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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 1 

Corrections to the MODIS Aqua Calibration Derived 
From MODIS Aqua Ocean Color Products 

Gerhard Meister and Bryan A. Franz 


Abstract — Ocean color products such as, e.g., chlorophyll-a con- 
centration, can be derived from the top-of-atmosphere radiances 
measured by imaging sensors on earth-orbiting satellites. There 
are currently three National Aeronautics and Space Administra- 
tion sensors in orbit capable of providing ocean color products. 
One of these sensors is the Moderate Resolution Imaging Spec- 
troradiometer (MODIS) on the Aqua satellite, whose ocean color 
products are currently the most widely used of the three. A recent 
improvement to the MODIS calibration methodology has used 
land targets to improve the calibration accuracy. This study eval- 
uates the new calibration methodology and describes further cal- 
ibration improvements that are built upon the new methodology 
by including ocean measurements in the form of global temporally 
averaged water-leaving reflectance measurements. The calibration 
improvements presented here mainly modify the calibration at the 
scan edges, taking advantage of the good performance of the land 
target trending in the center of the scan. 

Index Terms — Calibration, image sensors, remote sensing. 

I. Introduction 

T HE feasibility of deriving ocean color products (e.g., 
water-leaving radiances 1 and chlorophyll-a concentration) 
was demonstrated by the Coastal Zone Color Scanner, which 
was launched in 1978. It provided limited global coverage over 
a period of eight years. The Sea- viewing Wide Field-of-view 
Sensor (SeaWiFS) provided full global coverage from 1997 to 
2010, adding critical bands in the VIS and NIR spectrum. Since 
then, there have been four more sensors providing ocean color 
products with full global coverage: 1) two Moderate Resolution 
Imaging Spectroradiometer (MODIS), which were launched in 
1999 on the Terra satellite and in 2002 on the Aqua satel- 
lite; 2) the MEdium Resolution Imaging Spectrometer, which 
was launched in 2002 on the ENVISAT platform; and 3) the 
Visible Infrared Imager Radiometer Suite (VIIRS), which was 
launched in 2011 on the Suomi NPP satellite. The ENVISAT 
mission ended April 8, 2012, due to a communication loss with 
the satellite. Of the remaining three sensors in orbit, MODIS 
Aqua is the most heavily used by oceanographers because the 
VIIRS data are still in beta stage (unvalidated) and the MODIS 
Terra products are compromised by sensor artifacts [6] . There- 


Manuscript received April 15, 2013; revised November 18, 2013; accepted 
December 10, 2013. 

The authors are with the Ocean Ecology Branch, NASA Goddard Space 
Flight Center, Greenbelt, MD 20771 USA (e-mail: gerhard.meister@nasa.gov). 

Color versions of one or more of the figures in this paper are available online 
at http://ieeexplore.ieee.org. 

Digital Object Identifier 10. 1109/TGRS. 20 13. 2297233 

^ee Franz et al. [5] for a recent definition of the term. 


TABFE I 

Center Wavelengths of the MODIS Ocean Color Bands 


Band 

8 

9 

10 

11 

12 

13 

14 

15 

16 

Wave- 

length 

[nm] 

412 

443 

488 

531 

547 

667 

678 

748 

869 


fore, MODIS Aqua ocean color data are crucial for continuing 
the ocean color climate data record started by SeaWiFS. All 
future references in this paper to MODIS will refer to the 
MODIS on Aqua (the calibration status of MODIS Terra up 
to 2011 is described by Meister and Franz [10]; a recalibration 
of MODIS Terra using the results for MODIS Aqua described 
in this paper was implemented in 2013). 

Ocean color products are extremely sensitive to radiometric 
trending errors. SeaWiFS achieved long-term trending accuracy 
on the order of 0.1% [2], with lunar calibrations being the 
primary calibration method. Although MODIS is capable of 
viewing the moon as well, it cannot base its calibration on 
the moon the way SeaWiFS did. The main reason is that the 
MODIS radiometric degradation has been strongly scan angle 
dependent. Since the moon is measured by MODIS through 
the space view port [14] at a fixed angle (at the beginning of 
scan), additional calibration sources are needed to determine 
the radiometric degradation at the remaining scan angles. 

