Environmental Engineering Reference
In-Depth Information
Fig. 8.4
Scatter plots showing effects of the SNO calibration on the error statistics and distribu-
tion of the MSU channel 2 brightness temperature difference between NOAA-10 and NOAA-11.
(
a
) SNO data between
T
L
(N10) and
δT
L
¼ T
L
(N11)
T
L
(N10); (
b
) SNO data between
T
b
(N10)
and
T
b
(N10), where
T
L
represents linear calibrated brightness temperature and
T
b
the SNO-calibrated brightness temperature (Plots from Zou et al.
2006
)
δT
b
¼ T
b
(N11)
difference time series of the gridded temperature. In this approach, a series of sensitiv-
ity experiments were conducted in which
μ
N10
changed in a reasonable range [e.g.,
0-12.5 (sr m
2
cm
1
)(mW)
1
μ
N10
,asetof
calibration coefficients for all other satellites were obtained sequentially from
regressions of their SNO matchups. These calibration coefficients were then applied
globally to every observation footprint to obtain a Level-1c radiance dataset for each
satellite from Eq. (
8.1
). Next, a limb correction was applied to adjust different incident
angles of the off-nadir footprints to the nadir direction, and global ocean-mean
brightness temperatures were further obtained by averaging seven near-nadir, limb-
corrected radiances for each sensitivity experiment. Similar to Fig.
8.3
, the ocean-mean
data are used here for evaluating inter-satellite radiance biases that are related to
instrument temperature variability.
The global ocean-mean inter-satellite bias variability, as measured by the mean
standard deviation (
for all MSU channels]. For each given
σ
m
) of the inter-satellite difference time series for all satellite
pairs, is evaluated for all the sensitivity experiments. Figure
8.5
shows
σ
m
versus
μ
N10
for all the sensitivity experiments. The quantity
is a measurement of
instrument calibration errors related to the instrument temperature signals in the
radiance datasets. Figure
8.3
showed an example of this quantity for a particular
satellite pair. The final calibration point for
σ
μ
N10
is selected when the mean
instrument calibration error is minimized.
The new calibration coefficients resulted in a FCDR with much smaller solar
heating-related calibration errors compared to the prelaunch calibration. Figure
8.6
shows a similar global ocean-mean inter-satellite brightness temperature difference
time series as in Fig.
8.3
except for the SNO-calibrated radiances. As seen, the
instrument temperature-related variability as observed in Fig.
8.3
for NOAA-10
through NOAA-14 is mostly removed, and their inter-satellite biases are signifi-
cantly reduced. Quantitatively,
the inter-satellite biases and
σ
m
for the SNO
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