The NPP Instrument Calibration Support Element (NICSE) is one of the elements within the NASA NPP Science Data Segment (SDS). The primary responsibility of NICSE is to independently monitor and evaluate on-orbit radiometric and geometric performance of the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument and to validate its Sensor Data Record (SDR) [1]. The NICSE interacts and works closely with other SDS Product Evaluation and Analysis Tools Elements (PEATE) and the NPP Science Team (ST) and supports their on-orbit data product calibration and validation efforts. The NICSE also works closely with the NPP Instrument Calibration Support Team (NICST) during sensor pre-launch testing in ambient and thermal vacuum environment [2]. This paper provides an overview of NICSE VIIRS sensor post-launch calibration support with a focus on the use of sensor on-board calibrators (OBC) for the radiometric calibration and characterization. It presents the current status of NICSE post-launch radiometric calibration tool development effort based on its design requirement

Butler, James

Chiang, Kwo-Fu

McIntire, Jeffrey

Schwaller, Matthew

Xiong, Xiaoxion

NASA Technical Reports Server

POST-LAUNCH CALIBRATION SUPPORT FOR VIIRS ONBOARD 
NASA NPP SPACECRAFT 
 
Xiaoxiong Xiong1, Kwo-Fu Chiang2, Jeffrey McIntire2, Mathew Schwaller1, and James Butler1 
 
1Sciences and Exploration Directorate, NASA/GSFC, Greenbelt, MD 20771, USA 
2Sigma Space Corp., 4801 Forbes Boulevard, Lanham, MD 20706, USA 
 
 
ABSTRACT 
 
The NPP Instrument Calibration Support Element (NICSE) 
is one of the elements within the NASA NPP Science Data 
Segment (SDS). The primary responsibility of NICSE is to 
independently monitor and evaluate on-orbit radiometric 
and geometric performance of the Visible Infrared Imaging 
Radiometer Suite (VIIRS) instrument and to validate its 
Sensor Data Record (SDR) [1]. The NICSE interacts and 
works closely with other SDS Product Evaluation and 
Analysis Tools Elements (PEATE) and the NPP Science 
Team (ST) and supports their on-orbit data product 
calibration and validation efforts. The NICSE also works 
closely with the NPP Instrument Calibration Support Team 
(NICST) during sensor pre-launch testing in ambient and 
thermal vacuum environment [2]. This paper provides an 
overview of NICSE VIIRS sensor post-launch calibration 
support with a focus on the use of sensor on-board 
calibrators (OBC) for the radiometric calibration and 
characterization. It presents the current status of NICSE 
post-launch radiometric calibration tool development effort 
based on its design requirements.  
 
1. INTRODUCTION 
 
The NPOESS Preparatory Project (NPP) was developed as a 
risk reduction and bridge mission between the NASA Earth 
Observing System (EOS) and the National Polar-orbiting 
Operational Environmental Satellite System (NPOESS). The 
NPOESS program has recently been reconstructed and 
transitioned to the Joint Polar Satellite System (JPSS) and 
the Defense Weather Satellite System (DWSS). VIIRS is a 
key instrument on-board the NPP spacecraft, which is 
scheduled for launch in October 2011. Currently, all five 
flight instruments for the NPP mission have been fully 
integrated into the observatory, undergoing through various 
spacecraft-level testing. Along with VIIRS, the instruments 
are the Cross-track Infrared Sounder (CrIS), Ozone 
Mapping and Profiler Suite (OMPS), Clouds and the Earth 
Radiant Energy System (CERES), and the Advanced 
Technology Microwave Sounder (ATMS). To a large 
extent, the VIIRS instrument was developed from the 
Moderate Resolution Imaging Spectroradiometer (MODIS), 
one of the key instruments for the NASA EOS Terra and 
Aqua missions, with improvements made in a number of 
areas. VIIRS collects data in 22 spectral bands with 
wavelengths from 0.41 to 12 µm and provides daily global 
observations of the land, ocean, and atmospheric 
parameters. To date, Terra MODIS has successfully 
operated for more than 11 years and Aqua MODIS for more 
than 9 years. Extensive on-orbit calibration and 
characterization activities have been implemented for each 
instrument. As a follow-on instrument for the NASA EOS 
MODIS, VIIRS has significantly benefitted from MODIS 
experience [3]. In addition to the lessons learned from 
MODIS pre-launch calibration and characterization 
activities, many of its on-orbit operation and calibration 
approaches have been considered and planned for VIIRS, 
including lunar observations and spacecraft maneuvers 
designed to support its on-orbit calibration.  
 