An onboard solar diffuser is central to the calibration of the 
MODIS ocean color bands [15]. It is viewed by MODIS in the 
second half of the scan, providing another calibration source at 
an angle sufficiently different from the lunar view angle. For 
MODIS bands 8-12 (see Table I), these two calibration sources 
provided a calibration that, with only minor adjustments (e.g., 
destriping [11], seasonal gain corrections [12], etc.), resulted 
in reasonable trends for ocean color products [4] during the 
early years of the mission. Note that, for bands 13-16, solar 
diffuser measurements were the sole calibration source because 
the lunar measurements of these bands are partially saturated. 

However, starting from 2008, it became clear that additional 
corrections were necessary for bands 8 and 9 in the later part 
of the mission. These corrections are described in [9]. These 
corrections used the ocean color products from the SeaWiFS 
instrument as a vicarious calibration source. Unfortunately, the 
demise of SeaWiFS in 2010 required a new approach. 

In 2011, the MODIS Calibration Support Team (MCST) 
developed a new method for determining the radiometric degra- 
dation of the MODIS bands [13]. In the case of MODIS Aqua, 
desert sites are now used to support the derivation of the 
radiometric degradation as a function of scan angle for bands 8 


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Fig. 1. (a) SeaWiFS Rrs at 412 nm, 15-day L3 file (days 53-77 of 2009). 

(b) Measured TOA radiance L m at 412 nm as measured by MODIS Aqua on 
day 65 of 2009. (c) Vicarious TOA radiance vLt at 412 nm (from SeaWiFS 
L3). (d) Ratio Lm/vLt. 


and 9. These new corrections have been applied to the MODIS 
products in 2012 with the “MODIS Collection 6” release in 
early 2012. The analysis presented in this paper starts with the 
MODIS Collection 6 calibration as provided by MCST. 

In Section II, we briefly describe the cross-calibration ap- 
proach developed by the Ocean Biology Processing Group 
(OBPG) that is central to this paper. In Section III, we use 
the cross-calibration approach to demonstrate that the MODIS 
Collection 6 calibration approach produces results that lead to 
consistent ocean color products for the central parts of the scan, 


TOA radiance ratios for band 8, mirror side 1, detector 1 
1.10 

1.05 

F00 

ni 

Y 0.95 
0.90 

0.85 
0.30 

0 500 1000 1500 

Frame number 

Fig. 2. (Red line) Correction coefficients Mu as a function of frame number, 
derived from the (black dots) ratios Lm/vLt (see Fig. 1 for geographic 
distribution) for MODIS band 8, detector 1, mirror side 1, day 65 of 2009. 

but not for the edges of the scan. Then, in Section IV, we apply 
the cross-calibration approach using only MODIS data from 
the central part of the scan as a calibration source in order to 
improve the calibration at the scan edges. 

II. Methodology 

The methods underlying the analysis presented in this paper 
have been presented before; thus, only a short summary will be 
given here. 

The temporal anomaly plots show the difference of a global 
average of an ocean color product from the annual cycle as a 
function of time. The temporal anomaly plots used in this paper 
are based on the global average for deep-water ocean (depth 
> 1 km). The scan angle anomaly plots show the level-2 (L2, 
unaggregated) ocean color product as a function of scan angle 
for a given day, divided by the corresponding level- 3 (L3) bin 
[averaged over time (seven days) and area (9 km x 9 km)] and 
averaged over deep-water regions. A more detailed explanation 
of the algorithms used for the temporal anomaly plots and the 
scan angle anomaly plots is given in [6] . 

The cross-calibration method was introduced by 
Kwiatkowska et al. [8] and applied to MODIS on Terra. 
Its first application to MODIS on Aqua is described in [9]. 
In each case, coefficients were derived, which corrected the 
MODIS top-of-atmosphere (TOA) radiances and the MODIS 
polarization sensitivity as a function of time and scan angle, 
minimizing the difference to SeaWiFS L3 ocean color products. 
The coefficients are defined by Gordon et al. [7], i.e., 

L m = Mn * (L t + m 12 • (Q t cos 2a + U t sin 2a) 

