**TRACK A YOTO DRIFTER**

For many years scientists have used ocean drifters to track currents and
learn about the ocean. Modern technology now allows us to use satellite
communications to relay the position of these drifters and track them in
almost real time. And through the global network provided by the
internet, you too can have access to this exciting and important data.
Do you know where ocean currents flow? What if an oil spill occurred in
the Caribbean Sea, would Florida beaches be at risk from floating oil?
Can drifter data be used to predict where icebergs are to prevent ships
from hitting them? Do ocean currents transport heat as well as water,
and does this play a role in our climate and weather? What role do
currents play in the world's fisheries? To answer these and other
exciting questions about the ocean, track a YOTO drifter. Follow the
simple activity directions to learn how to plot drifter positions on a
chart, draw drifter tracks, and calculate their speed and direction of
movement. Then see if you can answer some of the questions given at the
end of the activity.

Materials needed for track-a-drifter activity:

Activity text with sample drifter data, a ruler with mm/cm scale,
pencil, calculator and YOTO Drifter Tracking Chart (download a page size
version from the website, order one by fax at 303-202-4693, or call
1-800-USA-MAPS for a poster size version at and ask for the YOTO Drifter
Tracking Chart, USGS publication \# TBA).

**1. LEARNING HOW TO USE LATITUDE AND LONGITUDE TO PLOT DRIFTER
POSITIONS ON A CHART.**

Where are you???????

Before you can plot drifter positions on a chart, it is crucial to
understand the concept of location as a function of latitude and
longitude. A latitude or longitude is similar to an x or y coordinate on
a graph or grid, except in this case the grid overlays the spherical
Earth. Because the Earth is round, we use an angular distance, rather
than a straight distance to measure from a point of origin (usually 0,0
on a graph). On the Earth, the origin or 0,0 point is the center point
of the Earth (fig. 1). Where then on the Earth, would the distance from
the origin in a north-south direction be zero? It is along the east-west
circle at the equator, we call this zero latitude. Both latitude and
longitude are measured in degrees, minutes and seconds. There are 360
degrees in a circle, 60 minutes in a degree and on a chart, 100 seconds
in a minute. Latitude is measured as the angular distance in degrees
north or south of the equator, the north and south pole are located at
90 degrees north and south latitudes respectively. East - West running
circles on a globe which connect points of equal latitude are called
parallels of latitude.

Where on the Earth is the east - west distance from the origin equal to
zero? Along a circle that goes through and intersects at the poles, but
which one? A long time ago it was decided that the zero circle would be
at the line which passes through Greenwich, England. This is often
called the Prime Meridian, or the zero longitude line. Longitude is
measured as the angular distance east or west of the zero longitude
line. North - South running circles which connect points of equal
longitude are called longitudinal meridians.

On a flat grid or graph we define a location by an x and y coordinate.
On the Earth's surface we can define a location by a latitude and a
longitude. On figure 1, point p is located at 40 degrees north latitude
and 60 degrees west longitude.

On a graph we can measure or calculate the distance between two points,
the same is true on the Earth's surface, using the latitude and
longitude system. On the Earth's surface, 1 degree of latitude equals
111 km or 60 nautical miles. Longitude is a bit more complicated because
the distance between meridians decreases to zero at the poles. However,
at the equator, 1 degree of longitude also equals 111 km or 60 nautical
miles.

![](media/image1.emf){width="3.5965277777777778in" height="3.625in"}

Figure 1: Diagram of latitude, longitude grid on a spherical Earth
(After Charton, 1988).

Practice your skills using latitude and longitude on the following
problems.

A. Listed below are pairs of latutude and longitude, can you find these
locations on the YOTO Drifter Tracking Chart.?

  ----------------- ----------------- -----------------------------------
  **Latitude**      **Longitude**     **Where are you?**

  26°N              80°W              

  15°N              90°W              

  42°30'N           71°W              
  ----------------- ----------------- -----------------------------------

B. Listed below are some places on the tracking chart, use latitude and
longitude to describe their location.

  ----------------------- ----------------------- -----------------------
  **Place**               **Latitude**            **Longitude**

  New Orleans, Lousiana                           

  The island of                                   
  Martinique                                      

  Key West, Florida                               
  ----------------------- ----------------------- -----------------------

**2. PLOTTING DRIFTER POSITIONS AND DRAWING TRACKS**

**Before using real-time YOTO data, practice with data from drifters
used in the past.**

A. Example data from two drifters are given below. Split into 2 groups
and plot these positions using latitudes and longitudes on the YOTO
tracking chart provided (page-size charts may be downloaded directly
from the website or ordered via fax from 303-202-4693 and a poster-size
chart for the classroom can be obtained by calling 1-800-USA-MAPS and
requesting publication \# TBA). Each position should be plotted by a dot
or pin (in the poster); if possible, label the date next to each
position.

