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Mapping the Harbor Floor With Sound

8th grade nonfiction passage about hydrographic surveying: 258 words, seven questions, an answer key and vocabulary.

8th grade nonfiction hydrographic surveying 258 words

Mapping the Harbor Floor With Sound

Ships need to know what lies beneath them, yet the bottom of a harbor is hidden under water that is too dark and muddy to see through. The people who map it are hydrographic surveyors, and their main tool is sound.

A survey boat carries a sonar unit fixed to its hull. The unit sends a pulse of sound straight down, and the pulse bounces off the bottom and returns. Because sound travels through water at a known speed, the time the trip takes reveals the depth. Modern units send out many pulses in a fan shape, so a single pass of the boat measures a wide strip of the bottom rather than a single line.

Depth alone is not useful without a location. A satellite positioning receiver on the boat records exactly where each measurement was taken. The boat then travels back and forth in careful parallel lines, like someone mowing a lawn, until the whole area is covered.

Surveyors must also correct for the tides. Water that is deep at high tide may be dangerously shallow hours later, so the surveyors record the water level and adjust every depth to match a standard reference level. Without this step, charts from different times would not agree.

The results become nautical charts, the maps that captains use to stay in safe channels and avoid sandbars and wrecks. Because storms and currents move sand and mud, the work is never really finished. Channels are surveyed again regularly, and a chart is only trustworthy while it is up to date.

Questions

  1. What is the main tool of a hydrographic surveyor? in the text

  2. How does the sonar unit find out how deep the water is? in the text

  3. Why does the boat travel back and forth in parallel lines? in the text

  4. Why must surveyors correct for the tides? in the text

  5. What do captains use nautical charts for? in the text

  6. Why is a depth reading not very useful without a location? think about it

  7. Why are the same channels surveyed again and again? think about it

Words to know

hydrographic
having to do with measuring and mapping bodies of water
sonar
a device that uses sound to find objects or measure depth under water
hull
the main body of a boat that sits in the water
tides
the regular rising and falling of the sea
nautical
having to do with ships and sailing
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 232 words · Flesch-Kincaid grade 3.9

Ships need to know what is under them. But the bottom of a harbor is hidden under dark, muddy water. Hydrographic surveyors map it. Their main tool is sound.

A survey boat has a sonar unit fixed to its hull. The unit sends a pulse of sound straight down. The pulse bounces off the bottom and comes back. Sound moves through water at a known speed. So the time the trip takes tells the depth. New units send many pulses in a fan shape. One pass of the boat measures a wide strip of the bottom, not just one line.

A depth is not useful without a place. A satellite receiver on the boat records where each measurement was taken. The boat goes back and forth in parallel lines, like someone mowing a lawn, until the whole area is done.

Surveyors must also fix for the tides. Water that is deep at high tide may be too shallow later. So surveyors record the water level and adjust each depth to a standard level. If they did not, charts from different times would not agree.

The results become nautical charts. Captains use them to stay in safe channels and avoid sandbars and wrecks. Storms and currents move sand and mud, so the work is never done. Channels are surveyed again and again. A chart is only good while it is up to date.

▲ This passage · 258 words · Flesch-Kincaid grade 8.1

Ships need to know what lies beneath them, yet the bottom of a harbor is hidden under water that is too dark and muddy to see through. The people who map it are hydrographic surveyors, and their main tool is sound.

A survey boat carries a sonar unit fixed to its hull. The unit sends a pulse of sound straight down, and the pulse bounces off the bottom and returns. Because sound travels through water at a known speed, the time the trip takes reveals the depth. Modern units send out many pulses in a fan shape, so a single pass of the boat measures a wide strip of the bottom rather than a single line.

Depth alone is not useful without a location. A satellite positioning receiver on the boat records exactly where each measurement was taken. The boat then travels back and forth in careful parallel lines, like someone mowing a lawn, until the whole area is covered.

Surveyors must also correct for the tides. Water that is deep at high tide may be dangerously shallow hours later, so the surveyors record the water level and adjust every depth to match a standard reference level. Without this step, charts from different times would not agree.

The results become nautical charts, the maps that captains use to stay in safe channels and avoid sandbars and wrecks. Because storms and currents move sand and mud, the work is never really finished. Channels are surveyed again regularly, and a chart is only trustworthy while it is up to date.

■ Harder · 291 words · Flesch-Kincaid grade 9.2

Ships need to know exactly what lies beneath them, yet the bottom of a harbor is concealed beneath water that is far too dark and muddy to see through. The specialists who map it are hydrographic surveyors, and their principal tool is sound.

A survey boat carries a sonar unit fixed securely to its hull. The unit sends a pulse of sound straight downward, and the pulse bounces off the bottom and returns to the boat. Because sound travels through water at a known speed, the time that the round trip takes reveals the depth. Modern units transmit many pulses in a wide fan shape, so a single pass of the boat measures an entire broad strip of the bottom rather than one narrow line.

Depth alone is of little use without a location. A satellite positioning receiver on the boat records precisely where each measurement was taken. The boat then travels back and forth in careful parallel lines, rather like someone mowing a lawn, until the whole area has been covered.

Surveyors must also correct for the tides. Water that is deep at high tide may be dangerously shallow only a few hours later, so the surveyors record the water level and adjust every depth to match a standard reference level. Without this step, charts made at different times of day would not agree with one another.

The results are turned into nautical charts, the maps that captains consult to remain in safe channels and to steer clear of sandbars and wrecks. Because storms and currents continually move sand and mud, the work is never truly finished. Channels are surveyed again at regular intervals, and a chart can be trusted only for as long as it remains up to date.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put hydrographic, sonar, hull, tides and nautical on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 3 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 6 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Mapping the Harbor Floor With Sound"?

It was written for 8th grade. It has 258 words and works out to a Flesch-Kincaid grade level of about 8.1. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are seven. 5 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 3 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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