Environmental Engineering Reference
In-Depth Information
2.00
N16/15
N8/7
N9/8
N10/9
N11/10
N12/11
N14/12
N17/16 N18/17
N15/14
1.85
1.70
1.55
1.40
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
5% absolute
10% relative to MODIS
1% per decade for
albedo
VIS/NIR
AVHRR IR
0.5 K absolute per
mission
requirement
0.5 K relative to IASI on MetOp
0.1 K per decade for
SST
HIRS
Not well defined
0.2 K relative to IASI on MetOp
0.1 K per decade for
temperature trend
AMSU
1.5-2 K
0.2 K relative to each other
on different satellites
0.1 K per decade for
temperature trend
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, perfor-
mance 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.
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