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Ocean Surface Topography from Space
Riding the Waves
June 01, 2008

One of JPL's most accomplished and critical oceanography studies continues with the launch of the Ocean Surface Topography Mission on the Jason-2 satellite, scheduled for June 2008 from Vandenberg Air Force Base. The mission is a follow-on to TOPEX/Poseidon and Jason-1, which have contributed to a climate data record of more than 15 years that has shown key indicators of how ocean circulation and global sea level are linked to climate change. Project Manager Parag Vaze and Project Scientist Lee-Lueng Fu provide an update.

Project Manager Parag Vaze
Project Manager Parag Vaze

Image credit: NASA/JPL-Caltech
What are the mission's main objectives?

Vaze: We will build on everything we've done before in space-based oceanography. From an organizational perspective, one of our objectives has been to transition our altimetry ocean data from pure research to a truly operational type of measurement, discovered and enabled on Topex and then refined on Jason. Now that people in the user community have recognized the utility of this, they would like to move it into an operational type of measurement.

What we've been able to do with our space-based ocean data is to achieve the goal of many missions, which is to take a discovery or a measurement and actually bring it into daily use.

And the way we're planning on doing that from an operational perspective is to have two new partners in this mission. As in the past we are working with Centre National d'Etudes Spatiales, the French space agency. Our new partners are the National Oceanic and Atmospheric Administration, from the United States, along with the European Organisation for the Exploitation of Meteorological Satellites, which provides meteorological products to the European community.

How is your mission an improvement on what Topex and Jason-1 have provided?

Vaze: It's clearly different from Jason-1; we're trying to enhance all aspects of it. From a JPL perspective it's particularly reflective in the main instrument we're providing, the advanced microwave radiometer, which was designed and developed here in Division 38, completely in-house. It's a significant generational improvement from the past radiometers we've been flying. Even on Jason-1, most of the basic design was on the order of 20 to 30 years old.

Now we have the advanced microwave radiometer, which is on the cutting edge in terms of electronics technology, the overall design, performance and reliability, which has been a significant achievement.

Project Scientist Lee-Lueng Fu
Project Scientist Lee-Lueng Fu Image credit: NASA/JPL-Caltech
Fu: Topex and Jason-1 performed excellently over the open ocean, and the advanced microwave radiometer will improve those measurements. In particular, the radiometer antenna is larger than that on Jason-1, leading to better resolution. For example, the radiometer will take accurate measurements up to 25 kilometers from the coast instead of Jason-1's 50-kilometer capability. Another key enhancement will be the data from the altimeter, which will provide much more accurate measurements near the coastlines -- within a couple of kilometers from the coast instead of 10 kilometers. We will therefore have much better coverage of the world's coastal zones. Most of the population lives close to the coast, so there's a lot of interest there, and getting more data is going to help with that.

Are there any significant lessons learned from Jason-1?

Vaze: Not so much from a problematic perspective but from a performance improvement perspective. For example, the advanced microwave radiometer's antenna has a whole new design that not only improves just the radiometer's performance, but we've done it synergistically with the altimeter, provided by the French space agency, that has also improved its performance such that the overall mission products can be significantly improved.

With these instruments on TOPEX/Poseidon and Jason-1 the main thing was to make sure they worked in the open ocean. Now that we know how to do that, we want to get measurements closer to the coast -- that's where the mission's impact on society makes a big improvement.

But we still need lots of coverage to understand currents, sea-level rise, tides and their interactions, and one of the most interesting phenomena, eddies, which are localized phenomena that happen in the open ocean. One of the things we're looking forward to is a dual operation with Jason-1, where we can increase our resolution by two.

How will that work? What are the advantages?

Vaze: A tandem operation with Jason-1 helps us in two ways: we can quickly calibrate our instruments to continue our data records between the two missions, and it also increases our resolution because we have two altimeters on slightly separate ground tracks and similar overflight.

We will actually launch to a slightly lower orbit than Jason-1, then over a period of a month or so, there will be some small corrections to get into the exact orbit as Jason-1. We will follow roughly between one and 10 minutes behind Jason-1 on the exact same ground track and orbit.

That's our calibration validation phase -- not only our individual instruments but between the two satellites. One of the challenges is to how to bridge the data records between the two missions; there are always some differences in the measurements. We expect this phase to take roughly six months.

Is this is a classic example of a great international mission?

Vaze: I believe so. The policy among all our partners is that all of the data is free and publicly available and was intended to be used by the global community. One of the most interesting things in my history with this program is when we have science team meetings, there's a map of the global community and we can see it blossoming and growing across all areas of the world, including places like Africa and Asia -- where there hasn't been a big space emphasis -- but the utilization of this data, and the science research behind it, has been significant.

