This convolves the thermal band, sensitive to emitted radiation, (with its lower resolution 120 m. pixels) with two infrared bands, 5 and 7 (with their 30 m. pixels). In this color composite generated with Idrisi, the thermal band image (check TM 6 again) exerts a dominating control. In the Idrisi mapping two colors - reds and blues - greatly outweigh any greens contributed by light tones in band 7. The reds largely represent the warmer surfaces, and the blues the cooler, as recorded in band 6. Note that the blues extend over a broader fraction of the slopes in the hills than might be expected from the shadow effects seen in other bands; in other words, the bulk of the back slope areas receiving less direct sunlight respond by returning less thermal radiation. However, some areas of blue that lie on the fore slopes are occupied by the uplands vegetation at g and the grasslands at v which offset the direct heating effect through cooling by evapotranspiration. Other areas supporting vegetation, as at y, and also along streams have dark red tones, not because they are hotter but their tonal expressions in 5 and 7 are darker (almost no blue or green inputs).

Both urban communities are characterized by several shades of red, with the street patterns showing through owing to their sharper definition in bands 5 and 7. This is in part due to the "urban island" thermal effect, the tendency of populated areas to be made warmer because of heat-absorbing materials (darker streets, tar-covered roofs, etc.), reduction in surface areas maintaining vegetation, and heat emitted from furnaces, air- conditioners, and other human activities. Fully perceptible is the thermal plume emanating from the power plant (t) but the ocean sediments introduce no noticeable effect.

Some areas seen as green in the composite include the beach bar and several of the extraction pits (u). These surfaces highly reflect in most bands, hence, their light tones in 5 and 7 combine the blues and greens assigned to these bands whereas their darkness in 6 (reflective materials do not heat up as much) leaves red out.

Lets now experiment briefly with combining one of the longer reflective IR bands (7, assigned to green) with the vegetation band TM 4 (blue) and the ocean water/sediment band TM 1 (expressed in red) as produced by the Idrisi Composite function which takes three 8 bit bands and converts it to a single 8 bit image that mimics the result of using the three bands to make a true 24 bit color image. The result is a colorful rendition that, in some respects, shows certain features to their best advantage.

Again, blues and reds are the prevailing colors, with greens subordinate. The blues almost totally correlate with vegetation which is made to stand out in sharp contrast to most areas that either lack this cover or now support dormant grasses, etc. (note the active grasslands in lighter blue). The reds are tied into three principal surface classes: the waves (note the bluish-purple tones within them, representing the band 4 contribution); the sediments; and the towns, with the red streets speckled by blues from local vegetation. The greens are confined mainly to some specific features that are relatively brighter in band 7 and darker in 1 and 4, including areas in the hills around Los Osos and some uncultivated areas (m) in valleys. Note scattered greens along the otherwise bright slopes.

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