+ mi 3 (— Qt sin2<r + U t cos2<r)) (1) 

where (L t , Qt,U t ) are the first three components of the Stokes 
vector at the TOA, L m is the radiance measured by MODIS, 
and a is a rotation angle to adjust for different reference frames 
used in the calculation of Q t and U t . The coefficients Mn, ran, 
and ran are derived as a function of time; scan angle; and for 
each MODIS detector, mirror side, and bands 8-14. For Mn, a 
value of 1.0 corresponds to no correction relative to the MCST 
calibration. For ran and ran, values of 0.0 correspond to no 



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MEISTER AND FRANZ: CORRECTIONS TO THE MODIS AQUA CALIBRATION 


3 


Band 8 



Fig. 3. Cross-calibration coefficients Mu for (diamonds) MODIS Aqua 
(with old MCST calibration) to SeaWiFS monthly measurements (R2010.0) 
and (solid line) MODIS Aqua (with new MCST calibration) to SeaWiFS clima- 
tology at nadir (frame 675) and end of scan (frame 1250). Data are for mirror 
side 1, detector 1, bands 8-10 (see plot title), without temporal averaging. 


Anomaly inRrs (412) for Deep-Water 



0.0Q10 


0,0005 


-0.0005 


-o.oo io 


Jan Jan Jan Jan Jan Jan Jan Jan Jan 

2003 2004 2005 2006 2007 2003 2009 2010 2011 


0.0000 


Fig. 4. Temporal anomaly plot for MODIS Aqua Rrs at 412 nm (band 8), 
using MCST’s new MODIS Collection 6 calibration approach. The temporal 
anomaly is the difference to the mean seasonal cycle. The mean seasonal cycle 
is calculated by averaging the MODIS Aqua data for each month of the year 
over all years of the mission. Black dots show anomalies for each month 
(averaged over four days, for each month), blue line shows anomalies smoothed 
over time (seven-month boxcar average), and the gray area shows the range of 
linear trends (derived from 2cr uncertainties of the linear fit). See Section II and 
[6] for further details regarding the calculation of the temporal anomaly. 

Rrs at 412 nm] 2 and the TOA radiance measured by MODIS 
Aqua [see Fig. 1(b)]. For the solar and viewing geometry of 
the MODIS Aqua data, the SeaWiFS Rrs is converted to TOA 
radiance by an inverse atmospheric correction (see [5]), using 
information about the aerosols derived from the MODIS Aqua 
NIR bands (i.e., it is implicitly assumed that the MODIS NIR 
bands do not need corrections). The resulting vicarious TOA 
radiance vL t is shown in Fig. 1(c). Qualitatively, the results 
look very similar to the TOA radiances measured by MODIS 
Aqua. However, the ratio of the two [see Fig. 1(d)] reveals that 
there are differences on the order of several percent. 

The corrections are derived for each mirror side and detector. 
As an example, the ratios L^/vLt in Fig. 1(d) only for mirror 
side 1 and detector 1 are shown as a function of frame number 
in Fig. 2 [note that frame number (1-1354) is proportional 
to scan angle (—55° to +55°) for MODIS Aqua]. A fourth- 
order polynomial as a function of frame number is fitted to the 
data (red line in Fig. I). 3 The values of this polynomial are 
the correction coefficients Mp for this particular day, band, 
detector, and mirror side. Before applying the correction to 
MODIS Aqua data for ocean color processing, the correction 
coefficients Mp are temporally smoothed by fitting a fifth- 
order polynomial as a function of time. 


sensitivity to polarization. Note that for MODIS Terra, a signif- 
icant change in polarization sensitivity was derived, whereas for 
MODIS Aqua, no significant change in polarization sensitivity 
was detected, and therefore, the prelaunch polarization sensitiv- 
ities are applied, and only Mu are retrieved. A separate paper 
is in preparation, which focuses on the on-orbit change in the 
polarization sensitivities for both MODIS instruments. 

The cross-calibration method is illustrated in Fig. 1. The 
input data are shown on the top: the SeaWiFS truth data [see 
Fig. 1(a); temporally averaged ocean color product, in this case, 


III. Cross Calibration of MODIS to SEAWiFS 

This section will demonstrate that the new MCST calibration 
(Collection 6 release 2012) produces superior results relative to 
the previous calibration. The previous calibration was evaluated 

2 Rrs is remote sensing reflectance (see [1] for a definition); it is essentially 
the normalized water-leaving radiance divided by the solar irradiance. 