Example Drifter Data

Drifter #1

+-------+---------+---------+-------+----------+----------+---------+
| Date  | L       | Lo      | Time  | Distance | Speed    | Di      |
|       | atitude | ngitude | Int   |          |          | rection |
|       | (°N)    |         | erval | (nm)     | (mph)    |         |
|       |         | (°W)    | (     |          |          |         |
|       |         |         | days) |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 8-    | 15      | -74     | 0     |          |          |         |
| 25-96 | °32'00" | °49'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 8-    | 14      | -75     | 3     |          |          |         |
| 28-96 | °40'00" | °48'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9     | 14      | -76     | 3     |          |          |         |
| -2-96 | °14'00" | °45'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9     | 14      | -77     | 3     |          |          |         |
| -5-96 | °07'00" | °50'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9     | 15      | -79     | 3     |          |          |         |
| -8-96 | °12'00" | °10'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9-    | 16      | -80     | 3     |          |          |         |
| 11-96 | °44'00" | °04'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9-    | 17      | -81     | 3     |          |          |         |
| 14-96 | °49'00" | °03'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9-    | 18      | -82     | 3     |          |          |         |
| 17-96 | °53'00" | °01'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9-    | 19      | -82     | 3     |          |          |         |
| 20-96 | °40'00" | °47'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9-    | 20      | -82     | 3     |          |          |         |
| 23-96 | °02'00" | °58'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+

Drifter #2

+-------+---------+---------+-------+----------+----------+---------+
| Date  | L       | Lo      | Time  | Distance | Speed    | Di      |
|       | atitude | ngitude | Int   |          |          | rection |
|       | (°N)    |         | erval | (nm)     | (mph)    |         |
|       |         | (°W)    | (     |          |          |         |
|       |         |         | days) |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10    | 28      | -80     | 0     |          |          |         |
| -4-96 | °12'00" | °00'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10    | 30      | -80     | 3     |          |          |         |
| -7-96 | °20'00" | °02'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 30      | -79     | 4     |          |          |         |
| 11-96 | °51'00" | °49'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 32      | -77     | 3     |          |          |         |
| 14-96 | °18'00" | °55'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 32      | -78     | 3     |          |          |         |
| 17-96 | °23'00" | °01'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 33      | -77     | 3     |          |          |         |
| 20-96 | °01'00" | °06'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 33      | -77     | 3     |          |          |         |
| 23-96 | °18'00" | °03'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 35      | -74     | 3     |          |          |         |
| 26-96 | °17'00" | °53'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 37      | -69     | 3     |          |          |         |
| 29-96 | °54'00" | °54'12" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 11    | 37      | -67     | 3     |          |          |         |
| -1-96 | °00'00" | °39'96" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+

After plotting each position, connect the points. This is a **drifter
track.**

Have the two groups plot their positions and tracks on the poster size
chart.

Are they the same or different? Go on to explore why the tracks are
different by learning how to calculate drifter speed and direction.

**3. CALCULATING DRIFTER SPEED AND DIRECTION**

Speed is a measure of how fast an object (including people) moves across
a given distance. To calculate speed we take the distance covered and
divide by the time it took to cross that distance:

Speed (m/s) = Distance (m) ÷ Time (s)

The units used to describe speed can vary. For instance, if you are
calculating the speed of a train, you may want to use mph (miles per
hour) or kph (kilometers per hour). However, if you are tracking the
path of a snail you may want to use cm/h or inches/h.

Practice calculating speed using different units for the examples given
below.

