Comprehension
(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 distance. Prior to the mid-1960's the interpretation of film images was the primary means for remote sensing of the 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 phenomena as the reflection of light waves outside the visible 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.

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 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 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 large areas. Regional maps present compositional, structural, 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 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 specific field and laboratory measurements, but the maps must 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 overall interpretation. Since detailed geologic mapping is generally conducted in small areas, the continuity of regional features that have intermittent and variable expressions is often not recognized, but in the comprehensive views of Landsat images these continuities are apparent. However, some critical information cannot be obtained through remote sensing, and several characteristics of the Landsat MSS impose limitations on the acquisition of diagnostic data. Some of these limitations can be overcome by designing satellite systems specifically for geologic purposes; but, to be most effective, remote-sensing data must still be combined with data from field surveys and laboratory tests, the techniques of the earlier twentieth century.
Question: 1

By using the word "interpretative" in line 40, the author is indicating which of the following?

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When a question asks for the meaning of a word in context, look for signal words like "because," "since," or "due to" in the surrounding text. These words often point directly to the definition or justification you need.
Updated On: Oct 4, 2025
  • Some maps are based more on data from aerial photography than on data from field operations.
  • Some maps are based almost exclusively on laboratory measurements.
  • Some maps are based on incomplete data from field observations.
  • Some maps show only large geologic features.
  • Some maps can be three-dimensional.
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The Correct Option is C

Solution and Explanation

Step 1: Understanding the Concept:
This is a "word in context" question. We need to understand why the author chose the word "interpretative" to describe geologic maps. The explanation is usually provided in the sentence itself or the surrounding sentences.
Step 2: Key Formula or Approach:
The passage states, "...the maps must be interpretative because field measurements are always limited by rock exposure, accessibility and labor resources." The word "because" explicitly gives the reason. We need to find the answer choice that best paraphrases this reason.
Step 3: Detailed Explanation:
- The reason given is that field measurements are "limited." This means the data gathered on the ground is inherently incomplete.
- When data is incomplete, geologists must make educated guesses or interpretations to fill in the gaps and draw a coherent map.
- (C) This option perfectly captures this idea. "Incomplete data from field observations" is a direct paraphrase of measurements being "limited by rock exposure, accessibility and labor resources."
- (A) and (B) focus on the source of the data, but the key issue raised by the author is the incompleteness of the data, whatever its source.
- (D) and (E) describe characteristics of some maps but are not the reason the author gives for why they are "interpretative."
Step 4: Final Answer:
The author uses the word "interpretative" to indicate that geologists must infer or deduce the full picture from the partial data they are able to collect in the field.
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Question: 2

With which of the following statements about geologic mapping would the author be most likely to agree?

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For "author would agree" questions, look for statements that are strongly and directly supported by specific phrases or sentences in the text. Be wary of options with extreme words like "only," "not," "never," or "always," as they are often too strong to be fully supported.
Updated On: Oct 4, 2025
  • Geologic mapping is basically an art and not a science.
  • Geologic mapping has not changed significantly since the early 1960's.
  • Geologic mapping will have limited practical applications until remote-sensing systems are perfected.
  • A developmental milestone in geologic mapping was reached in 1972.
  • Without the present variety of remote-sensing techniques, geologic mapping could not be done.
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The Correct Option is D

Solution and Explanation

Step 1: Understanding the Concept:
This question asks us to identify a statement that aligns with the author's overall perspective on geologic mapping as presented in the passage.
Step 2: Key Formula or Approach:
We need to evaluate each statement against the information and tone of the passage. The correct answer will be directly supported by the text.
Step 3: Detailed Explanation:
- Let's look for evidence for each statement.
- (D) The passage explicitly states that the acquisition of the first multispectral data from the Landsat satellite in 1972 "attracted the attention of the entire geologic community." This is presented as a major turning point in the field. This language strongly supports the idea that 1972 was a "developmental milestone."
- (A) This is too extreme. The author describes mapping as incorporating "a large, varied body of specific field and laboratory measurements," which clearly makes it a science, even if it has an "interpretative" component.
- (B) This is directly contradicted by the passage, which describes the significant shift from film photography to digital multispectral imaging starting in the mid-1960s.
- (C) The author states that mapping already has "important practical applications" (line 32). They are not waiting for perfected systems.
- (E) This is too strong. The author presents remote sensing as a tool that "augments" and "facilitates" conventional methods, not as a prerequisite without which mapping "could not be done."
Step 4: Final Answer:
The author highlights the 1972 Landsat data acquisition as a pivotal event that captured the attention of the entire geologic community, marking it as a significant milestone.
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Question: 3

