Example Visualizing Altimetry Data
1. Windows PC and Macintosh users: To start the Visualizer, navigate to the directory on your computer where you installed the package, double-click the IDL project file "glas_visualizer.prj" and type icesatvis_ds at the IDL prompt.
Unix users: To start the Visualizer, navigate to the directory where you installed the package [your_directory_name]. Then type:
$ cd scf_visualizer/your_directory_name/
You can also run the Visualizer from anywhere, using the following command:
The following window appears:
2. Click Select from Specific Data Set. The following window appears:
Note the Data Release field with a default value of 21 already filled in. Click Pick next to a data set ID and select a file to view. Refer to the following table for names of each altimetry data set ID:
|Short Name||Long Name|
|GLA01||GLAS/ICESat L1A Global Altimetry Data|
|GLA04||GLAS/ICESat L1A Global Laser Pointing Data|
|GLA05||GLAS/ICESat L1B Global Waveform-based Range Corrections Data|
|GLA06||GLAS/ICESat L1B Global Elevation Data|
|GLA12||GLAS/ICESat L2 Antarctic and Greenland Ice Sheet Altimetry Data|
|GLA13||GLAS/ICESat L2 Sea Ice Altimetry Data|
|GLA14||GLAS/ICESat L2 Global Land Surface Altimetry Data|
|GLA15||GLAS/ICESat L2 Ocean Altimetry Data|
When you have selected all of the files you need, click Display Data to continue.
3. An Elevation Profiles window appears with thumbnail images of decimated elevation profiles for each pass. A Groundtracks window also appears.
4. Right-click on a thumbnail in the Elevation Profiles window to highlight the specific pass in the Groundracks window.
If the file contains more than four passes, then click Next or Previous in the Elevation Profiles window to show the additional passes.
5. Left-click on a thumbnail in the Elevation Profiles window. The corresponding ground track is highlighted, and a GLAS Series Plot Sets window appears. Only plot set buttons that are applicable to products you select are active; other plot sets are disabled.
6. Select the desired plot sets (for this example, select Elevations and Waveform Characteristics); then click Launch Selected Plot Sets. You may need to resize the GLAS Series Plot Sets window to see the launch and exit buttons.
GLAS Elevation Plot Set
The GLAS Elevation Plot Set window displays a time-series plot of surface elevation for the selected pass. If you selected a GLA12 file, the geoid surface and DEM surface are also plotted. The top portion shows time-series plots of specific parameters, and the bottom portion shows differences between any two parameters you select with the Choose buttons near the bottom of the window.
tude and longitude of the end points of the displayed section. (Not every plot set has these buttons, but a future release of the Visualizer will enable them for all plot sets.) The default plot title gives the starting date and time (UTC), ending time, and the pass ID. Some plot sets automatically show only the first shot of each second until zoomed in sufficiently to reveal other shot numbers; this is indicated by the "(1Hz)" notation.
Left-click and drag the turquoise vertical lines to set a zoom range, then click Zoom. These cursors are initially at the left and right sides of the plot. A new plot set will appear, showing only the zoomed region.
The Curves button lets you select which curves (currently available in the plot set) to show in the plot. You can also change the color and line properties of individual curves and output data values to the screen. For GLA06 and GLA14 only, you can write product fields to a tab-delimited ASCII file using the "Dump Field..." entry. A future release of the Visualizer will enable this feature for all products. See "SCF_DVUG_NSIDC.doc" for details. Some curves now have an entry labeled Dump Field… This allows you to dump to an ASCII file the product-file field that was plotted as that curve, along with the unique index, shot number, time (J2000 UTC seconds), latitude, and longitude, for each shot or record. So far this is only available for GLA06, 12, 13, 14, and 15 curves on the Elevations series plotset, but it will be implemented for the rest in future releases.
The Properties button lets you change scales and other plot properties for creating publication-ready plots. The Print button creates a Postscript version of the plot. Both the series and difference windows are plotted. The ThumbnailViewer and ThumbnailZoom "Print..." button option, "Print data rec of 1st tn" has been removed. Instead, try zooming on the thumbnail you want and use the "Print data..." options on the Curve menu for the curve you are intereseted in.
The Save/Res Props... button lets you save the current plot and curve properties (including which curves are plotted) to a file, or restore saved properties from a file. Properties for both the data and difference plots are saved, but the selection of curves differenced are not; this functionality will be added to a future release of the visualizer. You can only restore properties to a plot of the same type. The x-axis range was removed in this version of the Visualizer, because it often caused the plot to appear blank. When saving properties, be sure to specify a directory for which you have write permission; the default is the one from which you launched the visualizer.
Click Close PS File when finished.
Important note: If you try to create either the Postscript or ASCII file in a directory with no write permission, the visualizer may crash. The default is the directory from which the visualizer was run.
Right-click on a time-series plot to position a vertical red line. Then click Show on Ground Track to highlight the portion of the pass shown in the plot and display a diamond-shaped marker at the corresponding location of the red line. If you are working with a GLA01 file, you can click Display Waveforms to bring up a window showing individual waveforms beginning at the ground location corresponding to the red line. If you also selected a corresponding GLA05 file, the waveform plots will include waveform parameterization results.
If you selected a GLA01 file but not GLA05, only the raw waveform is displayed. The raw waveform is in red and the fit is in blue. Only the raw waveform displays for GLA01 files. Each waveform shows a unique index and shot number, shot time in J2000 seconds, latitude and longitude, and elevation (GLA05 only). The X scale shows relative time in nanoseconds; the Y scale units vary with each curve. Latitude and longitude are uncorrected GLA05 locations; if GLA05 is not available, predicted GLA01 locations are given. The Curves button on this multi-waveform plot offers the same display capabilities as on the individual waveform plots described earlier. Left-click on a waveform thumbnail to display a Zoomed Waveform window.
Please consult "SCF_DVUG_NSIDC.doc," which is included in the Vizualizer GZIP file , for further details of display options.
GLAS Waveform Characteristics Plot Set
The GLAS WF_CHAR plot set is similar in appearance to the Elevation plot set described above. The top portion shows time-series plots of specific parameters, and the bottom portion shows differences between any two parameters you select with the Choose buttons near the bottom of the window. Initially the transmitted energy and received energy profiles are plotted. You can also plot the following by clicking Curves. Many other waveform and fit characteristics are available too.
- Received and transmitted energy from GLAO1
- Received and transmitted gain from GLA01 and/or GLA05
- Waveform compression information
- The difference (in km) between the received echo peak and the transmitted waveform peak
- Proximity of the echo peak to the last telemetered gate
- The width of the signal based on first and last threshold crossings
- The difference between the first threshold crossing and the last gate
- The time in digitizer counts (nanoseconds since the digitizer was turned on) of the transmit peak
- The maximum amplitude of the smoothed waveform