2.6. 波段信息特性1¶
Now look at TM band 7
which is centered near 2.2 µm in the reflected IR band. The image has
some similarities to bands 1 and
4 but there are several obvious differences.
All water is now completely dark (no signs of reflecting sediments).
Only faint traces of the wave breakers remain. The beach sand is
somewhat brighter than in band 4. The sun-facing slopes in the hills
seem to be moderately brighter than in the other two bands. A bit more
detail emerges in the partially shadowed slopes. Some areas, such as
crop fields, that were quite bright in 4, are again dark as in 1. The
mystery area near **s** shows some internal
pattern or structure, including elongate strips of lighter and darker
that provides another clue to its identity. The towns have a more
diffuse street pattern and are generally darker overall. The extraction
pits so prominent in band 1 are almost impossible to pick out in band 7.
Next, we will examine
band 6 - the emitted thermal band (10.5- 12.5 µm). Remember that the
spatial resolution for this band is 4 times coarser - 120 m compared
with 30 m - than the other bands. The effect of this reduced resolution
is immediately evident in viewing the subscene in that many details
discernible in the other bands tend to be "smeared" out in this one. Yet
the main elements you have come to know from bands already scanned are
still readily recognized.
事实上，丘陵地形更像是一个三维再现，因为面对太阳的斜坡和阴影较冷的斜坡之间的强烈对比，现在呈现出相当均匀、黑暗、阴影的模式。这一对比给这一部分的场景提供了优越的地形起伏感，也突出了山谷地区。
一些中灰色调，如 **v** ，表示草地覆盖层的冷却效果。一个非常明亮但孤立的点 **h** 与莫罗岩相吻合，莫罗岩具有裸露的岩石表面和陡峭的斜坡，吸收太阳辐射并加热，从而释放热能。这些城镇被标为黄色，灰色水平适中，这表明它们比自然的山坡要凉快一些，但在市中心地区有几个较浅的色调，通常比居住区（有草坪和更多的树木）暖和。
1-8 Speculate on why the upper right corner area of TM 6 is notably darker. `ANSWER <answer.html#1-8>`__
在白天的热红外图像中，水的热容量明显高于陆地上大多数干燥的物质，它比大多数接受阳光直射的陆地表面更冷。（第9节讨论了热成像，并回顾了在不同辐射温度下色调特征显示的原则。）水的热容量在这幅图像中很明显，在这幅图像中，海洋和海湾有中等程度的深灰色水平。如果这幅图像是在夜间拍摄的，那么水将以比邻近陆地更轻的色调来表达，因为它保留了大量的内部热量。另一方面，土地看起来更暗，因为它辐射吸收的太阳能，从而冷却到比水低的辐射温度。
太平洋上显示的稍浅灰色区域的不均匀图案在这里并不真实，而是与传感器特性相关的类似噪声的伪影。有一种模式是反常的和有意义的。在摩罗岩的北部和西部，海水中呈现出一种不规则的图案，色调较浅，像一股沉积物从海岸进入海洋。这正是我们对附近发电厂的期望 **t** ）它把加热后的废水倒入附近的死水中。