Observation of Disaster Areas During the Night. Contributions of ALOS-2 and Expectations for ALOS-4 [Space Brothers Collab #28]
“Space development” describes a wide range of developments and their objectives. In this series, we will contemplate the present and future of space development with Astronaut Serika Ito, who has been appointed Chief Dream Officer of Warpspace.
In the 28th edition, we welcomed Mr. Shinichi Sobue, Mission Manager of the Advanced Land Observing Satellite-2 “ALOS-2” of the Japan Aerospace Exploration Agency (JAXA), to share with us the work of a mission manager and the contribution of earth observation satellites to disaster damage assessment.
The mentor and astronauts brought him to JAXA.
Serika: This time, we visited the Tsukuba Space Center to talk with Shinichi Sobue, Mission Manager of ALOS-2.
Mr. Sobue: Serika, it’s a great pleasure to see you!
The reason I joined the National Space Development Agency of Japan (NASDA, now JAXA) was because a professor in my university laboratory was involved in the space experiment conducted by astronaut Mamoru Mohri when he became the first Japanese to fly on the Space Shuttle. My major at university was robot control, but I was vaguely interested in space. As I was looking at the picture of Mr. Mohri and the university professor together, I thought I wanted to join NASDA, too.
Serika: So you did! What projects have you worked on at NASDA/JAXA so far?
Mr. Sobue: After graduating from university, I first worked at the Earth Observation Center in Hatoyama, Saitama Prefecture. The Earth Observation Center has a huge parabolic antenna that receives data from Earth observation satellites.
I joined NASDA in 1989, just before the launch of the ocean observation satellite “Momo-1b” (MOS-1b) in 1990, and in 1992, Japan’s first satellite equipped with Synthetic Aperture Radar (SAR), “Fuyo-1” (JERS-1), was scheduled to be launched. I was in charge of the system to provide data received and processed after launch.
What is a SAR satellite?
A satellite radiates radio waves to the earth’s surface and produces images from the reflections. It is characterized by its ability to observe the earth’s surface at night and in bad weather.
The system in those days was completely different from that of today. JERS-1 acquired data on the entire surface of the earth (the entire globe), and this data was used for land surveys, natural resource surveys, agriculture, forestry, fisheries, environmental conservation, disaster prevention, coastal monitoring, etc.
Observation data was recorded on magnetic tapes like large cassette tapes on board, and the data was received by playing back the tapes taken when JERS-1 passed over the ground station.
Ground stations were put in Alaska, the U.S., and some other nations. In the mid-1990s, with the rapid spread of the Internet in the U.S., it became possible to send data online from Alaska to Japan.
I also participated in the KAGUYA (SELENE) project, a lunar orbiter launched in 2007, because I was told that “looking at the Earth is the same as looking at the Moon.
Serika: The lunar topographic data taken by KAGUYA was also used for the SLIM (Small Lunar Module Demonstrator) lunar landing in January 2024! I expect that KAGUYA’s data will be used in future manned lunar exploration as well.
Features of ALOS-2 and 4
Serika: What kind of satellite is ALOS-2? Could you tell us again?
Mr. Sobue: ALOS-2 was launched in May 2014, and its strength is that it is equipped with a SAR sensor in a wavelength band called the L-band.
Most SAR satellites use sensors in the X-band and C-band wavelength. SAR satellites are used to detect changes in the earth’s surface by making multiple observations of the same location and comparing the data (interferometric SAR), but since Japan is heavily forested, especially in summer, X-band SAR data cannot be compared after a month of observation. Therefore, ALOS-2 is equipped with an L-band SAR sensor, which has a longer wavelength than X-band SAR and can detect the ground surface through vegetation.
The ALOS-4, the successor to ALOS-2, which will be launched in 2024, is also equipped with an L-band SAR sensor.
Although ALOS-2 and ALOS-4 are two separate projects, they are satellites in the same family, so the project members of ALOS-2 and ALOS-4 are discussing and working together so that they can be operated in cooperation.
