494
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
20.5 RESULTS
20.5.1 gRace twSa veRSuS IN SITu MeaSuReMentS in illinoiS
Figure 20.5 presents the comparison of 7-year (2003–2009) monthly observed
TWSA and GRACE TWSA data in Illinois. GRACE data taken from three data processing centers (CSR, GFZ, and JPL), each with three different smoothing radii (500
km, 300 km, and nonsmoothed), are plotted together to quantify the range of uncertainty involved in GRACE data processing by different institutes and methods. Since
GRACE data in June 2003 and January 2004 were missing, they were replaced by
the linear interpolation from the data of adjacent 2 months. Also notice that GRACE
data from July to October 2004 provided by GFZ seem to be problematic.
As shown in this plot, the amplitude and seasonal variations of GRACE TWSA
track those of in situ measurements reasonably well, although certain substantial
differences exist in month-to-month variations. The correlation coefficients between
observed TWSA and CSR/GFZ/JPL GRACE TWSA are 0.67/0.65/0.50 for the 500-km
smoothed data, 0.71/0.62/0.59 for the 300-km smoothed data, and 0.73/0.52/0.59 for the
nonsmoothed data. The GRACE TWS data satisfactorily capture the rising trend
of storages during the period from mid-2007 to 2009 for both positive and negative annual peaks, as well as the magnitude of the trough that occurred in the mid2005 droughts in Illinois. However, although the nonsmoothed GRACE data match
100
50
–50
–100
2003
TWSA (mm)
2004
2005
2006
2007
2008
2009
2010
0
100
50
–50
–100
2003
TWSA (mm)
2004
2005
2006
2007
2008
2009
2010
0
100
50
–50
–100
2003
TWSA (mm)
2004
2005
2006
2007
2008
2009
2010
0
Obs.
CSR(500)
GFZ(500)
JPL(500)
Obs.
CSR(300)
GFZ(300)
JPL(300)
Obs.
CSR(0)
GFZ(0)
JPL(0)
(a)
(b)
(c)
FIGURE 20.5 Comparison between in situ observed 7-year (2003–2009) TWSA in
Illinois and corresponding GRACE TWSA. GRACE data are provided by CSR, GFZ, and
JPL, respectively, each with three different smoothing radius: (a) 500 km, (b) 300 km, and
(c) nonsmoothed.
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
20.5 RESULTS
20.5.1 gRace twSa veRSuS IN SITu MeaSuReMentS in illinoiS
Figure 20.5 presents the comparison of 7-year (2003–2009) monthly observed
TWSA and GRACE TWSA data in Illinois. GRACE data taken from three data processing centers (CSR, GFZ, and JPL), each with three different smoothing radii (500
km, 300 km, and nonsmoothed), are plotted together to quantify the range of uncertainty involved in GRACE data processing by different institutes and methods. Since
GRACE data in June 2003 and January 2004 were missing, they were replaced by
the linear interpolation from the data of adjacent 2 months. Also notice that GRACE
data from July to October 2004 provided by GFZ seem to be problematic.
As shown in this plot, the amplitude and seasonal variations of GRACE TWSA
track those of in situ measurements reasonably well, although certain substantial
differences exist in month-to-month variations. The correlation coefficients between
observed TWSA and CSR/GFZ/JPL GRACE TWSA are 0.67/0.65/0.50 for the 500-km
smoothed data, 0.71/0.62/0.59 for the 300-km smoothed data, and 0.73/0.52/0.59 for the
nonsmoothed data. The GRACE TWS data satisfactorily capture the rising trend
of storages during the period from mid-2007 to 2009 for both positive and negative annual peaks, as well as the magnitude of the trough that occurred in the mid2005 droughts in Illinois. However, although the nonsmoothed GRACE data match
100
50
–50
–100
2003
TWSA (mm)
2004
2005
2006
2007
2008
2009
2010
0
100
50
–50
–100
2003
TWSA (mm)
2004
2005
2006
2007
2008
2009
2010
0
100
50
–50
–100
2003
TWSA (mm)
2004
2005
2006
2007
2008
2009
2010
0
Obs.
CSR(500)
GFZ(500)
JPL(500)
Obs.
CSR(300)
GFZ(300)
JPL(300)
Obs.
CSR(0)
GFZ(0)
JPL(0)
(a)
(b)
(c)
FIGURE 20.5 Comparison between in situ observed 7-year (2003–2009) TWSA in
Illinois and corresponding GRACE TWSA. GRACE data are provided by CSR, GFZ, and
JPL, respectively, each with three different smoothing radius: (a) 500 km, (b) 300 km, and
(c) nonsmoothed.