nasa viirs characterization support team (vcst ......aqua use definitive ephemeris data 27 hour...

(SNPP + J1/N20 + J2) VIIRS Geolocation Status

NASA VIIRS Characterization Support Team (VCST)

Geometric Calibration Group

Guoqing (Gary) Lin, SSAI/GSFC code 619

Robert E. Wolfe, NASA/GSFC Code 619

James C. Tilton, NASA/GSFC Code 606

Ping Zhang, Bin Tan, SSAI/GSFC Code 619

John Dellomo, GST/GSFC Code 619

NASA MODIS/VIIRS STM Calibration Workshop

Silver Spring, Maryland

18 October 2018

Acknowledgements

• Thanks to Carol Davidson & her Land SIPS (formerly

Land PEATE) Team for processing control point

residuals and testing Geo LUTs updates

• Thanks to Fred Patt of NASA Ocean Group for helping

us understanding and resolving issues related to

ephemeris and attitude data

• Thanks to the NOAA STAR VIIRS SDR Team and many

other branches of the JPSS Program

Lin et al., 18 Oct 2018 VCST/GEO 2

Outline

• SNPP VIIRS Geolocation Performance and Trends

• J1/N20 VIIRS Geolocation Performance and Trends

• Some expectations of J2 VIIRS

• Improvements and future work

• Conclusions


VIIRS Geolocation Performance

Residuals SNPP

VIIRS C. 1.0

J1/N-20

VIIRS Prel.

Aqua

MODIS C6.1

Terra

MODIS C6.1

Track mean 13 m 7 m 1 m 0 m

Scan mean 4 m -24 m 0 m 0 m

Track RMSE 58 m 62 m 46 m 43 m

Scan RMSE 52 m 59 m 53 m 44 m

Data-days 2447 (6.7 yrs) 282 (0.8 yrs) 5910 (16.2 yrs) 6725 (18.4 yrs)

Missing days 1 6 10 59

Daily matched

GCPs w/ I1/B1

204 183 223 258

• Nadir equivalent accuracy (RMSE – Root Mean Square Error) . (MODIS for reference)

– Meet Spec: 125 m (1s); within 20% I1 HSI (375 m) = 75 m @ nadir for VIIRS

– Band-to-band mis-registration to other bands adds bias to RMSE to :

• MODIS – VIIRS differences

Aqua use definitive ephemeris data 27 hour latency

SNPP attitude data is not as good, see Slide #13

DEM resolutions: older 1 km for VIIRS vs newer 0.5 km for MODIS C6/C6.1

22 s RMSE


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Years since Jan. 1, 2000

Daily 16-day Global 16-day S. Hemisphere 16-day N. Hemisphere

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Lin et al., 18 Oct 2018

SNPP C1 geolocation errors

Started 1/19/2012

Cryo door open

VCST/GEO 5C1.1 RMSE Track: 58 m Scan: 52 m, nadir equivalent

±20% I-band pixel size

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Scan r

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Scan angle (deg)

SNPP Scan Angle Residuals


Track

Scan

VCST/GEO 6


Strange pattern is being corrected,

see Slides 10 - 12

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Daily 16-day Global 16-day S Hemi 16-day N Hem

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J1/N20 preliminary geolocation errors

Started 12/14/2017

Nadir door open

VCST/GEO 7Preliminary RMSE Track: 62 m Scan: 59 m, nadir equivalent

-25

-20

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-10

-5

0

5

10

15

20

25

17.92 18.00 18.08 18.17 18.25 18.33 18.42 18.50 18.58 18.67 18.75

Mo

un

tin

g r

ota

tio

n (

arcs

ec)

Time (years from c. 2000)

J1 R/P/Y correction needed & in-work

Roll Pitch Yaw

J1 temporal pointing variation is large (>

SNPP). Yaw and pitch pointing variations

cause geolocation error ~ 250 m @ edge

of scan.

MODIS-like correction is being worked

for both SNPP and J1 pointing variations.


VCST/GEO 7

J1 DNB geolocation


Courtesy of Wenhui Wang and Slawomir Blonski of NOAA STAR

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696

896

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6

Mea

sure

d s

can

off

set

(m)

FPA

X-o

ffse

t (m

m)

Sample# at mid-points of 114 scan chips

J1/N20 DNB scan geo offset (LSIPS LUT r2)

FPA equivalent Local ground offset-750

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300

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Mea

sure

d s

can

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sdet

(m)

FPA

X-o

ffse

t (m

m)

Sample # at mid-points of 167 scan chips

J1/N20 DNB scan geo offset (LSIPS LUT r1)

