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Unit One: Ocean Observing Systems

Part 1: Virtual Field Trip with Real-Time Data
(Go to Part 2: Field Trip to an Observing Buoy)

Objective: Students will compare and contrast the applications of discrete and continuous data.

Background | Materials | Procedure

Background

We have been using the terms "discrete" and "continuous" to describe data. Mathematics is said to be the language of scientists, so let’s take a closer look at what these terms really mean from a mathematician’s viewpoint and how they relate to observing systems.

Mathematicians define discrete data as information based on counts. Only a finite number of values are possible, and the values cannot be subdivided meaningfully.

A good example of discrete data would be the number of glasses damaged in a shipment delivered to a store.

Another example: Population data. It's discrete because you are generally counting people and putting them into various categories like gender, race or age. So what about the "2.4 children" statistic for average households? This illustrates the point that some data cannot be broken down into smaller units and maintain meaning.
Resource: http://www.isixsigma.com/dictionary/Discrete_Data-226.htm

So what is continuous data? Mathematicians say that continuous data are information that can be measured on a continuum or scale. Continuous data can have almost any numeric value and can be meaningfully subdivided into finer and finer increments, depending upon the precision of the measurement system.

Examples of continuous data are money, temperature, time, volume and size.

As you can see, you actually get more information from continuous data than from discrete data.

As you can see, you actually get more information from continuous data than from discrete data.

Simply stated…we will use the terms continuous and discrete more loosely to describe HOW we are using observing data. Discrete will refer to data consisting of unconnected distinct sampling efforts or “one time” sampling at a point in time. Continuous will refer to uninterrupted sampling over time. Resource: http://www.isixsigma.com/dictionary/ContinuousData-96.htm

You and your students can draw more examples of discrete vs. continuous data from the NOAA Web site: http://precip.fsl.noaa.gov/hourly_precip.html, which compares continuous and discrete weather data.

So…How does this relate to Ocean Observing Systems?

Advances in technology have allowed scientists to collect a wide variety of data, both with discrete and continuous methods. Scientists still rely on discrete measurements for many studies, while continuous measurements provide information on changes and episodic events not available from discrete site measurements.

Ocean observing systems data allow scientists to understand features in space (such as managing a fisheries stock) and events in time (such as storms). Here we will take a look at the advantages and disadvantages of both types of measurements using the Choptank River in Maryland as an example.

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Materials

Computers with Web access
Student Worksheet

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Procedure

Have the students surf the following Web sites and then answer questions on the worksheet:

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Part 2: Field Trip to an Observing Buoy
(Go to Part 1: Virtual Field Trip with Real-Time Data)

Objective: Using boats, drifters, an observing buoy and other equipment, students will compare physical data gathered via discrete and continuous methods of measurement

Materials:

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Procedure:

  1. Divide into 4 groups. Each group will have at least one drifter, one hand held GPS unit and a method of following the drifter in the river (boat, canoe, kayak etc.)

  2. Select a Site: Each group will select a site to deploy their drifter(s). Site selection will be made based on mode of water transportation and possible changes in currents due to land structures, shallow areas, jetties, and other structures in the Choptank River.

  3. Using the charts provided, select your site for your group, and based on the tide chart provided, predict the movement of your drifter.

  4. Deployment: Each group will deploy their buoy at their pre-selected site at a given time. Using a GPS unit, drifters will be tracked from a boat for a period of 2 hours. Movement will be recorded using a GPS unit and plotted on a nautical chart of the area.

  5. Back at the Laboratory, we will calculate current speed using the direction and distance the drifter traveled in the given period of time.
    (use http://www.indo.com/distance to determine the distance between points)
    Your students will need to understand 1) latitude and longitude and how to plot it, 2) how to calculate velocity of an object. There are good sample problems and general information on ocean drifters at http://www.drifters.doe.gov/track-a-yoto/track-a-drifter.html.

  6. During the tracking period, we will collect temperature, salinity, nutrients and current speed from a research vessel at the location of a moored observing buoy in the Choptank River. We will monitor and record the current speed through the water column from the surface to the bottom. Current meters have several different sampling strategies. There are some that measures the current at a single point in the water column. Examples include MAVs, S4s, BASS, and ADVs. For example, an S4 current meter is designed to measure the true magnitude and direction of horizontal current motion. The voltage is sensed by the two pairs of titanium electrodes symmetrically located on the sensor. The data obtained is then stored and downloaded to a computer. Others measure the current throughout the water column. For example, BASS, ADCPs, and ADPs all measure the current using acoustics.

  7. We will record the data and download it from the CTD to a computer.

  8. Finally, we will return to the laboratory and compare these data to that available on the Web from the CBOS buoy.

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