Fu: There's one particularly interesting example from Australia. A team of Australian rowers recently set a record of rowing from New Zealand to Australia. Their adventurous journey had benefited from using the information on ocean currents from Jason-1 data. That type of information was very useful to them by optimizing their route of rowing.

Also, our information on currents is used by the offshore drilling industry in the Gulf of Mexico. The routes of towing drilling rigs have been optimized from using the information. The cost savings from minimized rig down-time and transportation expenses amount to more than half a million dollars from one single operation. And this information is not exclusive to our country. Similar applications are taking place in northern Europe. There are a lot of activities in the North Sea, where they use altimeter data for currents, wind and waves all the time.

Another great use of our data is for hurricanes because the altimeter measures the heat stored in the upper ocean and thus provides information on how much fuel lies below the surface for driving the hurricane, which is important in predicting how strong the hurricane will become. That is a unique piece of information because just knowing the sea-surface temperature, whose information content is only skin deep, is not enough for making such predictions.

All of the partnership efforts so far have been tremendous. The planning and collaboration between NASA and the French space agency goes back to 1983, about 10 years before the launch of TOPEX/Poseidon, and is now used as model for the way to conduct international missions.

TOPEX/Poseidon is best known for the El Niño and La Niña phenomena; what other types of significant climate/weather revelations can we expect from OSTM?

Vaze: What I look forward to is the major application of our data in day-to-day forecasting models for weather and other events such as hurricanes. I expect that someday we will have made a big improvement in the understanding of these critical events, especially along the coastlines - to me, that's going to be the biggest improvement and most beneficial short-term impact in terms of mission return. The long-term study will also lead to a greater understanding of the ocean's role in the global climate system.

Fu: The discovery of El Niño and La Niña certainly made TOPEX/Poseidon famous, not only for the public but also for the scientific community. We documented for the first time the evolution of a big El Niño and a big La Niña - from 1997 to early 2000 -- after that, the El Niño and La Niña both became smaller. This kind of a variation of a well-known, short-term climate phenomenon is very important because now we've found the connection between El Niño and much larger-scale change in the Pacific Ocean, the Pacific Decadal Oscillation. We've just begun understanding the interactions between the Pacific Decadal Oscillation and ocean circulation.

TOPEX/Poseidon planners, including myself, had a lot of doubt when we first began seeing these tiny, minute changes of global sea level; we wondered, was it a true signal or just an error? Over 10 years, through extensive analysis and validation, we knew this was probably the first truly global measurement of sea-level change. And sea-level change reflects a potentially serious consequence of global warming, which has timescales of over decades, so it's critical to continue this important data record of global sea-level change.

How far into the future?

Fu: Indefinitely. What we have done so far is just the minimum to understand the ocean, which influences climate in a tremendous way. Every day we have to deal with weather; climate is long-term changes in weather with much bigger magnitude. Now we have the technology; we have no choice but to continue. It is the responsibility of our generation.

What is next after OSTM, or do you look that far ahead?

Fu: We do look ahead. There is currently a plan for Jason 3. Both the French space agency and the European Organisation for the Exploitation of Meteorological Satellites want to continue and have secured half the funding for Jason 3; the other half will come from the United States with the National Oceanic and Atmospheric Administration as the lead agency. And the international scientific community is behind us.

For the future, beyond Jason, I'm working on a very exciting project called the Surface Water Ocean Topography mission, which will bring the current capabilities to measure the ocean surface to the next level - on a scale of 1 to100 kilometers - these are the scales of ocean turbulence, which influence the oceans' intake of heat and carbon dioxide, in a profound way.

This is a significant technology challenge, so it falls under NASA's priority. This is exactly what NASA was established for - to drive the edge of technology to benefit the science.

About how many people are on the science and operations teams? How many from JPL?

Fu: we have six JPL principal investigators on the team. Overall, there are 74 principal investigators from 16 countries around the world.

Vaze: Right now we're a small team, since we've delivered our instruments and are preparing for launch, but the developmental team was 40 to 50 people spread across divisions 33, 38 and 31.

How are launch preparations at Vandenberg? What is your launch window?

Vaze: We are on schedule for a June 15 launch. All preparations are in place and we're continuing through our standard process of final checkouts and reviews but so far it's going extremely well.

We will be ready to launch daily, with a Nine-minute window in which we could launch and fully achieve our mission objectives.

We're launching very early in the morning, at 1:47 a.m., so we hope to see a spectacular launch. I can't be sure, but I think there's a very good chance folks in the Los Angeles area can see our launch as our flight path moves south along the coastline.

We're excited and are expecting a successful launch, and we look forward to seeing all our hard work over the years pay off, getting our data back and having scientists use it to see the impacts it makes on daily life.

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