System Level Approach to Characterization
and Radiometric Calibration of Space Based
Electro-Optical Sensors
Joe Tansock, Alan Thurgood, Mark Larsen
Space Dynamics Laboratory
Joe.Tansock@sdl.usu.edu
435-797-4369
2-5 December 2003
International Workshop on Radiometric and Geometric Calibration
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Outline
• Philosophy
– What is meant by a complete calibration
• Planning
• Subsystem/Component Measurements
• Sensor-Level Engineering Calibration
• Sensor-Level Calibration
– Facilities
– Data Collection
• On-Orbit Calibration
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International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy – Complete Cal
• A complete sensor calibration:
– Provides a thorough understanding of sensor operation and
performance
– Verifies a sensor’s readiness for flight
– Verifies requirements and quantifies radiometric and
goniometric performance
– Converts sensor output to engineering units that are
compatible with measurement objectives
– Provides traceability to appropriate standards
– Estimates measurement uncertainties
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International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy – Cal Domains
• A complete calibration will address five responsivity domains:
– Radiometric responsivity
•
•
•
•
Radiance and irradiance traceable to NIST
Response linearity and uniformity corrections
Nominal/outlying pixel identification
Transfer calibration to internal calibration units
– Spectral responsivity
• Sensor-level relative spectral response
– Spatial responsivity
• Point response function, effective field of view, optical distortion, and
scatter
– Temporal
• Short, medium, and long-term repeatability, frequency response
– Polarization
• Polarization sensitivity
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International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy – Cal Domains
• The goal of calibration is to characterize each domain
independently
– Together, these individually characterized domains comprise a
complete calibration of a radiometric sensor
• Domains cannot always be characterized independently
– Complicates and increases calibration effort
– Example: Spectral spatial dependence caused by Stierwalt effect
• Calibration parameters are grouped into two convenient
categories:
– Calibration equation
• Converts sensor output (counts, volts, etc.) to engineering
units
– Radiometric model
• All parameters not included in calibration equation but required
for complete calibration
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International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy – Cal Equation
Typical Radiance (Extended Source) Calibration Equation
for Imaging Array Based Radiometer
 1 
 1   BkGI  FNL,k (rT ,k ,t  rO,k ,t )  rB,k ,t  
LM ,k,t  

 rk,t  
 
FFF,k FFF,k,t
 LL,t 
 LL,t  

LM ,k ,t
Measured Radiance [W/cm 2sr]
L
Array-average peak-radiance responsivity [counts per W/cm 2sr]
 L ,t
Array-average peak-radiance responsivity change vs. time [unitless]
rk ,t
Corrected detector response [counts]
Bk
Bad detector mask function [unitless]
GI
Gain or integration normalization factor [unitless]
FNL,k 

Nonlinearity correction function [counts]
rT ,k ,t
Raw detector response [counts]
rO , k ,t
Detector offset correction [counts]
rB , k ,t
Linearity corrected response due to telescope thermal emission [counts]
FFF , k
Flat-fielding or non-uniformity coefficient [unitless]
FFF , k ,t Flat-fielding or non-uniformity coefficient change vs. time [unitless]
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k
Detector index - parameter is unique to each detector
t
Time - parameter varies as a function of time
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Calibration Philosophy – Rad Model
Typical Radiometric Model Parameters for
Imaging Array Based Radiometer
Radiometric Model Parameters
Noise equivalent radiance
ICU Response settling time
Saturation equivalent radiance
ICU Response Repeatability
Noise equivalent irradiance
ICU Response Uniformity
Noise equivalent temperature
Dark offset repeatability
Saturation equivalent irradiance
Dark offset drift rate
Illuminated Short-Term Repeatability vs. Radiance
Point source repeatability (short, medium, and long)
Saturation Response
Extended source repeatability (short, medium, and long)
Relative Spectral Responsivity
Angular measurement accuracy and precision
Effective Field-of-View
Polarization Sensitivity
Point Response Function
Uncertainty
Modulation Transfer Function
Off-axis rejection
Near angle scatter
Optical Distortion
Array coalignment
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International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy – SI Units
• Express calibration results in SI units
– Standards maintained by national measurement institutes
– Recommended Practice: Symbols, Terms, Units and
Uncertainty Analysis for Radiometric Sensor Calibration,
NIST Handbook 152, Clair Wyatt, et. al.
– http://ts.nist.gov/ts/htdocs/230/233/calibration/uncert/index.ht
m
• Contains Links for
– Guidelines for Evaluating and Expressing the
Uncertainty of NIST Measurement Results, 1994
– Guide to the Expression of Uncertainty in
Measurement, International Standards Organization
(ISO), 1993
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International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy - Uncertainty
• Components of standard uncertainty are identified by taking
partial derivative of calibration equation with respect to each
parameter
• Combined standard uncertainty
– Law of propagation of uncertainty
N 1 N
 f  2
 f   f  2
2
 c      i  2    
  i , j