3 Note that, in [9], a third-order polynomial was used; a fourth-order polyno- 
mial was chosen to match the MCST approach, which also uses a fourth-order 
polynomial. 


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1.2 


1.1 


nLw (41 2) Ratio for 2002 289 


nLw (412) Ratio for 2002 288 


m 1.0 

—I 


0.9 


0.8 


Mirror-Side 1 

1.2 

: Mirror-Saide i 

Mirror-Side 2 


: Mirror-Side 2 : 


1.1 

r - 


5 

: : 

: a M J 

c 

rfi i n 

r Li L 


Cv 1 -U 

1 

\ ^***mf^ \ 

E- ~ 

0.9 

- - 


0.8 

1 t t I l . — L r * 1 I i I ( 1 1 1 1 I I 1 i I . ,_J 


0 200 400 600 800 1000 1200 

Scan Pixel 


0 200 400 600 800 1000 1200 

Scan Pixel 



200 


400 


600 800 
Scan Pixel 


1000 


1200 


200 


400 


600 800 
Scan Pixel 


1000 1200 


1.2 


nLw (412) Ratio for 2011 353 


Mirror-Side 1 
Mirror-Side 2 



1.2 


1.1 


: Mirror-glide 1 
. Mirror-Side 2 


| 

co 1,0 


0,9 


0.8 


nLw (412) Ratio for 2011 353 

1 1 1 1 1 1 1 1 1 1 r 



200 


400 


600 800 
Scan Pixel 


1000 1200 


200 


400 


600 800 
Scan Pixel 


1000 1200 


Fig. 5. Response versus scan plots for MODIS Aqua Rrs at 412 nm (band 8) in (top) late 2002, (middle) late 2006, and (bottom) late 2012, (left) using MCST’s 
new MODIS Collection 6 calibration approach and (right) adding the cross-calibration correction. 

in a previous paper ([9]), and some of the previous results will ibration and the SeaWiFS monthly climatology (a climatology 
be shown here for comparison purposes. The cross-calibration needs to be used to retrieve data beyond the end of the SeaWiFS 
coefficients from the paper of Meister et al. will be compared mission). Note that these cross-calibration coefficients are only 

with the cross calibrations derived using the new MCST cal- used here; the following section describes the approach for the 


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MEISTER AND FRANZ: CORRECTIONS TO THE MODIS AQUA CALIBRATION 


5 


Band 8 



Band 10 



Band 9 



Band 1 1 



Fig. 6. Cross-calibration coefficients Mu for MODIS Aqua to itself at beginning of scan (green, frame 100), nadir (blue, frame 675), and end of scan (red, 
frame 1250). Data are for mirror side 1, detector 1. The solid line shows the original M\\ from each month; the dashed line shows the Mu after temporal 
smoothing (fitting a third-order polynomial as a function of time). 


derivation of the cross-calibration coefficients that are applied 
in the operational ocean color processing. 

Fig. 3 shows the two sets of cross-calibration coefficients for 
two scan angles: near nadir (frame 675) and close to the end of 
scan (frame 1250, scan angle of about 46.5°). The band 8 cross- 
calibration coefficients for the old calibration (diamonds in 
Fig. 3) show, starting from 2007, a strong increase at the end of 
scan and a decrease for nadir. On the other hand, the new band 8 


coefficients (solid lines in Fig. 3) are much closer to 1, and only 
starting from 2011, the end of scan data consistently differ from 
unity. This means that the new calibration approach by MCST 
is much more consistent with the assumption that there are no 
long-term trends in the water-leaving reflectance in the global 
oceans than the previous MCST calibration approach. This is 
confirmed by the temporal anomaly plot shown in Fig. 4, which 
shows a decline of the MODIS Aqua 412-nm Rrs of about 


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6 


5% over ten years. This is a significant improvement over the 
previous MCST calibration approach, which showed a drop of 
about 20% (see [9, Fig. 8]) over eight years. 

There is an improvement for the other bands as well, as 
shown for bands 9 and 10 in Fig. 3, but the effect is strongest 
for band 8. 

