Virtual Globes: Technical experiments

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.

Since many of our data sets are time series, and global change is only apparent over time, we are experimenting with the time series capabilities of Google Earth. Google Earth v4, released on January 8, 2007, implements KML v2.1 to enable time series animations on the virtual globe. Time series animations are memory and bandwidth intensive, but users with a substantial amount of memory and good connectivity can install Google Earth 4.0.2722 or better to view some of the time series data sets below.

We have animated a variety of time series data to explore the usefulness of the technology. All use the Timeline widget that is new in Google Earth v4. If you are unfamiliar with the Google Earth Timeline widget, see Virtual Globes: Google Earth Timelines. Comments and feedback will be appreciated.

Files	Topic	Technical notes	Source data
Download Visualization of ICESat Shots in Google Earth (VISGE) over Anchorage AK (KML, 4 KB)	Elevation	Technical notes: 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.	GLA06 Product
Download the World Glacier Inventory (KML, 3 KB)	Glaciers	Technical notes: Since the World Glacier Inventory contains over 100,000 records, a PostgreSQL database with a PostGIS extension was selected to store the data. GeoServer was used as the server to allow dynamic access to the data. Since GeoServer is an open source server and creates KML automatically, our KML file connects to the PostGIS datastore and allows dynamic access to the World Glacier Inventory via a WMS call to GeoServer. A styled layer descriptor was selected to display the point data and a KML template was created at NSIDC to make the database output easier to understand.	World Glacier Inventory
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 Wilkins Ice Shelf imagery of the Spring 2008 break up event. (KMZ, 20 MB)	Ice Shelves	Technical notes: The Wilkins Ice Shelf imagery for this animation was derived from the MODIS Level 1B Calibrated Radiances product available at Goddard Space Flight Center. The true color images contained in this KMZ file are 250 meter resolution and were processed using the MODIS Swath-to-Grid Toolbox (MS2GT). The Wilkins break up event occurred over the period of a few days in early 2008 and, like the Larsen B break up in 2002, it is an example of how Antarctic ice shelves are becoming increasingly unstable. In an effort to closely monitor ice shelves and outlet glaciers the NSIDC processes and archives MODIS imagery daily of 20 areas along the Antarctic coast. The images in the ice shelf archive are available for download from the Antarctic Glaciological Data Center at NSIDC.	Antarctic Ice Shelf imagery
Download IABP buoy data for July 20 - August 18, 2008 (KMZ, 480 KB)	Buoy Data, Sea Ice	Technical notes: The International Arctic Buoy Program maintains a network of drifting buoys in the Arctic Ocean. For this demo we used daily data from a large number of buoys. We have not color coded the buoys as we did in the previous demo - but we have created some different labeling options to see what that might be like. We have also included sea ice concentration and extent as optional background layers. Eventually we'd like the buoy animation to be near real time and updated daily.	IABP Buoy data
Download IABP ARGOS buoy data for 1985-1994 (KMZ, 480 KB)	Buoy data, Sea Ice	Technical notes: The International Arctic Buoy Program maintains a network of drifting buoys in the Arctic Ocean. The buoys in this demo are the 24 ARGOS buoys deployed between 1985 and 1994. To simulate a larger quantity of buoys deployed at one time all 24 buoys have been animated as if they were deployed in 2007. We color coded the buoys to reflect the recorded air temperature and added the monthly average sea ice extents as an additional layer.	IABP ARGOS Buoys
Download MODIS Daily Snow Cover browse (monthly KML files, 12 KB each)	Snow cover	Technical notes: NSIDC has been generating browse imagery of the gridded MODIS daily snow product for several years, so we already had the images we needed to load into Google Earth. The advantage for the user is the ability to view the browse images quickly, rather than having to click on each daily image. Moreover, users interested in a specific region can zoom in and inspect the browse for only that region, looking for the conditions they want.	MODIS Snow Cover Products
Download subsetted SSMI images. (KML, 90 KB)	Brightness temperature	This test is comprised of a few sample channels (19H, 22V, 37V, 85V, 85H) over a 40 day time period (August 1, 1996 through September 9, 1996). The original data were gridded on a North Polar Azimuthal projection. The subsetted region covers the North Pole, Greenland, and Hudson Bay. Technical notes: NISDC's Graphical Interface for Subsetting, Mapping, and Ordering (GISMO) subsetter has been generating subsets of SSM/I and AVHRR gridded data since the turn of the century, but we have not offered quick-look browse in the past. Some minor additions to the processing system that performs the subsetting enabled the creation of Google Earth compatible browse images and a KML file to animate them. As an added bonus, it is possible to animate two parameters simultaneously and adjust the transparency of the top layer to see how they correlate or interact. If that proves useful we may investigate creating false color animations in a similar manner.	DMSP SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures
Download NPEO buoy data file for Google Earth (KML, 3 KB)	Air temperature; atmospheric pressure measurements; infrared radiance; longwave radiation; shortwave radiation; surface winds; wind direction (wind speed, wind vectors); visible radiance	Technical notes: Point data is much easier to animate, as one does not have to generate the imagery, and both network and memory requirements are minimized. This sequence shows an animation of hourly data gathered from a buoy for almost a year. As an added bonus, the animation highlights faulty locations in the data that might be harder to find through simple inspection of the table. Near the end of the animation, the buoy races down the east coast of Greenland and one can get a sense of the current speed.	North Pole Environmental Observatory (NPEO) Weather and Radiation Buoy Data, 2002-2004
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.	None

Files

Topic

Technical notes

Source data

Download Visualization of ICESat Shots in Google Earth (VISGE) over Anchorage AK
(KML, 4 KB)

Elevation

Technical notes: 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.

