Lorraine Remer: From satellites, we’re able to look at the Earth as a unit, as a globe, as one thing. And nothing brings it home more to me than to watch dust plumes start from one continent and visually see them cross oceans and reach another continent.
Lorraine Remer is a physical scientist at NASA. She studies airborne dust from space, using a satellite imaging tool that can captures images of almost the entire globe in a single day, day after day. She said some plumes of dust in Earth’s atmosphere are 2,000 kilometers wide – that’s about the distance from New York City to Miami, Florida.
Lorraine Remer: When I talk about dust in a global sense, what we’re really talking about is a relatively fine mineral particle. It’s most likely from a place that used to be a lake and had a lot of sediments deposited when the lake dried up and left these exposed particles. So when the wind comes up, they’re very lightweight and can be transported pretty high up into the atmosphere. Then they hit the upper layer winds and are transported far distances, across oceans.
Remer said thousands of tons of dust sails from the Sahara desert in Africa into South America’s Amazon rainforest.
Lorraine Remer: The dust from Northern Africa that is transported to South America from the Amazon may be benefited from this transport by adding iron nutrients to the soil for the terrestrial plant life to grow. But again, these are hypotheses. They’re still being explored, whether they’re actually taking place or not.
She said the dust in the large plumes that travel across the globe isn’t like sand particles you might encounter in some more localized dust storms.
Lorraine Remer: Dust can mean many things. I’m from Southern California, and I’ll visit my parents who live in the Coachella Valley, which is near Palm Springs. If I go in February, at least one time during my five-day visit, we’ll have a dust storm. The wind blows real hard, and there are a lot of particles, almost like small sand particles, that are suspended near the surface. We don’t go out on that day because that dust would pit the windshield on your car. But that dust never really gets up high in the air and gets transported, because it’s like sand.
Dr. Remer spoke about the instruments aboard the Aqua satellite and other Earth-orbiting satellites that study airborne dust. Some have a broad focus, while others have a more narrow focus but capture greater detail.
Lorraine Remer: The Aqua satellite has several different instruments on the satellite. And the one I’m most familiar with is MODIS, also known as the Moderate Resolution Imaging Spectral Radiometer. Its advantage is that it sees over a 2,000-kilometers swath, as it circles the globe. It gives you the ability to image the globe, almost the whole globe, in one day. So you can see broad expanses of the globe. There are other satellite instruments on Aqua, and on other satellites flying, that also see dust. But they have a more narrow focus, so, while they may get more detailed measurements of the dust, they don’t see the whole picture in a broad way.
Remer said the Aqua satellite – and its MODIS instrument – produce vivid, striking images
Lorraine Remer: But these are calibrated instruments and they provide data, quantitative data that we can use and interpret. We can try to understand dust characteristics a little bit better than if we were just visually seeing the dust. We can get down to optical properties of the dust, and maybe how it affects climate and other things like that.
She said that the MODIS instrument reflected solar radiation from the Earth surface.
Lorraine Remer: So what happens is that sunlight comes from the sun, comes down through the atmosphere, and is reflected by the dust particles in the atmosphere and also by the ground. It’s that reflected sunlight that MODIS is measuring. We can get numbers from this. We break it down into different wavelengths, different colors. And from this information we can determine a lot about the dust. We can determine its color, or its spectral properties and how much of it exists there, how much reflected radiation we receive versus what we would expect from the Earth’s surface, to tell us how much dust is in the atmosphere.
Our thanks today to NASA’s Aqua Mission, improving our knowledge of our home planet through satellite observations.