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You become cognizant of areas occupied by hills and low mountains because of a distinctive light-dark pattern that gives the impression of an irregular surface - one of some relief. Map makers achieve this effect by using gray-tone shading that "tricks" the mind into perceiving the impression of undulating topography. In this image, as in aerial photographs, the same effect is produced by the variations in surface illumination related to the interplay of the angle of solar irradiation and the direction and inclination of slopes. Slopes (as at d whose faces incline toward the sun, i.e., are more likely to be at high angles to solar rays, will reflect a high percentage of light back towards the sensor on the spacecraft (or camera on an airplane). These surfaces will appear brighter (lighter tones). Slopes (e) that lie away from the sun, i.e., have faces that are at lower angles relative to incoming radiation, will reflect much of that light away from the sensor and thus appear variably darker, that is, they are more or less in shadow. These generally are rendered in medium gray patterns, within which other patterns, representing specific features or objects, may be discernible owing to tonal contrasts (look at f. If the slopes are steep, and/or the sun angle is lower, the slopes tend to progressively darker (approaching black tones in the imagery).

In this subscene, most slopes in this and the other bands are very light toned. This implies a scarcity of growing (green) vegetation and/or possible bare rock surfaces. In this Fall image, the hills are in their late stage brown phase and the influence of chlorophyll on reflectance is low. At higher elevations vegetation is greener and denser, as at (g), because more moisture is available (due to condensation of fog and local geology/topography). This denser vegetation appears in darker tones in band 1 and band 3 because chlorophyll absorbs blue and red wavelengths. In band 2 the green vegetation is only slightly darker than the dry grass in adjacent areas because chlorophyll reflects green most strongly in that part of the visible spectrum. As was evident in oblique air photo and the ground based photo , bedrock of granite is exposed in places within the scene. The best example, at (h), is Morro Rock itself, which is displayed in this image as a bright (sun-facing surface) spot just below a dark spot (its shadow).

Two patterns correlate with actively-growing vegetation (which appear as somewhat darker tones in the first three TM bands [especially 1 and 3] ).At (i), long thin lines of dark tones correspond to vegetation, mostly trees and bushes, that cluster along the banks of narrow, probably intermittent, streams in the hills. Other, similar tones (as at j) in more irregular patterns are usually associated with copses and irregular stands of trees, some of which are noticeable in the aerial oblique photograph. At (k) and elsewhere, primarily in the valleys and lowlands, rectangular to somewhat irregular sub-equant to elongate dark-toned patterns are the expression of agricultural field plots containing actively growing crops (inspect the aerial oblique photograph again). Other irregular patterns in these settings, as at (l), may be fields of brush or scrub (see foreground in this photo) or even wetlands. Still other darker-toned areas, as at (m) and (n), that spread over wider expanses are likely either open uncultivated or now barren fields or lowlands that are sporadically covered with natural vegetation.

The large, roughly triangular area on which (o) is centered lies at the end of the small river (p) that courses across the terrain in the valley through which Highway 1 passes. At least part of this feature is a delta that has built up into Morro Bay. The vegetation it supports, rendered in moderately dark tones in this band, is characteristic of wetlands that develop as saltwater marshlands along a coast.

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Code 935, Goddard Space Flight Center, NASA
Written by: Nicholas M. Short, Sr. email: nmshort@epix.net
and
Jon Robinson email: Jon.W.Robinson.1@gsfc.nasa.gov
Webmaster: Bill Dickinson Jr. email: rstwebmaster@gsti.com
Web Production: Christiane Robinson, Terri Ho and Nannette Fekete
Updated: 1999.03.15.