The ALOS-2’s 3-meter fine-scale observation range was 50 km, but the ALOS-4’s range extends to 200 km. Image: Haruka Inoue
Another feature of ALOS-2 and 4 is that they use orbits that pass over any area on Earth at noon and midnight local time. SAR satellites that emit radio waves by themselves consume a lot of power, so they often use orbits where the sun hits them in a certain direction, and power is easily secured.
But ALOS-2 and 4 chose orbits that pass overhead at noon and midnight to quickly gather information in the event of a disaster. When a disaster such as a landslide, tsunami, or flood occurs in the middle of the night, it is both too dangerous and too dark to fly aircraft or have people survey the area. In order to deploy emergency vehicles immediately the next morning to the areas considered to be most damaged, we need information on the full extent of the damage by 5:00 am. That’s why ALOS-2 and 4 make observations at night, and we automate data analysis so that we can provide the data to the relevant agencies by the next morning.
ALOS-2 and 4 are also equipped with an AIS (Automatic Identification System) to receive vessel identification signals. In-SAR data, the ocean appears dark, but ships appear bright. SAR data shows the ocean darkly, but the ship brightly, so SAR satellites can detect vessels that have turned off their AIS.
“Mission Manager” manages satellite operations and data usage
Serika: I’m starting to understand the characteristics of ALOS-2 and ALOS-4! What is the role of a “mission manager,” Mr. Sobue? I’ve heard of a “project manager”…….
Mr. Sobue: Basically, JAXA’s satellite projects last from the development phase to the end of regular operations. The project manager is responsible for overseeing the entire process from satellite development to operation, from research and development of technology to operation and data utilization, in order to achieve the success criteria (success criteria) determined for each satellite, while the mission manager is responsible for managing the entire operation and data utilization after the technology development is completed. Mission managers, on the other hand, are responsible for the overall management of operations and data use after the technology development is complete. I took over the project during the regular operation period, so after serving as the project manager, I am now the mission manager.
In the case of ALOS-2, this includes providing relevant organizations with observation data that can be used for crustal deformation, such as land subsidence, so I decide where to observe, how to pass it on to users, and how to cooperate with overseas organizations. If space debris comes close to the satellite, I also operate the satellite to keep it away from the debris.
A mission manager’s job differs depending on the use of the satellite, but it is no different from that of a project manager in that we manage people, goods, and money to ensure the success of the project.
Serika: I see, I understand now! When a disaster occurs, how is ALOS-2 data used?
Mr. Sobue: For example, when an earthquake strikes, we use the data to see where sediment movement has occurred, as well as ground shifting.
©︎ Geospatial Information Authority of Japan
©︎ Cabinet Office
This time, satellite data was provided by the International Disaster Charter and Sentinel Asia, in which space agencies from various countries provide each other with Earth observation satellite data in the event of a disaster, and private companies in Japan also provided data.
Although such satellite data can be used by specialists like us and the central government, it is difficult for the general public to decipher the information from SAR data and to use it directly in local governments in disaster areas. So I think it will be difficult to promote the use of satellite data.
In the future, we are going to focus more on fixed-point observations of volcanoes using ALOS-2 and ALOS-4. We can see how the shape of a mountain changes as magma rises and falls, using data from SAR satellites and ground-based instruments. ALOS-2 will observe about 50 active volcanoes, and ALOS-4 will observe about 110. Such data can be used by the Japan Meteorological Agency and other agencies as a reference when setting volcano warning levels.
Serika: So SAR data can also be used for volcano observations! By the way, what is this sensor-like object?
Mr. Sobue: This is a water level sensor for paddy fields.
Serika: Why does JAXA have a sensor for paddy fields?
