Quarterdeck Volume 5, Number 3, December 1997
When you decide to retrieve data from a TABS buoy, you can view a page with four graphs stacked on top of each other. The odd-looking one at the top is a "stick plot."
Each "stick," or vector, contains three pieces of information about water movement: direction, time, and magnitude (strength).
Imagine a small arrowhead on the end of each stick. Arrows would point in the compass direction the current is heading. A stick pointing toward the upper right of the page is pointing northeast, a stick pointing to the bottom of the page is pointing south, and so on. In Example A, compass directions are posted at the end of each stick. For clarity, this graph only includes every 6th hourly reading.
All graphs on the page share the same time axis at the bottom of the page. Progress from left to right along the time axis represents forward progress in time. The base of each stick marks the time when that measurement was made. Each stick represents a current reading taken every 30 minutes. Time is marked in Universal Coordinated Time (UTC).
Central Standard Time (CST) = UTC - 6 hours
Central Daylight Savings Time (CDT) = UTC - 5 hours
The graduated vertical lines on the left side of the graph are scales for estimating speed in either centimeters/second or knots. These scales work differently from a traditional y-axis. Rotate the scale or the stick you are measuring so that the two are parallel to each other. You can use a ruler to measure the stick and then hold the measurement alongside the scale to estimate speed. Example B shows two sticks rotated to align parallel to the speed scales.
Send comments about the content of this page to quarterdeck@ocean.tamu.edu.
Send comments and questions about this web site to web@ocean.tamu.edu.