FPA equivalent Local ground offset

nadirnadir

~5 km bias ~200 m

~200 m ~20 m

On-orbit Cal, further

VCST/GEO 8

Expectations for J2 VIIRS


• Band-to-band co-registration -- good

• Pointing – good

• Geolocation – should be good with on-orbit calibration

• Line spread functions (LSFs) / modulation transfer functions

(MTFs) – mostly good, except DNB at low light

VCST/GEO 9

0

1

-1 -0.5 0 0.5 1 1.5 2 2.5 3

Spat

ial r

esp

on

se

Distance from sample center (HSI)

Illustration of Simulated J2 DNB LSF at low light

nominal LSFSidelobe -1Sidelobe-2System LSF

Scan direction

Incorrect J2 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

0

5

10

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20

25

30

35

40

45

50

10 100 1000 10000

% s

ide

lob

e

Peak dn

%sidelobe vs peak_dn (HGA & HGB)

"Optimal light level"

"Bonus light levels"

Envelope

dn at Lmin =

3 nW/cm^2/sr

Agg32, Agg1

Envelope

Answer:

Lsight = Ltel - 1/M ( Ltel – Lhamvector)

where M = -4 (not +4 as we are currently

using), which affects line of sight due to

the parts of RTA/HAM motion non-

linearity (non-synchronization), which

are large enough to skew the errors

outside of ± 20% I-band pixel size

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0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300

LOS d

evia

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Encoder Sequence, 3rd scan 20130410T1325z -- S-NPP3rd scan 20180104T1812z -- J1/N20

VIIRS HAM encoder non-linearity

S-NPP J1/N20

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Scan r

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Scan angle (deg)

SNPP VIIRS geolocation errors in scan direction

VIGMU:VIIRS instrument geometric model update

• Puzzle: ground geolocation

SW is supposed to correct

RTA/HAM motion non-linearity

• Long term trend from SNPP

VIIRS still shows the pattern,

but in the opposite direction


Image flipping

before HAM

Image flipping

Image flipping after

HAM

Lsight = Ltel - 1/M ( Ltel – Lhamvector)

where M = -4 (not +4 as we are

currently using), which affect non-

synchronization of RTA/HAM only


VIGMU tests – J1 & NPP


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J1, 4/7/ - 5/8/2018

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SNPP, 4/7/ - 5/8/2018

VCST/GEO 12

10

100

1,000

10,000

183 366 548 731 914 1,096 1,279 1,461 1,644 1,827 2,009 2,192

Pe

ak

RSS

(RP

Y)

(arc

sec)

Time (Days since 10/28/2011)

3s=108, 99.73% 3s=36, 99.73%

SNPP SC attitude performance- - Spec outage and trend


8/23/2012

using ~90% data

Large circles for control spec outage; Small dots hint knowledge spec outage

Star tracker cooling improved SNPP attitude performance

We are seeking for further improvements3

We are developing SW with Kalman filter to refine the attitude for NASA SIPSs

J1 is performing better but we are monitoring

Roll: 5,666”

Trackers TEC 0oC-10oC

9/22/2016 Day 1791

Data up to

8/7/2017

Day 2110

1st year

3. My eRooms > S-NPP Flight Operations and Support > FARB > All Discussion Topics--Artifacts and Minutes > DR 6348--SNPP STAR TRACKER

DEGRADATIONS OVER MISSION LIFE: ATTITUDE EXCURSIONS AND LUNAR INTRUSIONS > SNPP ADCS and Geolocation Report

2nd year 3rd year 4th year 5th year 6th year

VCST/GEO 13

https://jpss-erooms.ndc.nasa.gov/eRoomhttps://jpss-erooms.ndc.nasa.gov/eRoom/JPSSFlightOperationsandSupport/SNPPFLIGHTOPERATIONSANDSUPPORThttps://jpss-erooms.ndc.nasa.gov/eRoom/JPSSFlightOperationsandSupport/SNPPFLIGHTOPERATIONSANDSUPPORT/0_4cbdhttps://jpss-erooms.ndc.nasa.gov/eRoom/JPSSFlightOperationsandSupport/SNPPFLIGHTOPERATIONSANDSUPPORT/0_4e86https://jpss-erooms.ndc.nasa.gov/eRoom/JPSSFlightOperationsandSupport/SNPPFLIGHTOPERATIONSANDSUPPORT/0_17c66

SNPP Events

data exclusion for now


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viir

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Time (hours from 2015-08-19T00:00z)

snpp scc 1 sec time err track_shift scan_shift

1 second time error

onboard of SNPP

14:24:40.6z

21:16:30.6z

Leap second insertions: 2012-07-01, 2015-07-01, 2017-01-01

Inclination adjustment maneuvers: poor pointing ~ 2 hours after

#1-4: 2014/ 7/30+9/10+10/15+11/12;

#5: 2015 9/23; #6: 2016 9/29;

#7: 2017 9/28; #8: 2018 9/27.

