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Introduction to Physical Oceanography
Homework Set 2
Due 10 September 2008

Late homework will cost 15 points per week or part of a week it is late.


Those who produce data know that all data has sampling and instrument errors. Those who use data frequently assume the data are correct. This can be dangerous. The purpose of this homework is to help you become familiar with satellite measurements of ocean winds. Where do satellites measure winds? How often? With what spatial resolution? Do data have errors? Do data made from the same satellite but processed by different groups agree? Do winds measured by different satellites agree? To learn more about the wind-measuring systems in section 4.4 of the textbook before doing the homework.

In doing this assignmnet, data for questions 1and 2 must be from the same day. Data for questions 3 and 4 must be from the same day. This is necessary so data can be compared. Enter data from questions 1A3, 1A4, 1A5, 1B2, 1B3, 1B4, 2A3, 2A4, 2A5 in a spreadsheet so results can be compared. Do the same for 3B and 4A2.

  1. SeaWinds: SeaWinds is a a special radar, called a scatterometer, on the QuikSCAT satellite. The radar measures centimeter-wavelength radio waves reflected from the sea surface. Data from the instrument are used to calculate ocean surface wind speed and direction.
    1. Go the the QuikSCAT Wind Page Global map from the NOAA CoastWatch who operate the Ocean Surface Winds data Page.
      1. Click on one of the two global map mosaics for six time periods to enlarge the plot.
      2. Download and print out the image. Circle the area with the maximum storm winds.
      3. When were data collected?
      4. What is the latitude, longitude, date, and time where maximum storm winds were measured?
      5. What is the velocity of the maximum storm wind on the plot?
      6. Where is the maximum located? Give approximate location such as 1000 km southwest of San Francisco.
    2. All MetSat also distributes SeaWinds data. Look at their Global Map.
      1. Download and print out the image. Circle the area with the maximum storm winds.
      2. When were data collected?
      3. What is the latitude, longitude, date, and time where maximum storm winds were measured?
      4. Click on the region of maximum winds. What is the velocity of the maximum storm wind on the plot?
    3. Using information from the SeaWinds Web page and the All MetSat web pages, answer these questions.
      1. When was the instrument launched?
      2. What is the swath for this instrument?
      3. What percent of the ocean is viewed every day?
      4. What is an ascending pass? A descending pass? If you cannot find the data at these web sites, you may need to do a Google search.

  2. Special Sensor Microwave/Imager: The Special Sensor Microwave/Imager SSM/I is an instrument carried on satellites operated by the Defense Meteorological Satellite Program DMSP. Data from the instrument are used to calculate ocean-surface wind speed.
    1. Go the the Global SSMI Wind Page from the NOAA CoastWatch who operate the Ocean Surface Winds data Page.
      1. Click on one of the two global map mosaics for six time periods to enlarge the plot.
      2. Download and print out the image. Circle the area with the maximum winds.
      3. When were data collected?
      4. What is the latitude, longitude, date, and time where maximum winds were measured?
      5. What is the velocity of the maximum wind on the plot?
      6. Where is the maximum located? Give approximate location such as 1000 km southwest of San Francisco.
      7. How does this global wind map differ from the CoastWatch QuikSCAT map you printed for problem 1 above?
    2. Using information from the Special Sensor Microwave/Imager and Defense Meteorological Satellite Program web pages:
      1. What is measured by the instrument? Please give the physical variable(s) that is(are) directly measured.
      2. What is the swath width of the sensor?
      3. How far back in time are data from SSM/I available?

  3. Regional Real-Time Data: Suppose you need real-time winds from the Gulf of Mexico. Go back to the CoastWatch wind pages and access the Gulf of Mexico Winds from SSMI and Gulf of Mexico Winds from SeaWinds.
    1. Click on the Gulf of Mexico link (there are several links on two pages).
    2. At what times are data available over the past 24 hours for the Gulf of Mexico? You may need to click on the foreward or back arrow at the bottom of the page to see other recent plots.
    3. Print the SSM/I and QuikSCAT wind maps.
    4. Are any of the plots useful for mapping winds throughout the Gulf of Mexico?


  4. Real-Time Data From Remote Sensing Systems: QuikSCAT and SSM/I data are also available from Remote Sensing Systems. Remote Sensing Systems and NOAA process QuikSCAT winds differently. Does the different processing make much difference? Let's find out for one case.
    1. From the QuikSCAT Browser, Click on the Gulf of Mexico. When the new window opens, use the pull-down Image size menu to select medium. Click on Update Display.
      1. Print the daily map.
      2. When were data collected?
      3. How does this map compare with the NOAA QuikScat map of winds from the Gulf of Mexico that you printed out earlier?
        1. Are the times the same?
        2. Do the plots show the same features?
        3. Do they have the same maximum winds?

  5. Wind for Local Models: You are asked to run a local ocean circulation model of Galveston Bay and local offshore waters. The model has 6-hour time steps, it is run every day, and it needs present values of winds over the area. What wind data set will you use, and why? Please state what data sets you considered, and why one is better than the others for this problem. See Ports and Gulf of Mexico Coastal Ocean Observing System.

Revised on: 27 August, 2008

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