Based on the experience and lessons from MODIS on-orbit 
operation and various calibration activities, NICSE has 
planned and developed a number of tasks to support the 
NPP VIIRS on-orbit calibration and characterization [4]. 
Examples from MODIS data are provided in this paper to 
demonstrate the use of sensor performance monitoring tools. 
 
2. PRE-LAUNCH SENSOR CHARACTERIZATION 
 
The VIIRS flight model unit 1 (F1) sensor has undergone 
through a comprehensive set of pre-launch calibration and 
characterization activities. The ambient phase testing was 
conducted from June 2007 to June 2008 at Raytheon’s Santa 
Barbara Remote Sensing (SBRS) facility. Afterwards, the 
sensor was transported to Raytheon's El Segundo facility for 
sensor level thermal vacuum testing in the summer of 2009. 
In January 2010, the VIIRS F1 sensor was shipped to Ball 
Aerospace and Technology Corporation (BATC) in Boulder 
for integration, with other instruments, into the NPP 
spacecraft. Subsequently, performance testing was 
performed under ambient conditions from February 2010 to 
January 2011. From early March to late April of 2011, the 
NPP spacecraft successfully completed a series of tests 
under thermal vacuum conditions. After completing the 
remaining post thermal vacuum testing activities, the 
https://ntrs.nasa.gov/search.jsp?R=20120002313 2019-08-30T19:05:54+00:00Z
spacecraft will be transported to Vandenberg AFB and is 
scheduled for launch in October 2011.  
 
All the pre-launch tests have been carefully designed prior 
to testing. A large amount of functional and radiometric 
calibration test data sets have been extensively analyzed by 
NASA NPP teams, including both NICST and NICSE. The 
analysis results have been documented in technical reports 
or memorandums for future reference purposes.  
 
3. ON-ORBIT CALIBRATION AND 
CHARACTERIZATION ACTIVITIES 
 
Similar to MODIS, VIIRS carries a set of on-board 
calibrators (OBC), which include a solar diffuser (SD) and a 
solar diffuser stability monitor (SDSM) for its reflective 
solar bands (RSB) calibration and a blackbody (BB) for the 
thermal emissive bands (TEB) calibration. Although the 
solar diffuser collects data every orbit, the SDSM, designed 
to track on-orbit changes in SD bi-directional reflectance 
factor (BRF), is scheduled only on a regular basis. The 
combined SD and SDSM calibration data provide absolute 
radiometric calibration for RSB at the sensor level.  The 
instrument on-board blackbody is nominally controlled at a 
fixed temperature to provide information needed for TEB 
scan-to-scan radiometric calibration algorithm. Periodically, 
a sequence of warm-up and cool-down (WUCD) operations, 
which vary the BB temperature from instrument ambient to 
315 K, will be carried out over its entire mission in order to 
evaluate and maintain the TEB calibration and data quality. 
As expected, the designs and functions of VIIRS OBC are 
very similar to that of MODIS.  
 
In addition to regular observations made by the VIIRS OBC, 
a number of special activities that involve spacecraft 
maneuvers, such as roll, yaw, and pitch maneuvers, have 
been planned and evaluated for their on-orbit 
implementation. These activities are designed and 
developed based on the experience from heritage sensors as 
an effort to further improve sensor characterization and 
calibration quality.  
 