Fig. 3 shows that some issues still remain. The end of 
mission decline in band 8 was mentioned earlier; the end-of- 
scan correction coefficients for band 9 are too low at both 
the end and the beginning of the mission, but too high in the 
middle. This is confirmed in Fig. 5, which shows the scan angle 
anomaly for band 8 at three dates (2002, 2006, and 2011). The 
ordinate in these plots is the global average of the L2 data from 
the date given in the plot title, divided by the corresponding 
seven-day L3 file, plotted as a function of scan angle/pixel 
(see [6] for further details regarding the scan angle anomaly 
evaluation procedure). In 201 1, the global average is too low at 
the end of scan relative to the middle and the beginning of scan. 
Note that, in 2002, there is no apparent scan angle anomaly for 
band 8. 

IV. Cross Calibration of MODIS to MODIS 

The use of a climatology (as was done in the previous sec- 
tion) is useful for evaluating different calibration approaches, 
but it is an unsatisfying calibration approach in itself because 
the resulting ocean color products will, by design, never show 
global secular trends. Therefore, a different approach is pre- 
sented here. 

The new MCST approach resulted in cross-calibration coef- 
ficients that were close to unity in the center of scan, but some 
differences at the end of scan (see Fig. 3) and at the beginning 
of scan (not shown) remain. The differences are concentrated 
in the first and last 300 frames of the scan. Therefore, we 
derived L3 global ocean color products with the new MCST 
calibration approach, using only frames 300-1050. These L3 
data were then used as a calibration source (instead of the 
SeaWiFS climatology) to derive cross-calibration coefficients 
for all frames (1-1354). The resulting coefficients are shown in 
Fig. 6. As expected, the coefficients for the center of scan do not 
show strong temporal dependence, whereas for the scan edges, 
particularly at the end of scan, there is a trend for most bands. 

Note that the strong decrease in Mu at the end of scan for 
bands 8 and 9 was derived for the MCST calibration table ver- 
sion V6. 1.15.2. Partly in response to this result, MCST has pro- 
vided updated calibration tables to the OBPG (V6.1.17.7_OC 
and later, not used in this paper) that largely remove this effect. 

The temporal anomaly based on these new cross-calibration 
corrections is shown in Fig. 7 for Rrs at 412 nm. The strong 
downward trend in the data that did not have the cross calibra- 
tion applied (see Fig. 4) has been removed. It can be also seen 
that although the data have been cross calibrated to itself, the 
long-term averages in the Rrs product vary with time (higher 
than average at the beginning and end of mission, lower from 
2010 through 2011). The long-term averages are determined 
by real physical changes of the observed product and the 
accuracy of the MCST calibration in the central part of the scan 
(frames 300-1050). 


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Fig. 7. Temporal anomaly plot for MODIS Aqua Rrs at 412 nm (band 8), 
using cross calibration of MODIS to itself. 

The band 8 scan angle trends in 2006 and 2011 of the data 
processed without cross calibration (plots on the left in Fig. 5) 
have been removed as well (plots on the right in Fig. 5). A small 
residual decrease in the water-leaving radiance with increasing 
frame number (or “scan pixel” in Fig. 5) remains in 2011 
even after applying the cross-calibration corrections. The noise 
around frame 800 in 2002 and 2006 is most likely due to glint 
(the glint in MODIS Aqua is usually located around that frame 
or scan angle). 

The correction coefficients were derived for all MODIS 
ocean color bands (except for the NIR bands). Although the 
corrections are typically on the order of less than 1% for 
bands 10-14, they result in improved ocean color products 
[evaluated by scan angle anomaly plots (see Fig. 8 as an 
example), where the averages are closer to the 1.0 line for the 
cross-calibrated data] . 

