Looking at the Seasons from Space

By the calendar, Spring in the Northern Hemisphere began on 21 March. At our house, we heard the first robins singing on 27 February. Snow is still possible in Colorado for a few more months, but the air temperatures are, on average, getting warmer. The trees are leafing out.

On the GLOBE web site, you can see some reports of budburst. These reports should creep northward in the Spring in the Northern Hemisphere. Similarly, you might also look for how far north the Rubythroated Hummingbirds have gone (also see www.rubythroat.org). Most importantly, look for other signs of Spring’s arrival (or Autumn’s arrival) at your home or school. From my time working in the tropics, the biggest changes seem to have to do with rainfall.

Want to see the seasons from space? A recent issue of EOS, which is published by the American Geophysical Union, points to a web site — bluemarble.nasa.gov, where you can do just that.

I found it most interesting to compare the winter image to the summer image. Looking at where I live, in the west-central United States, the ground appears brownish when there is no snow. This fits with what I saw outside. The grasses were dormant, and the trees had lost their leaves. In the summer, the same area is green, because the satellite, like us, “sees” the leafed-out trees and green grasses. How do things change where you live? How does it compare to what the satellite image shows?

These images are from the Terra MODIS (MODerate-resolution Imaging Spectroradiometer), and they have a resolution of 500 meters. This is big enough to see a big lake, but not a football field. Before the images could be produced, the effects of clouds, dust, haze, and even the air between the satellite and the surface had to be removed.

Happy Earth Day!