NOAA Teacher at Sea
Onboard NOAA Ship Ronald H. Brown
July 4 – 23, 2004
Mission: New England Air Quality Study (NEAQS)
Geographical Area: Northwest Atlantic Ocean
Date: July 9, 2004
Weather Data from the Bridge
Time 8:00AM ET
Latitude- 43 43.31N
Longitude- 66 15.13 W
Air Temperature 11 C
Air Pressure 1010 Millibars
Wind Direction at surface SE
Wind Speed at surface <5 MPH
Wind Direction at 1 Kilometer- E
Wind Speed at 1 Kilometer <5 MPH
Wind Direction at 2 Kilometers E
Wind Speed at 2 Kilometer <5 MPH
Cloud cover and type Fog
One of the blind men observed an elephant and said it is like a tree, another said it was like a rope, another said it is like a water hose. Which was correct?
This morning I visited with Christoph Senff and Rich Marchbanks. After lunch I visited with Alan Brewer. All three are here from NOAA’s Environmental Technology Lab in Boulder, Colorado. Chris and Rich are operating a LIDAR, which remotely measures amount of ozone in the atmosphere. Alan has a Doppler LIDAR which remotely measures wind speed and direction. By “remotely,” that means they can measure ozone and wind from 3-4 kilometers away. An amazing thing about many of the instruments on board is that they have been designed and built by the scientists themselves. They can’t just run down to some high-tech store and buy their equipment, what they need isn’t for sale anywhere. They decide what needs to be done, and then they design and build the equipment that will do the job. The LIDARS that are being used here on the BROWN and in the rest of NEAQS project are examples of some of that “homemade” equipment.
In the case here on the ship “homemade” certainly does not mean it is just thrown together, held up with bubble gum, baling wire and duct tape. The LIDARS and the other instruments on board are extremely intricate, sophisticated and complicated devices.
To understand the very basics of how a LIDAR can detect ozone and air movement forget about LIDARS and just think about a normal flashlight. Pretend that you go outside in the middle of a completely dark night, no light from anywhere. Point your flashlight straight up and turn it on. Now imagine that there are a flock of white pigeons circling overhead, you will not see them unless the light from your flashlight hits them and then bounces back into your eye (hopefully it’s just the light that gets in your eye).
Now imagine that several of the pigeons poop and their poop is completely black and is between you and the pigeon. Yeah I know pigeon poop is usually white but for now pretend it is black. Because the poop is completely black when your beam of light hits the poop the light will not bounce off, instead it will be absorbed by the poop. The more poop in the air the more of the light is absorbed and less light bounces back to your eye.
Picture this. You are standing in the dark with your flashlight. The pigeons are circling over your head- between you and them is their poop. Quickly turn your flashlight on and then back off and measure the amount the amount of light that leaves. The light shoots up through the poop (which absorbs some of the light) and hits the pigeons. Some light bounces off the pigeons back through the poop and to your eye. You measure the light that comes back. By figuring out how much light was absorbed by the poop you can get an idea of how much is in the air above you.
Instead of visible light other wavelengths of light, like ultraviolet (UV) and infrared (IR), are used. Christoph, Rich and Alan use a laser rather than a flashlight and their LIDARs can turn the light on and off in nanoseconds. They can also measure many things about the light that leaves the laser and the light that returns.
Let’s take this one step further. Imagine that flashlight, dark night and poop and pigeons over head again. Also imagine that you can measure how long it takes for the beam of light to go out to some pigeons and then bounce back to your eye. If you know how fast the light is going you could calculate how far away they are and where the poop is located. If we put this all together and measure both how much light bounces back and how much time the light has traveled, you could determine the amount of poop at different distances.
Enough pretending and imagining, lets get back to the LIDARs. Light travels approximately 186,000 miles every second (it is about 25,000 miles around the equator) and the LIDARS can measure the time it takes the light to travel just a few hundred yards. Rich and Christoph’s ozone LIDAR is sensitive enough to measure ozone in parts per billion from 2-3 kilometers away and Alan’s LIDAR can measure wind speed and direction 3-4 kilometers away from here. They do this using a principal similar to the flashlight example, but obviously much more complicated. Chris and Rich’s ozone LIDAR uses a UV laser, picked specifically because its light will bounce off particles in the air (the pigeons) and be absorbed by ozone molecules (the pigeon poop). Allan uses an infrared laser that will bounce off particles floating and moving with the air. The particles, which are much too small to be seen would, as Allan said, seem like boulders to the beam of light.
What that all means, is that for the next six weeks along the ship’s path, the LIDAR’s will be measuring the amount of ozone pollution in the atmosphere, the wind speed and the wind direction.
The ozone LIDAR’s will eventually be used to show the amount and location of ozone pollution in the atmosphere from about 50 meters above the ocean surface up to 2-3 kilometers. The Doppler LIDAR data will be used to make a similar map of the wind speed and direction during the 6 weeks at sea. Eventually these and other data can be merged and compared.
What about those blind men examining the elephant? The first had grabbed the leg, the second had grabbed the tail and the third had grabbed the trunk. None of them of course had a complete picture of the elephant. During NEAQS-ITCT, hundreds of people are examining an elephant this summer. Individually they cannot give us a clear picture of the elephant. The elephant is air pollution. The more parts that can be accurately examined the better the picture. Instead of a trunk, tail and leg to observe, the scientist are examining the many kinds of chemicals in the pollution, the particles in the air, the movement of the pollution and the movement of the air. Different methods can be used to insure accuracy. Once each part of the elephant has been thoroughly examined and understood and all of the blind men evaluate their observations maybe they will have at least a partial picture of the elephant.
Question of the Day
What does LIDAR stand for?
How much of a second is a nanosecond?