Remote Sensing Tutorial Page 3-6

Not only can Landsat and other space observation systems efficiently monitor transient ecological maladies such as insect defoliation (as you saw in the Pennsylvania "exam") but, similar to our clearcutting examples we have already examined, these systems can follow long term changes in resource use, such as strip mining and the progress of land reclamation (again, in the Pennsylvania case study).

Many ecological problems (some are actual disasters) occur within very short time frames. Except in isolated wilds, forest fires usually burn for a few days until brought under control. A fire in the Fishlake National Forest near Beaver, Utah (about 60 km [40 miles] ESE of the White-Mountain scene you will examine in Section 5), was imaged by the NOAA-9 AVHRR (1 km ground resolution), on June 17, 1996.

This false color composite was made by assigning the channel 1 image to red, channel 2 to green, and channel 3 to blue. In this version, the grayish smoke shows as yellow and the fire, at the head of the smoke column, appears as bright blue. Major fires are commonly imaged by meteorological and land-observing satellites, and the extent of the burn damage is easily assessed afterwards by the dark patterns in the visible bands. These dark patterns are usually evident as bright patches in thermal imagery because of the blackbody effect (see Section 9).

On a greater scale of view, forest fires in three separate areas, one in Borneo, north of Java, and two in Sumatra, in 1997 were imaged by NOAA-14 (at a resolution of 4 km [2.5 miles]), as seen here:

Natural catastrophes, such as volcanic eruptions, are a much feared and often unavoidable calamity to people living in proximity. We can monitor the eruption and its aftereffects by satellite (see page 12-5). For instance the 1980 eruption of Mt. St. Helens, in Washington State, is quite familiar to Americans (also on page 12-5) The gradual plant regrowth in the ash deposits around the site has been followed over the years in Landsat imagery.

Overseas, major eruptions affecting populations seem to occur every few years. The June 15, 1991, event at Mt. Pinatubo on the island of Luzon in the Philippines is a classic example. After almost 600 years of dormancy, earthquakes around it began in April of 1991. Their increase prompted evacuation of more than 50,000 people. Just three hours before the main eruption, the AVHRR on NOAA 7 imaged the billowing clouds of water vapo,r mixed with ash, that foretold the impending climax. This three-band color composite shows the eruption material interspersed with clouds associated with Typhoon Yunya (left image). The peak eruption (right image), of the violent Plinian type, sent pumice, ash,

and chemical aerosols above 12,200 m (40,000+ ft), leaving behind a 2 km (1.2 mi) wide caldera (cavity) that displaced most of the summit. Sulphuric acid was a major constituent of the aerosols that spread worldwide, affecting the weather and climate for the next five years. In the immediate vicinity, ash deposits surrounded the volcano for 20 km, destroying most of the heavy forests. That is evident in this before and after pair of images, obtained by the Multispectral Electronic Self-Scanning Radiometer (MESSR) on the Japanese MOS (Marine Observation Satellite) operated by NASDA.

Two final examples, show water pollution in remote sensing images. The image below, made by the Coastal Zone Color Scanner (CZCS) on Nimbus 7 (see Section 14), shows the shallow shelf region of the Atlantic Ocean in the Long Island Bight, south of New York City. For decades, a train of barges has carried waste materials (euphemism for garbage) several times a week to an offshore dumping site. The barges move in a zig-zag pattern that leaves a distinctive curlicue pattern of pollution, which is readily apparent in this color composite image.

Another dreaded ocean contaminant is oil spills. Oil is noted for "calming the waters", i.e., reducing the degree of wave disturbance, making it visible in certain bands. Multiple oil leaks in the Arabian Sea, west of Bombay, India, are obvious in the SIR-C radar image below. Their darkness is not due to oil the color or light absorption but to the decreased backscatter of the radar beam (see Section 8 for the principles).

We will illustrate other agricultural, forestry and ecological applications in this tutorial (several appear in Sections 6, 16, and 17). The text will introduce more of the possibilities that space imagery affords in monitoring and inventorying crops, grasslands, forests, wetlands, and other ecological niches. But, now let's take leave of the countryside and rural settings to examine another contrasting use cities and other land-use patterns, as satellite sensors can depict them.

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