Double Hands-On Assignment: Satellites Maps of Sea-Surface Temperature (SST) and Ocean-Weather Buoys

The bird's-eye view of the ocean afforded by satellites has changed the way we perceive the ocean. The complex patterns of ocean circulation, the large-scale variations in sea-surface temperatures and the patchiness of phytoplankton populations are just a few of the many wonders only recently revealed to us through satellites.

In tandem with satellites, ocean weather buoys (which also measure ocean properties) have increasingly populated the oceans because of their ability to enhance and verify satellite measurements (especially when clouds obstruct satellite measurements) and for the information they provide on temporal processes, changes in ocean properties that occur over time.

The sensor packages flown on satellites come in all types and varieties. Many satellite sensors rely on detection of different wavelengths of electromagnetic radiation, such as infrared radiation, which can be used as a measure of heat, and certain wavelengths of visible light, which can be used to estimate chlorophyll. These detectors are known as passive sensors, because they respond to a signal already present in the environment. Other sensors, known as active sensors, emit some kind of active signal to produce a response from some variable in the environment. For example, the TOPEX-Poseidon satellite, which measures the height of the sea surface, sends out a radar signal and measures very precisely the time it takes for the signal to bounce of the sea surface and return to the satellite. Knowing the speed of the signal and the time it takes to traverse from the satellite to the sea surface and back again gives a very accurate idea of the distance between the satellite and the sea surface. This information can be used to compute the height of the sea surface relative to the Earth's geoid (something you can look up if you are interested).

Passive and active sensors can also be attached to buoys, which may be permanently attached or may drift freely in the ocean. However, many other kinds of instrument packages can be attached to buoys. Water-sampling devices, autoanalyzers and other chemical detectors, plankton collectors, sediment traps, oxygen sensors and current meters are just a few of the many instruments found on buoys.

Despite their technical complexity, the data provided by satellites and weather buoys is readily available to you, the aspiring meroplankton-of-an-oceanographer. Most of us are already familiar with the satellite images featured in our local newspapers or on the Weather Channel. What you might not have known is that these satellite pictures (lots of them) and hourly updates from weather buoys are posted on the World Wide Web.

Interpreting Satellite Imagery

One of the advantages of living in the Internet-age is that we can collect oceanographic data without even leaving our homes. It's kind of like Jim Stafford sings: "Take a trip and never leave the farm."

The information provided by satellites and ocean buoys enables oceanographers to integrate large-scale spatial data and long-term temporal data with their own studies. We will acquire data from satellites and buoys that provides spatial and temporal information for our study sites over the period of our investigations. We will concentrate on the satellite images and buoy data that show sea-surface temperatures and oceanographic properties along the California coast.

Our journey into satellite oceanography takes us to the web site for NASA's SeaWiFS Project at seawifs.gsfc.nasa.gov/SEAWIFS.html. SeaWiFS stands for Sea-viewing Wide Field-of-view Sensor, which is a fancy way of saying that this satellite measures ocean color. Ocean color measurements provide information on the concentration of chlorophyll, or phytoplankton, in the ocean. Spend some time familiarizing yourself with the project. It's a fascinating story and their web site offers lots of beautiful color images and layperson's explanations to describe the project.

The National Oceanic and Atmospheric Administration provides up-to-date satellite images of sea-surface temperatures around the globe. Go to this page http://www.osdpd.noaa.gov/PSB/EPS/SST/contour.html. You should see a page entitled Experimental SST Contour Charts. Don't be alarmed by the experimental nature of these pages. Feel privileged that you are taking part in a genuine cutting-edge research effort!

Scroll down to 14 km California Coast. You have a choice of choosing a color image. Choose the Color image. If you have a color printer, print it out. You may want to set the page to print in Landscape mode to fit it all on the page. If you don't have a color printer, then complete the questions below looking at your screen or find a classmate who has printed the color image. You may also save the image by right-clicking on it (with your cursor placed over the image) and choosing SAVE PICTURE AS in the pop-up menu. You may then view or print the image from an image editor, such as Microsoft Photo Editor or a similar program. Just remember where you saved it.

Complete the following on a separate sheet of paper. PLEASE include the questions and write your name on every page!
1. Record the title of the image.
2. What are the dates for the image that you have downloaded?
3. What is the range of latitudes covered by the image? Are they North or South?
4. What is the range of longitudes covered by the image? Are they East or West?
5. What is the range of temperature values on the color scale at the bottom of the image?
6. Now comes the tricky part. Fill in the sea-surface temperature values for each latitude/longitude pair listed in the table below. Use the color key to determine the temperature value for each location. For locations where no data are available (either because the location is on land or because there are no data), write N/A (not available) in the box.

Latitude >>>Longitude 30 ºN 34 ºN 38 ºN
135º W
130º W
125º W
120º W
115º W

Answer the following questions.
1. How does sea surface temperature vary as a function of latitude for any given longitude? How does it vary as a function of longitude for any given latitude? In other words, describe the general trends of sea surface temperatures in a North-South and East-West direction. (Hint: do they get colder, warmer, stay the same, make sudden jumps, etc.)
2. What is the sea surface temperature off the coast at Newport Beach?
3. What are the principal advantages of satellite measurements of sea-surface temperature? What are the disadvantages?

Interpreting Ocean Buoy Data

Now we will find the latest data reports from the weather buoy at Catalina Island and other nearby locations and use it to compare to our satellite image.

Go to www.ndbc.noaa.gov/. This is the home page for the National Data Buoy Center. Spend a few moments browsing the site to familiarize yourself with the different kinds of buoys, where they are located and how they report back to the WWW.

Click on the link for Station Information. (www.ndbc.noaa.gov/stations.shtml). Next, click on the link for NDBC Station Locations, Information and Data (www.ndbc.noaa.gov/Maps/wrldmap.shtml). Find our region (the Southwest U.S. Region) on the Moored Buoy and C-Man Location Map and click on it. You should see a map of southern California with dots representing moored buoy stations. Choose one of those dots. You should see Current Observations and Observations for the past 12-24 hours. If you do not, choose another station. Print or save this page for future reference.

Record the Station Name and Number and answer the following questions on a separate page. PLEASE include the questions and write your name of every page!
1. What is the time and date for the latest observations as listed at the top of the page, right under "Conditions at Buoy # 46025 as of .....)?
2. What is the current sea surface temperature in Fahrenheit and Celsius?
3. What is the current dominant wave period?
4. What is the current wind direction and trend in atmospheric pressure (rising, falling, steady)?
5. What is the time for the first observation listed in the table of previous observations? What is the time for the last observation? How many hours have passed between the earliest observation in the table and the latest observation?
6. Look at the column marked WTMP. What is the "starting" sea-surface temperature and what is the latest sea-surface temperature listed in the table?
7. What is the trend for sea-surface temperature over this period?
8. How do the sea-surface temperature values in the table of buoy data compare to the sea-surface temperature you determined from the satellite image? Discuss why they are the same or different.
9. What are the advantages of moored buoys for obtaining oceanographic information? What are the disadvantages?
10. What are the advantages of using humans to collect oceanographic data? Why is research aboard ships and from shore still useful for understanding the ocean?