Since launch in December 1999, the MODIS ProtoFlight Model (PFM) onboard the Terra spacecraft has successfully operated for more than 11 years. Its Flight Model (FM) onboard the Aqua spacecraft, launched in May 2002, has also successfully operated for over 9 years. MODIS observations are made in 36 spectral bands at three nadir spatial resolutions and are calibrated and characterized regularly by a set of on-board calibrators (OBC). Nearly 40 science products, supporting a variety of land, ocean, and atmospheric applications, are continuously derived from the calibrated reflectances and radiances of each MODIS instrument and widely distributed to the world-wide user community. Following an overview of MODIS instrument operation and calibration activities, this paper provides a summary of both Terra and Aqua MODIS long-term performance. Special considerations that are critical to maintaining MODIS data quality and beneficial for future missions are also discussed

Angal, Amit

Barnes, William

Salomonson, Vincent

Wenny, Brian N.

Xiong, Xiaoxiong (Jack)

NASA Technical Reports Server

Summary of Terra and Aqua MODIS Long-term Performance 
 
Xiaoxiong (Jack) Xiong1, Brian N. Wenny2, Amit Angal3, William Barnes4, and Vincent Salomonson5 
 
1Code 614.4, Sciences and Exploration Directorate, NASA/GSFC, Greenbelt, MD 20771, USA, 
2Sigma Space Corp., 4801 Forbes Boulevard, Lanham, MD 20706, USA, 
3Sciences and System Applications Inc., 10210 Greenbelt Road, Lanham, MD 20706, USA, 
4University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA, 
5University of Utah, Salt Lake City, UT 84112, USA 
 
 
ABSTRACT 
 
Since launch in December 1999, the MODIS ProtoFlight 
Model (PFM) onboard the Terra spacecraft has successfully 
operated for more than 11 years. Its Flight Model (FM) 
onboard the Aqua spacecraft, launched in May 2002, has 
also successfully operated for over 9 years. MODIS 
observations are made in 36 spectral bands at three nadir 
spatial resolutions and are calibrated and characterized 
regularly by a set of on-board calibrators (OBC). Nearly 40 
science products, supporting a variety of land, ocean, and 
atmospheric applications, are continuously derived from the 
calibrated reflectances and radiances of each MODIS 
instrument and widely distributed to the world-wide user 
community. Following an overview of MODIS instrument 
operation and calibration activities, this paper provides a 
summary of both Terra and Aqua MODIS long-term 
performance. Special considerations that are critical to 
maintaining MODIS data quality and beneficial for future 
missions are also discussed. 
 
Index Terms - MODIS, Terra, Aqua, Calibration 
 
1. INTRODUCTION 
 
MODIS is a key instrument for NASA’s Earth Observing 
System (EOS). Since launch, its ProtoFlight Model (PFM) 
has successfully operated onboard the Terra spacecraft for 
more than 11 years and its Flight Model (FM) onboard the 
Aqua spacecraft has also successfully operated for more 
than 9 years. MODIS observations are made in 36 spectral 
bands, including 20 reflective solar bands (RSB) and 16 
thermal emissive bands (TEB), and at 3 spatial resolutions at 
nadir, 0.25 km for bands 1-2, 0.5 km for bands 3-7, and 1.0 
km for the remaining spectral bands. Since launch, both 
Terra and Aqua MODIS have produced an unprecedented 
amount of data products and significantly contributed to 
Earth remote sensing research activities and applications [1]. 
In addition to design improvements made over its heritage 
sensors in terms of its spectral range, spatial resolutions, and 
data coverage, MODIS was developed with very stringent 
calibration requirements to be met throughout its entire 
mission. As a result, the MODIS instrument was built with a 
complete set of on-board calibrators (OBC), including a 
solar diffuser (SD), a solar diffuser stability monitor 
(SDSM), a blackbody (BB), and a spectroradiometric 
calibration assembly (SRCA) [2]. 
Both Terra and Aqua MODIS went through extensive 
pre-launch calibration and characterization activities. Their 
OBC were also fully characterized by the instrument vendor 
using well calibrated ground testing equipment. During its 
on-orbit operation, the on-board BB is constantly controlled 
at a nominal temperature while the SD/SDSM and SRCA 
are operated on a regular basis. MODIS OBC are used to 
track changes in sensor radiometric, spectral, and spatial 
properties and to support MODIS level 1B (L1B) look-up-
table (LUT) updates and algorithm improvements [2-5]. 
This paper provides an overview of both Terra and Aqua 
MODIS on-orbit operation and calibration activities and an 
update to their long-term performance. Although having 
operated beyond their specified design life of 6 years, on-
orbit performance shows that both Terra and Aqua MODIS 
instruments as well as their on-board calibrators are still 
able to provide satisfactory functions and allow high quality 
data products to be continuously generated. In general, Aqua 
MODIS has shown better performance than its predecessor, 
Terra MODIS. Also discussed in this paper are special 
issues that are critical to the L1B calibration quality and 
lessons learned that could benefit future sensor development 
and operation. 
  
