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Questions and Answers
What is the method of determining the effective capacity of a body of water that requires a moderate degree of precision?
What is the formula for stream discharge?
What is the point on the celestial sphere directly beneath the observer?
What is the great circle of the celestial sphere where a plane, perpendicular to the plumb line at the place of observation and passing through the center of the earth, cuts the celestial sphere?
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What is the prolongation of the earth's polar axis?
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What is the method of locating sounding used where the boat proceeds to the intersection of any two range lines and soundings are taken?
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What is the formula for the area in each section using the Velocity-Area Method?
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What is the vertical line at the location of the observer which coincides with the plumb line and is normal to the observer's horizon?
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What is the primary purpose of hydrographic surveys?
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What is the term for the average height of the sea for all stages of the tide?
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What is the process of measuring the depth of a body of water at a particular point?
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What is the term for the half-daily cycle of rhythmic rise and fall of the surface of oceans, seas, lakes, bays, rivers, and other bodies of water?
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What is the term for an echo-sounding equipment that produces, transmits, and receives the sound waves, then calculates the depth based on the time interval of the echo's return?
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What is the term for the process of selecting the most suitable manner of executing a survey?
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What is the term for the remote sensing method that uses light in the form of a pulsed laser to measure ranges/distances to the Earth?
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What is the term for the method of finding the coordinates of a point in a body of water using three known control points?
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Study Notes
Hydrographic Surveys
- Hydrography is the process of gathering information about bodies of water and adjacent land areas.
Preliminary Steps
- Reconnaissance is a preliminary step in selecting the most suitable manner of executing a survey.
Tides and Water Levels
- A tide is the daily cycle of rhythmic rise and fall of the surface of oceans, seas, lakes, and other bodies of water due to gravitational attraction.
- Mean Sea Level is the average height of the sea for all stages of the tide.
Measuring Water Depth
- Soundings involve measuring the depth of a body of water at a particular point.
- Echo Sounding measures water depth by sending high-frequency sound waves to the water bed and timing their return.
- A Fathometer is an echo-sounding equipment that produces, transmits, and receives sound waves, calculating depth based on the time interval of the echo's return.
Positioning and Mapping
- An Electronic Positioning System uses unmodulated radio waves to determine distance between a ship and ground stations based on travel time of the waves.
- LIDAR (Light Detection and Ranging) is a remote sensing method that uses light to measure ranges/distances to the Earth.
Water Management
- Dredging is the process of widening, enlarging, cleaning, or deepening of channels in harbors, rivers, and canals.
- Dams are barriers built to hold back or impound water.
Surveying Methods
- Three Point Resection is a method to find the coordinates of a point in a body of water using three known control points.
- Stream Velocity is the speed of water flow in a channel.
- The Cross-section Method is used to determine the effective capacity of a body of water when a moderate degree of precision is required.
- The Contour Method is used to establish a reference base line or shore traverse to locate the water line and desired shore topography.
Formulas
- Stream discharge: Q = AV
- Area in each section using Velocity-Area Method: a = ½ (b1+b2) h
Locating Soundings
- Intersecting Range Lines is a method of locating soundings where the boat proceeds to the intersection of any two range lines and soundings are taken.
Astronomical Observations
Celestial Bodies
- Celestial Poles are points on the surface of the celestial sphere pierced by the extension of the earth's polar axis.
- Celestial Axis is the prolongation of the earth's polar axis.
- Zenith is the point where the plumb line at the place of observation projected above the horizon meets the celestial sphere.
- Nadir is the point on the celestial sphere directly beneath the observer, opposite to the zenith.
Observer's Reference Points
- Observer's Horizon is a great circle of the celestial sphere where a plane, perpendicular to the plumb line at the place of observation and passing through the center of the earth, cuts the celestial sphere.
- Observer's Vertical is a vertical line at the location of the observer, coinciding with the plumb line and normal to the observer's horizon.
Celestial References
- Celestial Equator is a great circle perpendicular to the polar axis of the celestial sphere, an extension of the plane of the earth's equator outward until it intersects the celestial sphere.
- Vertical Circle is a great circle passing through the observer's zenith and any celestial body, perpendicular to the horizon.
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Description
Test your knowledge of hydrographic surveys, reconnaissance, and oceanographic concepts such as tides and water bodies.
