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(This passage is adapted from an article published in 1981.)
The term "remote sensing" refers to the techniques of
measurement and interpretation of phenomena from a dis-
tance. Prior to the mid-1960's the interpretation of film
images was the primary means for remote sensing of the
(5) Earth's geologic features. With the development of the
optomechanical scanner, scientists began to construct digital
multispectral images using data beyond the sensitivity range
of visible light photography. These images are constructed
by mechanically aligning pictorial representations of such
(10)phenomena as the reflection of light waves outside the vis-
ible spectrum, the refraction of radio waves, and the daily
changes in temperature in areas on the Earth's surface.
Digital multispectral imaging has now become the basic
tool in geologic remote sensing from satellites.
(15) The advantage of digital over photographic imaging is
evident: the resulting numerical data are precisely known,
and digital data are not subject to the vagaries of difficult-
to-control chemical processing. With digital processing, it is
possible to combine a large number of spectral images. The
(20)acquisition of the first multispectral digital data set from
the multispectral scanner (MSS) aboard the satellite
Landsat in 1972 consequently attracted the attention of the
entire geologic community. Landsat MSS data are now
being applied to a variety of geologic problems that are
(25)difficult to solve by conventional methods alone. These
include specific problems in mineral and energy resource
exploration and the charting of glaciers and shallow seas.
A more fundamental application of remote sensing is to
augment conventional methods for geologic mapping of
(30)large areas. Regional maps present compositional, struc-
tural, and chronological information for reconstructing
geologic evolution. Such reconstructions have important
practical applications because the conditions under which
rock units and other structural features are formed influence
(35)the occurrence of ore and petroleum deposits and affect the
thickness and integrity of the geologic media in which the
deposits are found.
Geologic maps incorporate a large, varied body of spe-
cific field and laboratory measurements, but the maps must
(40)be interpretative because field measurements are always
limited by rock exposure, accessibility and labor resources.
With remote-sensing techniques it is possible to obtain
much geologic information more efficiently than it can be
obtained on the ground. These techniques also facilitate
(45)overall interpretation. Since detailed geologic mapping is
generally conducted in small areas, the continuity of
regional features that have intermittent and variable expres-
sions is often not recognized, but in the comprehensive
views of Landsat images these continuities are apparent.
(50)However, some critical information cannot be obtained
through remote sensing, and several characteristics of the
Landsat MSS impose limitations on the acquisition of diag-
nostic data. Some of these limitations can be overcome by
designing satellite systems specifically for geologic pur-
(55)poses; but, to be most effective, remote-sensing data must
still be combined with data from field surveys and labora-
tory tests, the techniques of the earlier twentieth century.
17.By using the word "interpretative"in line 40, the
author is indicating which of the following?
(A) Some maps are based more on data from aerial
photography than on data from field operations.
(B) Some maps are based almost exclusively on labor-
atory measurements.
(C) Some maps are based on incomplete data from
field observations.
(D) Some maps show only large geologic features.
(E) Some maps can be three-dimensional.
18. With which of the following statements about geologic
mapping would the author be most likely to agree?
(A) Geologic mapping is basically an art and not a
science.
(B) Geologic mapping has not changed significantly
since the early 1960's.
(C) Geologic mapping will have limited practical
applications until remote-sensing systems are
perfected.
(D) A developmental milestone in geologic mapping
was reached in 1972.
(E) Without the present variety of remote-sensing
techniques, geologic mapping could not be done.
19. According to the passage, measurements of which of
the following can be provided by the optomechanical
scanner but not by visible-light photography?
(A) The amount of visible light reflected from oceans
(B) The density of foliage in remote areas on the
Earth's surface
(C) Daily temperature changes of areas on the Earth's
surface.
(D) The degree of radioactivity emitted by exposed
rocks on the Earth's surface.
(E) Atmospheric conditions over large landmasses
20. It can be inferred from the passage that a major disad-
vantage of photographic imaging in geologic mapping
is that such photography
(A) cannot be used at night
(B) cannot focus on the details of a geologic area
(C) must be chemically processed
(D) is always enhanced by digital reconstruction
(E) cannot reflect changes over extended periods of time
21. It can be inferred from the passage that Landsat images
differ from conventional geologic maps in that Landsat
images
(A) reveal the exact size of petroleum deposits and ore
deposits
(B) indicate the continuity of features that might not
otherwise be interpreted as continuous
(C) predict the movements of glaciers
(D) provide highly accurate data about the occurrence
of mineral deposits
(E) reveal the integrity of the media in which petro-
leum deposits and ore deposits are found
22. The passage provides information about each of the
following topics EXCEPT
(A) the principal method of geologic remote sensing prior to the mid-1960's
(B) some of the phenomena measured by digital multi-spectral images in remote sensing
(C) some of the practical uses of regional geologic maps
(D) the kinds of problems that are difficult to solve solely through conventional methods of geologic mapping
(E) the specific limitations of the Landsat multi-spectral scanner
23. The passage suggests which of the following about the "conventional methods" mentioned in line 29?
(A) They consist primarily of field surveys and laboratory measurements.
(B) They are not useful in providing information necessary for reconstructing geologic evolution
(C) They have rarely been used by geologists since 1972.
(D) They are used primarily to gather compositional information about geologic features.
(E) They are limited primarily because of difficulties involved in interpreting film images.