Despite the small magnitude of the corrections for bands 
10-14, the OBPG chose to apply them for bands 8-14. Pre- 
viously, temporally dependent corrections were only applied 
for bands 8 and 9 (see [9]). An interesting example is shown 
in Fig. 8. The lines (each line represents one of ten detectors) 
are spread around their mean for the plot on the left for frame 
numbers less than 700; they converge to their mean in the right 
plot. This means that a detector bias (which results in image 
striping) at the beginning of scan is corrected by the cross- 
calibration coefficients. Note that the ratio of TOA radiances to 
water-leaving radiances in the open ocean is typically around 20 
in the green wavelength bands; this leads to larger magnification 
of a calibation error in the ocean color product than in the blue 
bands (their ratio is about 10), but it also means that those bands 
are more sensitive to errors that are not related to the calibration 
(e.g., errors related to the removal of sun glint). 

It is challenging to display the derived cross-calibration co- 
efficients in a concise way because there are several dimensions 
that need to be considered (temporal, scan angle, spectral, 
mirror side, and detector). Fig. 9 shows the dependence of the 
cross-calibration coefficients Mu as a function of time for band 
8 for both mirror sides and all ten detectors. It can be seen that 
in 2002, the Mu for all detectors and both mirror sides are close 


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MEISTER AND FRANZ: CORRECTIONS TO THE MODIS AQUA CALIBRATION 


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3 

OJ 


0 2Q0 400 600 800 1000 1200 

Scan Pixel 



L2 


nLw (531) Ratio for 2011 353 

Mirror-Side 1 ' 

Mirror-Side 2 


11 



0.9 


0,8 


_j i i i i 


0 200 400 600 800 1000 1200 

Scan Pixel 


Fig. 8. Response versus scan plots for MODIS Aqua Rrs at 531 nm (band 1 1) in late 2011, using (left) MCST’s new MODIS Collection 6 calibration approach 
and time-independent scan angle correction and (right) cross-calibration of MODIS to itself. 


together for each of the three frames shown. This is consistent 
with the two top plots in Fig. 5, which show that there is no 
residual scan angle dependence in any mirror side or detector; 
therefore, no corrections are needed. In 2006, the two mirror 
sides clearly differ in Fig. 5, with mirror side 2 higher than 
mirror side 1 at the beginning and in the middle of the scan 
and lower at the end of scan. This is consistent with the Mu 
shown in Fig. 9, where mirror side 2 is higher than mirror side 1 
in 2006 for frames 100 and 675, but lower for frame 1250. 
For 2011, both Figs. 5 and 9 show detector variations at the 
beginning of scan (but no clear mirror side separation) and a 
distinct separation of the mirror sides in the middle of the scan. 

V. Conclusion and Outlook 

The new MODIS calibration approach by MCST using desert 
targets [13] is much more consistent with the assumption that 
there are no long-term trends in the water-leaving reflectance in 
the global oceans than the previous MCST calibration approach. 
This was shown by performing cross calibration of MODIS 
Aqua to the SeaWiFS climatology (see Fig. 3). The resulting 
cross-calibration coefficients are much closer to unity with the 
new MCST calibration than with the previous approach. 

The improvement is largest for the central part of the MODIS 
scan (frames 300-1050). At the scan edges, residual trends 
remain, particularly for bands 8 and 9 (412 and 443 nm, respec- 
tively). In order to improve the calibration of the scan edges, a 
L3 (global, temporally averaged) data set was produced from 
MODIS data using only the central part of the MODIS scan. 
The scan angle restricted L3 data were used to derive cross- 
calibration coefficients for all scan angles. As expected, the 
derived cross-calibration coefficients were close to unity for the 
central part of the scan. The corrections for the scan edges are 
up to 3% for 412 nm. They decrease with wavelength to about 
0.5% for the red wavelength bands (see Fig. 6). Applying the 
corrections in the production of ocean color products leads to 
improvements in the temporal trends of the globally averaged 
water-leaving reflectances (see Fig. 7) and to the scan angle 
dependence (Figs. 5 and 8). The corrections presented here 
are part of the MODIS Aqua reprocessing that occurred in 
May 2012 (referred to as “R2012.0”). 


Bond 8 f Frome 100 



Fig. 9. Cross-calibration coefficients for all ten detectors and both mirror 
sides for MODIS Aqua band 8. Solid (dashed) lines show mirror side 1 (2). 
Detectors 1-10 are color-coded from black/purple to orange/red. Frame num- 
bers are (top) 100, (middle) 675, and (bottom) 1250. 


