Lab 1.1 – How are data about the ocean collected?
Fundamental concept: Recognize several of the common sensors and platforms used to collect oceanographic data
Preparation for: All Labs
Estimated time to complete: 20-30 minutes
Materials needed: None
Oceanographers use a variety of ocean technology to collect data about the oceans. In-situ observations collect data in the water using sensors on ships and submersibles. These types of measurements are very useful, but limited in extent. Remote sensing provides a way to fill in data gaps. Remote sensing is a method of collecting data without direct contact with the medium. Satellites are one remote sensing platform. Satellites are equipped with instruments that can make measurements of the ocean, including water color, sea surface height and the intensity of local gravity. These types of measurements have become a big part of the data set that scientists use to get a more complete understanding of the ocean.
The following video will help you understand sampling for data.
Tools of Science: Sampling
The OOI collects data at several locations around the world. Each location has a variety of instruments (called sensors), mounted on different platforms. The entire collection of platforms and instruments at one location is called an array.
Oceanographic instruments can be installed on a variety of platforms. These platforms are just the physical setting for the instruments. They can be ships, buoys, remotely operated vehicles, satellites or the sea floor. The platform and instruments chosen are matched to the questions being asked. Below is a short description of some of the platforms used by oceanographers, and an explanation of when they might choose to use them.
- Autonomous Underwater Vehicles (AUVs) – are essentially underwater drones or robots, except that rather than having an operator drive them in real time they are programmed to follow a particular path. Operators may be on a vessel or even on shore, and they program an AUV with instructions for where, when, and what should be sampled. AUVs may have a variety of sensors for sampling or surveying such as cameras, sonar, temperature and depth sensors. AUVs store data until it can be retrieved after the AUV is recovered at the end of a dive. AUVs can range in size from small (some gliders are 1-2 meters long) to very large (several meters long) and are powered by batteries. Some may be recharged via solar energy, while others are recharged aboard a ship or brought back to land. AUV’s can be deployed for long periods of time and re-sample areas on an hourly, daily, weekly or monthly timeline without having a ship present. AUV data can be the same type of data that is collected from research vessels but offers the opportunity to collect the data at a very reduced cost.
- Gliders – Gliders are essentially underwater drones, except that rather than having an operator drive them in real time they are programmed to follow a particular path. Gliders are capable of moving in both the horizontal and vertical. They typically have instruments installed on them and record the data until they come to the sea surface. Then they radio the data to a satellite. Scientists can download the data from the satellite for analysis. While at the surface scientists can also give the glider new instructions, via the satellite link. Glider data can be the same type of data that is collected from research vessels. The glider offers the opportunity to collect the data at a very reduced cost. Such data are used to get a 3-D map of the properties of seawater, such as temperature or salinity.
- Remotely Operated Vehicles (ROV) – Are underwater robots that are controlled by someone on the surface. ROVs are tethered to the research vessel or sometimes a HOV via a cable that transmits power to the ROV and data back to the ship. These allow scientists to explore the ocean without being in the ocean themselves and eliminates physiological constraints of the human body. An onboard video camera sends images to the ship via the tether and allows an operator to see real-time images to drive it with a joystick similar to playing a video game. The ROV has an advantage over AUV’s in that there are manipulator arms with attachments that can grab something, or a slurpy gun to capture small organisms, or take sediment samples with a small corer. ROVs typically have a variety of instruments to collect data via sensors, still cameras, and samplers that may be changed out depending on the data wanted by the scientists. ROVs allow for a real time human observation while eliminating the risk involved in using manned submersibles. This makes longer dives possible and is a more cost effective way to explore the deep ocean than using HOVs.
Learn about being an ROV Pilot as a career with this Nautilus Live video:
- Human Occupied Vehicles (HOV) – often called “Subs” are underwater vehicles typically manned with a driver and a scientist. While this allows for real-time observation, the time underwater and depth to which it can dive is constrained by the fact that an environment with oxygen and proper pressure must be maintained for the people inside. They require a ship for deployment but operate untethered from the ship. Like ROVs, they have a variety of sensors,still cameras, video cameras, arms with manipulators and a variety of sampling attachments. The advantage to HOVs is real-time observation by the scientists onboard, but the disadvantage is the cost and risk to human life should something go wrong.
