# Part 3—Generate Time Series Plots

## Step 1 – Consider How to Calculate the Rate of Station Motion

The rate of station motion is a measure of its change in position over time. Given that your spreadsheet describes a series of positions at different times, it seems that it would be simple to calculate the rate of station motion using the standard distance formula (Distance = Rate X Time). However, as daily positions of the station show substantial variation, the long term trend of the station's change in position is a much more valid measurement of a station's motion.

To calculate the velocity of a station, the GPS data are plotted into graphs comparing position to time. This type of graph is called a **Time Series Plot (TSP)**. The slope of the trend line of data in a TSP reveals the velocity of the station in a specific direction.

In this activity, you will construct a North TSP and an East TSP to calculate the station's velocity in each direction. You'll combine these two velocity vectors to calculate the total horizontal motion of the station. The vertical motion of the GPS station will not be explored in this activity; however, it is a useful parameter for analyzing crustal movement near glaciers, volcanoes, calderas, and normal and reverse faults.

## Step 2 – Prepare your Spreadsheet for Graphing

- Save your spreadsheet from Part 1 as an Excel Worksheet (.xls)
- Choose
**Edit > Move or Copy Sheet...**and copy your current worksheet onto a new worksheet for making graphs.

- On your second worksheet, delete the top 8 rows of information to make it easier for you to generate graphs.
- Apply appropriate formats to the first four columns of data.
- Click in a column header to select the column.
- Choose
**Format > Cells...** - Select
**Date**for the first column with**Type: mm/dd/yy**, and**Number**, with 2 decimal places for the next three columns.

- Save your file again.

## Step 3 – Generate a Time Series Plot (TSP) for the North Position Data

- Click the column A header to select the
**Date**column. - Control-click (Command-click on a Macintosh) the column B header to add the
**North**column to your selection. NOTE: When you come back to these instructions for the East Time Series Plot, use this same method to select two columns of data that are not directly next to one another. - Click the Chart Wizard icon or select
**Insert > Chart...** - Make a graph that shows Dates on the
**X**axis and North Positions on the**Y**axis. Choose the XY (Scatter) under Chart Type and the first example under Chart Sub-type (scatter). Click**Next**. NOTE: Depending upon your version of Excel, the directions may look slightly different for selecting Scatter Charts. - In Step 3 of 4 in the Chart Wizard,
- click the
**Titles**tab and give descriptive names to your graph and both axes. - under the
**Legend**tab, uncheck the**Show Legend**box as legends have no meaning for scatter plots. - choose your own preferences for options under the other tabs.

- click the
- In step 4 of 4 in the Chart Wizard, click the radio button to place the chart
**in a new sheet**and click**Finish**. - Take a look at your graph... The X axis may appear in the middle of the graph, but if you have Dates along the X axis and North positions on the Y axis, choose
**File > Save**to save your work.

**Series**that will be plotted on the X and Y axes.

In Step 2 of 4 of the Chart Wizard, the Data Range tab will show the cell addresses of all the cells you selected. For the North example, this includes addresses in columns A and B. As your data are in columns, the **Columns** radio button should be selected.

Still in Step 2 of 4, click the **Series** tab to check or modify which data series will be plotted on each axis. You want to plot **Date** values (cell addresses from column A) on the **X** axis, and **North** positions on the **Y** axis. NOTE: In some versions of Excel, the data range and cell addresses can be checked or adjusted by selecting **Chart > Source Data...**

## Step 4 – Clean up the Graph

- Change the placement where the
**X**axis crosses the**Y**axis.- Double-click any number on the
**Y**axis. - Click the
**Scale**tab. - For the
**Value (x) axis crosses at**, type in the minimum Y value from your graph, for example**-10**, then click**OK**.

- Double-click any number on the
- If necessary, adjust the number format and grid units of the X axis.
- Double-click any date on the
**X**axis of your graph. - If your dates appear in an odd format, click the
**Number**tab and select**Date**. Under**Type**select the mm/dd/yy option. - If your data are 'squished' in the middle of the graph, click the
**Scale**tab and change the values in the**X**axis scale so the data fill the graph. - Make any other adjustments as desired to change the appearance of your graph then click
**OK**.

- Double-click any date on the
- Save your file.

**Talk About It...**

What does this graph tell you? Think about and discuss what the graphical representation of the data indicates about the location on Earth where the data were collected.