Sharp-eyed satellite begins to pay off

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Landsat-D - a satellite so sharp-eyed it should distinguish between hemlock and fir trees - is bringing new precision to the task of monitoring Earth's resources from space.

Scientists have only recently begun sifting the images being sent back by the satellite since it was launched last July. Already they say they are impressed with the performance of its Earth-scanning sensors.

Like its three predecessors, the Landsat-D sends back ''pictures'' of large patches of the earth from its 438-mile-high orbit. But the increased resolution of these views makes them more useful.

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A sophisticated sensor called a thematic mapper can distinguish objects less than 100 feet in size. That compares with a resolution of 260 feet for the earlier satellites. Landsat-D images of the capital of the United States are sharp enough to show the shadow of the Washington Monument.

For timber companies, such precision means better woodland surveillance. ''With the first three Landsats, everything looked fuzzy and milky,'' says G. Robinson Barker, manager of the St. Regis Paper Company's Forest Resource Information System. ''But now we are getting much better definition.''

Among those who may gain the most from the new Landsat data are energy and mineral companies. Industrial geologists have profited from previous Landsat missions. But the scanners on the latest spacecraft are better tailored to their needs.

The satellite can pick up data from several new spectral bands in the infrared region. These should reveal subtle differences in mineral-bearing clays. As it is, exploration companies have been relying more and more on ''space prospecting.'' By combining satellite data with information gathered by aircraft and on the ground, they can better pinpoint promising areas or, what is equally important, avoid unpromising regions.

Space data do not guarantee pay dirt. ''It's a supplementary type of data set ,'' explains Raymond Sadowski, a geophysicist with Amax Exploration Inc. Nevertheless, he adds, ''It gives us a new look at old areas.'' This is why ''there is an increasing emphasis on remote sensing throughout the industry,'' says Floyd Sabins, a senior research associate at the Chevron Oil Field Research Company.

Landsat-D's performance also sharpens concern over the fate of this useful system. The Reagan administration has yet to decide who should manage it. Some administration planners would like to spin off both Landsat and weather satellite operations to private industry. Until this issue is resolved, Landsat users cannot plan on using such satellite surveillance in the long term. This uncertainty puts a damper on the enthusiasm Landsat's technical performance has aroused. Warning: iron does burn

Cargoes of scrap iron are smoldering in ships' holds and flashing into fire when offloaded. The world's maritime industry has been ill prepared for the fact that, in some forms, iron burns.

Metal turnings, steel and iron chips, and spongy pellets of so-called direct-reduced iron can heat spontaneously, even ignite, when exposed to dampness and air. The report of a panel of the National Research Council (US National Academy of Sciences) warns that this hazard is rapidly increasing as steelmakers use more and more of these flammable materials.

Some 25 incidents are listed as occurring since 1968. Although there are probably other cases not cited, this is a small number. But the panel expects world trade in such material to increase fivefold by 1985 (from a base of less than 0.75 million metric tons). It is likely to double again between then and 1990.

Thus, the panel warns, there is an urgent need for understanding the technical nature of the danger and for working out procedures or regulations to counter it.

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