Climate satellite set for launch

Gosat will greatly improve monitoring of greenhouse gases

A Japanese spacecraft is due to launch on a mission to help scientists understand and monitor how the Earth's climate is changing.

Gosat is a two-metric-tonne Earth-orbiting satellite which will map the abundance of greenhouse gases in the atmosphere, and where they are.

The probe will lift off from the Tanegashima launch site in southern Japan early on Thursday.

It will orbit the planet at an altitude of 666km during its five-year mission.

Japan's Space Agency Jaxa says Gosat (Global Greenhouse Observation by Satellite) will "contribute to the international effort toward prevention of (global) warming".

They say that monitoring greenhouse gases is vital to promote and support measures designed to mitigate against climate change.

The Kyoto Protocol came into force in February 2005 is a comprehensive set of rules for reducing and restricting greenhouse gas emissions.

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The Gosat mission is designed to identify and monitor sources of CO2, to support compliance with international treaties and agreements such as Kyoto.

But it could also shed light on a key problem in climate science.

Only about 50% of carbon emitted into the atmosphere, for example from fossil fuel combustion and land use, stays there. Most of the remainder is mopped up by the forests and oceans, which act as "sinks".

However, there appears to be a large carbon sink missing.

"Based on our best knowledge about the forest and ocean net sinks, we are 'missing' a carbon sink of 1-3 petagrams," said Paul Palmer, a collaborator on the mission from the University of Edinburgh.

For comparison, one petagram is equivalent to about one million, million kilograms.

Gosat (also known by its Japanese name Ibuki) will take measurements of two key greenhouse gases - carbon dioxide (CO2) and methane (CH4) - over nearly the entire surface of the planet.

It will carry two sensors, a Fourier Transform Spectrometer (FTS) and a Cloud and Aerosol Imager (CAI).

Emission and absorption

The FTS uses the technique of optical interference to measure greenhouse gases from space.

The CAI will capture images of the atmosphere and the Earth's surface, characterising thin clouds and airborne vapour. This information will be used to correct measurements made by the FTS.

Another satellite designed to carry out greenhouse gas observations is the US space agency's (Nasa) OCO (Orbiting Carbon Observatory) satellite.

Due for launch in late February, OCO can pinpoint the key locations on the Earth's surface where CO2 is being emitted and absorbed.

"The OCO and Gosat satellites are trying to measure the same quantity. However, their science objectives differ in subtle ways," Paul Palmer explained.

"The primary objective of the OCO mission is to find the CO2 sinks. The primary objective of the Gosat mission is to identify and monitor CO2 sources, to monitor treaty compliance. But Gosat data will also be used to quantify sinks."

Gosat is set to blast off between 0354 and 0416 GMT on Thursday from Tanageshima.