According to NPP flight operation design, VIIRS will be 
scheduled on a near monthly basis to view the Moon using 
the same strategy developed for MODIS lunar observations. 
As an effort to support this activity, a special VIIRS lunar 
view planner tool has been developed from MODIS 
experience. Figure 1 displays two recent Moon images from 
the Aqua MODIS RSB Band 1 (0.65 µm; nadir resolution 
250m) in 2011 (March and April). These data are collected 
through the instrument Space View (SV) port during 
regularly scheduled lunar roll maneuvers. The timing of the 
lunar observations and spacecraft roll angles are predicted 
by the lunar planner tool developed by the MODIS 
Characterization Support Team (MCST). A similar tool is 
being adopted by MCST and NICSE analysts for future 
VIIRS lunar observations. Results from lunar view data 
analysis will provide an assessment of sensor radiometric 
calibration stability [5].  
 
 
Fig. 1 Consecutive Aqua MODIS monthly lunar images were 
observed by Band 1 (0.65 µm) in March and April 2011.  
 
 
4. TOOL DEVELOPMENT STATUS 
 
MODIS lessons and the experiences transferred from MCST 
at NASA Goddard Space Flight Center (GSFC) have 
significantly helped NICSE plan and develop a large 
number of post-launch tools for VIIRS on-orbit radiometric 
calibration and characterization. These new tools include 
algorithms and functions that are commonly used for 
MODIS. The VIIRS tools can be categorized in five areas 
described below.  
 
4.1. Input and output tools  
 
The VIIRS SDR operational code ingests the sensor Raw 
Data Record (RDR) and produces SDR and OBC 
intermediate product (OBC-IP) for every granule. The SDR 
contains calibrated Earth view data of each spectral band 
while the OBC-IP contains telemetry data and detector raw 
response from the internal on-board calibrators, which 
include the SD, SDSM, BB, and SV. The OBC-IP reader 
opens and reads the data in HDF format. It produces the 
output to be used for the OBC calibration tools. An image 
visualization tool was developed to display the SDR and 
perform certain statistical analysis on the SDR. Another tool 
was also developed to read the Telemetry RDR for trending 
purposes. In addition to data readers, NICSE is required to 
have the ability to modify the SDR calibration Look-Up-
Tables (LUTs) used by the NPP data production system. 
The LUTs change tool can alter the array dimension and 
modify the content of each LUT.  
 
4.2. OBC calibration tools  
 
Radiometric calibration support is one of the important tasks 
in the NICSE design requirement. Each VIIRS detector 
(TEB and RSB) will be calibrated on-orbit using the OBC. 
Separate tools have been developed to compute detector 
calibration coefficients using the SD/SDSM for the RSB and 
the BB (during WUCD) for the TEB. The tools also 
compute each detector’s signal to noise ratio (SNR) and 
other quality assurance characteristics. The algorithms used 
in the VIIRS SDSM calibration tool are similar to those for 
the MODIS instrument, likewise for the SDSM planner tool 
which can predict the calibration time periods in order to 
command SDSM operation in advance.  
 
4.3. Lunar calibration tools  
 
Lunar observations will also be used to support the VIIRS 
instrument calibration. Because of this, a lunar view planner 
tool has been developed, based on the MODIS lunar 
planner, to predict the lunar view observation opportunity. 
This planner tool predicts when and where the Moon will 
appear with respect to NPP orbit and VIIRS geometry, and 
at what phase angle. Such prediction can provide an 
accurate spacecraft roll maneuver schedule to both the 
spacecraft and instrument operation teams. NICSE requires 
the ability to use lunar view data to assess the absolute and 
relative radiometric response of VIIRS RSB detectors. The 
analysis of lunar view data, which is not part of the SDR 
operational production code, will be performed offline. 
Figure 1 shows examples of Aqua MODIS lunar 
observation. The results of the analysis will provide useful 
sensor characterization, including detector response 
comparison with respect to the SD calibration, relative 
spatial calibration of band-to-band registration (BBR), 
detector gain ratios, and other characteristics.  
 
