The presentation stressed the importance of a pre-launch test plan and a post-launch CalVal plan in the geometric aspects of instrument focal length, spatial responses, band-to-band registration, pointing, geolocation and long-term monitoring

Davidson, Carol

Dellomo, John

Lin, Guoqing (Gary)

Tan, Bin

Tilton, James C.

Wolfe, Robert E.

Zhang,  Ping

NASA Technical Reports Server

Overview of JPSS VIIRS
geometric calibration and validation
NASA VIIRS Characterization Support Team (VCST)
Geometric Calibration Group
Guoqing (Gary) Lin1,2, Robert E. Wolfe2
1, Science Systems Applications, Inc., Lanham, MD
2, NASA Goddard Space Flight Center, Greenbelt, MD
Contributors:
James C. Tilton2, Ping Zhang1,2, John Dellomo3,2, 
Bin Tan1,2, Carol Davidson & Land SIPS Team1,2
3, Global Science & Technology, Inc., Lanham, MD
SBG Workshop, 12 - 14 June, 2019, Washington, DC
CalVal Session: Thursday, 13 June 2019
https://ntrs.nasa.gov/search.jsp?R=20190027537 2019-09-26T19:14:34+00:00Z
Outline
• Introduction
– Motivation, VIIRS whiskbroom scanner 
• Focal length
– Effects on geolocation, BBR & scan-to-scan underlaps
• Spatial response tests
– MTF, under-/over-sampling, optical/electronics anomalies
• Band-to-band registration (BBR) tests
– Crucial for Level-2 data retrievals
• Pointing and geolocation
• Long term trending and correction
• Other issues, concerns and challenges
• Concluding Remarks
VCST/GEO  2Lin & Wolfe, 13 June 2019
Artifacts from MODIS are mentioned sometimes
Motivation
• For accurate Level-2 data retrievals
– Geolocation accuracy is usually better than ½ pixels (3σ)  
– Band-to-band registration (BBR) is usually > 80% 
sample overlap (3σ)
• Keys to mission success
– Well written geometric requirements
– Good pre-launch test and analysis plan
– Good post-launch CalVal plan
VCST/GEO  3Lin & Wolfe, 13 June 2019
Whiskbroom VIIRS scanner
VCST/GEO  4
Rotating 
Telescope 
Assembly 
(RTA)
Aft Optics 
Assembly 
(AOA)
Half Angle 
Mirror 
(HAM)
Track 
direction
Scan 
direction
Θ
.
Θ/2
.
Nadir
Fold mirror
Rotating Telescope 
Assembly (RTA) captures 
light from the Earth and 
other calibration sectors.
Half Angle Mirror (HAM) de-
rotates incoming light into 
the fixed Aft Optics 
Assembly (AOA) that 
houses the detectors.
VIIRS (Visible Infrared Imaging 
Radiometer Suite) scanning 
geometry
Lin & Wolfe, 13 June 2019
Nominal Timing Offsets (in Moderate Band Sampling Interval units) Relative to Focal Plane Reference Axis.
Focal Plane Reference Axis
VIS/NIR 
FPA
S/WMIR 
FPA
LWIR 
FPA
20 15 10 5 0 -5 -10 -15 -20
M5 M7 I2 I1 M3 M4 M2M6 M1
M14
Even
Odd
DNB
M13M12I4I3M10M11M8M9
Ground Scan Direction
M15 M16B M16A I5
Even
Odd
DNB*
(*DNB not to scale)
VIIRS Band/Detector Physical Layout
Offset of Each Band Relative to the Focal Plane Reference Axis (ref: Geolocation ATBD)
3 focal planes: VisNIR, SWMIR, LWIR; + 1 Day-Night band (DNB) (no BBR Spec)
21 bands (16 M-bands (M16A, M16B merged in space or just sent down one), 5 I-bands)
16 detectors in each M-band (750x750 m nadir); 32 detectors in e ch I-band (375x375m)
All I-bands across the focal plane assemblies (FPAs) are located close 
together to mitigate on-orbit jitter impact
Shortwave midwave infrared (S/WMIR) FPA bands spread out the most 
in scan direction, 38 samples apart from M13 to M9 
VCST/GEO  4Lin & Wolfe, 13 June 2019
Ground coverage:
M-band Sample, Aggregation Sample Numbers & Pixel Size
On-board sample deletion deletes 2 M-band (4 I-band) detectors in the 2 sample aggregation zone and 4 M-band (8 I-
band) detectors in the no-aggregation zone. The numbers in parentheses for the “Sample no.” and “HSI Scan (m)” are 