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The cross-calibration approach was also used in the previous 
reprocessing (“R2010.0”), but with a fundamental difference: 
SeaWiFS L3 data were used as a calibration source for bands 8 
and 9 (no temporally dependent corrections were applied for 
bands 10-14). Therefore, the MODIS Aqua data at those wave- 
lengths were not independent products anymore; in effect, they 
were tied to the SeaWiFS record. The new approach presented 
in this paper uses only MODIS Aqua data as input for the cross- 
calibration analysis; therefore, the ocean color products from 
R2012.0 can be considered independent of SeaWiFS. 

As a next step, the OBPG is planning to apply the same 
methodology to MODIS Aqua bands 1, 3, and 4 (645, 469, and 
555 nm, respectively). Initial results indicate that the correc- 
tions needed for these bands are small. 

The methodology presented here is not applicable to the 
MODIS on Terra because the radiometric degradation issues 
on MODIS Terra are much more severe than those on MODIS 
Aqua [6], such that no extended part of the MODIS Terra scan 
can be used as a calibration source for the cross-calibration 
analysis. Instead, the OBPG will use the MODIS Aqua data 
set as a calibration source for the cross-calibration of MODIS 
Terra. Therefore, the long-term global trends of the MODIS 
Terra ocean color products should be identical (or at least 
very similar) to those of MODIS Aqua. The value of the new 
MODIS Terra products will be the increased amount of L2 data 
available, improving daily global coverage. 

Data from the VIIRS sensor on Suomi NPP will provide 
an independent data set that can be directly compared with 
the MODIS record, potentially even merged. The radiometric 
degradation trends of the VIIRS sensor (minor degradation 
in the blue wavelengths, significant degradation for the NIR 
wavelengths [3]) are very different from those on MODIS; thus, 
such an analysis should be beneficial for both sensors. Note 
that, if indeed the largest challenge for the calibration of VIIRS 
is the calibration of the NIR bands, the cross-calibration method 
used here is of limited value because it requires well-calibrated 
NIR bands. 

Acknowledgment 

The authors would like to thank the staff of the OBPG for 
their support, as well as J. Sun from MCST. 

References 

[1] K. L. Carder and R. G. Steward, “A remote-sensing reflectance model of a 
red-tide dinoflagellate off west Florida,” Limnol. Oceanogr.,\o\. 30, no. 2, 
pp. 286-298, 1985. 

[2] R. E. Eplee, J. Sun, G. Meister, F. S. Patt, X. Xiong, and C. R. McClain, 
“Cross calibration of SeaWiFS and MODIS using on-orbit observations 
of the moon,” Appl. Opt., vol. 50, no. 2, pp. 120-133, Jan. 2011. 

[3] R. E. Eplee, K. R. Turpie, G. F. Fireman, G. Meister, T. C. Stone, 

F. S. Patt, B. A. Franz, S. W. Bailey, W. D. Robinson, and C. R. McClain, 
“VIIRS on-orbit calibration for ocean color data processing,” in Proc. 
SPIE Earth Observ. Syst. XVII, J. J. Butler and J. Xiong, Eds., 2012, 
vol. 8510, p. 85101G. 

[4] B. A. Franz, P. J. Werdell, G. Meister, S. W. Bailey, R. E. Eplee, Jr., 

G. C. Feldman, E. Kwiatkowskaa, C. R. McClain, F. S. Patt, and 
D. Thomas, “The continuity of ocean color measurements from SeaWiFS 
to MODIS,” in Proc. SPIE, 2005, vol. 5882, pp. 304-316. 

[5] B. A. Franz, S. W. Bailey, P. J. Werdell, and C. R. McClain, “Sensor- 
independent approach to the vicarious calibration of satellite ocean color 
radiometry,” Appl. Opt., vol. 46, no. 22, pp. 5068-5082, Aug. 2007. 


[6] B. A. Franz, E. J. Kwiatkowska, G. Meister, and C. R. McClain, “Moder- 
ate Resolution Imaging Spectroradiometer on Terra: Limitations for ocean 
color applications,” J. Appl. Remote Sens., vol. 2, no. 1, pp. 023525-1- 
023525-17, Jan. 2008. 