Sobue： We are in the process of verifying whether or not we can use L-band SAR satellite data to determine the water level in rice paddies by transmitting it through the rice plants. So I’ve been going to the rice paddies all the time recently, and in fact, I’m going to install this water level sensor in the rice paddies tomorrow as well. When rice paddies are planted and left filled with water, methane will continue to be discharged. It is said that if the water is drained for two weeks about a month after rice planting, methane emissions will be reduced by 40%. There is an emerging need to know the exact water level in the rice paddies for carbon credits, but so far we have only been able to use data from ALOS-2.
In Japan, we have an abundance of water and food, and we may think that we will never run out of energy, but we should not underestimate the importance of the natural environment.
Cooperative Observation with Commercial Satellites
Serika: Recently, private companies have been building a constellation of Earth observation satellites. What are your expectations for the private sector?
Mr. Sobue: I would like to collaborate with them to assess damage in the event of a disaster. The ALOS series satellites have a wide swath, but we only get a chance once every 14 days to observe under the same conditions so that we can compare archived images with interferometric SAR analysis and other methods.
ALOS-2 had a swath of 50 km, but ALOS-4 will have a swath of 200 km. But 200 km is still not enough. When we were designing ALOS-4, we thought 200 km of observation would be enough, but when a linear rainfall event occurs, landslides occur in multiple locations, and 200 km is not enough to cover the entire disaster area. If the Nankai Trough earthquake, which is a cause for concern, occurs, a width of 1,000 km must be observed.
As the number of private-sector satellites increases, we will be able to conduct coordinated observations with the ALOS series satellites. For example, when a disaster occurs, it would be great if a large satellite like the ALOS series satellite could first image a large area to find areas where landslides or flooding are occurring, and then a commercial satellite could observe these areas every three hours.
To achieve this kind of tasking coordination, the current system requires that satellite observation data be received and processed on the ground and then sent to the partner companies to see if they are willing to respond, which is not very smart. In the future, if we can process the data observed by the satellite in orbit and send it to the collaborating satellite, we will be able to make observations much faster. In our future satellite plans, we are looking into the possibility of cooperative observation for ship detection, for example.
Serika: So you are talking about sharing roles between JAXA’s large satellites and small satellites from private companies?
Mr. Sobue: Yes, that’s right. What I feel is critical right now is the lack of human resources in Japan who can analyze satellite data. Many people want to use satellite data, but not many are interested in analyzing it.
I also think it is dangerous to rely too much on AI and machine learning to analyze satellite data. The reason is that we cannot tell whether the results of the analysis are really correct just by analyzing the data using AI or other methods.
Recently, the cloud is being used more and more to process satellite data. Satellite data is now distributed on the cloud, and for example, ALOS-2 data is registered there. However, as satellite data is redistributed, there is a fear that the data will become proprietary, and we at JAXA will not be able to guarantee its quality. We would not know if someone is deliberately rewriting the data. It is difficult to know how to maintain the certainty of the data.
Serika: As satellite data becomes more accessible, it seems that new challenges will arise. Finally, why do you think space development is necessary, Mr. Sobue?
Mr. Sobue: There are two reasons. The first is that there are things that can only be seen and done from space. This is exactly the case with the earth’s surface taken by Earth observation satellites and the movement of clouds and water vapor taken by meteorological satellites. Satellite communications and satellite broadcasting are also assets that make good use of space. In the future, we may be able to use “solar power generation satellites” that generate solar power in space and transmit the power to the ground.
The second reason is that we need to know about space to understand what kind of beings we are. For example, there is the “Giant Impact Theory” that says the moon was formed by debris scattered around the earth after a celestial body collided with it. If this theory is correct, the Moon may still contain rocks from the time of the Earth’s birth that can provide information about the Earth’s past. If we can study Venus, whose surface temperature is about 460°C due to the greenhouse effect caused by carbon dioxide, it may be useful for countermeasures against global warming, right?
Serika: It seems that by learning about the universe, we can get hints for solving the mysteries of the beginnings of humankind and the Earth, and for understanding the Earth in the future. Thank you very much!
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