+-----------------+-----------------+-----------------+-----------------+
| Object          | Distance        | Time            | Speed           |
+-----------------+-----------------+-----------------+-----------------+
| Airplane        | 700 miles       | 2 hours         |                 |
+-----------------+-----------------+-----------------+-----------------+
| Snail           | 1.2 cm          | 1.5 hours       |                 |
+-----------------+-----------------+-----------------+-----------------+
| Whale           | 25 nm\*         | 5 hours         |                 |
+-----------------+-----------------+-----------------+-----------------+
| Cheetah         | 24 miles        | 15 minutes      |                 |
|                 |                 |                 |                 |
|                 | (38 km)         | (.25 hours)     |                 |
+-----------------+-----------------+-----------------+-----------------+

\* nautical miles

Sometimes we use an arrow to represent speed, with the size of the arrow
being proportional to the speed. If 1 cm = 1 mph, then the Airplanes
speed could be represented by an arrow that is 350 cm long. Yikes! that
is a long arrow, in this case it would be better to use 1 cm = 35 mph
and our arrow would be only 10 cm long.

If we use 1 cm = 1mph, then the snails arrow would only be 0.8 cm long,
that is a pretty short arrow. Using 1 cm = 10 mph, draw below the arrows
which would represent the speeds of the whale and cheetah.

  ----------------------- -----------------------------------------------
  Whale                   

  Cheetah                 
  ----------------------- -----------------------------------------------

Speed describes how fast or slow an object moves, but it does not tell
us anything about the direction of movement. If we combine the speed and
direction of an object, it is called velocity. Velocity can be shown
using a vector (an arrow which shows direction and speed).

On maps and charts there is usually some sort of compass rose which
shows direction on the map, below is an example:

![](media/image1.emf){width="1.56875in" height="1.5138888888888888in"}

N = North, S = South, W = West, E = East

If a direction is between 2 of the major directions (N,S,E and W), then
the directions are combined. An arrow pointing to a direction between
North and East, would be pointing Northeast (NE). What direction are the
arrows below pointing, write it below each arrow.

![](media/image1.emf){width="1.4159722222222222in"
height="0.6243055555555556in"}East ![](media/image2.pct){width="46.0in"
height="104.0in"} ![](media/image1.emf){width="0.9715277777777778in"
height="0.9715277777777778in"}

a\. b.

Example

For each of the arrows below, measure its length and using a scale of 1
cm = 10 mph, determine what speed it represents and name the direction
it is pointing (this is its velocity).

![](media/image1.emf){width="1.31875in" height="0.5833333333333334in"}
![](media/image1.emf){width="0.6111111111111112in"
height="0.6111111111111112in"}
![](media/image1.emf){width="0.49930555555555556in"
height="1.582638888888889in"}

a West (20 mph) b. c.

Draw arrows which represent the speed and direction for the following
velocities.

a\. 20 mph, south b. 30 mph, southwest

Now go back to the data tables for Drifters 1 and 2. In the spaces
provided, measure or calculate the distance betwen drifter locations,
calculate the drifters speed and for each time interval name the
direction it is traveling on the chart. On the chart provided there is a
scale to use to measure the distance between each drifter location and a
compass rose to judge its direction of movement. On the drifter tracking
chart, 1 cm = approximately 125 nm.

**4. AVERAGING AND DRIFTER TRACKS**

When analyzing Drifter tracks, it is very important to understand the
concept of averaging and how averaging will affect your results. You
have just calculated the speed of the Drifter over a set of 3 day
intervals, each speed is therefore a 3-day average. If the satellite got
jammed for 2 days, and we only got a position once over a 5 day period
and calculated speed over that time, it would be a 5-day average.

Because water movement in the ocean is not necessarily a steady process
(having constant speed or direction), the length of time we use in
averaging can produce very different results. In the table below
recalculate Drifter 1 and 2 speeds based on the given time intervals. To
calculate distance, be sure to measure between the correct dates.

Drifter #1

+-------+---------+---------+-------+----------+----------+---------+
| Date  | L       | Lo      | Time  | Distance | Speed    | Di      |
|       | atitude | ngitude | Int   |          |          | rection |
|       | (°N)    |         | erval | (nm)     | (mph)    |         |
|       |         | (°W)    | (     |          |          |         |
|       |         |         | days) |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 8-    | 15      | -74     | 0     |          |          |         |
| 25-96 | °32'00" | °49'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9     | 14      | -76     | 6     |          |          |         |
| -2-96 | °14'00" | °45'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 9-    | 16      | -80     | 9     |          |          |         |
| 11-96 | °44'00" | °04'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+

