Stories tagged remote sensing


Adios El Niño, Hello La Niña?: The Pacific has switched from warm (red) to cold (blue).
Adios El Niño, Hello La Niña?: The Pacific has switched from warm (red) to cold (blue).Courtesy NASA

How to measure ocean temperature

There are many ways to measure the temperature of an ocean. Oceans are big and temperatures at different locations vary. To get a sense of whether the ocean is warming or cooling, lots of spread out measurements need to be made.

  • Thermometers under buoys or ships Since about 1990 an extensive array of moored buoys across the equatorial Pacific Ocean has beamed temperature data from a 1 meter depth up to a satellite. Lots of ships are also recording their intake water temperatures but the depths and locations vary making this data harder to use.
  • Satellite remote sensing NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) SST satellites have been providing global SST (Sea Surface Temperature) data since 2000. Unlike buoys, the satellites can sense the surface temperature everywhere. The temp measured is of the surface only, though. The surface "skin" temp can be quite different than the temp of the water below because of things like evaporation, wind, sunshine, and humidity. Also, cloud cover prevents satellites from sensing surface temperatures.
  • Acoustic Tomography Sound, especially low frequencies, can travel long distances under water. Since the speed of sound under water varies with temperature, measuring how long sound takes to travel a certain distance will give you the average temperature of the water over that distance. Acoustic Thermometry of Ocean Climate (ATOC) is using trans-basin acoustic transmissions to observe the world's oceans, and the ocean climate in particular.
  • Ocean Surface Topography By bouncing microwaves off the the ocean surface and using GPS location, satellites can precisely measure the height of any spot on the ocean surface. Reasoning that water expands and contracts as it heats and cools, then so too would the height of the sea surface. I think Ocean Surface Topography is the easiest and best technique for measuring ocean temperature.
    In a 2005 study researchers compared satellite measurements of sea surface height in the northeast Pacific Ocean from 1993-2004 to recordings of sea surface temperature in the region during the same period. The sea surface height measurements proved to be as accurate as temperature measurements as indicators of ocean conditions resulting from long-term climate cycles as well as being more consistent. PhysOrg

El Niño and La Niña effect on hurricanes

Ocean temperature information is useful in predicting hurricane season severity and forecasting individual storm severity. The image above shows that the Pacific Ocean is changing from hot to cold.

A La Niña is essentially the opposite of an El Niño. During a La Niña, trade winds in the western equatorial Pacific are stronger than normal, and the cold water that normally exists along the coast of South America extends to the central equatorial Pacific. La Niñas change global weather patterns and are associated with less moisture in the air, resulting in less rain along the coasts of North and South America. They also tend to increase the formation of tropical storms in the Atlantic.

"For the American Southwest, La Niñas usually bring a dry winter, not good news for a region that has experienced normal rain and snowpack only once in the past five winters," said Patzert. NASA


Spray: Spray being deployed by Brian Guest, at WHOI, in 2004. Courtesy: Jeffrey Sherman Research Specialist and designer of the SOLO microstructure profiler and 'Spray.'

Think you could swim 2,484 nautical miles
(1 nautical mile = 1.15 miles) across the Atlantic Ocean? This month, Spray, will embark on its mission to swim from the southern tip of Greenland to the coast of Spain. Spray is an autonomous underwater vehicle, AUV for short, created by the Woods Hole Oceanographic Institution in Massachusetts and the Scripps Institution of Oceanography in California.

    Spray's primary goals include:

  1. completing the lengthy swim;
  2. gathering signs of global warming;
  3. enabling scientists to have a constant telepresence in the ocean

Spray will act as an “aquatic sentinel” collecting data on temperature, currents and salinity. This information will assist scientists in furthering their knowledge base pertaining the role oceans have on global climate. Dr. Russ Davis, from the Scripps Institution of Oceanography in San Diego stated "The key is that Spray can stay at sea for months at relatively low cost, allowing us to observe large-scale changes under the ocean surface that might otherwise go unobserved." If Spray completes this mission, the robot will break its personal record of 1,864 nautical miles for the longest distance ever traveled by an AUV. GO SPRAY!!!

Check out this graphical representation of Spray in action.


Tongue ESP: The tongue can be used to sense input from machines via a grid of electrodes placed on the tongue which is stimulated with electricity.

Using Tongue ESP?: She probably isn't but could be in the future.
Courtesy Creap

What extra sensory perceptions would would you like? Seeing behind your back? Smelling odorless gasses like carbon monoxide? How about seeing in the dark? Sensors already exist that can do these things. All that is needed is a way to input what they sense into our brains. The most common way to input information from external sensors is visually. We can use our eyes to see distant airplanes or weather clouds on a radar scope. We can read how much carbon monoxide is in the air we breath by looking at a meter.

Suppose we need to sense things without using our eyes. Most often when we cannot see, we use our fingers to get information. Blind people use a cane to feel thier way around. Sometimes they tap their cane and listen for echoes to sense a barrier.

Another way to sense data about our environment is with our tongue. Suppose a ten by ten grid of electrodes were placed on the tongue and small voltages were used to create various patterns of sensation on the tongue. Just like bumps on paper can create thousands of words for people trained to read braille, the hundred electrodes on the tongue can allow trained people to sense data from sonar, radar, toxin detectors, or any other data measurable by various sensors.

At the institute for Machine and Human Cognition (IFHMC) Anil Raj is principle investigator in research titled: Adaptive Human/Machine Multi-sensory Prostheses. They are working on TSAS: Tactile Situation Awareness System. The research is exploring how electrodes on the tongue or in a body suit can allow users to receive input from external devices. Such input is desirable when your hands and eyes are already too busy or when they cannot be used.


Grainy Mars Orbiter pictureCourtesy NASA

For the first time ever, a spacecraft has taken a picture of another spacecraft orbiting around another planet. The Mars Global Surveyor, which has been floating around Mars since 1997, was able to take this grainy picture of its sister probe, Odyssey. Odyssey arrived at Mars in 2001. It's exciting to be able to see evidence of our successful missions to another planet beamed back from millions of miles away.

In the future these probes may be able to take pictures of fellow spacecraft to help us fix problems and guide discovery. Imagine if a lander got lost on the Martian surface: orbiting probes might be able to tell us back here on Earth what happened, and where things went wrong. This sort of interaction between probes will be essential for our further exploration of the universe, especially to places where humans might not be able to travel.