Mathematical Physics and Astrophysics/Environment/Life and Health

Yukihiro Takahashi

Investigating Earth and Planetary Environments Using Remote Sensing

Yukihiro Takahashi , Professor

Faculty of Science, Graduate School of Science (Department of Earth and Planetary Sciences, School of Science)

High school : Chiba-Higashi High School (Chiba Prefecture)

Academic background : Graduate School of Science, Tohoku University

Research areas
Earth and Planetary Science
Research keywords
Solar System, Remote Sensing, Natural Disaster Science, Forestry Science, Climate Change

What Kind of Research are You Conducting?

Picture 1 Pirka Telescope of 1.6 m Diameter and Observed Jupiter

I am developing a wide range of remote observation using lights and radio waves from the earth and planets. Picture 1 (left) shows a Pirka telescope at the Faculty of Science observatory, which has the third largest reflector with a diameter of 1.6 m in Japan and one of the largest telescopes in the world used mainly for observing the planets of our Solar System. The Venus climate orbiter “Akatsuki” launched in 2010 is equipped with five meteorological cameras, among which three cameras were developed and are operated by our group. Our goal is to carry out organized observations of Venus using both the Pirka telescope on the ground and Akatsuki cameras. Picture 1 (right) shows the image of Jupiter taken by a newly developed spectral camera, which also successfully provided the data of the wavelike structure that was previously found only by the imager onboard the Cassini spacecraft and the Hubble space telescope (HST).

Picture 2 Microsatellite “Raijin 2”

Picture 2 shows the microsatellite “RISING-2” or “Raijin (meaning thunder god in Japanese) -2” measuring 50 cm wide and weighing around 40 kg, which we co-developed with Tohoku University and launched in May, 2014. Picture 3 (left) shows an image of Minamiuonuma City in Niigata Prefecture, taken by the telescope mounted on RISING-2, which achieved a 5 m resolution, the world finest from a satellite of this size. This telescope is equipped with a filter utilizing liquid crystal technology, which was not only used for the spectral camera on the Pirka telescope, but it is the first in the world to be developed for space use. This enables high resolution imaging at a 400 wavelength, which large satellites were unable to achieve.

Picture 3 Ground (left) and Typhoon (right) observed by “Raijin 2”

Picture 3 (right) shows a gigantic typhoon image from the fish-eye camera mounted on RISING-2, which provides the whole image with resolution even higher than that of a meteorological satellite. The microsatellites such as the RISING-2 can be developed at one hundredth of the cost and in one tenth of the time period compared with larger satellites, and they have the potential to radically change future space development, in particular, the aspects of remote sensing

Panel 1 Asian Lightening Discharge Observation Networks

 Panel 1 shows the site locations of a lightning discharge observation network (upper left), observation antennas (upper right), which our group installed in Southeast Asia, and the distribution of the observed lightning discharges (lower right). The simultaneous records of radio waves emitted during lightning discharges and the GPS time allow us to estimate the locations and energies of almost all the lightning discharges occurring in this area. The information on the lightning discharges is expected to incur the lowest cost while being an accurate tool to observe the activity of cumulonimbus clouds which cause torrential rainfalls.


What was the Impetus Behind This Research?

 When I was a third grader in elementary school, I decided to become an astronomer and watched the night sky with a hand-made telescope almost every night. I was admitted to the Physical science course (including astronomy and geophysics) at Tohoku University although I was not accepted when I first applied. However, the Department of Astronomy was focusing mostly on theoretical research at the time. I then changed to the geophysics course program because they put more energy on observation, which led me to start looking for a way to conduct research on planets. At the beginning, however, my research concerned the space around earth, and then for my doctoral thesis, I studied the aurora using the data I obtained as a member of the 33rd Japanese Antarctic Research Expedition team. Soon after becoming an assistant professor, I participated in the observation of a new kind of lightning named sprites, which occur between the earth and space. I was lucky to be able to find another type of luminous phenomenon, named Elves later, and I became totally immersed in this field. I came up with the idea to build artificial satellites to observe the sprites and ELVES from directly above and I found a laboratory to partner with in the Graduate School of Engineering. This triggered me to start developing the university satellites including the RISING-2. In addition, we built the observation networks of lightning strokes to investigate the mechanisms of sprites and ELVES because they are caused by regular lightning strokes. This proved very useful for understanding natural disaster science or climate change, specifically for torrential rainfalls. On the other hand, I believe the observation of the lightning discharge activities is beneficial for research of the atmospheric structures or the meteorology of the planets, because they also happen on planets other than the earth. This led me to become involved in the Venus exploration program and the construction of the Pirka telescope.


What Will be Your Next Goal?

Fig. 1 Constellation with Microsatellites

 Since I started working at Hokkaido University in 2009, I have been communicating with many colleagues from a number of other areas besides space science. I noticed that the sophisticated microsatellites equipped with advanced sensors, such as a liquid crystal filter telescope, are very useful for forestry science, agriculture, fishery science and environmental science. And now, I have been participating on joint projects with professors in such areas. This is a great advantage of Hokkaido University, which is unavailable in other universities around the world. There are more and more joint projects with other Asian countries, and we are accepting excellent students who work on space development and utilization every year. In the future, we hope to realize a constellation consisting of 50 or even 100 microsatellites, led by Hokkaido University, to help contribute to the fundamental sciences as well as help in disaster prevention and environmental issues.