Climate Sense

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bserving

, P

redicting

and

rojecting

limate

onditions

GCOM-W data products will include brightness

temperatures (Tb) and geophysical parameters in

swath form. In addition, spatially and temporally aver-

aged global grid products will be generated. Since the

Tb values are fed into retrieval algorithms to derive all

the geophysical parameters and are directly used in the

numerical data assimilation scheme, well-calibrated

and stable Tb data is necessary. Eight geophysical

parameters will be retrieved and processed as standard

products.

GCOM-C

For this series the four primary parameters will be

atmosphere, ocean, land and cryosphere to best reflect

the human contribution to climate change. In the

atmosphere category measurements will centre on

aerosol and cloud. In order to observe aerosol over land,

three observation methods will be employed, namely:

an ordinary split window method, a near-UV method

and a polarimetry method.

In order to monitor the ocean, low polarization

sensitivity for precise ocean colour observations and

a 250 metre resolution near coastal areas is needed,

because primary productivity depends largely on the

coastal environment. For the land, a 250 metre reso-

lution, as well as multi-angle observation are planned

so that it is possible to precisely evaluate vegetation

and land use change, including primary production

and deforestation. The cryosphere also requires a 250

metre resolution to more accurately estimate loss of

ice sheet, as well as snow physical characteristics. The

aerosol effect on snow is a particularly important issue

that needs to be monitored.

The total number of observation channels has been

reduced compared to the previous GLI sensor by opti-

mizing the objectives in each area. The signal to noise

ratio at standard radiance is over 200 for the visible

and near-infrared channels, while the noise equivalent

temperature difference is lower than 0.2 Kelvin for

thermal infrared (TIR) channels.

To optimize broad spectral range requirements the

system is split into two sensors. For visible and near-

infrared a push-bloom type sensor called the Visible and

Near Infrared Radiometer (VNR) was selected to attain

multi-angle polarimetry and non-polarimetry observa-

tion. To successfully achieve this with a whisk-bloom

type sensor is difficult, as it requires a tilt mechanism

and low polarization sensitivity, which are difficult to

incorporate because of the sensor’s size and catoptric

character. For non-polarimetry observation, the system

has three telescopes to cover a wide area, and for polar-

imetry observation the system has two telescopes. For

shortwave infrared and thermal infrared, the system

has a whisk-bloom type sensor called, simply, Infrared

Scanner (IRS) to take over from the GLI system. Each

VNR and IRS has an on-board calibrator to manage

change.

The SGLI/VNR will cover a relatively large area for

a push-bloom type sensor. Because of this, the obser-

was to improve the reliability and extend the lifespan of the units

from three to five years. As a result, a redundant momentum wheel

and an interface board for two signal processor circuits were added.

The basic concept of AMSR2 is almost identical to that of the

AMSR-E: conical scanning system with large offset parabolic antenna,

feed horn cluster to realize multi-frequency observation, external cali-

bration with two temperature standards and total-power radiometer

systems. The 2-metre diameter of the antenna, which is larger than

that of AMSR-E, provides a better spatial resolution under the same

orbit altitude of around 700 kilometres. There is also an allowance for

slight underlaps in the 89 gigahertz scans, due to the narrower beam

size of AMSR2 with the same sampling interval of AMSR-E. The C-band

receiver uses additional 7.3 gigahertz channels to mitigate potential

radio frequency interference. An incidence angle of 55 degrees (over

the equator) was selected to keep consistency with AMSR-E. The

observational swath width of 1,450 kilometres, combined with the

selected satellite orbit, will provide almost complete coverage of the

entire Earth’s surface within two days, independently for ascending and

descending observations.

Overview of the AMSR2 sensor unit

Image: JAXA

Instrument

Orbit

Size

Mass

Power

Launch

Design Life

Status

Advanced Microwave Scanning Radiometer-2

Sun-synchronous orbit Altitude: 699.6km (over the

equator) Inclination: 98.186 degrees; Local time of

descending node: 13:30

5.1m (X) * 17.6m (Y) * 5.0m (Z) (on-orbit)

1940kg

Over 4050W

JFY2011 (beginning of CY2012)

5 years

Phase-C study started in JFY2008

Major characteristics of the GCOM-W1 satellite

Source: JAXA