2. OPERATION AND CALIBRATION 
 
MODIS on-orbit operation and calibration activities are 
planned and implemented by the MODIS Characterization 
Support Team (MCST) at NASA/GSFC. Since launch, 
Terra MODIS has operated using A-side configuration 
(launch to October 2000), B-side configuration (October 
2000 to June 2001), then A-side configuration (July 2001 to 
September 2002), and finally a configuration with A-side 
https://ntrs.nasa.gov/search.jsp?R=20120003101 2019-08-30T19:29:11+00:00Z
electronics and the B-side formatter (September 2002 to 
present). In addition to a few spacecraft and sensor 
anomalies and events during the early part of the mission, 
Terra MODIS has experienced an SD door operational 
anomaly in May 2003. As a result, the SD door was 
purposely fixed at the open position with its screen in place 
starting from July 2003. On the other hand, the Aqua 
MODIS operation has been very stable. Except for being in 
the safe mode for a few very short periods due to spacecraft 
related anomalies at mission beginning, Aqua MODIS has 
operated continuously using the B-side configuration. The 
use of B-side electronic configuration for Aqua MODIS on-
orbit operation was based on both A-side and B-side 
performance determined from extensive pre-launch 
calibration and characterization. 
MODIS on-orbit calibration activities include regular 
SD and SDSM calibration events and near-monthly lunar 
observations for the RSB. In an effort to establish on-orbit 
calibration scale for each RSB detector and track changes in 
its response over time, the SD/SDSM operations were 
scheduled more frequently at the beginning of both Terra 
and Aqua missions. Normally, the BB temperatures are 
constantly controlled for the scan-by-scan TEB calibration. 
Periodic BB warm-up and cool-down (WUCD) operations 
with BB temperatures varying between 272K and 315K are 
also carried out to support the TEB on-orbit calibration. The 
SRCA is operated monthly in the radiometric mode but less 
frequently for the spectral and spatial modes. As shown in 
Table 1, from launch to present (May 04, 2011), Terra 
MODIS has scheduled and executed more than 320 
SD/SDSM operations, 100 scheduled lunar observations, 75 
BB WUCD cycles, and 240 SRCA calibration events 
(radiometric, spectral, and spatial combined). As expected, 
the corresponding numbers of Aqua MODIS OBC 
operations are smaller than that of Terra MODIS. In 
addition to its OBC and lunar observations, several special 
operational activities, including spacecraft maneuvers, have 
been carried out to improve MODIS on-orbit calibration and 
data quality [3-5]. 
Table 1 Summary of MODIS on-orbit calibration activities (as 
of May 04, 2011). 
  SD / 
SDSM 
MOON BB 
WUCD 
SRCA 
RAD 
SRCA 
SPET 
SRCA 
SPAT 
Terra 322 102 76 133 48 63 
Aqua 212 81 39 105 27 45 
 
3. ON-ORBIT PERFORMANCE 
 
Terra and Aqua MODIS instrument temperatures are 
illustrated in Figures 1 and 2 on a weekly average basis over 
their respective missions. The temperatures during the 
periods with special calibration activities and events are 
excluded from the averages. At the beginning of its mission, 
Terra MODIS operation was carried out using different 
configurations. Since September 2002, it has been operated 
using a configuration combing A-side electronics with the 
B-side formatter. The use of different electronic 
configurations for Terra MODIS has led to small noticeable 
discontinuities in its instrument temperatures. Aqua 
MODIS, however, has been using the same B-side 
configuration over its entire mission. The long-term changes 
in instrument temperatures are generally very small, less 
than 3.5 K for Terra MODIS over 11 years and less than 2.0 
K for Aqua MODIS over 9 years. The seasonal oscillations 
are expected and the peak-to-peak variations are typically 
within 2.0 K. Figures 1 and 2 demonstrate that the 
spacecraft and MODIS instrument operation environment 
and conditions have been very stable over their entire 
missions. The temperatures of the MODIS scan cavity, the 
scan mirror, and the warm focal plane assemblies (FPA) for 
the VIS and NIR spectral bands all show a nearly identical 
trend to the instrument temperatures. 
   
