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NASA SWOT (Surface Water and Ocean Topography) satellite, launched on December 16, to survey all water on Earth
Interview with Jean Bergeron, Missions Scientist, Canadian Space Agency

WT Staff

Interview with Jean Bergeron, Missions Scientist, Canadian Space Agency

WT: SWOT is a satellite that went up into space on December 16, 2022. It was launched in California with a mission to be the first satellite to survey all water on earth. Led by NASA and France with contributions from the Canadian Space Agency and the United Kingdom, it will observe fine details of hydrological and oceanographic knowledge.

Thanks for doing this Jean.

Jean Bergeron: The pleasure is mine.

WT: Can you give us a rough idea of when this idea was hatched to launch? What was the in-between and how did the process work?

Bergeron: SWOT has come a long way, these discussions started long before I joined CSA. SWOT has been roughly twenty years in the making, from the time scientists started to think about this wide-swath capability to monitor surface water. Until then, there were only satellites equipped to look at the water elevation with a fine, one-dimensional look, directly under the orbit track, giving a very limited view of what’s really happening.

It's only about ten years ago that NASA knocked at the Canadian Space Agency’s door to bring us on board.

CSA has the “space heritage” in key technology for SWOT, particularly what we call the extended interaction klystrons (EIK) which amplify the power needed by the wide-swath altimeter instrument. This is the main novelty of SWOT. Canada had the space heritage in the development of this key component, of course, NASA is interested in leveraging this expertise. This is how things evolved. 

From our point of view, this is helping our Canadian industry become further-renowned experts in cutting-edge technology and allows us to participate in SWOT science development, and the SWOT science team. We have had an agreement with Canadian departments to ensure that our Canadian scientists are ready to ingest this data once it becomes available, to advance models and algorithms.

WT: The Canadian contribution to this satellite comes down to a “klystron”, is that right?

Bergeron: Extended-interaction klystron (EIK), yes.

WT: The first time I heard of a klystron was in a book about the Spanish civil war, a guy called Hanson was trying to develop radar to see the German bombers before they got there. Is this the same klystron that we are talking about today? Are you really expanding the use of these klystrons?

Bergeron: I can’t comment on the origin of the klystron technology. All I can say is what its purpose is right now, to amplify the power that is needed by the main instrument (of SWOT).

WT: This satellite has two antennae, is this the big breakthrough? How do you get (surface water) depth out of using your klystron technology? Can you talk about how you measure that third dimension of water?

Bergeron: Essentially SWOT has two arms. The concept here is to use radar interferometry. A pulse of microwaves will be emitted from the satellite, will reach the surface and will come back to the satellite. The return signal will be measured simultaneously by two antennae separated by a 10m boom on the satellite. Based on the difference in the properties of the signals that are returned, as measured by these two arms, we can infer information about the change in (water) elevation.

WT: One quote I read about this mission is that it gives privileged access to software tools required to understand SWOT. Can you tell my viewers what kind of software you need, and why is this so very important?

Bergeron: The software referred to here is the instrument simulator. A few years ago, when we were developing this mission, we had expectations regarding what the instrument would actually see, but until actual measurements are taken, we can’t evaluate its performance. We typically build software ahead of time that will simulate this data, specs on the instrument itself, the kind of orbit it will follow, and the noise coming from the surface, adding in all the potential noise contributions from various sources as much as we can. This shows us what instruments should be seeing under these conditions. This allows us to determine how the satellite will behave under certain conditions, so we can push the limits. What happens if it is very windy on the surface? Or, if it’s not windy, how does this change what the satellite should see? The extended interaction klystron (EIK) is how the satellite sends the microwave pulse to the surface. EIK bunches the energy up to give a really strong pulse. Without EIK, a weaker continuous signal would be emitted, but it would not be strong enough to bounce back and read the satellite with a significant signal.

WT: This EIK is an amplifier of the signal then, more powerful, is that correct?

Bergeron: An analogy would be to have a regular flashlight. In the dark from far away, you would see a faint light. This (technology) is more like a lighthouse, a strobe light, shorter pulses, and much brighter.

WT: I read SWOT could help us be better prepared for flooding. What does this mean, why does this matter to someone who may or may not be flooded in the immediate future?

Bergeron: The answer is two-fold. The first is, SWOT is expected to improve our ability to monitor current inland water bodies. Of course, areas that are flooded should be detected, provided the flooded area is large enough. This is not just detecting the (area) limits of the flood area but also how high it goes. You can imagine that having a centimetre of water on your property is not the same as having a meter of water on your property; the extent of damage will not be the same at all.