for dual-gain M-bands before aggregation, SDR of which are available to the ground as intermediate products. 
Using altitude 828 km over the equator. Nominal EFL & scan rate in J1 (SNPP 0.4% faster) 
no scan overlap scan overlap on-board sample deletion
3-sample (3x1)
aggregation
2-sample (2x1) 
aggregation
no (1x1)
aggregation
Scan direction
Track 
direction
nadir
−5
6.
04
o
−4
4.
67
o
−3
1.
59
o
−1
50
6 
km
−8
81
 k
m
−5
23
 k
m0 
km
HSI Scan (m)  771(257)                                 1152(384) 768(384)            1277(638) 638(638)                      1600(1600)
HSI Track (m)  738                                                    888                                    1113            1603
Sample No.   1600(3152)                           1009(1377) 1008(1376)          641(641) 640(640)                           1(1)
VCST/GEO  6
Pixel size = HSI: Horizontal Sampling Interval
Lin & Wolfe, 13 June 2019
Focal length
• A small variation of focal 
length results in appreciable 
geolocation errors.
• It also results in BBR errors 
for detectors at the ends of 
arrays and bands far apart 
on the focal plane(s)
• It may result in scan-to-scan 
underlaps in the track 
direction in cross-track 
scanner design
• It affects the complexity of 
instrument optics (& cost)
Lin & Wolfe, 13 June 2019 VCST/GEO  7
Altitude
/range
Ground object
Focal length
Lens
FPM (focal plan module)
xX
Y
Z
-0.8%
-0.6%
-0.4%
-0.2%
0.0%
0.2%
0.4%
0.6%
0.8%
DN
B
M
5
M
7 I2 I1 M
4
M
11
M
10 I3 I5
VIS/NIR                       |        S/MWIR        | LWIR
J1 VIIRS EFL deviation (% nominal)
-0.8%
-0.6%
-0.4%
-0.2%
0.0%
0.2%
0.4%
0.6%
0.8%
DN
B
M
5
M
7 I2 I1 M
3
M
4
M
11
M
10 I3
M
15
M
16 I5
VIS/NIR                       | S/MWIR     | LWIR
SNPP VIIRS EFL deviation (% nominal)
Overall Result
2x1 Agg. Zone
1x1 Agg. Zone
MODIS & VIIRS focal length variations
• A 0.5 % difference in EFL (effective focal length) can cause the geolocation of the center of the first 
or last of the 40 MODIS 250 m detectors to have a systematic error of 24 m at nadir.
• A 0.5 % EFL error without scan rate adjustment results in VIIRS M13-M9 BBR error a 48 m nadir 
equivalent offset in the scan direction in the non-aggregated zones
Lin & Wolfe, 13 June 2019 VCST/GEO  8
-0.8%
-0.6%
-0.4%
-0.2%
0.0%
0.2%
0.4%
0.6%
0.8%
1 2 13L 14L 3 4 10 12 6 7 31 32
NIR             |            VIS            |S/MWIR| LWIR
Terra MODIS EFL Deviation (% nominal)
-0.8%
-0.6%
-0.4%
-0.2%
0.0%
0.2%
0.4%
0.6%
0.8%
1 2 13L 14L 3 4 10 12 6 7 32
NIR             |              VIS              |S/MWIR| LWIR
Aqua MODIS EFL Deviation (% nominal)
0100
200
300
400
500
-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90
Di
st
an
ce
 (m
)
Latitude (deg)
nadir distance_to_next_scanline
Scan-to-scan underlaps
VCST/GEO  9
• Widest underlaps occur at nadir near 15N at ~ 70 
m in this case. They narrow down as J1 goes 
north or south due to increasing altitude.  They 
also close in off nadir angles (@ ~10 deg) due to 
bowtie effects 
• High terrain widens the underlaps.
• SNPP VIIRS has less of this issue because of its 
shorter focal length and scan rate (~0.4%)
Underlap
overlap
-90
-60
-30
0
30
60
90
-180 -150 -120 -90 -60 -30 0 30 60
350
370
390
410
430
450
470
-30 -15 0 15 30 45 60
Di
st
an
ce
 (m
)
Latitude (deg)
nadir distance_to_next_scanline
Underlap
Within scan
Inter-scan
Inter-HAM-sides
where F = effective focal length, p = detector “pitch” interval in the track direction, n = # detectors, h = range, T = scan period, 
i=inclination angle (in Earth Centered Inertial frame) > 90 deg for VIIRS/MODIS, VECI = spacecraft ground speed in the inertial 
frame, Vearth0 = speed of earth rotation at equator, Overlap < 0 indicates underlap.
𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂 = 𝑛𝑛 𝑝𝑝
𝐹𝐹
ℎ − [𝑉𝑉𝐸𝐸𝐸𝐸𝐸𝐸 − 𝑉𝑉𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒0 cos 𝑖𝑖]𝑇𝑇,    if < 0  underlap
Lin & Wolfe, 13 June 2019
Track LSF anomalies
• Track LSFs (line spread functions) are obtained by instrument staring 
into stepping illuminated reticle slits
• SNPP VIIRS band M12 was found having anomalous LSFs in the track 
direction due to workmanship
• The detector #1 has the worst performance, which went through 
additional testing under thermal vacuum conditions.
Lin & Wolfe, 13 June 2019 VCST/GEO  10
Scan LSF anomalies
Lin & Wolfe, 13 June 2019 VCST/GEO  11
trailing side of 
the detector/slits
False signal, 
coming from 
the trailing 
side of slits
J2 agg18
HGB
• Scan LSFs are obtained by 
instrument scanning static and 
phased illuminated reticle slits
• SNPP VIIRS M11 scan LSFs
• Suspected internal reflection
• The LSFs are parameterized in 
MTF (modulation transfer function), 
under-/over-sampling, etc
• J2 Scan LSFs from 2nd (B) high 
gain detector array (HGB) in DNB
• Electronics anomaly
• Incorrect voltage setting causes 
the charge in the current sample to 
remain behind in the transfer gate 
and be deferred into the next 
sample in the scan direction
BBR test results
Good BBR is crucial for Level-2 data retrievals
Lin & Wolfe, 13 June 2019 VCST/GEO  12
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
M1 M2 M4 M3 I1 I2 M7 M5 M6 M13 M12 I4 I3 M10 M11 M8 M9 I5 M16 M15 M14
B
an
d 
O
ffs
et
 (M
-H
SI
)
Band Name
Scan Agg1x1
Scan Agg2x1
Scan Agg3x1
Track
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
M1 M2 M4 M3 I1 I2 M7 M5 M6 M13 M12 I4 I3 M10 M11 M8 M9 I5 M16 M15 M14
B
an
d 
O
ffs
et
 (M
-H
SI
)
Band Name
Scan Agg1x1
Scan Agg2x1
Scan Agg1x1
Track
 SNPP VIIRS scan rate is not fast (~0.4%>nominal) enough to match the shortened 
focal length (~0.5%<nominal) that results in higher BBR errors in the scan direction 
 J1 bands on cold FPAs shifted ~ 50 m from bands on VisNIR FPA in the track 
direction (affects downlink w/ differential encodingdata compression)
S/MWIR FPA LWIR FPAVisNIR FPA
J1
SNPP
Hot
Cold
Pointing and geolocation
• Pre-launch instrument pointing tests mainly align nadir 
pointing (encoders) in the earth view (among other 
alignments in other sectors), which is used in look-point 
equation for ground geolocation product processing.
• Pre-launch spacecraft tests include instrument-to-
spacecraft interface rotation matrix, which is usually 
corrected for proper geolocation in on-orbit operations.
• On-orbit spacecraft (SC) ephemeris (position & velocity) 
provides along-track nadir pointing. Attitude provides 
correction for SC nadir pointing.
• RTA/HAM timestamps provide off-nadir along-scan 
motion and pointing to the ground. 
Lin & Wolfe, 13 June 2019 VCST/GEO  13
On-orbit geolocation error detection
CPM (control point matching) program
VCST/GEO  14
 tm
x  
tmα  
tmβ  
Scan 
direction 
(sample) 
Track 
direction 
(detector) 
scp  
α -plane 
β -plane 
tmu  
• Landsat red band (0.63 – 0.69 µm) 30 m resolution
• Mostly cloud clear sub-scenes 800x800-pixels (24 x 24 km) 
(to be refreshed to 1400x1400-pixels (42 x 42 km))
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
-1.25 -1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1 1.25
Ba
nd
 I1
 sp
ati
al 
Re
sp
on
se
 (n
.d.
)
Along-scan Position (post-aggregation HSI)
Agg1x1 Meas.
Agg2x1 Meas.
Agg3x1 Meas.
Agg1x1 Ideal
Agg2x1 Ideal
Agg3x1 Ideal
• LSFs are used to simulate VIIRS band I1 (0.62 – 0.68 µm)
images
• Square LSF in track direction (& scan direction for DNB)
• Triangular LSF in scan direction for VIIRS, trapezoidal 
