SST from VIIRS on NPP: prelaunch
preparations and post-launch
validation
Peter J Minnett & Robert H Evans
Meteorology & Physical Oceanography
Rosenstiel School of Marine and
Atmospheric Science
University of Miami
Miami FL USA
Outline
• Description of VIIRS – Visible/Infrared
Imager/Radiometer Suite
• SST retrievals
• Cal/Val approach
All information about VIIRS is from
publicly accessible sources.
NASA SST Science Team Meeting
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NPP payload
From http://modis.gsfc.nasa.gov/sci_team/meetings/201001/presentations/plenary/gleason.pdf
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VIIRS
• The Visible/Infrared Imager/Radiometer Suite collects
visible/infrared imagery and radiometric data.
• Applications include atmospheric clouds, earth radiation budget,
clear-air land/water surfaces, sea surface temperature, ocean color,
and low light visible imagery.
• Primary instrument for satisfying 22 Environmental Data Records
(EDRs) and 2 Key Performance Parameters (KPPs): Imagery &
sea surface temperature.
• Multiple VIS and IR channels between 0.3 and 14 μm
• Imagery (I) Spatial Resolution: ~370m @ nadir / 750m @ edge of
swath
• Moderate (M) Spatial Resolution: ~740m @ nadir / 1500m @ edge
of swath
• Swath width ~3000km
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VIIRS Components
•
•
•
•
•
Spectral Bands:
– Visible/Near IR: 9 plus
Day/Night Band
– Mid-Wave IR: 8
– Long-Wave IR: 4
Imaging Optics: 18.4 cm
Aperture, 114 cm Focal
Length
Band-to-Band
Registration (All Bands,
Entire Scan)
> 80% per axis
Orbital Average Power:
240 W
Mass: 275 Kg
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VIIRS innovations
•
•
•
•
Rotating telescope primary optics
Two-sided “Half-Angle Mirror” (HAM)
Multiple detectors (16) per spectral band
On-board pixel aggregation
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VIIRS
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Risk reduction by using components derived
from heritage instruments:
• Rotating Telescope from SeaWiFS
• Black-body from MODIS
• Multiple Focal Plane Arrays and Multiple
Detector Assemblies from MODIS
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Pixel Aggregation
• Each “pixel” has
three rectangular
detectors in the scan
direction
• Detectors have a 3x1
aspect ratio
• These are aggregated
in threes, then twos,
then no aggregation,
across the scan.
• This is an attempt to
provide near uniform
spatial resolution
across the swath.
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VIIRS vs MODIS spatial resolution
From http://www.ipo.noaa.gov/ams/2010/posters/AGU_AMS-RAY_NGASVIIRSHeritageSystems-SNODGRASS_GUENTHER_ANDREAS-WE_PRINT-PR.pdf
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VIIRS SST Bands
Spectral bands
are a subset of
MODIS bands
GSD = Ground
sampling
distance
These are
very
promising
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VIIRS SST Uncertainty Estimates
• The sources of error the VIIRS SSTs fall into two categories:
– associated with imperfections in the instrument
– arise from imperfections in the atmospheric correction algorithm.
• The instrumental effects include:
– The inherent noise in the detectors, the Noise Equivalent Temperature
Difference (NEΔT)
– Band-to-band registration (BBR)
– Modulation Transfer Function (MTF)
– Imperfections in the knowledge of angular dependence of the
reflectivity of the “Half Angle Mirror”
– Calibration errors, such as imperfections in the knowledge of the
emissivity and surface temperature of the on-board black body target,
and of stray radiation falling on the detectors.
• Uncertainties will be established soon after launch using
multiple techniques.
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VIIRS SST algorithms
Daytime NLSST algorithm:
where a0, a1, a2, a3 are coefficients derived by regression analysis, T11 is the measured brightness
temperature at 11 µm (VIIRS band M15), T12 is the measured brightness temperature at 12 µm
(VIIRS band M16), RSST is a modeled, first guess SST, and z is the sensor zenith angle.
Night-time NLSST algorithm:
where a0, a1, a2, a3 are coefficients derived by regression analysis (but are different from those in
Equation 12), T3.7 is the measured brightness temperature at 3.7 µm (VIIRS band M12).
