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ANSWERS


7-1: The mosaic here has several of the problems inherent to aerial products. The amount of sidelap was minimal, so the pictures could not be trimmed. The inherent average gray levels darken from the central area of each picture, such that the boundaries between photos are emphasized. Exact joins are difficult owing to edge distortions. This gives the mosaic an overall blocky or patchwork appearance that detracts somewhat from its presentation of the feature content. With great care and expense, photo processing can minimize this tonal vignetting, yielding a photomosaic of the quality we saw for the Los Angeles MSS scene on page 4-1 (and shown again on the next page). BACK


7-2: The ERTS image lacks the undesirable vignetting (change in tonal levels going from center to edge) found in the uncontrolled U-s mosaic. I have never seen a vignetting effect in a Landsat image; this angular fall down in radiance and hence gray levels going outward towards the edge is compensated for in the image production program. BACK


7-3: Several reasons: At the time there were few ERTS (Landsat) images as yet acquired; the GE photolab had little experience at this stage in processing and printing such that the color level and balance were uniform; there was unfamiliarity with the digital image processing programs available to operate on ERTS imagery; this mosaic was made by simple overlay rather than by butt joints (side by side; no overlap). BACK


7-4: If you look carefully, you will see slightly lighter or darker average tones in pictures located both within the Mojave Desert and in the mountains around Los Angeles. Not conspicuous, but an indication that AeroService had trouble in getting exact tonal matches. Some parallel dark banding in the Mojave Desert may be a processing artifact. BACK


7-5: Of course, most features in the black and white 15 m panchromatic images are sharper. But to me the singlemost striking pattern is the more pronounced street patterns. BACK


7-6: Find the Salton Sea. That image and the one above both are lighter in average tone than the areas to their west. In fact you can probably see the upper image (showing block fault mountains in the Mojave Desert) as a distinct square. This is a single orbital strip taken at a different time in which different average radiances were sensed, and the photographic compensation doesn't quite allow a near-perfect tonal match with the images on either side. Although subtle, this seems to persist in the other images making up that orbital set. BACK


7-7: In the DEM map, the only dark tones are related to the artificially added shadow effects; in the Landsat mosaic shadows are present and show where topographic relief is strong, but there are tonally distinctive gray levels associated with vegetation, water, and other types of features that differ in their reflectances. BACK


7-8: There is no conspicuous blue in the scene, because there was no blue band on ERTS. However, a blue filter was applied to the green band, with little effect. The green of the vegetation was produced by projecting IR band 6 through a green filter. BACK


7-9: The MODIS image was acquired during a time when most of Alaska was blanketed by snow, giving the white tones that dominate the image. BACK


7-10: The broad band of dark red covering most of Brazil, into Bolivia and Colombia, corresponds to the Amazon Basin forests. Other heavily forested areas also show as red. BACK


7-11: Broad valleys cutting into the Alps suggest glaciation in the past (a few glaciers still present and active). These valleys are not in the Apennines, indicating that they were not high enough in the past (and today) for cold temperatures to have allowed extensive glaciation to have taken place. BACK


7-12: Alexander the Great (356 to 323 BCE) was the son of King Philip of Macedon (northern part of Greece) who received much of his formal education from Aristotle. Alexander was a military genius who began his conquests while still a teenager. By the time of his premature death at 32, he had built the greatest empire (in area) prior to the Roman Empire some 200 years later. On his last expedition he moved into the Indian subcontinent, conquering today's Afghanistan and (in part) Pakistan, reaching the Indus River. Tiring of this constant warfare, and becoming somewhat dissipated, he decided to return his army ultimately to Macedon, after a planned entry into parts of Arabia not then under his control. To toughen the army, he decided to forego use of ships of transport and march instead into what is now southern Iran (Persia then). But, he did not anticipate the harsh, rugged mountains and deserts they had to cross - these show up well in the mosaic and the next image below. It exhausted his men and he himself suffered with them, becoming ill. He got as far as Babylon (south of today's Baghdad), worsened and died (one theory speculates that he was poisoned). Afterwards, his family and his generals gradually lost their hold on the empire, much of which was reconquered by the Romans. BACK


7-13: Look for a roundish blue lake in the first image, that appears again in the next two images. Al-Qaeda personnel moved south and east of this valley into high and desolate mountains. BACK