Drag make-up maneuvers: 28 DMUs up to 2018-07-17.

VCST/GEO 14

We will “hide” the

granules where

geolocation accuracy is

poor.

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Dis

tan

ce (m

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Latitude (deg)

nadir distance_to_next_scanline

J1 VIIRS Scan-to-scan underlaps

J1/N20 VIGMU test data

• 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 speed (~0.4%)

Underlap

overlap

-90

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Dis

tan

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Latitude (deg)

nadir distance_to_next_scanline

Underlap

Within scan

Inter-scan

Inter-HAM-sides

where F = effective focal length = Mag x aft optic focal length, p = detector “pitch” interval in the track direction, n = #

detectors, h = range from satellite to earth terrain surface altitude, T = scan period, i=inclination angle (in ECI) < 90 deg for J1,

VECI = spacecraft ground speed in the inertial frame, Vearth0 = speed of earth rotation at equator, Overlap < 0 indicates underlap.

𝑂𝑣𝑒𝑟𝑙𝑎𝑝 = 𝑛𝑝

𝐹ℎ − [𝑉𝐸𝐶𝐼 − 𝑉𝑒𝑎𝑟𝑡ℎ0 cos 𝑖]𝑇, if < 0 underlap


On-orbit focal length measurements


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1D

NB

DN

B

DN

B

DN

B

M2

M4

M3 I1 I2 I2 I2 I2

M7

M7

M7

M7

M5 I3 I3 I3 I3

M10

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M15EF

L d

evia

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No

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Band Name

EFL on-orbit measurements for SNPP VIIRS

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B

DN

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DN

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L d

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No

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Band Name

EFL on-orbit measurements for J1/N20 VIIRS

VisNIR FPA LWIRS/MWIR

VisNIR FPA LWIRS/MWIR

VCST/GEO 16

• A +0.1% EFL change means +12 m change in scan-to-scan underlap where it exits.

See poster for details, including BBR

Future work1) Routine monitor and LUTs update as needed

2) VIGMU (VIIRS instrument geometric model update):

test production

3) Corrections for temporal pointing variations:

test production

4) Refresh ground control points with Landsat-8 images

5) Replace attitude in SC diary with Kalman filtered data

6) Replace ephemeris in SC diary with GPS data

7) Update DEM from 1 km to 500m resolution

8) Automate GEO LUT updates

9) Create Level-1 geolocation web (needed?)

Anything else?

Any change in priority order above?Lin et al., 18 Oct 2018 VCST/GEO 17

Conclusions

• SNPP VIIRS geolocation performance is good

– mean errors for I- & M-bands are ~ 10 m and uncertainties are ~ 60 m

at nadir, statistically

– DNB geolocation accuracy is only spot-checked and it is ok

– The attitude system underperforms geolocation error up to 7 km

occurred occasionally. Attitude HW needs maintenance, and their

output will be tweaked on the ground (re-working ephemeris and

attitude data)

• J1/N20 VIIRS geolocation performance is ok– Early on-orbit calibration reduced biases from O(1km) to O(10m), including DNB

– Correction for large pointing variation was worked, and will be operationalized soon

• J2 (N21) VIIRS geolocation is expected to perform fine


Questions?

Q: Do random variables exist?

A: Not really.


Q: What do we do?

A: Careful trending and de-trending.

Backup Slides


y = 2.691x - 28.462R² = 0.3732

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16-day Global16-day Global Linear (16-day Global)

y = 0.382x - 1.8738R² = 0.0165

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SNPP Long-Term Trending and Correction


De-trending was worked and will be operationalized soon

Linear trend and annual cycle

Linear trend and weak annual cycle

VCST/GEO 21

SNPP sun angle dependence


y = 0.0012x2 - 0.3587x + 19.644R² = 0.4179

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Shift

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Sun angle (degrees)

Track residuals (adjusted & demeaned) vs. Sun angle

y = 0.0016x2 - 0.3713x + 16.848R² = 0.4163

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Sun angle (degrees)

Scan residuals (adjusted & demeaned) vs. Sun angle

Correction is in-workVCST/GEO 22

SNPP orbit position errors (wrt GPS)

SNPP

2016-09-

21+22


Spec : 75 m, 3-sigma

Plot courtesy: Fred Patt


Correction is in-work

J01

2018-06-

10+11

Along-track pos err wrt gps

Cross-track pos err wrt gps


J1/N20 orbit position errors (wrt GPS)

Plot courtesy: Fred PattCorrection is in-workLin et al., 18 Oct 2018 VCST/GEO 24

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