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Post launch validation
The approach will be based on experience gained
from AVHRR, (A)ATSR and MODIS, and will
involve comparisons with:
• Other validated satellite data sets (e.g. AVHRR,
AATSR, MODIS…)
• Drifting and moored buoys
• Ship-based radiometers – M-AERI, M-AERI
Mk2, ISAR…..
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SST validation using
ship-board
radiometers
Radiometers installed on ships
for the validation of MODIS
skin SSTs.
Top: the ISAR mounted above
the bridge of the M/V Jingu
Maru.
Middle: M-AERI mounted on
the NOAA S Ronald H. Brown.
Bottom: M-AERI mounted on
an upper deck of the Explorer
of the Seas.
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M-AERI validation data
M-AERI cruises since the launch of Terra used for the validation of
MODIS skin SSTs
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M-AERI Mk 2
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ISAR VOS cruises for SST validation
Real-time
transmission of data
via Iridium, on-thefly validation is
feasible.
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19
SST radiometers - 2009
3rd Miami IR Radiometry Workshop
Traceability to SI references is a prerequisite for CDRs
20
Validation with buoys
Buoys provide many more opportunities of “matchups ” than radiometers.
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GHRSST Diagnostic Data Set
Location of the 250 HR-DDS global data comparison
locations for SST in situ and satellite retrievals.
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DDS time series
Example of time series of DDS data including multiple satellite data,
in situ measurements, NWP analysis fields and OI fields. This allows
rapid comparison between VIIRS SSTs and other SSTs.
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In situ data → LUT generation to product validation
A
Gather in situ
0
1
D
Analyze
Matchups →
Quality Test
Hypercube
LUT
G
2
Process
VIIRS SDR
→ EDR,
Diagnostics
Analyze
Diff wrt
Reference,
Time Series
Hovmueller
plots
C
Acquire, load
SDR and
reference
field inputs
Generate
extraction files
Quality
control
Buoy
MAERI, ISAR
Real time or
retrospective
Process
SDR,
Navigate →
EDR,
Matchup
records
B
1
F
E
Update L2gen
with revised
LUT and
tables
H
2
I
Correct
algorithm as
necessary,
update and reprocess
0
Current status at L-351
•
•
•
•
•
•
•
•
Instrument level T/V testing completed, and some optical cross-talk issues
identified – but not expected to be dominant source of SST error
Instruments integrated on NPP spacecraft at Ball Aerospace & undergoing testing
Post-launch SST validation plans being set up: coordination between May
(NAVOCEANO), Ignatov (NOAA –STAR), Emery (U. Colorado) & Evans –
Minnett (U Miami)
New validation sensors (M-AERI Mk2) being developed
Real-time data transmission being tested
Software being installed and tested, including match-ups “on the fly”
Data streams being established and tested
Anticipated validation data:
– Satellite fields (MODIS, AVHRR, AATSR)
– Buoys
– Radiometers (2 M-AERIs; 2 M-AERI Mk2s, 2 ISARS)
•
Logical framework for feedback to improve retrievals being established
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VIIRS & NPP
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Summary
• VIIRS has the potential to provide high quality
SSTs.
• Post launch validation will focus on comparison
with:
– Satellite SST fields
– Buoys
– Radiometers
• Contribution to SST CDR requires validation with
NIST-traceable radiometers – facilitated through
Miami Infrared Radiometry Workshops.