4.4. RVS characterization tools  
 
The Response Versus Scan angle (RVS) of the VIIRS Half 
Angle Mirror (HAM) has been measured during pre-launch 
testing. On orbit, the RVS of the VIIRS HAM is not 
expected to degrade and change as much as the MODIS 
Scan Mirror. However, similar tools that can track the RVS 
change through the Earth view sector have been considered 
and developed based on MODIS experiences. For the RSB, 
analyzing the Earth view SDR data is the primary method 
for tracking the change of the relative RVS on-orbit. SDRs 
over relatively uniform ground targets will be selected for 
RSB RVS trending and characterization. For the TEB, the 
RVS can be measured again on-orbit using the dark Deep 
Space Maneuver (DSM) observations through the nadir 
Earth view port during the NPP pitch maneuver. A TEB 
RVS tool has been developed to facilitate offline calibration 
with respect to deep space at various scan angles on both 
HAM sides. By using these tools during post-launch 
operation, NICSE can characterize the HAM RVS and 
update the RVS LUTs for potential improvements of the 
SDR.  
 
4.5. Trending tools  
 
A variety of post-launch trending tools were developed to 
track short-term and long-term detector stability and 
instrument telemetry points. Trending the detector scan-to-
scan raw DN is a fundamental method to check for 
abnormal behavior of the detector response, especially 
useful for the TEB because of the scan-to-scan calibration 
algorithm. The DN trending tool will be widely used post-
launch to examine detector response whenever there is a 
change in the detector’s gain or detector signal-to-noise 
(SNR) level. The trending results of this analysis tool can 
help assess the sensor’s health and data quality. As for 
detector noise characterization, similar tools will be used to 
trend detector short-term and long-term stability in terms of 
SNR for the RSB and noise equivalent difference in 
temperature (NEdT) for the TEB. These trending results 
help monitor any change of the VIIRS detectors in terms of 
gain, noise, and out-of-family behaviors. The outcome of 
this analysis will assist the decision of recommending SDR 
LUT updates. The detector trending tools are band, detector, 
and HAM side dependent.  
 
 
Fig. 2 Aqua MODIS blackbody temperature profiles during the 
WUCD activity in February 2011.  
 
The VIIRS post-launch characterization often requires 
information derived from measurements of many 
temperature telemetries, including those measuring the 
OBC-BB, the cavity, the HAM, the focal planes, and the 
electronic circuit card assemblies. Major temperature 
telemetry points related to VIIRS SDR radiometric 
calibration and characterization have been selected and 
applied to the telemetry trending tool. Some of the 
temperatures, such as those from the OBC-BB and HAM, 
are actually used in the radiometric calibration algorithm of 
the SDR operational code. Figure 2 shows trending plots of 
Aqua MODIS blackbody temperature profiles at two fixed 
temperature plateaus, controlled at 285K and 315K, during a 
BB warm-up and cool-down (WUCD) cycle. These charts 
demonstrate the use of an NICSE developed tool to track 
BB temperature scan by scan, which is needed in the VIIRS 
SDR (equivalent to MODIS Level-1B data) TEB 
radiometric calibration. There are twelve temperature 
thermistors embedded in the MODIS BB while VIIRS only 
has six. Data shown here are the mean and the standard 
deviation error bar of six selected MODIS BB thermistors 
(out of twelve) at mirror side (MS) 1 during a 5-minute 
granule. Only half of the data are plotted for clarity. The 
standard deviations of six thermistors temperature are about 
0.02K and 0.06K at 285K and 315K respectively. Based on 
the results from the VIIRS thermal vacuum test, the VIIRS 
BB performed better than MODIS BB in terms of thermal 
uniformity. During the VIIRS F1 sensor level testing at hot 
plateau, the standard deviations of BB thermistors at 283K 
and 315K are 0.007K and 0.004K, respectively. The 
periodic BB WUCD operations will provide useful data to 
assess and validate the non-linearity of the TEB detector 
response.  
 