Dive Deeper: Alvin makes it real
- Moorings – Moorings are comprised of an anchor, a buoy and some instruments either on the buoy or on the line connecting the anchor and buoy. They provide a platform where continuous measurements can be made at a particular location. In the OOI program there are often instruments that measure atmospheric data, like wind speed and direction. Instruments on the line between the buoy and the anchor could be measuring current speed and direction, or properties of the water, like temperature, salinity, dissolved oxygen concentration, etc.
- Profilers – A Profiler is a tethered vehicle that moves through the water column carrying instruments, which sample vertically through the water column. Profilers either track along the mooring riser (wire-following profilers), or include a winch that pays out line allowing the profiler to rise through the water column until a fixed depth
Irminger Sea surface mooring
Diagram of Endurance surface mooring
- Cabled – In some places there are many instruments installed on the seafloor, such as at the site of an active volcano. These instruments collect data related to volcanism, like earthquake magnitude and frequency and the change in tilt of the sea floor. Since these instruments are far below the sea surface they have to use underwater cables to transmit this data to shore. Thus these collections of instruments (arrays) are called cabled arrays.
- Telemetered – Many of the OOI locations have several buoys located close to each other (thus these are also called arrays). The data from the instruments on these buoys is transmitted to the top of the mooring, and then telemetered through a satellite to land where scientists can easily access the data. Therefore these are called telemetered arrays.
- Ships – Ships as a platform provide flexibility, but at a cost. When oceanographers go to sea on a research vessel they can examine data as it is collected and make changes to the sampling program based on what they observe. But ship time is expensive, and not an efficient way to repeatedly take the same type of samples in the same location (as can be done with moorings or arrays) or locations (as can be done with gliders). Neither arrays nor gliders allow scientists to collect physical samples, so if water or rock samples are required a ship is the platform to choose.
- Satellites – Satellites are used to both collect and transmit data. With the right instruments they can collect any type of data that can be remotely measured. There are ways to do this so we can measure sea surface temperature, sea surface height and the color of the water. This last property helps in remotely measuring phytoplankton concentrations. And satellites are useful in collecting data from moorings and arrays and transmitting it to scientists in the lab.
- Thermistor – moorings, arrays, research vessels and gliders often have a temperature sensor called a thermistor.
- Pressure sensor – pressure sensors are also common on most platforms. Why would scientists be interested in pressure? Because that tells them the depth of the pressure sensor. For this reason pressure sensors are usually paired with other sensors so we know the depth of the measurement.
- Conductivity sensor – Seawater conducts electricity, and the amount of electricity that is conducted depends on the salinity of the water. Salinity is an important control on water density so conductivity sensors are found on many of the platforms mentioned above.
- Seismometer – Seismometers measure the shaking of the Earth, with several one can determine the location and magnitude of earthquakes. Earthquakes provide information about solid earth processes, for example they may be useful in predicting volcanic eruptions.
- CTD – is an acronym for conductivity (salinity), temperature and depth, and is a multi-sensor unit that may be manually deployed off a ship. Smaller CTD units may be autonomous and incorporated into gliders, moorings or profilers. It is essential for determining the physical properties of water. A CTD unit used off ships is paired with a rosette of Niskin bottles to take discrete water samples at precise depths for chemical water analysis.
- Other sensors – there are lots of different types of sensors in the OOI program, only a few have been described above. There are sensors to measure the intensity of sunlight in the ocean (important in studies looking at primary productivity), the pH of sea water (important especially to the health of shelled organisms), and there are video cameras recording changes at the seafloor near an active volcano. Explore the OOI website to see all of the types of data that are collected in the program. In this lab we will work with just a few to sharpen your data analysis skills. Other labs in this series will introduce you to other sensors as you are presented with the data from the sensors.
Quick Check on Ocean Technology
- Which instrument measures the intensity of an earthquake or the shaking of the Earth?
- If you want to study life on the bottom of the ocean and need to observe a squid for a long period of time, but have limited funds, would you use an HOV or ROV? Explain why you chose your answer.
- Explain the difference between a Telemetered versus Cabled Array.
- Which type of sensor can be deployed off a ship, can detect depth, salinity and temperature of the water and take discrete water samples at specific depths?
- Which type of platform would you use to monitor wind speed and wave height?