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• Additional slides in reserve
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Major VIIRS Objectives
• High resolution imagery with near constant
resolution across scan
• Increased resolution of SST retrievals
• Disaster monitoring (Volcanic ash, Suspended
Matter, Floods, Fires, …)
• Increased accuracy/resolution of aerosols and
cloud properties
• Climate relevant accuracies……
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In situ and proxy data tasks
A
1
A
2
In Situ
Measurements
MAERI
In Situ
Measurements
ISAR
A
E
1
Matchup
database
RTE
simulation
I1
E
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In Situ
Measurements
MAERI
I
Telescope / HAM Synchronization Angles
Note –
successive
rotations of the
Rotating
Telescope
Assembly use
alternate sides
of the HAM
Spectral bands
are a subset of
MODIS bands
Silicon PIN Diodes
PV HgCdTe (HCT)
PV HCT
LWIR
S/MWIR
VIS/NIR FPA
VIIRS Bands
Band
Wavelength
(µm)
M1
0.412
M2
0.445
M3
0.488
M4
0.555
I1
M5
0.640
0.672
M6
I2
M7
0.746
0.865
0.865
M8
M9
I3
M10
M11
M12
I4
M13
M14
M15
I5
M16
Driving EDRs
Gain
Lmax Ltyp or
Range or Tmax
Ttyp
EOL Predicts, Nom Tolerance
FU w/ MIB Fix, F/:
6.20
SNR @ Ltyp or NEDT(K) @ Ttyp
SNR Margin
Required
Predicted
(%)
352
434
23.3
316
717
126.6
380
419
10.3
409
702
71.5
416
562
35.1
414
739
78.6
362
480
32.6
315
685
117.1
119
164
37.6
242
294
21.4
360
549
52.5
199
320
60.7
150
251
67.1
215
462
114.9
340
525
54.5
BOL Predicts, Nom Tolerance
FU w/ MIB Fix, F/:
6.20
SNR @ Ltyp or NEDT(K) @ Ttyp
SNR Margin
Required
Predicted
(%)
352
451
28.3
316
747
136.2
380
431
13.3
409
722
76.4
416
571
37.3
414
753
82.0
362
486
34.2
315
694
120.0
119
166
39.3
242
297
22.7
360
556
54.3
199
323
62.1
150
252
68.3
215
466
116.6
340
530
55.9
Ocean Color
Aerosols
Ocean Color
Aerosols
Ocean Color
Aerosols
Ocean Color
Aerosols
Imagery
Ocean Color
Aerosols
Atmospheric Corr'n
NDVI
Ocean Color
Aerosols
High
Low
High
Low
High
Low
High
Low
Single
High
Low
Single
Single
High
Low
135.0
615.0
127.0
687.0
107.0
702.0
78.0
667.0
718.0
59.0
651.0
41.0
349.0
29.0
349.0
44.9
155.0
40.0
146.0
32.0
123.0
21.0
90.0
22.0
10.0
68.0
9.6
25.0
6.4
33.4
1.240
1.378
1.610
1.610
2.250
3.700
3.740
4.050
Cloud Partical Size
Cirrus/Cloud Cover
Binary Snow Map
Snow Fraction
Clouds
SST
Imagery Clouds
SST
Fires
Single
Single
Single
Single
Single
Single
Single
High
Low
164.9
77.1
72.5
71.2
31.80
353
353
343
634
5.4
6.0
7.3
7.3
0.12
270
270
300
380
74
83
6
342
10
0.396
2.500
0.107
0.423
122
171
123
463
20
0.182
0.549
0.058
0.316
65.2
107.2
1956.7
35.3
95.4
117.4
355.5
85.3
33.8
74
83
6
342
10
0.396
2.500
0.107
0.423
122
171
123
463
20
0.182
0.549
0.058
0.316
65.2
107.2
1956.7
35.3
95.4
117.4
355.5
85.3
33.8
8.550
10.763
11.450
12.013
Cloud Top Properties
SST
Cloud Imagery
SST
Single
Single
Single
Single
336
343
340
340
270
300
210
300
0.091
0.070
1.500
0.072
0.067
0.030
0.414
0.029
35.4
133.9
262.5
146.7
0.091
0.070
1.500
0.072
0.067
0.030
0.414
0.029
35.4
132.7
262.5
146.7
Noise Component Breakdown
(single sample, no TDI or Aggregation)
1.0
0.9
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ISAR validation data
Real-time transmission of data via Iridium, on-the-fly validation is
feasible
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Temperatures are traced to NIST
1. On-board black-body cavities have
thermometers calibrated to NISTtraceable thermometers (SSEC)
2. Periodic calibration using a 3rd
black body in M-AERI zenith view.
3. Periodic calibration of M-AERI
system with a NIST-designed
Water-Bath Black-Body target at
RSMAS, using NIST-traceable
reference thermometers.
4. RSMAS Water-Bath Black-Body
target characterized with NIST EOS
TXR
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NIST EOS TXR
TXR characterizing the RSMAS WBBB
NIST water-bath black-body calibration
target
See: Fowler, J. B., 1995. A third generation water bath based blackbody source, J. Res. Natl.
Inst. Stand. Technol., 100, 591-599
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36
M-AERI
Cold finger,
Dewar and
detectors
Aft optics
Input
aperture
Stirling
cycle cooler
Interferometer
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The innards
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Wavelength calibration
Wavelength
calibration provided
by a HeNe laser
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