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GLIMS ASTER Browse

Introduction

Imagery from the ASTER instrument, archived at the LP-DAAC, is a primary source of imagery used within the GLIMS Project. Glacier outlines extracted from ASTER images, as well as from other sources, are ingested into the GLIMS Glacier Database in order to document and monitor changes in the spatial extents of glacier systems through time. Due to the high volume of ASTER imagery available, it is often difficult for GLIMS Regional Centers (GLIMS data providers, or RCs) to find images suitable for performing glacier analysis. Difficulties include finding ASTER scenes that: cover a specific region of the world, are captured during particular times of the year, have minimal cloud cover, and have optimal sensor gain settings for glacier mapping.

In order to address some of these difficulties the GLIMS Project has developed a unique subset of ASTER imagery that covers glacierized terrain. This dataset has been spatially selected from the pool of all available ASTER scenes based on an intersection of GLIMS regions that are known to contain glacierized terrain. This dataset attempts to make it easier to find, view, and order ASTER images that have been captured over areas where glaciers may exist.

NOTE: This subset of ASTER browse imagery is primarily tailored for use by the GLIMS community (Regional Centers, Stewards, and all other GLIMS data providers) as a means for finding suitable ASTER imagery for glacier analysis. Many of our collaborators obtain ASTER imagery free of charge, but the general public does not. Be aware that even though these tools make it easy to order ASTER imagery, the normal charges ($85 per scene currently) may apply to you.

Data Access

The GLIMS ASTER Browse data can be viewed in two ways, from within the GLIMS Glacier Viewer or within Google Earth. Both viewing options allow for temporal constraint of the data. Additionally, both options provide a spatial environment to view the the browse images as well as ways to easily order the actual ASTER data.

GLIMS Glacier Viewer

From within the GLIMS Glacier Viewer the GLIMS ASTER Browse data can be viewed and queried along with all the other GLIMS datasets available in the viewer (glacier outlines, WGI Points, etc.). ASTER image locations are drawn as boxes in the viewer with each box representing one image footprint. Using the query tools in the viewer, you can select one or many footprints and view the metadata associated with each image. Within the query results window, you can also follow a link to view the browse image for each scene, or follow another link to order the ASTER scene directly from the LP-DAAC.

Google Earth

Viewing the GLIMS ASTER Browse data within Google Earth is possible by downloading the following 'kmz' file and opening it in Google Earth. The data are divided into annual subgroups for the years 2000 to the present. Subsequently each annual group in divided into three layers representing image center points, image bounding boxes (polygons), and browse image overlays.

There is one point, polygon, and overlay for each ASTER image in the collection, and all three features can be turned on or off (by clicking the checkboxes) and constrained temporally using Google Earth's time window functionality in the upper right corner of Google Earth. To view the metadata of an image simply click on the center point push-pin of an image and a balloon will appear that displays the associated metadata and a link to order that scene. Upon initial loading of the data into Google Earth all data are turned off to prevent too many images being loaded at once.

To view the GLIMS ASTER Browse data in Google Earth, start by loading the following file:

GLIMS_ASTER.kmz

Data Creation

The GLIMS ASTER Browse data were generated by spatially selecting ASTER scenes from regions where glaciers are known to exist. Metadata on all ASTER imagery have been downloaded (and are frequently updated) from the EROS Data Center, via a system called ECHO. The metadata contains information on capture date, ASTER gain settings, instrument pointing angles, and many other attributes, as well as the latitude/longitude footprint of the area covered on the ground. Within the GLIMS database, these footprints are "intersected" with the GLIMS STAR Polygons, a set of static polygons that represent glacierized regions of the world. Only the ASTER scenes fall within one of the STAR polygons are selected and ingested into the GLIMS Glacier Database, where they become available for viewing by the public.

We also download from EROS the browse (reduced resolution) images for all the ASTER images over glacierized terrain, so in addition to viewing the location of ASTER scenes, you can also view these browse images. This allows you to visually determine a scene's quality before order it.

The following flow diagram shows the process of how the GLIMS ASTER Browse dataset is created: