Title: Radiometric Metrology for Remote Sensing
1Radiometric Metrology for Remote Sensing
- Carol Johnson
- Optical Technology Division
- National Institute of Standards and Technology
2NIST Overview
- The U.S. metrology and standards laboratory
- Non-regulatory agency in Dept. of Commerce
- Promotes U.S. economic growth by working with
industry to develop and apply technology,
measurements, standards - Four main components
- Measurement and Standards Laboratories
- Advanced Technology Program
- Manufacturing Extension Partnership
- National Quality Program
http//www.nist.gov/
3Interaction Dissemination
Examples Calibration Services Standard
Reference Materials Reference Information Database
s Special Publications Training
Conferences Special Tests
Irradiance Standard Lamps (FEL)
Documents what is traceability?
http//ts.nist.gov/ts/
4Metrology of Radiometry
- Scale realization
- electrical and dimensional metrology
(detector-based) - temperature metrology (source-based)
- Rules to remember
- compare like to like
- precision is not accuracy
- Thorough instrument characterization
- interdependent influencing parameters
- spectral, spatial, temporal, temperature,
polarization, flux level - Validate results
- through comparisons
- measurement of fundamental constants
5NIST Detector-based Irradiance
- Irradiance lamp standards are a primary means of
radiometric scale dissemination from NIST to
customers - Reduced the NIST uncertainties, up to a factor of
10 in the SWIR
Yoon, et al., Appl. Opt. 41 5879-5890 (2002).
6Comparison of Methods
7Like to Like RuleSpectrally
- Circled Region Upwelling in-water spectral
radiance derived using the two spectrographs in
the same system disagree in their region of
overlap - Spectral out-of-band an issue because the
calibration and measured source differ in their
relative spectral distributions - Solution thorough instrument characterization
using tunable lasers, Traveling SIRCUS (Spectral
Irradiance and Radiance Responsivity Calibrations
with Uniform Sources)
Red Spectrograph
Blue Spectrograph
8Like to Like Rule--Spatially
Issue Radiance calibration of 2D CCD framing
camera with Cassegrain-type foreoptics
Near field source of constant radiance that
overfilled the entrance pupil gave distance
dependent results (this is non-physical, radiance
is independent of distance!)
Use of a collimated source provided the required
characterization as well as a more accurate
radiance calibration
9SIRCUS Calibration Facility
A variety of tunable lasers
fiber-coupled into an integrating sphere
wavemeter
pump laser beam
cw dye laser
- Producing a
- spatially uniform,
- monochromatic,
- high flux,
- broadly tunable source
- of (known) radiance
Designed specifically for system level absolute
spectral responsivity calibrations of irradiance
or radiance systems Goal Calibrations at the
0.1 level
10SIRCUS Experimental Layout
Intensity Stabilizer
Chopper or Shutter
Radiometer under Test
Reference Radiometer
Spectrum Analyser
Wavemeter
Exit
Port
Computer
Speckle-removal System
Integrating Sphere
Lens
Monitor Detector (output to stabilizer)
11(No Transcript)
12Wavelength (?m)
13ASD Bandpass using SIRCUS
The visible near-infrared spectrograph (VNIR)
utilizes a linear photodiode array. The bandpass
must be determined using laser excitation at many
finely-spaced wavelengths. Shown are the result
for five adjacent pixels. This was done on the
visible SIRCUS facility.
The short wave infrared spectral regions has two
scanning spectrometers, each with a cooled
detector. The bandpass can be determined using
laser excitation at a single wavelength, shown
here from IR SIRCUS at 1598 nm and 2348 nm.
