Earth’s many environmental problems are often made strongly apparent and can be studied by remote sensing from satellites. Landsat satellite images vividly emphasize the urgency of the need for addressing these situations as humankind poises for a 21st Century race to understand its home planet before time runs out.
The Landsat Project, began in 1972 with the launch of the first satellite in the series, has provided a relatively continuous stream of images of earth. The changes observed have been striking and their implications disconcerting. Landsat 7 joined the still-operational Landsat 5 satellite in summer 1999 and resurveys the same location every 16 days. The Landsat Project, managed from Goddard Space Flight Center in Greenbelt, MD, has produced a continuous set of images of the planet from 1972 to present. One of the stories told by these images is of numerous environmental problems caused by human activities.
Planetary effects due to global warming, biodiversity loss, urban growth, desertification, deforestation, war,and fires can all be observed in Landsat images. In each of these cases, the trends are disconcerting and at rates that are often, at best, troubling.
In 1986, the Filchener Ice Shelf in Antarctica had three huge chunks break off and enter the ocean. This occurs because the huge Antarctica ice mass containing 90% of the planet’s ice has a fluid nature and slowly flows downhill toward the oceans.
The ‘shelf’ nature occurs as the ice extends out from the land over and into the ocean water and is eventually broken off. Rate of flow and of ice loss are monitored using Landsat images. Increased melting and movement of glaciers are a symptom of global warming.
Urbanization is occurring all over the planet and a host of Landsat images demonstrate this. Two United States examples feature Quicktime movies from Washington DC and neighboring Montgomery County, MD. In China, Beijing, already with a dense, high population in 1972, expands even further.
The urban growth doesn’t happen in a vacuum. Landsat images from Garden City, Kansas, show a major increase in center pivot irrigation between 1972 and 1988. This water is drawn from the Ogallala Aquifer at a rate that cannot be sustained. Worldwatch Institute states that the world food supply is in jeapordy due to decreasing ground water availability. Much of the food grown with underground aquifer water can be observed on Landsat images as collections of circles which are often the signature of center pivot irrigation operation.
Habitat changes are also easily distinguished by Landsat. Increasing rain forest deforestation due to logging near Santa Cruz, Bolivia, are depicted in a set of images spanning 1984 to 1998. Landsat images of Olympia National Forest in the Olympic Peninsula in Washington state show the regrowth of forest in logged areas from 1984 to 1995. Landsat imagery recorded record 1993 flooding on the Mississippi River which can be compared to images of more normal years. Some environmental scientists have suggested that if the original wetland areas in the watershed had still been in existence, little flooding would have occurred on the Mississippi in 1993.
War frequently leaves its stamp in the Landsat image archive in the form of smoke and changes in land use. The oil field fires in Kuwait in 1991, at the direction of Iraq’s dictator, are easily observed in Landsat images. In other events, farmers inability to plant crops or operate irrigation equipment are seen by Landsat as differences in the amount of vegetation showing on images over time.
The use of Landsat images is dependent upon appropriate use of ground truthing. Ground truthing is the process of evaluating on the ground what the Landsat data actually represents and how well the data resolves what is being studied. For example, a light brown pixel in the Sahara Desert may indicate an area where ground truthing has shown an average of 4 plant species to exist. The next darker shade of brown may show areas in the Sahara where up to 10 plant species exist. Ground truthing could and in all liklihood does indicate a different situation in the Mojave Desert.
In summary,
1)Landsat images readily show differences in the planet’s surface over time and space,
2)Ground truthing yields even more accurate information about what the images show, and
3)Landsat imagery has been a powerful tool in the quest to understand phenomena on earth. |
