GEO-SCI 103Exam # 1 Study Guide Lectures: 2-5Lecture 2 (September 4th): Locating Ourselves—Navigation -Latitude and Longitude: Where Are We?-How do we use the sextant and chronometer?-Navigational History: Who are Eratosthenes and Pytheas? If you know you latitude and longitude precisely, you will be able to pinpoint exact locations on the Earth’s surface with the unique set of coordinates on the grid system.Latitudethe angular distance of a place north or south of the Earth’s equator. They are made up of “parallels” which are the east and west gridlines parallel to the equator that make up the Northern and Southern Hemispheres. LongitudeThe geographic coordinate that specifies the eat-west position of a point on Earth’s surface. “Meridians” are the north-south grid lines that intersect at the poles—the Prime Meridian especially representing 0 degrees through Greenwich, EnglandFirst, we must note that the Earth spins 15 degrees per 1 hourSextantIt is a device that measures the angle between two objects. To find latitude, you must measure the angle between the horizon and the sun when the sun is at its highest point. However, we must use the chronometer to determine longitudeChronometeran instrument for measuring time, especially designed to keep accurate time in spite of motion, variations of temperature, humidity and air pressure. They were first developed for marine navigation—their prime use being astronomical observation to determine longitude. Example: Say the sun is set directly overhead, and your chronometer says the time is 3:00 PM. This means that 3 hours ago the sun was overhead at this latitude at 0 degrees longitude. THEREFORE, the sun moved 15 degrees 3 times, or a total of 45 degrees. Therefore, we would be 45 degrees West.-What are some modern Techniques of Navigation? Celestial, Radio Based (Loran) and satellite based navigation systems (GPS)?Eratosthenesfirst person to calculate the circumference of the Earth by applying a measuring system that accurately calculated the tilt of the Earth’s axis (23.5 degrees=axis of rotation) (June 21st)-Noticed that at high noon on June 21, the sun was directly overhead the city of Syene in Southern Egypt.-In Alexandria, where he lived, the sun cast a shadow of a tall monument that made an angle of 7.2 °-Knowing the distance between the two cities (approx. 500 miles in modern distance units) he was able to accurately estimate the circumference of the Earth using trigonometry. PytheasThe first person on record to describe the “midnight sun” where the nights are very short in summerand the sun does not set at the summer solstice. He developed a method to determine the angle between the horizon and the North Star otherwise known as one form of Celestial Navigation. - North Star at night or height of the sun at local noon provides latitude. Local noon compared to Greenwich, England is used to calculate longitude.Celestial NavigationUses position of sun and stars to determine location. - North Star at night or height of the sun at local noon gives latitude- Local noon compared to Greenwich used to calculate longitude - Pytheas developed method to determine the angle between the horizon and North StarRadio Navigation Systems- Land based signals- Radio beacons send signals from land-based stations- Time differences from three different beacons are compared- Position can be located by Triangulation (trigonometry)Satellite Navigation- Global Positioning System (GPS)- 24 Satellites: 21 primary, 3 orbiting “spares”, 10,900 miles up, each orbits twice/day- At least four satellites above horizon for every point on earth- Determines position using triangulation (trigonometry)Lecture 3 (September 9) -Water Depth Determination: How is it done? (soundings, echo sounding 2D, multi beam or Side Scan Sonar 3D)Echo Sounding- Prior to the 20th century, the only means of determining the depth of the ocean was through the method known as sounding.- Echo SoundingA sound transmitter mounted on the hull of a ship emits high frequency sound waves that travel through the water and are reflected off the seafloor. o These returned “echoes” are detected by a device called a hydrophone.- Numerous closely spaced echo sounder profiles can be used to construct a bathymetric map of the seafloor, which refers to the depth of the seafloor below the ocean surface.- Contour lines (isobaths) connect points that are at equal depths below sea level and provide a way ofvisualizing three dimensions on a flat piece of paper - Seismic Reflection ProfilingFurther refinement of the sounding techniques leads to the development of this device. The ship uses a low-frequency sound source such as an air gun that transmits loud “pops” through the water, which can more easily penetrate through the sea floor and show the thickness of buried sediments. o These analyses help with determining the origin and evolution of the ocean crust Advances in Seafloor research…Submersibles oGive researches the opportunity to dive to great depths in the ocean and observe first-hand and sample features of the ocean bottom-Map Making History (Matthew Maury)-Techniques to see the structure of the sub-seafloor (sediments and crusts). Seismic Reflection Profiles (used for science and hydrocarbon exploration)? Other techniques to map the seafloor (satellite altimetry)Maury Became the superintendent of the U.S. Naval Observatory where he published the Wind and Current chart of the North Atlantic, which showed sailors how to use the ocean’s currents and winds to their advantage and drastically reduced the length of ocean voyages. - Maury’s uniform system of recording oceanographic data was adopted by navies and merchant marines around the world and was used to develop charts for all the major trade routes. Seismic Reflection ProfilingFurther refinement of the sounding techniques leads to the development of this device. The ship uses a low-frequency sound source such as an air gun that transmits loud “pops” through the water, which can more easily penetrate through the sea floor and show the thickness of buried sediments. - These analyses help with determining the origin and evolution of the ocean crust Satellite Altimeters Very accurate, satellite-altimeter systems are needed for measuring the oceanic topography. Topex/Poseidon, launched in 1992, was designed to