The Cross-track Infrared Sounder:
Sensor Design & Projected Performance
Ronald Glumb & Joseph Predina
ITT Industries, ITT Aerospace/Communications,
1919 West Cook Road, P.O. Box 3700, Fort Wayne, IN 46801, USA
CrIS
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CrIS System
Overview
The Cross-track Infrared Sounder (CrIS)
• CrIS NPOESS Mission
– Retrieve temperature, moisture and pressure profiles of the earth atmosphere
– Component of the CrIMSS (Cross-track Infrared/Microwave Sounding Suite)
– NPP launch 2005, NPOESS launch 2007
• CrIS Space Segment
– 833 km orbit, 98.7 degree inclination, 101 minute period
– Measures upwelling IR radiance in 1305 spectral channels (3.9 um to 15.4 um)
– 918 Interferograms measured each cross-track scan (8 second period)
• 30 Earth scene Fields of Regard (FOR)
• 4 calibrations (2 Deep Space + 2 Internal Calibration Target)
– 1.25 Orbit Raw Data Record
• 35,062 FORs, 315,562 FOVs, 946,687 Interferograms
• CrIS Ground Segment
– Sensor Data Record (SDR) algorithms
• Transform CrIS interferograms into fully calibrated and geolocated spectra
– Environmental Data Record (EDR) algorithms
• Transform SDRs spectra into temperature, pressure and moisture profiles
CrIS
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Section 1 - 2
CrIS System
Overview
CrIS NPP Mission Scheduled for Early 2006 Launch
ModuleLevel
DDRs
PDR Phase 2
Phase
1
ATP
DDR
EDU3 Adds
1394 and GIID
Upgrades;
Available to
NPP 6-12
Months Before
First Flight Unit
DDDR
Detailed
Design
GIID Mods
EDU2 Build
EDU2
Test
Demos and Breadboards
CDR
EDU3 Build and Test
Plan Contract
(12/04)
2/05
Flight Unit #1 (NPP)
Build and Test
EDU1 at PDR
Validated CrIS
Design Concept
1999
CrIS
2000
Flight Unit #2
(Delivery in 2/06)
EDU2 Greatly Reduces Risk:
Flight-Like Hardware Built and
Tested Before CDR
2001
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2002
Section 1 - 3
2003
Flight Unit #3
(Delivery in 8/07)
2004
2005
CrIS System
Overview
Overall Relationship of CrIS RDRs, SDRs and EDRs
• 833 km orbit
• 98.7° Inclination
• CrIS
• ATMS
RDR = Raw Data Record ( Uncalibrated )
SDR = Sensor Data Record (Calibrated)
EDR = Environmental Data Record
Central or
Regional Ground
Stations
2,200 km
Swath
Decode
Spacecraft
Data
RDRs
to
Users
Raw
Uncalibrated
Data
Sensor
Calibration
Algorithms
SDRs
to
Users
Calibrated and
Geolocated
Radiance Data
EDR
Algorithms
EDRs
to
Users
• Temperature Profiles
• Moisture Profiles
• Pressure Profiles
20 minutes
CrIS
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Section 1 - 4
CrIS System
Overview
Characteristics of CrIS Scan Footprints
CrIS Field of Regard (FOR)
Definition
• 1 FOR = 9 FOVs
• 1 FOV = 3 IR bands
Single CrIS Scan Line
(full sweep, 30 FORs)
3.33 degree steps
Nadir
48.33 degree
0.963 degree
(14.0 km)
Anti-sun
3
6
S/C
Velocity
9
1.100 degree
Edge
(16.0 km)
2
5
8
1100 km
1
1.024 degree
(14.9 km)
4
7
0.897 degree
(13.0 km)
Three Successive
CrIS Scan Lines
(nadir to edge sweep)
CrIS
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Section 1 - 5
CrIS System
Sensor Design
Overview
Reqmnt ID
Requirement
SDRP907
Spectral Bands
SDRP944
Unapodized Spectral
Resolution
1/(2*max OPD)
SDRP3546
Spectral Uncertainty
SDRP6841
ILS Shape Uncertainty
SDRP3481
Radiometric Uncertainty
SDRP1033
System NEdN
SDRP3696
SDRP3696
LWIR
Scan Extent
SDRP882
SDRP3731
Mapping Uncertainty
LOS Jitter
MWIR
650 – 1095 cm
0.625 cm
-1
SWIR
1210 – 1750 cm
-1
1.25 cm
-1
2155 – 2550 cm
-1
2.5 cm
-1
-1
10 ppm (flight unit 1)
5 ppm (subsequent flight units)
10 ppm (flight unit 1)
5 ppm (subsequent flight units)
10 ppm (flight unit 1)
5 ppm (subsequent flight units)
0.5% FWHM
0.5% FWHM
0.5% FWHM
0.45%
0.58%
0.77%
See Chart
See Chart
See Chart
Same as LWIR
Same as LWIR
0.3
0.2
0.3
N/A
0.3
0.2
0.3
N/A
FOV Size (km)
70% width (in/x track)
50% width (in/x track)
10% width (in/x track)
1% width (in/x track)
FOV Shape Match (km)
70% width
50% width
10% width
1% width
SDRP3628
SDRP3630
CrIS
CrIS Science Mission Cardinal Requirements
11.8/12.7
13.2/14.2
14.9/16.0
16.8/18.0
0.3
0.2
0.3
N/A
30 x-track FORs: +/- 48.333
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o
1.5 km
50 rad/axis
Section 1 - 6
30 x-track FORs: +/- 48.333
1.5 km
50 rad/axis
o
30 x-track FORs: +/- 48.333
1.5 km
50 rad/axis
o
CrIS System
Overview
Predicted Sensor Noise Performance
NEdN (mW/m2 sr cm-1)
1.0
0.1
0.01
0.001
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2000
2200
2400
2600
Wavenumber(cm-1)
N EdT @ 250K
10
1
0 .1
0 .0 1
600
800
1000
1200
1400
1600
1800