14Radiometry Remote Sensing
- Radiometric measurements yield physical
information of complex systems - Required scientific accuracies are often state of
the art - Measurements require long time series anticipate
small changes - Characterization and calibration are pre-flight
- Radiometry is difficult and subject to systematic
effects
http//spot/colorado.edu/koppg/TSI/
15Technical Response
- Portable radiometers (ultraviolet to thermal
infrared) - Portable sources (characterization, calibration,
stability, solid state) - Calibration and characterization of flight
sensors ( one build) - Special measurements of sensor hardware (filters,
apertures, detectors) - Participation in intercomparison activities
- Pilot in artifact comparisons (reflectance,
aperture area) - Training and community participation
- Peer Reviews
- Publication of results ( 50 papers since 1995)
16Portable Radiometers
- Spectral coverage instrument design per
application - Characterized calibrated
- linearity, stability, spectral response, spatial
response, polarization sensitivity - calibration requirements impacted development of
new, tunable laser-based facility (SIRCUS) and
in-house vacuum chambers - Deployed since early 1990s in support of U.S.
remote sensing - Maintained by NIST, often as a shared resource
- Uncertainties for NIST instruments
- 0.5 in visible and near-infrared (VNIR)
- 1.7 in shortwave infrared (SWIR)
- 0.05 K in thermal infrared (TIR)
17Absolute Calibration for Thermal Infrared
System Capabilities Thresholds Objectives
Measurement range -2 to 40 ?C -2 to 40 ?C
Measurement precision 0.2 ?C 0.1 ?C
Measurement uncertainty 0.5 ?C 0.1 ?C
Long term stability 0.1 ?C 0.05 ?C
NPOESS IORDII
Measurement equation
S(T) signal R(?) depends on radiometer L(?,
T) depends on source
Vastly oversimplified (neglects background
sources) but illustrates the need for information
on the sensor and the calibration source(s).
18Rice Johnson, Metrologia 35, 505-509 (1998).
19Calibration of TXR at NIST
- Used TXR in Medium Background IR (MBIR) facility
at NIST. - Shroud can be cooled to 80 K or left at room
temperature. - Viewed 11 cm diameter cryogenic blackbody (BB).
- Radiance scale is currently from temperature
sensors in blackbody.
TXR Response to Blackbody
TXR
BB
20Measuring Emissivity Using Reflected Radiance
Lmeasured Lemitted(Tblackbody)
Lreflected(Tbackground)
From intercept eband 0.99826 /-
0.00037
21Thermal Infrared Transfer Radiometer (TXR)
At U. Miami for NASA EOS, May 2001
At ITT for NOAA GOES, July 2001
At LANL for DOE, July 1999 August 2001
22Arrangement for TXR measuring emitted radiance
TXR Scene Plate Ambient Temperature
Scene Plate Cooled to below Ambient
Diffuse Black Paint (both sides)
TXR
Blackbody Under Test 190 K lt T lt 340 K
Diffuse Black Paint
MLI
23Arrangement for TXR measuring reflected radiance
TXR Scene Plate Ambient Temperature
Raytheon Scene Plate 100 K lt T lt 320 K
Diffuse Black Paint (both sides)
TXR
Blackbody Under Test T 190 K
Diffuse Black Paint
MLI
24Example Result from TXR at GOES
- Temperature of radiating surface ? thermometer
reading. - Emissivity and temperature correction were
measured. - Temperature correction qualitatively in agreement
with GOES model. - Enables re-calibration of data with more direct
tie to NIST.
25Temperature Correction is Independent of
Wavelength
26Summary
- Recent advances in radiometric calibration and
characterization - SIRCUS (UV to IR)
- stable and accurate transfer radiometers
- New era for sensor performance possible
- adoption of SIRCUS facilities by industry
- pre-flight validation and comparison of
radiometric scales
27NIST Acknowledgements
- TXRJoe Rice
- Remote sensing calibration and validationSteve
Brown, Joe Rice, Ted Early - SIRCUSSteve Brown, Keith Lykke
- Detector radiometryJoe Rice, Jeanne Houston, Tom
Larason, George Eppeldauer
- Source radiometryHoward Yoon, Charles Gibson
- Optical properties and BRDFTed Early, Leonard
Hanssen - Colorimetry PhotometryYoshi Ohno, Cameron
Miller, Maria Nadal - Aperture areaToni Litorja, Joel Fowler
28External Support
- Air Force/Navy/Army Calibration Coordination
Group (CCG) - NASA EOS Project Science (Jim Butler)
- NASA SeaWiFS Project Science (Chuck McClain)
- NOAA/NESDIS (Dennis Clark, Eric Bayler, Steve
Kirkner) - Others DOE, DOD, IPO, USDA, Scripps