Q. What is it that will make GOSAT excel?
Current ground observation points: about 260
GOSAT's observation points: 56,000
First of all, GOSAT has very high-resolution spectroscopic capabilities. TANSO-FTS surveys infrared wavelengths with about 18,000 channels. The more channels a sensor has, the more precisely and sensitively it can monitor CO2 and methane. In other words, GOSAT can analyze infrared light in detail with 18,000 colors. GOSAT is almost like a flying spectrometer.
The sensor is also capable of detecting extremely delicate changes in the density of CO2, at 4 ppm (parts per million), a difference of four one millionths. The average density of CO2 in the Earth's atmosphere is 370 ppm, and the range of CO2 density change in one year is estimated at about 4 ppm. Therefore if a sensor cannot detect within that range, it is of no use. GOSAT is currently in development to attain an instrument sensitivity of 1 ppm, Detecting a difference of one one-millionth is like, for example, being able to detect four (4) eye-drops mixed in a 200-liter bathtub. Such precision is very challenging to achieve, but we are eager to reach the target.
Another notable feature of GOSAT is its 56,000 observation points around the world. The satellite will monitor the entire globe in three days, orbiting 14 times a day at an altitude of 666 km. With ground-based observation, a different observation instrument is used in each location, but GOSAT requires only a single instrument. This capability of acquiring global data every three days is another major feature of GOSAT.
Greenhouse gases are currently observed at 260 points around the world, and the data is distributed on the Internet by the World Data Centre for Greenhouse Gases (WDCGG). However, although these observation points are densely distributed in Europe, Japan and the U.S., there are very few points among the rest of the world. This current condition results in estimating an average measure of global warming, but not in details by regions or seasons. Especially with regard to oceans, we barely know where and how much CO2 is absorbed and emitted.
Thanks to a large number of institutes working on global-warming issues, many local phenomena have been observed and reported. For example, in the Amazon rainforest, scientists have found that methane is released from rotten tree roots after the river floods during summer, and in Siberia, it has been observed that melting permafrost is producing methane. However, we have no comprehensive worldwide global warming data in two-dimensional view, like a world map. GOSAT will be the first observatory that will steadily and globally monitor greenhouse gases at so many observation points, therefore great expectations are being placed on it.
Q. What was the development focus in particular?
Satellites are usually designed with a life expectancy of about three years, but GOSAT is designed to function for five years to reflect the first commitment period of the Kyoto Protocol. You cannot repair a satellite once it is launched, therefore naturally we are trying to use highly reliable components. On top of that, we have added backup systems to GOSAT, so that a malfunctioned component can be replaced. Every component is designed to have a redundant system, so observation can continue even if one fails.
Conventionally, installing backup systems in a sensor is not easy because it affects the sensor's performance; however the GOSAT sensor also has a redundant system built in. For example, for observing the Earth surface, satellites are usually equipped with only one mirror instrument that's steerable in all directions, but GOSAT has two systems that work independently. Therefore even if one of the mirrors completely breaks down, the other one would allow continuous observation.
We are also using various techniques to increase the reliability of the satellite body. For example, GOSAT has two solar array paddles, while other spacecraft often have just one. Unfortunate failure of the solar array paddle and power system on the Earth observing satellites ADEOS and ADEOS-II shortened their operation periods. Learning from those consecutive experiences, we decided to give GOSAT two solar array paddles. However, this is not the ultimate solution, since, if either paddle breaks, the satellite's power supply would be cut by half, and then it would be very difficult to operate the satellite. Satellites carry many instruments as well as sensors, so they need enough power not only to operate all the instruments but also to maintain the entire spacecraft at the right temperature. If power is reduced by half, GOSAT is designed to switch to energy-saving mode, so that, rather than just surviving, it will be able to continue at least basic observation. This was the most challenging task on this project.
I think GOSAT is one of the most reliable satellites and it is designed to guarantee five-year operation. I'd really like to make GOSAT successful.
Q. What is GOSAT's operation schedule after launch?
GOSAT is scheduled to be launched in 2008. During the first three months all functions of the satellite will be tested. Then in the following three months, science data will be collected intensively and calibrated with ground observation data. After we've verified their accuracy, GOSAT will finally start its assigned mission to acquire data.
GOSAT is a joint project by JAXA, which is responsible for the satellite and the sensors development, Japan's Ministry of the Environment (MOE), and the National Institute for Environmental Studies (NIES). MOE and NIES are in charge of data utilization. Utilizing the JAXA acquired data, NIES is responsible for analyzing the global distribution of CO2 and methane concentration, and the regional volume of absorption and emissions. It may take some time before preparing the data for distribution, however, we'll try to have free global data distribution within a year of the launch.
Q. Will scientific research be conducted with GOSAT observations?
The GOSAT Science Team has been formed with greenhouse-gas researchers as primary members. We have regular meetings with the scientists, and take their opinions into account on the technical aspects. Members of the Science Team will have access to the GOSAT data, and will publish their research. And since some members participate in the IPCC (Intergovernmental Panel on Climate Change), the data may also be used for that organization's reports. I believe research by American and European scientists will be published through the IPCC and others.
JAXA's key task, however, is to acquire reliable data. JAXA is not specialized in greenhouse gases research itself; therefore, I think that our major role is to support the researchers.
