Initial Publication Date: July 20, 2011

Part 2: Present Your Research

On Day 4, you began a simulated research project. The first step was to become familiar with the datasets, then you pre-processed some of the images and created a set of ROIs (Regions Of Interest) for your study areas. Today you'll use these ROIs to identify and measure monthly sea ice coverage data for each study area. The directions for this session will be less detailed than previous sessions—if necessary, return to previous exercises to review detailed instructions. Note: This WILL take both practice and patience, as well as trial and error to find out what works best for you without compromising the quality of your data. If these techniques don't work perfectly for you, read the directions again, then improvise.

Complete Pre-Processing

Before you begin data collection, download these additional sea ice images, import them into ImageJ, and save them in TIFF format. If you don't remember the import settings, see Day 4 Part 2.

Open these images from Day 4 in ImageJ. If any of them are missing or incomplete, return to Day 4 to complete them before continuing.

  • Arctic_2007September sea ice image (from Day 4), saved in TIFF format.
  • Arctic_Pixel_Area image (from Day 4) saved in TIFF format.
  • Arctic_ROI.zip file containing four (or more) carefully-made ROIs of your selected study areas. ROI Manager for your selected study areas.

Identify Sea Ice Extent for September 2007

The working definition of sea ice extent is that it includes all pixels with 15% or greater sea ice coverage.

  • Activate the Arctic_2007September image and use thresholding to highlight the pixels with values of 150 to 1000. This corresponds to 15–100% ice coverage. (Hint: Click the Set button and enter the min and max threshold values.)
  • Convert the threshold area into an ROI (Edit > Selection > Create Selection, add it to the ROI Manager, and name it Sep2007.

Measure Sea Ice Coverage For Your Study Areas

All your ducks are in a row—now you can start making measurements of the sea ice coverage for each of your study areas!

  • Choose Analyze > Set Measurements and turn off all of the measurements except Integrated Density and Display Label. Set an appropriate number of decimal places for your answer.
  • Activate the Arctic_Pixel_Area image.
  • In the ROI Manager, click the Sep2007 ROI then control-click (PC) or command-click (Mac) the Arctic Ocean ROI (that's the one everyone should have done on Day 4). When you click the second ROI, the More menu should automatically pop up.
  • Choose the AND operation from the More menu.
    • The AND operation creates a new ROI that is the intersection between the selected ROIs. This ROI represents the sea ice coverage IN the Arctic Ocean study area. You may add the new selection to the ROI Manager, but it is not required.

    CAUTION – Select None = Select All! If the sea ice extent and study area ROIs don't intersect, nothing is selected. Remember, in ImageJ no pixels selected is treated the same way as ALL pixels selected. In this example, measurement 3 is the area represented by the entire image!

    Bad Results

  • Choose Analyze > Measure to measure the area of the sea ice in the Arctic Ocean study region for September 2007.
  • Continue this process of "intersect and measure" for each of your study areas.

    Part 2 Assignment

    1. Repeat these measurements for at least 2 additional months for each of your selected study areas.
    2. If possible, transfer your measurements to a spreadsheet. (See Graph the Results on this page from the Introduction to Analysis workshop for instructions.)
    3. Go to the Part 2: Share and Discuss page and post a screen shot of your Results window or spreadsheet, along with a brief discussion of what you learned from the data and/or the process used to collect it. Where might errors have occurred in the process and what steps could you take to avoid or correct those errors.
    4. Share a brief outline of an investigation you might have your students carry out using image analysis techniques you learned during the advanced image analysis course, then engage in an online discussion, sharing and comparing ideas with colleagues.

    Source

    1Adapted from Earth Exploration Toolbook chapter instructions, "Whither Arctic Sea Ice?" under Creative Commons license Attribution-NonCommercial-ShareAlike 1.0.
    2Adapted from Eyes in the Sky II online course materials, Copyright 2010, TERC. All rights reserved.
    3New material developed for Earth Analysis Techniques, Copyright 2011, TERC. All rights reserved.