Concepts



Quick concepts:

How we know the vertical distances.

 

  1. The Earth's surface relief varies between its:

    Lowest point: "Challenger Deep in the Mariana Trench is the lowest point, lying -10,924 m below the surface of the Pacific Ocean."

    Highest point: "Mount Everest (Nepal-China) 8,850 m; K2 (Pakistan) 8,611 m."
    Data from the CIA World Factbook

  2. Types of maps that show the Earth's vertical height:
    Relief map

    Topographic map

    Bathymetric chart

  3. The height (elevation) of land and depth (bathymetry) of the sea is given relative to nean sea level. Since sea level isn't "flat" or perfectly spherical, even if it were possible to make it still, locating mean sea level in detail is a more difficult task than it might seem.
    http://www.esri.com/news/arcuser/0703/geoid1of3.html

Quick facts:

How do we know it?

  1. The elevation of surface features is known by surveying and using geometry in reference to other features where the elevation is already known.

  2. Elevation is now measured by instrumentation carried by satellites that use electromagnetic radiation rather than sound. The general principles are the same.

  3. Elevation is not usually measured by echo-sounding because sound waves do not travel through space.

  4. Bathymetry is measured by echo-sounding because electromagnetic radiation does not travel well through water. In air, the opposite is true.

Practical matters:

Why is it important to know?

  1. Knowing the elevation of the Earth's surface allows us to visualize the three-dimensional shape of the Earth's surface.

  2. Elevation differences and the resulting slope of the Earth's surface controls where runoff flows and where it might flood in a heavy rain.

  3. The largest land forms on each planet are shaped by large-scale processes.

  4. Why is it important to know things which are already known?

  5. Why is it important to know things that I'll never use again?
    You may change your mind about what you'll want to do. Politicians, scientists, ..., they all need to know many things to solve larger problems and to communicate with people in other specialties. Most scientists became experts by