Chapter 3: Technology in Oceanography

During this semester you are going to make extensive use of oceanographic data and images, the bulk of which has been made possible through the use of relatively new technology.  This chapter is a brief introduction to a few of the more important technologies used by oceanographers.

Echo sounders

Echo sounders aren’t new technology, they were developed in 1914 by one of Thomas Edison’s former employees to detect icebergs, but they are still hugely important.   They were first put into large scale use looking for submarines during World War II.  Navy boats were able to gather large amounts of data about the seafloor.  This data was then used to hand draw the first bathymetric maps of the seafloor and its contours.

A CTD being deployed from the deck of a research vessel. Image from Wikipedia

Echo sounders transmit sound waves from a device deployed on the bottom of a boat. These sound waves bounce off of anything they hit in the water column (such as a school of fish), or they bounce off the bottom.  The reflected sound waves are then picked up by a another sensor.  The difference in time between the sending pulse and the reflected pulse can be used to calculate depth.  Today, a modern multi-beam sonar can be used to generate a three dimensional picture of the bottom with very high resolution.

CTD’s

CTD’s are water sampling devices that are regularly deployed from oceanographic research vessels.  These devices collect water at depth and can be used to sample water conductivity, temperature, and pressure.  The device is a large scale, and modern version of the Nansen bottle, developed in 1910 by oceanographer and explorer Fridtjof Nansen.

Individual bottles can be triggered by computers on deck to close at selected depths, sealing water in as the device is brought from depth back to the surface.

Buoys, Drifters, and Drogues

A weather buoy, Image from Wikipedia

Buoys collect data for oceanographers and meteorologists. They can be fixed buoys or drifting buoys.  A fixed buoy will be tethered to the bottom of the ocean.  Fixed buoys have the advantage of being in places where humans often aren’t, but they do require regular maintenance.  You can look at the extensive network of buoys around the work at the National Data Buoy Center. Depending on the type of probes that have been attached, the buoys may collect data on temperature (in the air, at the surface, and at depth) wave height, wind speed and direction, as well as current speed and direction.  Fixed buoys can be used to read the weather, but they also serve to detect tsunamis and monitor tides.

Modern drifters are smaller than moored buoys, consisting of a small buoy 30-40 cm in diameter attached to a large “sock” called a drogue.  Drifters are designed to drift with the currents. The drogue fills with water and acts as a type of sea anchor, ensuring that the buoy will be moved by ocean currents, rather than wind currents.  Despite their smaller size, drifters have sensors that allows them to collect and transmit data on temperature and currents.  Click to watch an animated GIF of oceanographers deploying a drifter attached to a drogue, or click to see a map of all the world’s drifters currently deployed.

ROV’s

The ROV Hercules, image from NOAA

Diving to the bottom of the ocean in a manned submersible is a dream to many oceanographers.  As it turns out, however, doing so is incredibly expensive and not very comfortable.  In the 1980’s researchers increasingly turned towards Remotely Operate Vehicles and safer and lower cost solutions for ocean exploration.  Jason, first deployed in 1988 has been a highly successful ROV for WHOI Woods Hole Oceanographic Institute. Jason can be remotely operated from a ship above through a 10 km fiber optic cable that delivers data and electricity. Jason is equipped with sonar, cameras, lighting, and numerous sampling systems. Jason’s manipulator arms can collect samples of rock, sediment, or marine life and place them in the vehicle’s basket or on “elevator” platforms that float heavier loads to the surface. Click to watch a video of an undersea volcanic eruption recorded by Jason.

Hercules, a similar ROV operated by NOAA (the National Oceanographic and Atmospheric Association), can withstand the pressures of depths up to 4,000 meters allowing it to gather data and HD video over areas that have often been inaccessible to researchers.

Autonomous Unmanned Vehicles (AUV’s)

A slocum glider, image from whoi.

Autonomous Underwater Vehicles (AUV’s) are robotic vehicles that, depending on their design, can drift, drive, or glide through the ocean without real-time control by human operators.  There are multiple kinds of AUV’s. One example is the slocum glider. Shaped like a missile with wings, it runs on batteries can that can be recharged by the motion of its long sweeping dives.  They can be fixed with cameras and numerous instruments and be programmed to stay out for weeks at a time.  Relatively inexpensive, they are transforming the way oceanographers gather data on the continental shelf.  Woods Hole Oceanographic Institute uses a number of types of AUVs.  Click on the link to learn more about them.

Unmanned Aerial Vehicle (a.k.a drones)

The term drone was originally associated with military vehicles, but increasingly the future of “drones” is for domestic, industrial, and scientific research.  Currently, the Federal Aviation Administration is sorting out rules for the legal use of AUV’s in the United States.  Many researchers believe that drones have the capacity to change ocean observation and data collection in the same ways that AUV’s and buoys have been for the last thirty years.  At very least, AUV’s can provide a perspective that could only otherwise be obtained through a manned helicopter.

Satellites

(text adopted and modified from oceanmotion.org)

Satellites orbiting the around the Earth have provided scientists with vast amounts of data that have improved both weather predictions and oceanographic observations.