Figure 1 Terra MODIS instrument temperatures 
   
Figure 2 Aqua MODIS instrument temperatures 
The SWIR and MWIR spectral bands are located on 
the same FPA, called the SMIR FPA. It is nominally 
controlled at 83K together with another cold FPA, which 
hosts all the LWIR spectral bands. Figures 3 and 4 illustrate 
Terra and Aqua MODIS LWIR FPA temperatures, which 
are also on a weekly average basis. Ignoring changes caused 
by switching between different operational configurations, 
the cold plane assembly (FPA) temperatures are much better 
controlled in Terra MODIS than Aqua MODIS. The gradual 
small increase and noticeable fluctuations of the Aqua cold 
FPA temperatures in recent years are primarily due to the 
loss of its radiative cooler margin. Approximately starting 
from 2007, Aqua MODIS cold FPA temperature has 
increased about 0.15 K. In addition to seasonal variations 
and long-term increase shown in Figure 4, there exist similar 
orbit-to-orbit and daily variations in the Aqua MODIS cold 
FPA temperatures. 
 
Figure 3 Terra MODIS LWIR FPA temperatures 
 
Figure 4 Aqua MODIS LWIR FPA temperatures 
   
Figure 5 MODIS SD on-orbit degradation (launch to present) 
The SDSM is operated during each scheduled SD 
calibration. It is used to track on-orbit changes in SD bi-
directional reflectance factor (BRF). Figure 5 shows SD 
degradation for both Terra and Aqua MODIS. The SD 
calibration system was designed with an SD door. Normally 
it is closed except during regularly scheduled SD and SDSM 
observations. When both Terra and Aqua MODIS SD and 
SDSM were operated at the same frequency (or under the 
same condition) at the beginning of their missions, their SD 
degradation rates were nearly identical. Following an SD 
door operational anomaly that led to the decision to fix the 
SD door at the “Open” position in the middle of 2003, the 
Terra MODIS SD on-orbit degradation has become much 
faster than Aqua MODIS. As shown in Figure 5, changes in 
SD BRF are approximately 49% at 0.41 µm, 29% at 0.53 
µm, and 15% at 0.65 µm for Terra MODIS over 11 years, 
compared to the changes of 18%, 8%, and 4% at the 
corresponding wavelengths for Aqua MODIS over 9 years. 
Clearly, the SD degradation rate is strongly wavelength 
dependent for both Terra and Aqua MODIS with larger 
changes observed at shorter wavelengths. 
MODIS TEB calibration uses a quadratic algorithm 
with its linear gains computed from BB observations on a 
scan-by-scan basis. Terra MODIS BB is normally controlled 
at 290 K and Aqua MODIS at 285 K. Their weekly 
averaged BB temperatures are presented in Figures 6 and 7. 
BB temperatures during periodic WUCD events and other 
special calibration events are not included in the weekly 
averages. It is clear that Aqua MODIS BB operation has 
been extremely stable and there is essentially no long-term 
drift in the BB temperatures. For Terra MODIS, however, 
there exist a few small but expected changes due to the use 
of different instrument operational configurations. In 
addition, there are small seasonal variations of up to ±0.1 K 
for Terra MODIS BB temperatures that are closely matched 
to seasonal oscillations of instrument temperatures and a 
small long-term drift of approximately 0.03K. 
 
Figure 6 Terra MODIS on-board BB temperatures  
 
Figure 7 Aqua MODIS on-board BB temperatures  
In general, larger changes in detector responses (or 
gains) are observed at shorter wavelengths for the RSB, 
which also have noticeable mirror side and scan angle 
dependencies. Figure 8 shows on-orbit changes in mirror 
side dependent gains derived from SD and lunar 
observations for Terra MODIS band 8 at 0.41 µm. The SD 
and lunar observations are made at 2 different angles of 
incidence (AOI) to the scan mirror. For Aqua MODIS, as 
shown in Figure 9, the mirror side differences are relatively 
small. Changes, including mirror side differences, are much 
smaller for the spectral bands of longer wavelengths, such as 
the SWIR bands and TEB. In addition to changes in detector 
long-term responses, small short-term variations, less than 
±1.0%, exist in recent Aqua MODIS TEB LWIR detector 
responses, which are caused by variations in the cold FPA 
temperatures (Figure 4). The short-term variations, however, 
have little impact on data quality as MODIS TEB 
calibration is performed on a scan-by-scan basis. Among all 
490 detectors, there are 44 noisy detectors (30 from pre-
launch) and no inoperable detectors in Terra MODIS and 6 
noisy detectors (2 from pre-launch) and 13 inoperable 
detectors (10 from pre-launch) in Aqua MODIS. Most Terra 
MODIS on-orbit noisy detectors are located on the LWIR 
FPA and most Aqua inoperable detectors are in band 6 (1.64 
µm). 
 