GLA06 Product

Download the World Glacier Inventory (KML, 3 KB)

Glaciers

Technical notes: Since the World Glacier Inventory contains over 100,000 records, a PostgreSQL database with a PostGIS extension was selected to store the data. GeoServer was used as the server to allow dynamic access to the data. Since GeoServer is an open source server and creates KML automatically, our KML file connects to the PostGIS datastore and allows dynamic access to the World Glacier Inventory via a WMS call to GeoServer. A styled layer descriptor was selected to display the point data and a KML template was created at NSIDC to make the database output easier to understand.

World Glacier Inventory

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 Wilkins Ice Shelf imagery of the Spring 2008 break up event.
(KMZ, 20 MB)

Ice Shelves

Technical notes: The Wilkins Ice Shelf imagery for this animation was derived from the MODIS Level 1B Calibrated Radiances product available at Goddard Space Flight Center. The true color images contained in this KMZ file are 250 meter resolution and were processed using the MODIS Swath-to-Grid Toolbox (MS2GT). The Wilkins break up event occurred over the period of a few days in early 2008 and, like the Larsen B break up in 2002, it is an example of how Antarctic ice shelves are becoming increasingly unstable. In an effort to closely monitor ice shelves and outlet glaciers the NSIDC processes and archives MODIS imagery daily of 20 areas along the Antarctic coast. The images in the ice shelf archive are available for download from the Antarctic Glaciological Data Center at NSIDC.

Antarctic Ice Shelf imagery

Download IABP buoy data for July 20 - August 18, 2008 (KMZ, 480 KB)

Buoy Data, Sea Ice

Technical notes: The International Arctic Buoy Program maintains a network of drifting buoys in the Arctic Ocean. For this demo we used daily data from a large number of buoys. We have not color coded the buoys as we did in the previous demo - but we have created some different labeling options to see what that might be like. We have also included sea ice concentration and extent as optional background layers. Eventually we'd like the buoy animation to be near real time and updated daily.

IABP Buoy data

Download IABP ARGOS buoy data for 1985-1994 (KMZ, 480 KB)

Buoy data, Sea Ice

Technical notes: The International Arctic Buoy Program maintains a network of drifting buoys in the Arctic Ocean. The buoys in this demo are the 24 ARGOS buoys deployed between 1985 and 1994. To simulate a larger quantity of buoys deployed at one time all 24 buoys have been animated as if they were deployed in 2007. We color coded the buoys to reflect the recorded air temperature and added the monthly average sea ice extents as an additional layer.

IABP ARGOS Buoys

Download MODIS Daily Snow Cover browse (monthly KML files, 12 KB each)

Snow cover

Technical notes: NSIDC has been generating browse imagery of the gridded MODIS daily snow product for several years, so we already had the images we needed to load into Google Earth. The advantage for the user is the ability to view the browse images quickly, rather than having to click on each daily image. Moreover, users interested in a specific region can zoom in and inspect the browse for only that region, looking for the conditions they want.

MODIS Snow Cover Products

Download subsetted SSMI images. (KML, 90 KB)

Brightness temperature

This test is comprised of a few sample channels (19H, 22V, 37V, 85V, 85H) over a 40 day time period (August 1, 1996 through September 9, 1996). The original data were gridded on a North Polar Azimuthal projection. The subsetted region covers the North Pole, Greenland, and Hudson Bay.

Technical notes: NISDC's Graphical Interface for Subsetting, Mapping, and Ordering (GISMO) subsetter has been generating subsets of SSM/I and AVHRR gridded data since the turn of the century, but we have not offered quick-look browse in the past. Some minor additions to the processing system that performs the subsetting enabled the creation of Google Earth compatible browse images and a KML file to animate them. As an added bonus, it is possible to animate two parameters simultaneously and adjust the transparency of the top layer to see how they correlate or interact. If that proves useful we may investigate creating false color animations in a similar manner.

DMSP SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures

Download NPEO buoy data file for Google Earth (KML, 3 KB)

Air temperature; atmospheric pressure measurements; infrared radiance; longwave radiation; shortwave radiation; surface winds; wind direction (wind speed, wind vectors); visible radiance

Technical notes: Point data is much easier to animate, as one does not have to generate the imagery, and both network and memory requirements are minimized. This sequence shows an animation of hourly data gathered from a buoy for almost a year. As an added bonus, the animation highlights faulty locations in the data that might be harder to find through simple inspection of the table. Near the end of the animation, the buoy races down the east coast of Greenland and one can get a sense of the current speed.

North Pole Environmental Observatory (NPEO) Weather and Radiation Buoy Data, 2002-2004

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.

None

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NSIDC Virtual Globes: Technical Experiments

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