Going Further
Variations
- Go to the MODIS Rapid Response Image Gallery and enter Aral Sea in the Search field. Browse through the images and come up with your own research question about how the Aral Sea region has changed over time. Use the techniques in this chapter to quantify your study.
- Search the MODIS Rapid Response Image Gallery for images of the Aral Sea and try to pinpoint the date that the former island (named Vozrozhdeniye, which means "renaissance" or "rebirth") between the east and west portions of the sea became a pennisula of the mainland. Consider the implications for biodiversity for an island that becomes part of the mainland: for instance, are island species likely to spread to the mainland or will they become prey to mainland predators that now have access to them?
- Search for and download other images of the Aral Sea from MODIS and Landsat. Use a combination of techniques from this chapter to construct a more detailed record of how the area of the sea has changed over time.
Other Data
The process of setting a scale and making measurements from images is the same for any image in which the features appear in the same focal plane. Thus, the techniqes can be applied to any satellite image produced with a nadir (straight down) orientation, regardless of what parameter it measures or if the image is displayed in true or false colors. Additionally, this technique would work just as well for microscopic images as for satellite images. Two sites of special interest to this chapter are noted below.
EarthShots: Satellite Images of Environmental Change (more info) is a collection of registered time series images taken by Landsat instruments since 1972. You can use the same techniques presented in this chapter to set a scale and measure distances and areas in this collection of images.
Search on NASA Earth Observatory for the phrase time series to find "before and after" images. Set a scale for each image and make measurements to give a quantitative description of the change that occured.
Other Techniques
Occasionally, you may find an image that you would like to make measurements from, but its spatial resolution is not stated clearly. Here are some techniques you might use to set the scale for such an image.
- If the image contains a graphic distance scale, select a straight line along it, then choose Analyze > Set Scale... and enter the Known Distance indicated by the scale.
- If you can identify two specific features in the image, select a line between the two points then choose Analyze > Set Scale.... Find the Known Distance between the locations (by measuring it in an atlas, for example) and enter it along with the appropriate units of length.
- If you know the satellite instrument that recorded the image data, visit the instrument's Web site. Many instruments record data at a constant resolution or their data products are prepared at specific resolutions.
- You can occasionally open image files into a text editor application, and read recognizable header information that states the spatial resolution.
- Submit feedback to data sites, asking them to specifically state image resolutions.
Case Studies with Tool
The EET chapter Annotating Change in Satellite Images, offers techniques for outlining and annotating change in time series images. You can combine techniques from both chapters to further document change over time in satellite images.