Satellites are in constant motion. Satellites orbiting around the Earth have the minimum speed (typically 17,000 mph) needed to stay in orbit and not impact the Earth. The satellites orbit without any propulsion. They are constantly pulled down by the Earth’s gravity, but because of their high speed along the orbit (at a right angle to gravity), satellites do not hit the Earth. As Newton said: “Objects in motion tend to stay in motion”. Their inertia keeps them moving, and the force of Earth’s gravity bends their path around the Earth.  If a satellite stopped moving, then the force of gravity would pull it straight down to the Earth.

Some satellites depend on reflected solar energy to gather data and so can only work during the day. Others measure thermal radiation of objects and substances, or they generate their own radar or laser radiation. These satellites do not need the sun’s radiation and can collect data at night. A large percentage of Earth’s surface is covered by clouds every day. This blocks the reflection of visible light, and because of this, the images that NASA provides are typically composites built from many images using data collected over several days or weeks. Some wavelengths of electromagnetic radiation measured by satellites (radar, microwave) pass through clouds. It is important to study many different wavelengths of radiation, because each wavelength can provide more information about conditions of the surface that emitted or reflected the radiation.

What kinds of data are made available through the use of satellites?

Squickscat Sattelite, image from Oceanmotion.org (NASA)

  • Sea Surface Topography – The ocean’s surface isn’t flat, its dynamic. There are mountains, and valley’s.  However, the topography is spread out over such large distances that a boat moving over it could not sense it.  Using satellites such as TOPEX/Poseidon and Jason-1, scientists can measure the sea surface height (SSH) and use the information to study surface current, ocean circulation, and heat stored in the oceans, coastal tides, and ocean floor topography. These satellites use a radar altimeter that sends short pulses of electromagnetic radiation downward and analyzes the returned (reflected) signal. The time difference between sent and received signals gives the distance to the sea surface. The radar is able to determine the height of the satellite above the center of the Earth with an accuracy of +-2 cm. Changes in SSH may be due to variability of ocean currents, seasonal cooling and heating, evaporation and precipitation, and planetary wave/tsunami phenomena.
  • Sea Surface Temperature – Using satellites such as AVHRR on NOAA satellites, and MODIS on AQUA and TERRA, scientists can measure the sea surface temperature (SST) to understand the ocean’s affect on weather, study global climate change, and visualize surface water currents, turbulence and upwelling. The satellites measure thermal infrared radiation emitted by the sea surface to estimate its temperature. To correct for undetected clouds, which interfere with SST measurements, ship and buoy data are required to calibrate the SST values. Global SST maps are a composite of cloud-free data collected over a week or month.
  • Sea Surface Winds – Using the satellite QuikSCAT, scientists can measure sea surface winds that drive surface water currents, influence air-sea exchange of energy and mass, and affect regional and global weather. The SeaWinds instrument uses microwave radar to measure near-surface wind speed and direction continuously, under all weather and cloud conditions over Earth’s oceans. The SeaWinds instrument has a 1- meter diameter rotating dish antenna that produces two narrow beams that sweep in a circular pattern. The return radar pulses reveal details about wave patterns at the sea surface; these patterns help compute near-surface wind speed and direction.
  • Ocean Color – Satellites such as SeaWiFS Instrument on SeaStar, MODIS on AQUA and TERRA can detect microscopic photosynthetic organisms. This information can be used to study the distribution of marine life and how surface currents play a role in making nutrients available, regulating temperature, and dispersing populations.

Questions for Research:

  1. During expeditions, oceanographers spend a lot of time “mowing the lawn.”  What exactly does this mean and what is the benefit to oceanography?
  2. Go to the webpage of the National Data Buoy Center.  Select one buoy that is active (and preferably one that is recording multiple types of data). Record its location in latitude and longitude as well as current conditions at the location of the buoy.
  3. Here is an animation of drifter deployments between 1979 and 1984.  Here is a similar animation between 2005 and 2009.  Over the last thirty years how has the use of drifters evolved?
  4. The Ocean Observatories Initiative by Woods Hole Oceanographic Institution is a huge effort to monitor the health of the oceans using remote technology.  Go through the slide show and read the description of the effort.  What are they hoping to do and what technology will they be making use of.
  5. What is believed to have happened to the ROV Nereus while diving off the coast of New Zealand in 2014? How is the loss of a ROV much less of a big deal than the loss of a human piloted submersible?
  6. Click on the link to read a NYT article about slocum gliders.  After reading it, describe the advantages to using ocean gliders over traditional research vessels.
  7.  Besides the slocum glider, another type of AUV is the wave glider made by Liquid Robotics. Describe how the wave glider moves through the ocean and what its creators see as its potential to change ocean research.  If you would rather, you can watch an AP story on wave gliders on YouTube.
  8. Read about Saildrone.  Describe two types of data it can collect and one scientific problem that it could help scientists understand.
  9. (and 10) For these two questions.  Walk through the virtual tour of the University of Alaska’s oceanographic research vessel; The Sikuliaq.  Check out some of the videos (at home if need be) and describe two types of on board technology that you learned about.  Finally, describe what you thought of the boat.