Lab 1.3 – How do you know exactly where you are on Earth?
Fundamental concept: Students will locate OOI arrays on a world map by latitude/longitude
Estimated time to complete: approximately 30 minutes
Materials needed: none if online, printouts of maps from activity and a ruler or straight-edge if no internet access.
We use our cell phones or our car’s navigation system for directions to an address, but how does the phone know its location? What if we are out on the ocean where there are no roads or street signs, how do oceanographers know where we are on the vast blue ocean with no land in sight? Global positioning systems, otherwise known as GPS, are used to find locations on Earth from satellites. Multiple satellites are used to triangulate our position.
Global location is based on a grid system overlaid onto the surface of the Earth. Latitude lines start at the equator or 0 degrees (°) latitude. Latitude lines run east and west, parallel to the equator, and are measured in degrees north or south of the equator to 90° at the North or South poles. Latitude lines are equidistant from one another. One degree of latitude is divided into 60 minutes (‘). A minute of latitude is 1.15 miles or 1 nautical mile. One minute of latitude is further divided into 60 seconds (”). We represent latitude in degrees, minutes and seconds, with the direction of North or South; for example: 27° 12’ 28” N.
Figure 1.3.1 Latitude and Longitude grid system. Google Earth 2020.
Now that we know how far north or south of the equator we are, we need to know a more precise location. After all, we could be anywhere around the globe at the same latitude. The second part of the grid system we use is called Longitude. Longitude lines, or meridians, run from the North Pole to the South Pole. Unlike the equator that is the center of the sphere, the Prime Meridian or 0° Longitude is artificially set to run through Greenwich, England. It has been moved several times throughout history to run through other major cities. Longitude lines run north and south from pole to pole, which means they are not equidistant at different latitudes, they are farther apart at the equator than they are toward the poles. It takes the earth 24 hours to complete one rotation or 360°. So for every hour the Earth rotates 15° Longitude (360 degrees/24 hours = 15 degrees/hour). Longitudes are measured east or west of the Prime Meridian to 180° which is the Anti Meridian or the International Date Line. Longitude is written in degrees, minutes and seconds with the direction East or West of the Prime Meridian; for example: 85° 15’ 32” W.
Figure 1.3.2 Northern polar projection. Google Earth 2020.
With newer digital technology, latitude and longitude may also be expressed in decimal degrees. For our purposes, we will use the historic degrees, minutes and seconds format. When writing a location you must include both the latitude and longitude, starting with the latitude first; for example: 27° 12’ 28” N, 85° 15’ 32” W.
Reading latitude and longitude scales on maps
When looking at maps, it is important to pay attention to the latitude and longitude scale for that particular map. Tick marks between two degree numbers may be designating degrees, minutes, seconds or a combination depending on how zoomed in on a location on the map. Lets take a look at a couple of examples. Remember that 1 degree is equal to 60 minutes, You can use this information to determine the scale by looking at how many tick marks there are between the latitude or longitude on the scale. You can then estimate an even smaller scale between the tick marks.
Figure 1.3.3
Notice in scale A, both the latitude and longitude tick marks are equal, 30 minutes or 1 degree every 2 tick marks. In scale B, the latitude and longitude are different, the latitude tick marks depict 15 minutes each and the longitude tick marks are 20 minutes or 1 degree every 3 ticks. It is also very important to pay attention to the direction for increase or decrease. In scale A, you are increasing in latitude from top to bottom of the diagram while in scale B you are decreasing in latitude from the top to the bottom of the diagram.
Quick Check for reading latitude and longitude scales on maps:
Latitude and Longitude Activity
The following diagram (Figure 1.3.4) depicts the Ocean Observatory Initiative (OOI) Arrays.
Figure 1.3.4 OOI Array Locations.
- Which OOI Array is located at 42° 55′ 13” S, 42° 26′ 27” W?
- Which OOI Array is located at 50° 4′ 47” N, 144° 48′ 22” W?
Use the following maps Figures 1.3.5-1.3.10) to identify the plotted latitude and longitude (in degrees (°) and minutes (‘) only due to the size of the maps) of surface moorings located within each OOI Array. Remember to include direction N, S, E or W. Find the latitude and longitude of the center of the circle next to the array name.
Figure 1.3.5 Global Southern Ocean Array. GeoMap app 2020.
Figure 1.3.6 Coastal Pioneer and Global Irminger Sea Arrays. GeoMap app 2020.
Figure 1.3.7 Global Station Papa and Coastal Endurance Arrays. GeoMap app 2020.
Figure 1.3.8 Coastal Endurance Array. GeoMap app 2020.
3. What is the latitude and longitude of the Global Southern Ocean mooring (Figure 1.3.5)?
4. What is the latitude and longitude of the Global Irminger Sea mooring (Figure 1.3.6)?
5. What is the latitude and longitude of the Coastal Pioneer surface mooring(Figure 1.3.6)?
6. What is the latitude and longitude of the Coastal Endurance surface mooring (Figures 1.3.7 and 1.3.8) ?
Each OOI Array is comprised of moorings, platforms, and sensors that are at different latitude and longitude, depth, distance from shore or other geographic location. Some equipment is mobile, while others are fixed. For instance, in lab activity 1.2, you learned about zooplankton migration during the solar eclipse August 21, 2017. The data collected to detect this phenomenon was collected at the Endurance Array. The Coastal Endurance Array has an Oregon and Washington line. The purpose of the Endurance Array is a multi-scaled array that utilizes both fixed and mobile assets to observe cross-shelf and along-shelf variability in the coastal upwelling region of the Oregon and Washington coasts. The array also provides an extensive spatial footprint that encompasses an eastern boundary current and has connectivity with the OOI Cabled Array. The diagram below depicts the entire area of the Endurance Array.
Figure 1.3.9 Coastal Endurance Array diagram
Figure 1.3.10 Coastal Endurance Oregon and Washington Lines diagram
- Based on the above diagrams of the Endurance Array, how deep is the water where the Oregon Shelf surface mooring is moored (Figure 1.3.10)?
- What is the approximate range of latitude that is covered by the mobile assets (Nearest degree and minute only, Figure 1.3.9)?
- What is the name of the town where the shore station is located (Figure 1.3.9)?
