Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 1 C. Johnson Radiometric Metrology for Remote Sensing Carol Johnson Optical Technology Division National Institute of Standards and Technology

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 2 C. Johnson NIST 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

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 3 C. Johnson Interaction & Dissemination Examples: Calibration Services Standard Reference Materials Reference Information Databases Special Publications Training & Conferences Special Tests Irradiance Standard Lamps (FEL) On-line databases Technical Short Courses Blackbody Calibration Documents: what is traceability? Aperture Area

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 4 C. Johnson Metrology 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

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 5 C. Johnson NIST 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 (2002).

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 6 C. Johnson Comparison of Methods Low Background Infrared Facility (LBIR) Results from a Range of Blackbodies: Difference Between Measured and Predicted Radiance Temperatures

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 7 C. Johnson “Like to Like” Rule—Spectrally 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

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 8 C. Johnson “Like 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

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 9 C. Johnson SIRCUS Calibration Facility A variety of tunable lasers cw dye laser pump laser beam wavemeter fiber-coupled into an integrating sphere 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

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 10 C. Johnson Tunable Laser Wavemeter Integrating Sphere Exit Port Spectrum Analyser Lens Radiometer under Test Computer Reference Radiometer Intensity Stabilizer SIRCUS Experimental Layout Monitor Detector (output to stabilizer) Chopper or Shutter Speckle- removal System

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 11 C. Johnson

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 12 C. Johnson Wavelength (  m)

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 13 C. Johnson ASD 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. SWIR 1 SWIR 2

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 14 C. Johnson Radiometry & 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

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 15 C. Johnson 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) Technical Response

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 16 C. Johnson Portable 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 1990’s 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)

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 17 C. Johnson Absolute Calibration for Thermal Infrared NPOESS IORDII System CapabilitiesThresholdsObjectives Measurement range -2 to 40  C Measurement precision 0.2  C0.1  C Measurement uncertainty 0.5  C0.1  C Long term stability 0.1  C0.05  C 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).

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 18 C. Johnson Rice & Johnson, Metrologia 35, (1998).

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 19 C. Johnson Calibration of TXR at NIST TXR Response to Blackbody TXR BB 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.

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 20 C. Johnson Measuring Emissivity Using Reflected Radiance From intercept:  band  = / L measured = L emitted (T blackbody ) + L reflected (T background )

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 21 C. Johnson Thermal Infrared Transfer Radiometer (TXR) At ITT for NOAA GOES, July 2001 At LANL for DOE, July 1999 & August 2001 At U. Miami for NASA EOS, May 2001

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 22 C. Johnson Arrangement for TXR measuring emitted radiance Blackbody Under Test 190 K < T < 340 K TXR TXR Scene Plate Ambient Temperature Scene Plate Cooled to below Ambient Diffuse Black PaintMLI Diffuse Black Paint (both sides)

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 23 C. Johnson Arrangement for TXR measuring reflected radiance Blackbody Under Test T = 190 K TXR TXR Scene Plate Ambient Temperature Raytheon Scene Plate 100 K < T < 320 K Diffuse Black PaintMLI Diffuse Black Paint (both sides)

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 24 C. Johnson Example Result from TXR at GOES TXR Measurement GOES Model 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.

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 25 C. Johnson Temperature Correction is Independent of Wavelength

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 26 C. Johnson Summary 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

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 27 C. Johnson NIST Acknowledgements TXR—Joe Rice Remote sensing calibration and validation—Steve Brown, Joe Rice, Ted Early SIRCUS—Steve Brown, Keith Lykke Detector radiometry—Joe Rice, Jeanne Houston, Tom Larason, George Eppeldauer Source radiometry— Howard Yoon, Charles Gibson Optical properties and BRDF—Ted Early, Leonard Hanssen Colorimetry & Photometry—Yoshi Ohno, Cameron Miller, Maria Nadal Aperture area—Toni Litorja, Joel Fowler

Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 28 C. Johnson 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 External Support SeaWiFS