W a v e n u m b e r (c m -1 )
CrIS
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Section 1 - 7
CrIS System
Overview
CrIS Produces Superior Performance Compared to HIRS
While Retaining Comparable Size & Power Consumption
LWIR Spectra Measured By HIRS (12 Channels)
CrIS
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LWIR Spectra Measured By CrIS (713 Channels)
Section 1 - 8
40
Performance Above
Threshold (%)
12 cm
10 cm
30
8 cm
Volume
Constraint
20
10
5 cm
0
0.98
1
1.02
1.04
1.06
Relative Life Cycle Cost
An 8 cm CrIS Aperture Was
Selected as a Cost-Effective
Way to Improve EDR Performance
CrIS
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Section 1 - 9
Performance Above Threshold (%)
CrIS Was Optimized for a Very Specific
Atmospheric Sounding Mission
CrIS System
Overview
30
20
Cost
Constraint
Power
Constraint
4-Stage,
PV
Active,
PV
10
3-Stage, PC
0
0.9
1
1.1
Relative Life Cycle Cost
Photo-Voltaic (PV) LWIR
Detectors and a 4-Stage Passive
Cooler Result in Optimum
Cost Versus Performance
1.2
CrIS System
Overview
Key Technical Features of CrIS Sensor
CrIS Sensor Features
• Large 8 cm Clear Aperture
• Three Spectral Bands
• 3x3 FOVs at 14 km Diameter
• Photovoltaic Detectors in All 3 Bands
• 4-Stage Passive Detector Cooler
• Plane-Mirror Interferometer With DA
• Internal Spectral Calibration
• Deep-Cavity Internal Calibration Target
• Modular Construction
Physical Requirements
CrIS
Volume
Mass
80 x 47 x 56 cm
< 98 kg
Power
< 95 W
Data Rate
< 1.5 Mbps
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Section 1 - 10
CrIS System
Overview
Compact Optical Design Allowed the Largest Possible
Aperture Given Volume Constraints
Large 8 cm
Aperture Yields
Better NEdN
1.5% FOV
Co-registration
Achieved
Between Bands
Telescope Optics
Scan Mirror
Back End Optics
& Detectors
Cooled for Better
Noise
Performance
Detector Assemblies
CrIS
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Section 1 - 11
Interferometer Optics
CrIS System
Overview
Rigid Interferometer Structure with Balanced Mechanism
Minimizes Susceptibility to Spacecraft Vibration
Balanced Moving
Mechanism
Dynamically
Aligned Optics
Yields Stable ILS
Over Mission Life
Eliminates ILS
Tuning by
Ground
Algorithms
Input
High Tolerance to
Vibration Keeps
Noise Artifacts
from Being
Generated
CrIS
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Fast Reaction Servo
Controlled Optical
Alignment Mirror
Section 1 - 12
CrIS System
Overview
Post Interferometer Optical Processing Separates Optical
Energy into 3 Bands and 9 Fields of View
Athermalized Aft
Optics Assembly
(Cooled to 220K)
Bolt-Together
Detector
Optics Arrays
Boeing Advanced Photovoltaic Detectors
CrIS
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3-Element On-Axis Telescope
Section 1 - 13
Electrical
CrIS
System
Signal
Flow
Overview
Interferograms, Engineering Data & Science Telemetry
Comprise CrIS RDRs
SPACE SEGMENT - CrIS Sensor
Detector
DS
ADC
I (x )
Interferogram
Interferometer
(photons)
255 Tap
FIR
I (x )
L(s )
ES:
Earth Scene
DS:
Deep Space
ICT:
Internal Calibration Target
Filtering &
Decimation
Reduces
data rate
~
I ( x ) complex
Engineering Data
(three different types)
Must be
done first
real
ICT
Observed scene
Impulse Noise
Clipping
Bit trim format data
laser frequency info: NNe, NL
ICT emissivity tables & model
data
Polarization correction tbl (if
needed)
ILS parameters for 54 channels
CrIS mounting angles
LOS angles for each FOV
Signal ID/QC Data
IGM start time (UTC)
FOR index (0-31)
Band ID (LW,MW,SW)
FOV ID (1-9)
Sweep direction
ZPD min, max & position
Quality control flags
Impulse noise count
Bit
Trimming
Downlinked
to Earth
RDR
Packet
Encoding
Interferograms
Calibration
Data
Once per 8 seconds
Laser diode temperature/current
ICT, BS, Scan mirror
temperatures
All optic temperature telemetry
SSM pointing errors
Science TLM Data
Only Processing of Science Data Shown
CrIS
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Section 1 - 14
CrIS System
Overview
CrIMSS Projected Performance
1
30
100
100
25
Altitude (km)
10
Altitude (mbar)
Altitude (mbar)
“Threshold”
Performance
500
20
15
10
5
1000
1000
0
0.5
1
1.5
Retrieved Temperature
Error (K, rms)
CrIS
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0
0
5
10
15
20
Retrieved Moisture
Error (%, rms)
Section 1 - 15
25
0.0
0.5
1.0
Retrieved Pressure
Accuracy (%)
CrIS System
Overview
Expected Improvement Over HIRS
CrIS
CrIS
HIRS
HIRS
RMS Measurement Uncertainty, Global-Average Basis
CrIS
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Section 1 - 16