SWOT will provide regular observations of water surface extent and water surface elevation. That is in the short-term monitoring.

The second part lies in our effective ability to forecast these events and improvements in our ability to forecast. This is an indirect impact. The idea is, if we have a better idea of the current condition of our lakes and rivers, this is a better starting position to make a forecast. If we have a storm coming in, and the lakes and rivers are very low, then it is not expected the storm will have the same impact as when the lakes and rivers are already full. In this way, the SWOT can give us better knowledge of current conditions helping us improve our ability to forecast floods.

WT: If I have this right, this means that SWOT can predict (flooding)? Will it know where the water is coming from, also know where it is going, and how much water is going there?

Bergeron: That’s correct, yes. Understanding the connectivity of lakes and rivers and reservoirs.

WT: I read that SWOT will figure out how thick the arctic ice is. Can SWOT see how thick the ocean ice is in real-time? Is that also accurate?

Bergeron: It’s a very good question. This is something many of us are very interested in finding out. The reality is, SWOT is designed to measure surface water elevation. This is what all the missions have been designed for. Now, what else can it do? Snow and ice, for example, can we measure surface elevation? At this point, it is speculation, so I am not going to commit to answering this question, but many of us are looking forward to finding out.

WT: I read on the Canadian Space Agency site that SWOT will provide coverage for most lakes and rivers 4 times every three weeks, including northern Canada. Can you explain why four times, and why every three weeks?

Bergeron: There are many different orbits a satellite can follow. Some are designed to be in a geostationary orbit. From our point of view on the earth, they appear to be always at the same place in the sky, the equator for example. Others are helio-synchronous, organized to always take the same measurement at the same time every day. They are synchronized with the time of day and everything in between. 

SWOT does not fall in either of these categories. The orbit that it will follow, how it has been designed, it will orbit from near one pole to near the other pole, continuously. It will take 21 days to get back exactly to where it was 21 days previously. This is what will allow it to provide global coverage. Going from pole to pole means areas closer to the poles will get some overlapping measurements. It is expected that Canada, being closer to the pole, will have more frequent observations.

WT: If I am on some sort of flood response team, is the expectation that I can dial into a website for SWOT and see that water at a certain location was this high by last night and today is this high, is this accurate?

Bergeron: The data will be open to everyone, accessible, and free. Not before SWOT has gone through a number of steps; it just launched, so there are a number of steps to be completed before this data becomes available to everyone. Once it does, it is going to be a matter of a few clicks to go online and download the data to see what SWOT actually saw on a particular day on a particular area. One thing to consider is the latency between the time SWOT will take the measurement to the downlink and the processing, the data archive. The data distribution centre will need to perform a number of quality checks, and apply the algorithm to translate the raw data into something meaningful to users. This will take some time. The latency is the time between measurement and when the data is available to everyone.

WT: Do you see that latency being in hours, days, or weeks?

Bergeron: It depends on the data, some would be available ahead of others. I would not say hours, some data will be available in days or weeks.

WT: How long is this mission supposed to go on?

Bergeron: Baseline, the mission is designed for three years. Beyond that is speculation. We would all wish, assuming SWOT behaves as we want it to, we hope it lasts as long as it can. We have to go through the first crucial steps, then assuming this is all successful, it will last three years beyond that, I can’t say.

WT: I think I will wrap this up, is there anything else you would like to add? What do you suggest for students, to go to the site, and learn all about it? How do you recommend kids interact with SWOT for information about climate change?

Bergeron: Water is one of the most precious resources on earth. We know there are many lakes in Canada, but the reality is that only a small fraction, less than 1% are currently monitored for change in water surface elevation. 

So, how vulnerable are we in the face of climate change? 

Are these lakes filling up or empty, for example? This is not the kind of information that we (currently) have.

We hope that the time series that SWOT, and hopefully subsequent missions would be able to provide is a portrait of reality, and how vulnerable we really are. 

This is a mission that is designed by engineers. At the forefront of data analysis are many scientists. The impact of SWOT data and the kinds of applications that it can end up with are not restricted to STEM. I see a role for many different actors, from decision makers to business owners, to hydro-power companies, to communities that are trying to manage water to satisfy the needs of their communities. STEM is important but there is room in this SWOT mission for all kinds of backgrounds.

WT: Thank you, Jean, I will leave it there.


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