In September 2010, about one year prior to the scheduled 
NPP launch, NICSE has successfully completed initial 
development of all the tools and tested them by using 
MODIS proxy data as part of the NPP SDS requirements. 
Prior to NPP spacecraft launch, all the calibration tools will 
be updated and improved based on the latest VIIRS data 
format and calibration algorithms so that the VIIRS data can 
be handled correctly.  
 
5. FUTURE EFFORT AND SUMMARY 
 
The NICSE is currently engaged in two major activities: 
supporting NICST for assessment of VIIRS F1 pre-launch 
calibration testing and preparing for post-launch calibration 
activities. Following pre-launch spacecraft level calibration 
and test data analyses, the NICST efforts will be focused on 
sensor launch readiness support while NICSE will continue 
to support the same efforts, including development and 
validation of sensor SDR LUTs that are critical for the 
calibration during the initial phase of orbit operation. For the 
SDR validation support, NICSE works closely with NPP 
SDS Land PEATE on the development of Land PEATE 
version of SDR operational code (Ops code). NICSE has 
received, installed, and tested the latest SDR Ops code 
provided by Land PEATE. The Ops code includes 
calibration for geometric and radiometric modules.  
 
 
 
 
Fig. 3 VIIRS SDR Ops code radiometric calibration procedure.  
 
 
Figure 3 shows only the radiometric part of the Ops code 
run on the NICSE system. The NICSE’s major effort in 
support of VIIRS post-launch activities is involved with the 
radiometric calibration analysis for LUT improvement. 
Most of the tools described in this paper support such effort. 
With the ability to calibrate the detectors, update the SDR 
LUTs, and run the SDR Ops code to produce new SDRs, 
NICSE will be able to independently support VIIRS SDR 
validation.  
 
The NASA NPP NICSE will continue to develop, test, and 
improve the planned data analysis and instrument 
monitoring tools. In addition to continuously making 
progress to complete all the scheduled tasks, NICSE has 
actively involved in support of extensive efforts to transition 
NPOESS program to the Joint Polar Satellite System 
(JPSS). With lessons learned from MODIS experiences and 
VIIRS pre-launch data analysis, NICSE has demonstrated its 
capability to improve calibration tools and develop new 
algorithms in the future to better monitor and understand on-
orbit changes in the sensor behavior.  
 
6. REFERENCES 
 
[1] R. Sikorski, K. Chiang, M. Nishihama, R. Wolfe, X. Xiong, 
and M. Schwaller, “An Overview of NASA NPP SDS-NICSE 
Activities on VIIRS SDR Assessment,” Proceedings of IGARSS, 
296-299, 2010.  
[2] H. Oudrari, T. Schwarting, K. Chiang, J. McIntire, C. Pan, and 
X. Xiong, “A Methodology to Assess the Impact of Optical and 
Electronic Crosstalk in New Generation of Sensors Using Heritage 
Sensors,” Proceedings of IGARSS, 2691-2694, 2010.  
[3] X. Xiong, K. Chiang, J. Esposito, B. Guenther, and W. Barnes, 
“MODIS On-orbit Calibration and Characterization,” Metrologia 
40, 89-92, 2003.  
[4] K. Chiang, A. Wu, J. Sun, M. Schwaller, and X. Xiong, 
“Calibration Support for NPP SDR Assessment,” Proceedings of 
SPIE – Earth Observing Systems XV, Vol. 7807, 78071A, 2010.  
[5] J. Sun, X. Xiong, W. Barnes, and B. Guenther, “MODIS 
Reflective Solar Bands On-Orbit Lunar Calibration,” IEEE Trans. 
Geosci. Remote Sens., 45(7), 2383-2393, 2007.  
[6] “VIIRS Radiometric Calibration Algorithm Theoretical Basis 
Document ATBD,” not published.  
 
 
Earth View
Radiometric
Calibration
Geo-IP
OBC-IP
Dual-Gain-IP
SDRs
Rad Cal
LUTs
Rad Cal
Analysis
OBCs
Earth
View


Post-Launch Calibration Support for VIIRS Onboard NASA NPP Spacecraft

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