Figure 8 Changes in Terra MODIS band 8 (0.41 µm) gains 
 
Figure 9 Changes in Aqua MODIS band 8 (0.41 µm) gains 
Both spatially and spectrally, Terra and Aqua 
MODIS have demonstrated excellent stability. Except for a 
couple of bands, the changes in center wavelengths (CW) 
and bandwidths (BW) have been less than 0.5 nm and 1.0 
nm, respectively, for most VIS and NIR bands. On-orbit 
results also show that both Terra and Aqua MODIS have 
experienced little or no change in their along-scan and 
along-track band-to-band registration (BBR). For Terra 
MODIS, most band pairs continue to meet the specifications 
of ±0.1 km. For Aqua MODIS, large BBR offsets (0.3-0.4 
km in both directions) identified pre-launch remains 
unchanged on-orbit. It is anticipated that, with dedicated 
calibration efforts, both Terra and Aqua MODIS will 
continue to provide quality data products and make great 
contributions to a broad range of scientific studies and 
applications. 
As both instruments continue to operate beyond their 
6-year “design life”, the frequencies of some calibration 
activities, such as SD and SDSM operations, have been 
gradually reduced without impacting the existing calibration 
and data product quality. A newly developed approach of 
accurate mapping of the SDSM screen transmission has 
been applied to further improve the accuracy of tracking SD 
on-orbit degradation. Continuous studies will be conducted 
to examine the calibration impact, especially on the 
nonlinear calibration coefficients, due to Aqua cold FPA 
temperature variations. For the RSB, the most challenging 
task remains to be accurate determination of changes of 
sensor response versus scan angle. In addition to OBC and 
lunar observations at limited scan angles, the use of long-
term trends from ground targets over a wide range of scan 
angles has become an essential part of RVS 
characterization. As expected, special considerations and 
efforts have been made in support of science investigations 
as part of the efforts for collection 6 data product quality 
assurance. 
Many lessons have been learned from both Terra and 
MODIS instrument design, pre-launch calibration and 
characterization, on-orbit operation, calibration, and sensor 
performance, algorithm implementation, LUT updates, and 
calibration uncertainty assessment. As illustrated in this 
paper, no two sensors are completely identical and all sensor 
responses change on-orbit, large or small. Consequently, it 
is critical to maintain continuous calibration efforts 
throughout the sensor’s entire mission. MODIS lessons have 
already provided and will continue to provide valuable 
information for other mission and sensor development, their 
operation and important calibration activities. 
 
4. SUMMARY 
 
Terra and Aqua MODIS have successfully operated for 
more than 11 and 9 years, respectively. On-orbit calibration 
performance shows that both instruments and their on-board 
calibrators continue to be able to provide key design 
functions and to allow high quality data products to be 
generated for scientific studies and applications. Except for 
a couple of problems identified pre-launch, Aqua MODIS 
on-orbit overall performance has been better and more 
stable than Terra MODIS, especially for the bands at shorter 
wavelengths. MODIS experience and lessons learned 
through all phases will continue to benefit future earth-
observing sensors’ design, development, pre-launch and on-
orbit calibration. 
 
5. REFERENCES 
 
 [1] V. Salomonson, W. Barnes, X. Xiong, S. Kempler, and 
E. Masuoka, “An Overview of the Earth Observing 
System MODIS Instrument and Associated Data 
Systems Performance,”  Proc. IEEE International 
Geoscience and Remote Sensing Symposium, 
doi:10.1109/IGARSS.2002.01025746, pp. 970-972, 
2002 
[2] X. Xiong, K. Chiang, J. Esposito, B. Guenther, and 
W.L. Barnes, “MODIS On-orbit Calibration and 
Characterization,” Metrologia 40, 89-92, 2003 
[3] Barnes W.L., X. Xiong, T. Salerno, B. Breen, and C. 
Salo, “Operational Activities and On-orbit Performance 
of Terra MODIS On-board Calibrators”, Proceedings of 
SPIE - Earth Observing Systems X, Vol. 5882, 2005 
[4] X. Xiong, K. Chiang, J. Sun, W. Barnes, B. Guenther, 
and V. Salomonson, “NASA EOS Terra and Aqua 
MODIS On-orbit Performance,” Adv. Space Res., 43, 
413-422, doi:10.1016/j.asr.2008.04.008, 2008 
[5] X. Xiong, B.N. Wenny, and W.L. Barnes, “Overview of 
NASA Earth Observing Systems Terra and Aqua 
Moderate Resolution Imaging Spectroradiometer 
Instrument Calibration Algorithms and On-orbit 
Performance,” J. Appl. Remote Sens., Vol. 3, 032501, 
doi:10.1117/1.3180864, 2009 


Summary of Terra and Aqua MODIS Long-Term Performance

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