Eyes on Earth Episode 10 – Landsat and Water Quality
We tend to associate Landsat satellites with what we see on solid Earth, but they can also tell us much about the health of our inland and coastal ecosystems. Landsat can be used to monitor harmful algal blooms, for example. Eyes on Earth guest Dr. Nima Pahlevan, a Landsat Science Team member, is part of a research team that tracks algal blooms worldwide using Landsat data.
YOUNG: Hello everyone. Welcome to this episode of Eyes on Earth, a podcast that focuses on our ever changing planet and on the people from across the United States and the world who use remote sensing to help monitor and study the health and well-being of our planet. I am your host, Steve Young. Todayís guest is Dr. Nima Pahlevan, a government contractor and a remote sensing scientist with the Terrestrial Information Systems Lab at NASAís Goddard Space Flight Center. He is also a member of the Landsat Science team. Welcome, Dr. Pahlevan.
PAHLEVAN: Thanks for having me.
YOUNG: So, you study water quality in coastal and inland waters. Talk a little bit about coastal waters. What are the issues driving concerns about coastal water quality?
PAHLEVAN: Thatís twofold. Basically, there is on one side, we have climate change and extreme events like flooding, like significant amounts of rain, and droughts. On the other hand, we have human-induced activities, like agriculture. We have a lot of over fishing. We have over use of resources in coastal waters and inland. And all these variables together with climate change impacts, would have impact on the quality of water. They basically together increase the eutrophication in the water. Which is a significant problem. It overall changes the ecosystem of the coastal areas and any lakes and land bodies of water.
YOUNG: The same issues that drive concerns about coastal water would apply to inland waters as well?
PAHLEVAN: Absolutely. So, itís even worse because there are other aspects of usage of inland waters which is like recreation, tourism and many other factors, and it is normally surrounded by people living around it. So, there is all sorts of usage of inland waters, bodies of water, plus they could be used as water supplies, drinking water, so thatís even more concern because you have to be careful about whatís in the water that human beings tend to drink.
YOUNG: So how can sensors on the satellite 400 or more miles up in the sky tells us whatís in the water and what these hazards are?
PAHLEVAN: From the satellite, what we can see is the material that impacts the color of the water. Those are basically excessive chlorophyll or phytoplankton in the water which are tiny, teeny living material in the body of water. They are essentially the source of the food chain. If there are a lot of them, we see a significant greenness in the body of water. So, that is easily captured in the satellite images. The excessive greenness in the water could allude to a harmful algal bloom situation, which should be avoided by decision makers.
YOUNG: So you are creating water quality products to help decision makers and environmentalists? What are those products and how are they being used?
PAHLEVAN: They are basically chlorophyll A products which is the primary pigment in phytoplankton. These enable you to essentially track changes in the ecosystem, potential excessive growth of phytoplankton. Lack of phytoplankton could be a problem. We also can provide sediment, the amount of suspended sediment in the body of water because sediment increases the amount of light that satellite can see from the space. Thatís also something that can be derived from satellite measurements. We can also look at organic matter, dissolved organic matter in particular that is directly related to dissolved organic carbon, which is a very important parameter in dealing with carbon cycle and analogy.
YOUNG: So, how deep in the water can you look, and why is that important?
PAHLEVAN: So first and foremost is creating bathymetry, that is one of the major applications of satellite remote sensing aquatic environments. If there are not too many particles in the body of water, or simply put, if the water is not quite turbid, then you would be able to see the bottom as long as it is relatively shallow. So, it could vary from a meter or half a meter to 20, 30 or 150 meters in an ocean environment. So at that penetration, that varies from body of water to the other one. In coastal water, like in coral reef areas where water is in general clear, you would be able to see the bottom because there is not much turbidity and there is not much stuff in the water. So that penetration depth again varies from one-half a meter to 100-200 meter in the open ocean where the water is clear and there is not much stuff in the water. Itís important to be able to see the bottom when you are trying to achieve bathymetry and you also try to make an assessment of the health of coral reefs. So those are the areas where you really care whether you can see the bottom. But, in other areas, where you want to look at water quality, seeing the bottom could add complexity in terms of how you can estimate the quality of water. So, sometimes you want to see the bottom and sometimes you donít want to see the bottom. Itís a situation where you need to understand what youíre after.
YOUNG: So, with a satellite sensor, you could see 150 meters?
PAHLEVAN: Yes, you can in the open ocean, in the blue portion of the spectrum, blue-green 490 nanometer, you would be able to see that deep in a body of water.
YOUNG: So, the last question is how might Landsat 9 and future Landsat missions even other remote sensing platforms aid in your work going forward?
PAHLEVAN: So Landsat 9 is going to be very similar to Landsat 8. Our committee essentially will use some of the improved enhancement to Landsat 9. For Landsat 10 and beyond, again, we are hoping we can help environmentalists and water quality modelers and those decision makers who are after harmful algal bloom forecasting to be able to provide them higher-level products like the type of phytoplankton, the phytoplankton species, algal groups, size, classes, etc ... Those parameters could go into water quality models or help forecasting systems, harmful algal bloom forecasting systems in the future. Today we donít have these models, but in 10 years from now, looking ahead, we should have more accurate products.
YOUNG: Weíve been talking to Dr. Nima Pahlevan about his work using remote sensing to look at coastal and inland water quality. Itís been a wonderful conversation Dr. Pahlevan.
PAHLEVAN: Thanks again for having me.
YOUNG: We hope you come back for the next episode of Eyes on Earth. This podcast is a product of the US Geological Survey Department of the Interior. Thanks for joining us.