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Two examples of the thermal band (TM 6) on Landsat introduce the appearance of surfaces showing variations in temperature. The first is the familiar White Mountain scene studied in Section 5. Variations in temperature during a daytime pass over the site do not coincide with some of the alteration and rock type features but some correlation with dark surfaces is evident. A nighttime pass over Lake Erie exposes the expected thermal state of water as a heat retainer during land cooling.


White Mountain Thermal Features

Refresh your memory of the White Mountain scene, as recalled here in a color composite.

Color composite Landsat TM image of White Mountain, Utah.

Three broad geological categories dominate the scene: dark volcanics, alteration products derived from these, and the limestone mountain. The Landsat thermal Band 6 image greatly simplifies the apparent

Landsat thermal Band 6 image of White Mountain.

scene content. The warmest areas (shown in lighter tones in keeping with the convention that hot areas display in whites and light grays, and cold areas are in dark tones) are from the volcanics, most of which are dark basalts. These rocks are imperfect black bodies that absorb much of the solar radiation and re-emit it as strong radiators. The altered zones appear mostly in dark tones, implying that they absorb less solar energy, so that they have lower radiant temperatures. The limestones, in the field grayish surfaces with superficial brownish-red alteration, appear as moderately light tones, which are hard to distinguish from the volcanic expressions.

Lakes Erie/Ontario TM 6

For experimental reasons, operators activate Thematic Mapper Band 6 on Landsat occasionally at night to obtain thermal images. One example, a full scene acquired at 9:32 P.M. on August 22, 1982

Landsat TM thermal Band 6 image of Lake Erie and western Lake Ontario, August 22 1982.

shows the familiar east half of Lake Erie, PA, and the western part of Lake Ontario, NY. The land appears moderately cool (darker tones), with little detail, although the cities of Buffalo, NY (east tip of Lake Erie), and Toronto (top center) and Hamilton, Ontario (west end of Lake Ontario; locally hot because of steel mill effluents) may be discernible on a computer monitor from street patterns and slightly lighter (warmer) tones. A mottled pattern of variably warmer bands characterizes Lake Ontario. These bands relate to thermal overturning effects (thermoclines), which are possible in this deeper (237 m [777 ft]) lake. Lake Erie is uniformly "hot" because its shallowness (less than 67 m [220 ft]) inhibits this type of circulation. Warm rivers, such as the Niagara connecting the two lakes, stand in contrast to the land.


9-12
: Where is Niagara Falls? Any visual clues to where it should be? Is there anything in the imagery that might give you a clue as to which way the Niagara River is flowing? Is Toronto larger than Buffalo? What tone do the few clouds in the scene have? How might clouds be distinguish from smoke in this night scene? ANSWER


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Primary Author: Nicholas M. Short, Sr. email: [email protected]