In this excercice we will get to know Gabriel's measurement station and learn about what it measures. 

The video below explains a bit about Gabriel and what it measures. You can learn more, download data and view live measurements on this website.

 

  

The Measuring Station - Gabriel is named after "Sjur Gabriel", who is one of the main characters in the first novel of "Hellemyrs folket" by Amalie Skram. Gabriel is anchored on a small plateau in Store Lungegårdsvann right at Amalie Skram VGS in Bergen. The measuring station is a so-called profiling sea buoy , Ie it is used to measure and study the characteristics of the water.

The bend is a so-called profiling bend; This means that it consists of two main parts; The buoy itself floats with instruments mounted on top, and a CTD instrument hanging in a cable and lowered down and through the water column. This instrument gives us information about the properties of the water at different depths. CTD is an abbreviation for Conductivity, Temperature and Depth, which are the three most important parameters measured in such a vertical profile of the water column. From conductivity, salinity in the water can be derived, and together with temperature, this determines the density of the water and hence the layer distribution in the water column. Attached to this CTD are also sensors that measure oxygen, fluorescence and turbidity. Gabriel also has a weather station at the top which measures air pressure, wind speed and direction, and air temperature. The buoy is powered by solar panels and sends data continuously via a mobile network.

 

Map showing batymetry (depth) in Stor Lungegårdsvann in Bergen and the location of the observation station Gabriel (red star). The depth of which Gabriel is anchored is about 18m. Figure: Bergen Municipality.

Gabriel has been deployed in Stor Lungegårdsvann since June 2015 and has measured the page with the exception of short periods of maintenance. You can see graphically what has been measured on Gabriel's website under "visualization of data". Here you can also download data and copy to programs like Excel, Word, Geogebra or Matlab. White fields are periods that have not hosted measurements.

 

 

Gabriel is a hollow bend that is anchored to four moorings. The measuring instrument itself hangs in a cable into the bend and is lowered to the water at regular intervals. Figure: SAIV AS.

 

Excercise

A) Visit Gabriel's website ( www.ektedata.no ) See the video about Gabriel first and then go to the measurements from the last day at the bottom of the page (daily graphs). When was the last measurement shown there and what was the water temperature at 0.5m and 17.5 depth then?

B) What is a parameter? Explain what different parameters the buoy measures, what devices they have and what they can tell us. (Hint: You can find answers in daily graphs)

C) Where is the water warmest? At the bottom or near the surface? Visit www.ektedata.no/indhold/visualization-of-data to check if this is always the case. Why think this is so? Do you think this is a difference between freshwater and saltwater?

D) See if you find information on salinity. How does this vary with the depth and why?

E) Where do you think the water with low salt content comes from? And what about the salty water?

F) Use available sources and find out what we mean by "density". How do you think density may be in determining the distribution of where in the deep we have salt or colder water?

G) Explain why we use pressure in the ocean to measure depth. Used available sources. What is the device dbar and what is this equivalent to in depth devices?

H) Visit www.ektedata.no/indhold/visualization-of-data and check changes in water temperature over time. What season changes do you see? If you zoom in for a short period of time, can you see daytime variations in the water temperature?What do you think is controlling the water temperature?

I) Where is the oxygen content in the water column highest? Why and where does this oxygen come from?

J) What is turbidity and how do you think this is in Large Lungegårdsvann compared to an open sea, and why? At what depth is the turbidity the highest?

K) What is fluorescence and what do you think this can tell us something about? When in the year do you think this value will be highest and why? What do you think this value depends on? If Large Lung Water had been 300m deep, how do you think this value would be at the bottom then and why?

 

Extra

L) Why do you think we measure weather and sea in the same place? How can the weather affect the ocean or the ocean affect the atmosphere?

M) If the wind over the Big Lungegårdsvann increases what do you think happens to the water?

N) In the case of the bend Gabriel in Lungegårdsvann what do you think is most influenced by the density of the water;Temperature or salinity, and why?

O) Can you say something about climate change by looking at measurements from this bend? How or why not?

P) Now, we will learn how to copy data from Gabriel into Geogebra.

Load measurements of air temperature from Gabriel for each dive for a full week. 

Option 1: " Air temperature " 
Option 2: "All data in the period" 
Option 3: "17.06.2016-24.06.2016" ( DD.MM.YYYYY) 
Option 4: " All Depths " 

You will now get a .txt file with multiple columns downwards (columns go down). Copy these columns into the spreadsheet in Geogebra. The first column is time, the other is the number of the measurement and the third is the value of the measurement. Select the second and third columns, right-click and select  "lag liste med punkter" (create list width points). The X-axis in the graphics field now represents the time and the y-axis represents air temperature. Adjust the axes and create a customizable zoom so that the points in the digram fill the entire screen. Put names and devices on both axes. What is the air temperature at 06 June 19th? Can you color this point red? Finally create a screenshot of the graphic.

If you have problems, you See this video: How to load and chart data from Gabriel in Geogebra.

Use the RegSin [Name List] function in Geogebra to customize a sinusoidal curve for the measurements. Alternatively, you can use the "Data Analysis" button when you are in the Geogebra spreadsheet and select "Sin" in the drop-down window. Does the curve fit well?