According to the passage, measurements of which of the following can be provided by the optomechanical scanner but not by visible-light photography?

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"According to the passage" questions are often the most straightforward. The answer is usually stated almost verbatim in the text. Scan for the keywords from the question ("optomechanical scanner," "visible-light photography") to locate the relevant sentence quickly.
Updated On: Oct 4, 2025
  • The amount of visible light reflected from oceans
  • The density of foliage in remote areas on the Earth's surface
  • Daily temperature changes of areas on the Earth's surface
  • The degree of radioactivity emitted by exposed rocks on the Earth's surface
  • Atmospheric conditions over large landmasses
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The Correct Option is C

Solution and Explanation

Step 1: Understanding the Concept:
This is a detail-oriented question asking us to identify a specific capability of the optomechanical scanner that traditional photography lacks.
Step 2: Key Formula or Approach:
We need to find the section of the passage that describes the new phenomena measured by optomechanical scanners and see which of the options is listed there.
Step 3: Detailed Explanation:
- Lines 8-13 describe how these new images are constructed. It states they represent "such phenomena as the reflection of light waves outside the visible spectrum, the refraction of radio waves, and the daily changes in temperature in areas on the Earth's surface."
- The question asks what can be measured by the scanner but not by visible-light photography. "Daily changes in temperature" (thermal data) is one of the phenomena listed as being "beyond the sensitivity range of visible light photography."
- (C) This option is a direct quote from the passage.
- (A) Visible light reflection is what visible-light photography does capture.
- (B), (D), and (E) are not mentioned in this part of the passage as being measured by the scanner.
Step 4: Final Answer:
The passage explicitly lists "daily changes in temperature" as one of the types of data that optomechanical scanners can capture, which are beyond the capabilities of standard visible-light photography.
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Question: 4

It can be inferred from the passage that a major disadvantage of photographic imaging in geologic mapping is that such photography

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In passages that contrast an old method with a new one, look for sentences that explicitly state the "advantages" of the new method. The flip side of these advantages will be the inferred "disadvantages" of the old method.
Updated On: Oct 4, 2025
  • cannot be used at night
  • cannot focus on the details of a geologic area
  • must be chemically processed
  • is always enhanced by digital reconstruction
  • cannot reflect changes over extended periods of time
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The Correct Option is C

Solution and Explanation

Step 1: Understanding the Concept:
This is an inference question asking about a disadvantage of the older, photographic method. The passage contrasts photography with the newer digital method. The disadvantages of the old method are often presented as the advantages of the new one.
Step 2: Key Formula or Approach:
Find the part of the passage where the author compares digital and photographic imaging. The text will state an advantage of digital imaging which, by implication, is a disadvantage of photographic imaging.
Step 3: Detailed Explanation:
- Lines 15-18 state the "advantage of digital over photographic imaging."
- It says: "...digital data are not subject to the vagaries of difficult-to-control chemical processing."
- If digital data is advantageous because it is not subject to chemical processing, we can infer that photographic data is subject to chemical processing, and that this process is a disadvantage (it's "difficult-to-control").
- (C) This option correctly identifies this inferred disadvantage.
- (A), (B), and (E) are not mentioned in the passage as disadvantages.
- (D) is incorrect; the passage implies digital data can be used for reconstruction, but not that photography is always enhanced this way.
Step 4: Final Answer:
The passage highlights the benefit of digital data being free from the problems of chemical processing, which allows us to infer that the necessity of chemical processing is a major disadvantage of the older photographic method.
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