Climate Sense

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Long-term observations of global climate change

Kazuo Umezawa, Keiji Imaoka, Kazuhiro Tanaka, Yoshihiko Okamura, Japan Aerospace Exploration Agency

lobal warming has developed into a problem which if

ignored will see significant and detrimental changes to

the global environment. The fourth assessment report of

the Intergovernmental Panel on Climate Change states unequiv-

ocally that the climate is becoming warmer, citing observed

increases in global average air and ocean temperatures, as well

as widespread melting of snow and ice.

Observing climate change has its complexities. While some

symptoms of global warming are explicit the majority are more

discreet. In addition, such signals are affected by natural variabil-

ity and thus do not appear in a uniformed guise worldwide. As

such, any observational system for climate variability should be

thoroughly consistent, of an extensive duration and have global

coverage.

Japan Aerospace Exploration Agency (JAXA) is developing

the Global Change Observation Mission (GCOM) in response to

these requirements. GCOM will involve two medium-sized, polar

orbiting satellite series. The series will stretch over multiple genera-

tions, with one-year overlaps between consecutive generations for

inter-calibration. Two instruments were selected to cover the wide

range of geophysical parameters required: the Advanced Microwave

Scanning Radiometer-2 (AMSR2) for GCOM-W and the Second-

Generation Global Imager (SGLI) for GCOM-C. AMSR2 will cover

observations relating to the global water and energy cycle, while

SGLI will cover the surface and atmospheric measurements related

to the carbon cycle and radiation budget.

GCOM-W

GCOM-W will focus on long-term observations related

to global water and energy circulation, including the

monitoring of polar areas. To achieve the desired

results multichannel microwave radiometers will be

used, which are capable of capturing quantitative data

with the required frequency and at a global scale. More

specifically, the radiometers will be used to gather

quantitative measurements of given surface parameters

through non-precipitating and – in some cases – light

precipitating clouds. In addition, they will capture

vertically integrated layer information via the interac-

tion of microwave radiation with intercepting media,

such as rain drops or snow grain.

Leveraging the capabilities of AMSR2, GCOM-W will

observe various changes in the cryosphere including

variability in: sea ice, ice sheets and snow cover. Such

measurements are considered an excellent indication

of the potential extent and timing of global warming.

Changes in sea surface temperature, precipitation,

cloud water and water vapour will also be monitored in

association with air-sea interactions, such as the El Niño-

Southern Oscillation. Finally, surface soil moisture will be

observed to help quantitatively determine the water and

energy balance between the land and atmosphere.

The first generation GCOM-W (GCOM-W1) satel-

lite will be a medium-sized platform, smaller than the

ADEOS and ADEOS-II satellites. This is to reduce the

risk associated with large platforms that feature multi-

ple, valuable observing instruments. Also, since the

ADEOS-II problem was related to the solar paddle,

recent Japanese satellites almost always have dual solar

paddles. One concern relating to the dual-paddle design

was a possible influence on the Cold Sky Mirror (CSM)

field of view, introducing cosmic background tempera-

tures to the feed horns. We have assessed the direct

effects solar paddles have on the CSM by simulating

observed brightness temperatures and it was confirmed

that the direct effect was negligible. To avoid the

shading of the solar paddles by large AMSR2 antennas

and the effect to CSM mentioned above, the paddles

were designed to have longer booms. The local time of

the ascending node will be 13.30 to remain consistent

with the Aqua/AMSR-E observations.

The system Preliminary Design Review of the

GCOM-W1 satellite was completed in March 2008 and

the AMSR2 system critical design review (CDR) was

finished in November 2008. In designing the instru-

ments and interface for the spacecraft, the main goal

bserving

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Overview of the GCOM-W1 satellite

Image: JAXA