An important set of satellite observations of the global land surface is that from the AVHRR instrument aboard the NOAA environmental satellites. The AVHRR instrument records both the visible and near infrared wavebands, so that we can calculate the NDVI index of landcover greenness for the global land surface and examine how this changes with time.

I find the images of the changes in the landcover of the Earth shown here absolutely fascinating and difficult to accept. These images are not the imagination of a map maker, as are most of the maps of the Earth's surface that fill our atlases. These images are real observations. Each is a monthly-averaged view of how green the entire land surface of the Earth was during the period April 1985 to December 1988. The seasonal (within a year) change in the greenness of the landcover is obvious to the unaided eye as you scan down any one column or year. The climatic (between year) variation can be appreciated by comparing the row of images for any month.

Click here to view the Global NDVI sequence.

The space images of global landcover greenness are a relatively new phenomenon and largely due to the efforts of one scientist working for NASA, Dr Jim Tucker. The story of the development by him of the ideas and technological capacity to effect those ideas makes fascinating reading: see the book by Calder (1991).

There is an Australian connection. I have been collaborating with Jim Tucker over several years undertaking both the research and development needed to use these NDVI images to assess and monitor seasonal conditions, as well as droughts, for the whole Australian continent. There exists for the Australian continent a series of monthly NDVI images of landcover greenness that spans a longer period than the global set displayed before.

Click here to view the Australian NDVI sequence.

This is a remarkable set of images showing the greening behaviour of your home continent. This set of images was first made publicly available when "Looking Back" and its associated CD-ROM were published on 1992. Very few Australians appreciate the low productivity of our continent and how much it is influenced by climate. These satellite images allow us to see and appreciate the condition of the whole continent and to monitor trends over time. Truly, this represents an enormous advance in our capability to manage agricultural and pastoral resources, the landcover that feeds and clothes us, and many of our fellow human beings in other parts of the world.

Take time to explore how the landcover of the continent for a particular place (that is special to you) changes within and between years.