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Summary: Scientists at EROS use tools like Landsat to produce land cover maps, which tell us if landscapes are rural or urban, cropped or forested, wetland or shrubland. Those maps help scientists at EROS and around the U.S. study the impact of changes in land use on not just landscapes, but on ecosystems, patterns of resource use, wildlife habitat, and much more. In this episode, we learn about the basics of land use and land cover study research from Geographer Roger Auch.
Roger Auch – Land Use Young: Welcome to this episode of Eyes on Earth. We are a podcast that focuses on our ever-changing planet and on the people here at the Earth Resources Observation and Science Center, where we collaborate with colleagues across the US and world to monitor and study the health and well-being of earth. I’m your moderator, Steve Young. Today’s guest is Roger Auch, a research geographer here at EROS. Welcome, Roger. Auch: Hi, Steve. Young: Tell us a little bit about the kinds of things you study and the work you do at EROS. Auch: I consider myself a national and regional land use geographer. USGS does not map land use per se, we map land cover. But we use land cover as a surrogate for land use in many instances. Landsat provides a synoptic view of the earth, of parts of the earth at a time. It is considered a moderate resolution earth observing satellite. And so, right now the 30 meters is a good resolution to understand the landscape that it sees underneath. It flies in set orbits, it can capture a view of the same area of ground every 16 days. So, over years of time we can see if the land cover, and land use has stayed the same, has changed…lots of things. It’s kind of a great tool to start getting data, that we can then do an analysis on that data. Young: I understand that Landsat orbits the earth at an altitude of 438 miles. How is it possible to look at Landsat images of the same piece of ground over the decades from that height, and tell what the changes have been? I mean, how do we do that? Auch: The sensor is picking up pieces and parts of electromagnetic spectrum as it reflects off the land. We can then use those values to understand what that is. So water absorbs most of the visible light, so it tends to have a very low say in the near infrared, a very low reading. So, then you can say, “Oh, that’s water”. Or this reading, that tends to be evergreen trees. Or this particular reading tends to be asphalt or pavement. So, even though it is 400+ miles in space, we can get those readings that the sensor is capturing from the earth and make something such as land cover maps from that. And then we can take those land cover maps and do analysis of it and see trends of changes or the leading types of changes or the rates of change and things like that. Young: How much of a significant land cover change in this country simply relates to urbanization and the growth of our cities? Auch: Urbanization is a fairly…. probably the best well known and probably most thought about land change that occurs in the US and globally as well. One reason why that is, is because 80, 85-90% of the American population lives in some sort of metropolitan or micropolitan area. Most people live within built up areas. But actually, the amount of developed land in the United States is fairly small compared to the other big land uses and land covers, 5% plus or minus a little bit. But, urban land touches many other aspects of the country because the raw resources needed to keep people living in high density things, like urban areas, has to come from someplace else. You need food sources, so agricultural output goes to cities. You need building materials. So, when I built my house in ’08, the wood panels came from some rural place in Idaho. We need fuel sources. So, we mine areas for fuel. Urban areas can touch out and reach very rural areas and that’s the way it affects it. Young: Why should people care about land cover changing? Auch: Nothing in nature works in a vacuum. There’s always consequences and trade-offs on how we affect the land. If you put in a new business center, or retail center, you are converting land. You are changing it from agricultural or forest to this developed and built up. So, the negative aspect may be more urban water run-off coming off of that new parcel. On the other hand, it is providing many new jobs. We have to kind of balance or understand the cost of “if we do this it will change things here.” We have to weigh whether those costs are worth it or not. The problem is a lot of time we haven’t weighed the costs and we just do it and we find out the consequences later on. Young: Where do you see the value of remote sensing and tracking change into the future? Auch: The great aspect of remote sensing is, and Landsat in particular, is its time span. We’ve now had a Landsat flying for 45+ years, if I do the math right. We can see how the land has changed or stayed the same over time if we go over that entire record. I personally think the MSS holdings that we have here which was from the first couple of Landsats may be some of our most valuable data because that establishes a baseline. Of course, there was change happening before 1972, but that baseline gives us the ability to look forward. That’s one reason why it is important to keep satellites like Landsat going because we can increase the temporal span and change processes that may take longer than 30 years, we can start seeing where as if we just have 10 years of observation we may not see or understand those kinds of change processes. Young: Is the American landscape as a whole much different today than when the first Landsat launched in 1972? Auch: It depends on what kind of accounting method you use. The US land use system is a fairly mature system and we know what uses fit the best, some through some painful trial and error. For a kind of general land cover accounting, especially if you have only maybe 10 classes, it hasn’t changed that much. It’s the more complex aspect within those measurements. Take for example the southeast. It’s one of the biggest industrial forests in the world. Much of the forest in the southeast is fairly young. There is very little old growth forests in the south. The amount of forests may not have changed much but it may be much younger than it was in 1972. Or, it may be growing older than that. We also don’t see the aspects of intensity. We have some scientists here at EROS who are studying water usage by using remote sensing. The amount of irrigated farmland, has that gone up, has that gone down? Is that more concentrated? What other inputs? Are we using our land more intensely than we did in 1972? Probably so, but that’s not something we can directly measure just by doing land cover maps. We would have to do more information and more types of analysis for that. Young: We’ve been talking to Roger Auch about land cover, land cover change and his work here at EROS. It’s been a fascinating conversation, Roger, thank you. Auch: Thank you very much. Young: We hope you come back for the next episode of Eyes on Earth. Thanks for joining us. This podcast is a product of the US Geological Survey Department of the Interior.