, October 21-25, by invitation of Professor Qin Dahe, Director of the CMA and a member of the SSG. NSIDC director Roger Barry attended the meeting as co-Vice Chair of the SSG. He also attended the Second Session of the Chinese National Committee on Climate and Cryosphere on October 20, where detailed reports were presented on recent climate-cryospheric research by Chinese scientists in Antarctica and in China, particularly Tibet.
Other CIRES/Cryospheric and Polar Processes (CPP) researchers who participated in the ACSYS/CliC SSG were Koni Steffen, Chair of the ACSYS/CliC Observation Products Panel, and Mark Serreze, Chair of the ad-hoc Panel on Polar Products from Reanalysis. The ACSYS/CliC SSG discussions focused on plans for the final ACSYS Science Conference, to be held November 11-14, 2003, in St. Petersburg, Russia (contingent on final arrangements), the CliC Implementation Strategy, and coordination of CliC plans with Climate Variability and Change (CLIVAR) (particularly for the Southern Ocean), the Global Energy and Water Cycle Experiment (GEWEX), and the Scientific Committee on Antarctic Research (SCAR), as well as with national programs such as Study of Environmental Arctic Change (SEARCH). SCAR has agreed to support two representatives on the SSG.
For further information please visit the CliC Web site.
The fourth Snow Watch meeting was held October 31 - November 1, 2002, at the NOAA Silver Spring Metro Complex, Maryland. The workshop was hosted by Bruce Ramsay of the Office of Research and Applications, NOAA/NESDIS. Co-conveners were Dave Robinson, Department of Geography, Rutgers University; Dorothy Hall, Hydrological Sciences Branch, NASA/GSFC; and Roger Barry, WDC for Glaciology/NSIDC.
Previous Snow Watch meetings were held in 1981, 1985 and 1992, and their proceedings have been published in Glaciological Data Reports. The participants reported on recent studies of variations in snow cover and snow water equivalent, snow cover-climate interactions, and snow hydrology, from in situ and remotely sensed data on regional to global scales. In addition to papers and poster presentations, breakout groups met to consider snow observations, spatial variability, and trends and change detection. Recommendations of the groups will be included with the scientific papers in a report to be published by NOAA/NESDIS and NSIDC in 2003.
NSIDC welcomes its newest technical writers, Keri Webster and Amy Casey, to the staff.