uncertainty in the measurement accuracy and consistency, are not good enough for
climate change detection without recalibration and/or recharacterization.
Table 2.1 compares the current instrument performance specification, performance achieved, and climate change detection requirements. For example, for
albedo, the stability requirement is 1% per decade, while the current estimate is
no better than 5%. For the IR bands of AVHRR, the requirement is 0.1 K per
decade, but a 0.5 K variation is found from orbital variation alone.
Therefore, although the calibration system presented earlier appears to be very
simple, to achieve very accurate and consistent calibration that meets the needs of
climate change detection, it is not so straightforward. There are many science
questions to be answered, which ultimately determines the reliability of the data.
2.00
N8/7 N9/8
N11/10
N10/9
N12/11
N14/12
N15/14
N16/15
N17/16
N18/17
1.85
1.70
1.55
1.40
Reflectance Ratio
1.25
1.10
0.95
0.80
0.65
0.50
85
87
88
90
91
93
95
Year (YY)
96
98
00
01
03
05
Fig. 2.3 AVHRR channel 2 inter-satellite biases between successive satellites showing large
discrepancies between satellites when not well calibrated
Table 2.1 Instrument performance specification, and climate requirements
Specification
Performance achieved
Climate requirements
AVHRR
VIS/NIR
Æ5% absolute
À10% relative to MODIS
1% per decade for
albedo
AVHRR IR Æ0.5 K absolute per
mission
requirement
Æ0.5 K relative to IASI on MetOp Æ0.1 K per decade for
SST
HIRS
Not well defined
Æ0.2 K relative to IASI on MetOp Æ0.1 K per decade for
temperature trend
AMSU
1.5–2 K
Æ0.2 K relative to each other
on different satellites
Æ0.1 K per decade for
temperature trend
18
C. Cao et al.
climate change detection without recalibration and/or recharacterization.
Table 2.1 compares the current instrument performance specification, performance achieved, and climate change detection requirements. For example, for
albedo, the stability requirement is 1% per decade, while the current estimate is
no better than 5%. For the IR bands of AVHRR, the requirement is 0.1 K per
decade, but a 0.5 K variation is found from orbital variation alone.
Therefore, although the calibration system presented earlier appears to be very
simple, to achieve very accurate and consistent calibration that meets the needs of
climate change detection, it is not so straightforward. There are many science
questions to be answered, which ultimately determines the reliability of the data.
2.00
N8/7 N9/8
N11/10
N10/9
N12/11
N14/12
N15/14
N16/15
N17/16
N18/17
1.85
1.70
1.55
1.40
Reflectance Ratio
1.25
1.10
0.95
0.80
0.65
0.50
85
87
88
90
91
93
95
Year (YY)
96
98
00
01
03
05
Fig. 2.3 AVHRR channel 2 inter-satellite biases between successive satellites showing large
discrepancies between satellites when not well calibrated
Table 2.1 Instrument performance specification, and climate requirements
Specification
Performance achieved
Climate requirements
AVHRR
VIS/NIR
Æ5% absolute
À10% relative to MODIS
1% per decade for
albedo
AVHRR IR Æ0.5 K absolute per
mission
requirement
Æ0.5 K relative to IASI on MetOp Æ0.1 K per decade for
SST
HIRS
Not well defined
Æ0.2 K relative to IASI on MetOp Æ0.1 K per decade for
temperature trend
AMSU
1.5–2 K
Æ0.2 K relative to each other
on different satellites
Æ0.1 K per decade for
temperature trend
18
C. Cao et al.