x

x

x
i 1 
i 1 j i 1 
i 
i 
j 
N
2
– Where ƒ is a function (typically the calibration equation) with N
parameters
– If terms are independent, cross terms go to zero
2
 f 
 c2      i2
i 1  xi 
N
– If uncertainties are expressed in percent
N
    i2
2
c
i 1
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International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy - Uncertainty
Example On-Orbit Absolute Radiance
Uncertainty Budget for Imaging IR Instrument
Radiometric Measurement Accuracy (RMA)
Radiometric Measurement precision (RMP)
Short-Term Response Repeatability
(A)
Medium-term Response Repeatability
(A)
Long-term Response Repeatability
Internal Cal Measurements
(A)
On-Orbit Stellar
Measurements
(A & B)
Response Variability
Over FOR (function of
pointing mirror position)
Reflectance Variability
as Function of Angle
(A)
Reflectance variability
Due to Contamination
(A & B)
Peak Radiance
Responsivity Uncertainty
Peak radiance responsivity uncertainty
derived from ground calibration
Measurement Uncertainties
Standard Error of
Responsivity Coefficient
(A)
Linearity Correction
Uncertainty
(A)
Response Uncertainty Due to
Telescope Themal Emission
(A & B)
Integration Mode
Normalization
(A)
Source Uncertainties
Blackbody Emissivity Uncertainty
(A & B)
Calibrator Pointing Mirror
Reflectivity Uncertainty
(A)
Blackbody Temperature
Uncertainty
(A)
RSR Uncertainty
(A)
Responsivity Trend Correction Uncertainty
(A)
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Corrected Response Uncertainty
NUC Uncertainty
NUC Uncertainty
from Ground Calibration
Array Response Uniformity
to Extended Source
(A)
Extended Source
Radiance Uniformity
Uncertainty
(A & B)
NUC trend correction Unc
(A)
Integration Mode
Normalization Uncertainty
(A)
Linearity Correction Uncertainty
(A)
Response Uncertainty Due to
Telescope Thermal Emission
+ Dark Offset
(A & B)
Response Uncertainty Due to
Non-Rejected Earth Radiance
(B)
International Workshop on Radiometric and Geometric Calibration
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Calibration Philosophy – Phases of Cal
• A complete and methodical approach to sensor
calibration should address the following phases:
Calibration planning during sensor design
Ground measurements
Subsystem/component
measurements
Sensor-level engineering tests
and calibration
Sensor-level ground calibration
Integration and test
On-orbit measurements On-orbit calibration
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International Workshop on Radiometric and Geometric Calibration
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Calibration Planning
• Perform calibration planning during sensor design
– Sensor design should allow for efficient and complete
calibration
– Sensor design and calibration approach can be
optimized to achieve performance requirements
• Planning phase can help shake out problems
– Schedule and cost risk is minimized by understanding
what is required to perform a successful calibration
early in the design phase
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International Workshop on Radiometric and Geometric Calibration
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Calibration Planning
Mission Requirements
•
•
•
•
Identify instrument requirements
that drive calibration
Identify calibration measurement
parameters and group into:
– Calibration equation
– Radiometric model
Flow calibration measurement
parameters to trade study
– Schedule
– Sensor design feedback
– GSE hardware & software
– Measurement uncertainty
– Risk
Instrument Requirements
Calibration Measurement Parameters
• Calibration Equation
• Radiometric Model
Sensor
Design
Cost &
Schedule
Measurement
Uncertainty
Calibration
Planning
GSE Hardware
& Software
Perform trade study to determine
best calibration approach
Risk
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International Workshop on Radiometric and Geometric Calibration
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Subsystem/Component Measurements
• Subsystem and/or component level measurements
– Help verify, understand, and predict performance
– Minimize schedule risk during system assembly
• Identifies problems at lowest level of assembly
• Minimizes schedule impact by minimizing
disassembly effort to fix a problem
• System/Sensor level measurements
– Allow for end-to-end measurements
– Account for interactions between subsystems and
components that are difficult to predict
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International Workshop on Radiometric and Geometric Calibration
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Subsystem/Component Measurements
• Merging component-level measurements to predict
sensor level calibration parameters may increase
system-level uncertainties A,B
– SABER relative spectral responsivity (RSR)
• 9 of 10 channels < 5% difference
• 1 channel 24% difference (reason unknown)
A.) Component Level Prediction versus System Level Measurement of SABER Relative Spectral response,
Scott Hansen, et.al., Conference on Characterization and Radiometric Calibration for Remote Sensing, 1999
B.) System Level Vs. Piece Parts Calibration: NIST Traceability – When Do You Have It and What Does It
Mean? Steven Lorentz, L-1 Standards and Technology, Inc, Joseph Rice, NIST, CALCON, 2003
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International Workshop on Radiometric and Geometric Calibration
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Sensor-Level Engineering Calibration
• Engineering calibration
– Performed before ground calibration (Lesson Learned)
– Perform abbreviated set of all calibration measurements
– Verifies GSE operation, test configurations, and test procedures
– Checks out the sensor
– Produces preliminary data to evaluate sensor performance
– Feedbacks info to flight unit, calibration equipment, procedures, etc.
• Engineering calibration data analysis
– Evaluates sensor performance, test procedures, calibration
hardware performance and test procedures
• Based on results of engineering calibration, appropriate updates
can be made to prepare for ground calibration data collection
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International Workshop on Radiometric and Geometric Calibration
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Sensor-Level Ground Calibration
• Provides complete calibration
• Is performed under conditions that simulate operational
conditions for intended application/measurement
• Minimizes risk of not discovering a problem prior to launch
• Promotes mission success during on-orbit operations