[7] H. R. Gordon, T. Du, and T. Zhang, “Atmospheric correction of ocean 
color sensors: Analysis of the effects of residual instrument polarization 
sensitivity,” Appl. Opt., vol. 36, no. 27, pp. 6938-6948, Sep. 1997. 

[8] E. J. Kwiatkowska, B. A. Franz, G. Meister, C. R. McClain, and X. Xiong, 
“Cross calibration of ocean-color bands from Moderate-Resolution Imag- 
ing Spectroradiometer on Terra platform,” Appl. Opt., vol. 47, no. 36, 
pp. 6796-6810, Dec. 2008. 

[9] G. Meister, B. A. Franz, E. J. Kwiatkowska, and C. R. McClain, “Cor- 
rections to the calibration of MODIS Aqua ocean color bands derived 
from SeaWiFS data,” IEEE Trans. Geosci. Remote Sens., vol. 50, no. 1, 
pp. 310-319, Jan. 2012. 

[10] G. Meister and B. A. Franz, “Adjustments to the MODIS terra radiometric 
calibration and polarization sensitivity in the 2010 reprocessing,” in 
Proc. Earth Observ. Syst. XVI, J. J. Butler and J. Xiong, Eds., 2011, 
pp. 815 308-1-815 308-12. 

[11] G. Meister, E. J. Kwiatkowska, and C. R. McClain, “Analysis of image 
striping due to polarization correction artifacts in remotely sensed ocean 
scenes,” in Proc. SPIE, 2006, vol. 6296, p. 629609. 

[12] G. Meister, F. S. Patt, X. Xiong, J. Sun, X. Xie, and C. R. McClain, 
“Residual correlations in the solar diffuser measurements of the MODIS 
Aqua ocean color bands to the sun yaw angle,” in Proc. SPIE, 2005, 
vol. 5882, p. 58820V. 

[13] J.-Q. Sun, X. Xiong, A. Angal, H. Chen, and A. Wu, “On-orbit 
performance of the MODIS reflective solar bands time- dependent 
response versus scan angle algorithm,” in Proc. SPIE, 2012, vol. 8510, 
pp. 156-164. 

[14] J. Sun, X. Xiong, W. Barnes, and B. Guenther, “MODIS reflective solar 
bands on-orbit lunar calibration,” IEEE Trans. Geosci. Remote Sens., 
vol. 45, no. 7, pp. 2383-2393, Jul. 2007. 

[15] X. Xiong, J. Sun, X. Xie, W. L. Barnes, and V. V. Salomonson, 
“On-orbit calibration and performance of Aqua MODIS reflective solar 
bands,” IEEE Trans. Geosci. Remote Sens., vol. 48, no. 1, pp. 535-546, 
Jan. 2010. 


Gerhard Meister received the Diploma and Ph.D. 
degrees in physics from the University of Hamburg, 
Hamburg, Germany, in 1996 and 2000, respectively. 

From 2000 to 2010, he was with Futuretech Cor- 
poration, Ocean Biology Processing Group, NASA 
Goddard Space Flight Center, Greenbelt, MD, USA, 
where he has been a member of the Ocean Ecology 
Branch since 2010. His main focus is the calibration 
and characterization of satellite-based ocean color 
sensors such as the Moderate Resolution Imaging 
Spectroradiometer, the Sea-viewing Wide Field-of- 
view Sensor, and the Visible Infrared Imager Radiometer Suite. 


Bryan A. Franz received the B.S. degree in aero- 
space engineering from the University of Maryland, 
College Park, MD, USA, in 1988 and the M.S. 
degree in computer science from Johns Hopkins 
University, Baltimore, MD, in 1998. 

He is currently a Scientist with the Ocean Ecology 
Branch (Code 614.2), NASA Goddard Space Flight 
Center, Greenbelt, MD, USA, where he leads the 
ocean color reprocessing efforts for the Moderate 
Resolution Imaging Spectroradiometer (MODIS), 
the Sea-viewing Wide Field-of-view Sensor, and 
other sensors within the Ocean Biology Processing Group. He also serves as 
the Ocean Discipline Lead for the MODIS Science Team. His work focuses 
on atmospheric correction and bio-optical algorithms and calibration and 
validation for satellite remote sensing of marine environments, with emphasis 
on consistent processing methods across multiple missions.