(calculate-volume-greenland-ice-sheet-tutorial)=
# Calculate the volume of the Greenland ice sheet

The **Processing Toolbox** in QGIS provides a collection of tools and
pre-written algorithms that allow the user to perform a wide variety of raster
and vector data analyses. See the [QGIS
manual](https://docs.qgis.org/3.44/en/docs/user_manual/processing/toolbox.html)
for complete documentation on the **Processing Toolbox**.

In this tutorial, the user will utilize the **Processing Toolbox** with data in
QGreenland to calculate the Greenland ice sheet's volume. In doing so, the user
will become familiar with the how to use the **Processing Toolbox** to perform
geospatial analysis.


```{warning}
This tutorial assumes the user has a basic understanding of GIS and geospatial
data models (e.g., the difference between raster and vector data). If one if new
to GIS, it is reccomended to review QGIS' [Gentle Introduction to
GIS](https://docs.qgis.org/3.44/en/docs/gentle_gis_introduction/index.html)
first
```

## Open the Processing Toolbox

The **Processing Toolbox** can be opened from the menu bar by selecting **View
-> Panels -> Processing Toolbox**. This will open a new panel with a variety of
processing tools organized into groups.

![processing_toolbox](/_images/processing_toolbox.jpg)

```{note}
The **Processing Toolbox** can also be opened by clicking on the gear
![processing-icon](/_images/processing-icon.jpg) icon in the **Attributes
Toolbar** ![attributes-toolbar](/_images/attributes-toolbar.jpg).
```

## Use the Raster Surface Volume tool

In the **Processing Toolbox**, go to **Raster analysis -> Raster surface
volume**. This is an algorithm that calculates the volume under a raster grid’s
surface. Double-click **Raster surface volume** to open the tool's window, and
enter the following parameters:

* **Input layer** = Ice thickness (150 m)
* There will only be one option for **Band number**
* **Base level** = should already be set to 0. This is the minimum pixel value in
  the Ice thickness layer.
* **Method** = Count only above base level (since we are interested in ice thickness
  values greater than zero)
* Save the **Surface volume report**, the output for this algorithm, in a temporary file or in a
  desired location on one's computer.

![raster_surface_volume](/_images/raster_surface_volume.jpg)

Click **Run** and wait for the analysis to finish. The window will switch to the
**Log** tab, which shows log messages and results for the run. A **Results
Viewer** panel should open in a panel underneath the **Processing
Toolbox**. Close the **Raster surface volume** tool's window and click on the
"Surface volume report" entry in the **Results Viewer**. This will show a link to
a results HTML page that can be opened in your broswer. Open this file and
review the results.

![results_viewer](/_images/results_viewer.jpg)

The results file will contain information from the run, including which file was
analyzed, the calculated volume, pixel count, and total area. If one has
succuessfully run the analysis, the results should show that the Greenland ice
sheet has a volume of 2,965,561,810,382,715 m<sup>3</sup>, or about 3 million
km<sup>3</sup>.

## Summary

In completing this tutorial, the user has become familar with the **Processing
Toolbox** and has successfully utilized the **Raster Surface Volume** tool with ice
sheet thickness data included in the QGreenland core package to calculate the
volume of the Greenland ice sheet. Having accomplished this, the user is now
ready to explore other geospatial processing tools included in the **Processing
Toolbox** to further analyze other QGreenland data.