• For many sensor applications
– Detailed calibration is most efficiently performed during ground
calibration
– On-orbit calibration will not provide sufficient number of sources at
needed flux levels
– Operational time required for calibration is minimized
• Best to perform ground calibration at highest level of assembly
possible
– Sensor-level at a minimum is recommended
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International Workshop on Radiometric and Geometric Calibration
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Calibration Facilities
• Make sure calibration hardware has been tested and characterized
(Lesson Learned)
– Problems with calibration hardware may cause schedule delays
and degraded calibration
• If possible, integrate calibration measurements into single facility
(Lesson Learned)
– Minimizes calibration time by reducing or preventing repeated cycle
(i.e. pump, cool-down, warm-up) and configuration times
• Examples:
– The multi function infrared calibrator (MIC2) incorporates 4 source
configurations in single package
– SABER calibration facility
• Test chamber interfaced with collimator provided calibration
measurement configurations
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International Workshop on Radiometric and Geometric Calibration
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MIC2 Interfaced with Sensor Under Test
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MIC2 Source Configurations
Collimator Source
Scatter Source
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Extended Source
Jones Source
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SABER Calibration Facility
Test Chamber and Work Area
2-5 December 2003
Collimator
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SABER Calibration Facility
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Calibration Data Collection
• Develop and write calibration data collection procedures
– Include:
•
•
•
•
•
Test procedures
Time requirements
Preparation and data collection steps
Documentation of script files
Data collection log sheets
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International Workshop on Radiometric and Geometric Calibration
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Calibration Data Collection
• Data collection should be automated when possible and practical
– Automate with scripting language to make measurements efficient and
repeatable
• Data collection procedures should be detailed and mature
• Sensor engineers and/or technicians may assist with data collection
– Requires familiarity with sensor under test
– Makes shift work possible to facilitate schedule
• Data quality should be verified for its intended use with quicklook
analyses
• Contamination should be monitored using QCM and/or radiometric
techniques
– Quantify contamination levels
– Determine when corrective action is required
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International Workshop on Radiometric and Geometric Calibration
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Calibration Data Collection
• Data collection environment includes:
– Test conductor and data collection station
– Ground support equipment (GSE) computer
• Controls and views status of GSE
– Instrument computer
• Controls and views status of instrument
– Data collection computer
• Initiates and executes data collection
• Controls and monitors status
– GSE
– Instrument
– Quick look analysis station
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International Workshop on Radiometric and Geometric Calibration
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Calibration Data Collection
Instrument Computers & Racks
GSE Computer
Data Collection Computer
Quick Look
Analysis Station
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On-Orbit Calibration
• Calibration continues after sensor-level ground calibration
Sensor Design/Fabrication
Ground Calibration
On-Orbit Operations
Internal Calibration Unit (ICU) Response Trending
On-Orbit Calibration/Verification
• Track, trend, and update calibration throughout a sensor’s
operational life
– On-board internal calibration sources
– External sources
• Ground sources prior to launch
• On-obit sources after launch
• Verifies calibration and quantifies uncertainty
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International Workshop on Radiometric and Geometric Calibration
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On-Orbit Calibration
• On-orbit sources
– Standard IR stars
• Stars aBoo, aLyra, aTau, aCMa, bGem, bPeg
• Catalogs include IRC, AFGL, IRAS, MSX, 2MASS
– Planetary objects
• Planets provide bright variable sources
• Asteroids, moon, etc.
• Sometimes you have to be creative:
– Off-axis scatter characterization using the moon
– Reference spheres
– Other techniques
• View large area source located on surface of earth (remote
sensing applications)
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International Workshop on Radiometric and Geometric Calibration
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Summary
• What is meant by a complete calibration
• Calibration parameters are organized into two categories
– Calibration equation and radiometric model
• Overall calibration approach
– Perform calibration planning in parallel with sensor design
– Subsystem measurements are a good idea but don’t rely on these
measurements to give system level calibration
– Perform engineering calibration to verify GSE, test procedures, and
estimate sensor performance
– Obtain complete and thorough sensor level calibration
– Verify and/or update calibration throughout operational life
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International Workshop on Radiometric and Geometric Calibration
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The Annual Conference on Characterization & Radiometric
Calibration for Remote Sensing addresses characterization,
calibration, and radiometric issues within the IR, Visible and UV
spectrums.
Session Topics Include:
 Concepts and Applications of Measurement Uncertainty
 Solar, Lunar and Stellar Radiometric Measurements
 Pre-launch to On-orbit Calibration Transfer: Approaches and On-orbit
Monitoring Techniques
 Developing National Calibration/Certification Standards for EO/IR
Systems
Join us at Utah State University
September 13-16, 2004!
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International Workshop on Radiometric and Geometric Calibration
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