NSIDC Virtual Globes: Technical Experiments
This page lists some of our experiments with using Google Earth to visualize our data. These files illustrate capabilities we are interested in developing, as technology progresses. Each resulting file proves some capabilities, but also has limitations, as discussed below. These technical notes may be of interest to other Google Earth file developers.
Movie of sea ice extents, 1979-2008, on Google Earth (QuickTime, 1.6 MB)
Questions, comments or suggestions? Contact us at email@example.com.
|Files||Topic||Technical notes||Source data|
|Download Visualization of ICESat Shots in Google Earth (VISGE) over Anchorage AK |
(KML, 4 KB)
The Geosciences Laser Altimetry System (GLAS) takes 40 measurements per second, or about 240,000 measurements per orbit. At 14 orbits per day with campaigns lasting up to 30 days, the sheer quantity of measurements makes the display of GLAS data in a virtual globe a fairly challenging task. This experiment, named the Visualization of ICESat Shots in Google Earth (VISGE), seeks ways to make massive numbers of point measurements available in a virtual globe without overloading the system.
For a 5x5 degree area around Anchorage, Alaska USA, NSIDC has created subsampled files for each campaign, allowing users to visualize the coverage of the orbits. The full data is only loaded once the user has zoomed in to a sufficiently small area. For each campaign, NSIDC has created 2500 0.1x0.1 degree bins. Each bin file contains up to 3500 placemarks representing a GLAS footprint and providing access to the waveform image for that measurement.
For more information on this project, see the Visualization of ICESat Shots in Google Earth (VISGE) Overview Web page. In order to aid in the future development of this tool, please share your feedback on the usability of this interface by taking the VISGE Usability and Feature Request Survey.
|Download a file of the MODIS Mosaic of Antarctica (KML, 4 KB)||Antarctica||Technical notes: MOA provides a cloud-free view of
the ice sheet, ice shelves, and land surfaces at a grid scale of 125 m
and an estimated resolution of 150 m. All land areas south of 60°
S that are larger than a few hundred meters are included in the mosaic.
Also included are several persistent fast ice areas and grounded icebergs.
The MODIS data were acquired from November 2003 through February 2004.
To create the KML file, steps were taken to to resample the 16-bit 48333x41779 polar stereographic MOA image to an 8-bit 108000x27000 lat-lon image required by KML. The 16-bit gray level values of 15096 and 17283 were mapped linearly to 1 and 255, respectively, with 0 representing missing data. This is a "compromise" stretch so that both relatively high and low contrast features are visible. The image from this step was converted to a GeoTIFF and the GeoTIFF was then run through the Regionator.
Note that Antarctica appears surrounded by black ocean rather than blue ocean because missing MOA data having a value of 0 were not mapped to "transparent" before being run through the Regionator. We hope to fix this bug in a future version of the MOA KML.
|MODIS Mosaic of Antarctica|
|Download NSIDC field data file for Google Earth (KML, 3 KB)||Various||This file includes data from anywhere on the globe for which
the spatial coverage is adequately described by a one-degree bounding box,
representing data from a single "point."
Technical notes: This approach was a way of exploring how to most easily create a Google Earth file for our field data. We add such data sets to our catalog frequently, so coming up with a rule for identifying these data sets and adding them to the file would make it possible to somewhat automate maintenance of such a file. The resulting file is only a very limited part of our extensive data collection.
|Various data sets; links included with each pushpin|
|Download Screen Overlays example file (KML, 9 KB)||Screen Overlays||This file includes examples of how to use screen overlays
in Google Earth. No actual data or imagery is presented
Technical notes: Screen overlays are images placed on the screen to display ancillary information that puts the other information in context. Things like logos, titles, and legends are often displayed as screen overlays. See Virtual Globes: KML Screen Overlays for more information.