Drifter#2

+-------+---------+---------+-------+----------+----------+---------+
| Date  | L       | Lo      | Time  | Distance | Speed    | Di      |
|       | atitude | ngitude | Int   |          |          | rection |
|       | (°N)    |         | erval | (nm)     | (mph)    |         |
|       |         | (°W)    | (     |          |          |         |
|       |         |         | days) |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10    | 28      | -80     | 0     |          |          |         |
| -4-96 | °12'00" | °00'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 30      | -79     | 7     |          |          |         |
| 11-96 | °51'00" | °49'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+
| 10-   | 35      | -74     | 15    |          |          |         |
| 26-96 | °17'00" | °53'00" |       |          |          |         |
+-------+---------+---------+-------+----------+----------+---------+

Are your results different from the first time you calculated speed and
direction for these Drifters ? Why?

**ANALYSIS OF RESULTS**

1\. These Drifters are tracking ocean currents. What is the general
location of these currents and what is the main direction they are
moving? Is the direction of daily drift different from the direction
over a longer time scale ?

2\. Do both Drifters behave the same or differently? What might make the
currents (drifters) speed up, slow down or change direction?

3\. Did the number of days used to calculate the speed and direction
make a big difference?

4\. Do you think you could predict the position of a Drifter in the
future, for instance 3 days after your last position plotted ?

5\. Give one example of why it is important to understand how ocean
currents flow.

**REAL TIME YOTO DRIFTER DATA**

Now that you are an expert at plotting ocean Drifters and their tracks,
click into the YOTO Drifter data or tracks to obtain data from drifters
deployed in 1998. Plot their positions, calculate their speed, direction
and try to predict where they are going each day or week. Learn at the
same time as real scientists where ocean currents are flowing, and how
sea surface temperatures are changing.

**YOTO Drifter Questions**

1\. These drifters are tracking ocean currents. What is the general
location of these currents and what is the main direction they are
moving? Is the direction of daily drift different from the direction
over a longer time scale ?

2\. Do the number of days used to calculate the speed and direction make
a big difference?

3\. Go back to your chart and record the temperature next to each point.
Do you see any changes in temperature along the Drifter tracks? What
could cause temperature at the sea surface to change?

What role do sea surface temperatures play in climate and weather
patterns?

4\. Many organisms in the sea have young that begin life as small
floating creatures, called plankton. Even those organisms who in their
adult forms are strong swimmers or live on the bottom, may begin as
plankton and drift with the ocean currents. Understanding ocean currents
is therefore very important to our ability to assess the population
size, location, and breeding grounds in numerous marine species. For
instance, the spiny lobster, an important species in reef environments
and a commercial fishery, begins its life as a small, flattened
skelton-like creature, known as a phyllosome. As it develops, it can
drift for months in the ocean currents. Once it becomes a juvenile,
looking much more like the adult version; it settles to the sea floor
and begins its journey into adulthood. In South Florida spiny lobster
are commercially fished in some areas and protected in others, like the
Florida Keys National Marine Sanctuary. Scientists are studying currents
in an attempt to determine where Florida lobsters originate, thereby
providing answers to questions such as: is there a local source of
lobster larvae and do circular currents which keep them within the area,
or do larvae come from a distant upstream source somewhere in the
Caribbean ?

Using data from YOTO Drifters, you might be able to help answer this
important question.

If a lobster were to spawn just south of Jamaica in the Caribbean Sea,
and small phyllosomes began their journey as plankton, where would they
drift? In three months where would the closest land and reef habitat be
on which they might settle ?

5\. An oil tanker in the Gulf of Mexico collides with a pleasure yacht
just north of the western tip of Cuba in the Gulf of Mexico. If oil
starts seeping from the tanker where would the ocean currents carry it?
If the oil cannot be cleaned up while at sea or a big storm makes it
impossible to contain the spill, use Drifter data to predict which
coastal communities should make preparations to prevent damage to their
local environment.

6\. Scientists use data from satellites to obtain a view of the oceans
which would otherwise be impossible. With remotely sensed data
(satellite imagery), we can see large sections of the ocean at one time.
But how do we know that these images are accurate? Scientists do
something called ground-truthing. Ground-truthing is when ocean data are
collected in the same time and location as the image. Drifter data can
be used to ground-truth satellite images of sea surface temperature and
ocean color. Look at YOTO Drifter temperature data and compare these
results to the images of sea surface temperature provided. Would the
date of comparison make a difference?