LSFs in Agg2x1 and Agg3x1 zones for VIIRS
Lin & Wolfe, 13 June 2019
-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
0.7 0.75 0.8 0.85 0.9 0.95 1
Ge
o E
rro
r (m
)
Cross correlation coefficient
NPP VIIRS initial CPM results (nadir equivalent)
track shift scan shift
Initial SNPP/J1 VIIRS geolocation
VCST/GEO  15
2/2-17/2012
Before correction 2/23
-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
0.7 0.75 0.8 0.85 0.9 0.95 1
G
eo
 E
rr
 (m
)
Cross-correlation coefficient
J1 VIIRS initial CPM results (nadir equivalent)
track shift scan shift
• J01 launched 
– 2017-11-18T09:47z
• nadir door opened 
– 2017-12-13T16:45z
• Track offset ~ -1 km
• Scan offset ~ +2 km
1 day, 12/14/2017
Lin & Wolfe, 13 June 2019
• SNPP launched 
– 2011-10-28
• nadir door opened 
– 2017-11-21
• Track offset ~ -1 km
• Scan offset ~ +1 km
• RTA mirror tungsten 
degradation extended 
initial CalVal period 
Initial on-orbit corrections
VCST/GEO  16
Parameters At-
launch
LSIPS     
r1
2018-01-03
Deltas
“r1”
– “At-launch”
Roll (”) 0.9 -423.5 -424.4
Pitch (”) 51.1 300.5 249.4
Yaw (”) 80.5 99.4 18.9
J1/N20 VIIRS GEO LUTs updates
Here, roll, pitch and yaw are instrument-to-spacecraft mounting angles
NASA LPEATE (Land Product Evaluation and Analysis Tool Element) has evolved to 
LSIPS (Land Science Investigator-led Processing System) 
Lin & Wolfe, 13 June 2019
Parameters At-
launch
LPEATE 
r1
2012-02-23
Deltas
“r1”
– “At-launch”
Roll (”) 33.2 -227.3 -260.5
Pitch (”) 41.2 153.2 112.0
Yaw (”) -59.3 95.4 144.7
SNPP VIIRS geolocation parameter lookup tables (LUTs) updates
Long term trending and correction
VCST/GEO  17Lin & Wolfe, 13 June 2019
-50
-25
0
25
50
75
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Tr
ac
k 
(a
dj
.) 
re
s.
 (m
) 
Years since Jan. 1, 2000
Daily 16-day Global 16-day Southern Hemisphere 16-day Northern Hemisphere
AMSR-E, 2->0 rpm
2015-12-4T5:34zAMSR-E, 40->0 rpm
2011-10-4T7:27z
AMSR-E, 0->2 rpm
2013-12-5, 16:50 UTC
-75
-50
-25
0
25
50
75
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Tr
ac
k 
(a
dj
.) 
re
s.
 (m
) 
Years since Jan. 1, 2000
Daily 16-day Global 16-day Southern Hemisphere 16-day Northern Hemisphere
±20% 250m-band pixel size
Aqua MODIS C6.1 trend (upper) and correction (lower)
The stop-go-stop of the AMSR-E (Advanced Microwave Scanning Radiometer - Earth 
Observing System) antenna dish on the zenith deck affects thermal conditions of MODIS
Other issues, concerns & challenges
• Leap second handling
• Orbit maintenance maneuver handling
• Star catalog upload handling
• Star trackers re-alignment handling
• Star trackers degradation
• Onboard clock drifts
• Downlink bandwidth
VCST/GEO  18Lin & Wolfe, 13 June 2019
Details of these may be discussed at other times.
But,
the spacecraft design needs to take these into consideration.
Concluding Remarks
• Instrument focal length is a defining parameter affecting 
geolocation, BBR, optics design (& cost)
• Pre-launch testing is important to validate designs
• BBR (> 80% overlap) is crucial for Level-2 data retrieval
• A network of ground control points (chips) is needed to 
detect and correct geolocation errors
– Terrain correction (DEM (Digital Elevation Model) w/ compatible 
resolution) is needed for terrestrial applications
• Long term monitoring is needed to correct possible 
geolocation drifts to achieved better than ½ pixels (3σ) 
accuracy 
• Orbit operations need to be considered in designs
• Well written requirements, good pre-launch test & post-
launch CalVal plans are keys to mission success
VCST/GEO  19Lin & Wolfe, 13 June 2019


Overview of JPSS VIIRS Geometric Calibration and Validation

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