Radiometric Metrology for Remote Sensing Carol Johnson Optical

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 1 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 http: //www. nist. gov/ Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 2 C. Johnson

Interaction & Dissemination Examples: Calibration Services Standard Reference Materials Reference Information Databases Special Publications Training & Conferences Special Tests Aperture Area Irradiance Standard Lamps (FEL) Technical Short Courses Blackbody Calibration On-line databases Documents: what is traceability? http: //ts. nist. gov/ts/ Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 3 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 4 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. 41 5879 -5890 (2002). Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 5 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 6 C. Johnson

“Like to Like” Rule—Spectrally Red Spectrograph • Blue Spectrograph • • Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Circled Region: Upwelling inwater 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) Page 7 C. Johnson

“Like to Like” Rule--Spatially Issue: Radiance calibration of 2 D 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 8 C. Johnson

SIRCUS 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 Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Designed specifically for system level absolute spectral responsivity calibrations of irradiance or radiance systems Goal: Calibrations at the 0. 1 % level Page 9 C. Johnson

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

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

CO 2 10000 1064 nm (fundamental Nd: YAG) LBO OPO 1000 PPLN OPO (signal) PPLN OPO (idler) CO Existing Under Development 100 Quantum Cascade Lasers 10 CO 2 normal power CO 2 isotope power CO laser power (m. W) Quantum Cascade Laser PPLN OPO (signal) PPLN OPO (idler) Tandem OPO (with Cd. Se) 1 0. 1 Tandem OPO (with Cd. Se) PPLN OPO Difference (with Ag. Ga. S 2) 1064 nm (fundamental Nd: YAG) LBO OPO 1 2 5 Wavelength ( m) Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 12 10 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 2 SWIR 1 Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 13 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 http: //spot/colorado. edu/~koppg/TSI/ Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 14 C. Johnson

Technical 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) Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 15 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 16 C. Johnson

Absolute Calibration for Thermal Infrared System Capabilities Thresholds Objectives Measurement range -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). Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 17 C. Johnson

Rice & Johnson, Metrologia 35, 505 -509 (1998). Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 18 C. Johnson

Calibration 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 BB TXR Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 19 C. Johnson

Measuring Emissivity Using Reflected Radiance Lmeasured = Lemitted(Tblackbody) + Lreflected(Tbackground) From intercept: eband = 0. 99826 +/- 0. 00037 Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 20 C. Johnson

Thermal 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 Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 21 C. Johnson

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

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

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

Temperature Correction is Independent of Wavelength Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 25 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 26 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 Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 • 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 Page 27 C. Johnson

External Support • • • Air Force/Navy/Army Calibration Coordination Group (CCG) NASA EOS Project Science (Jim Butler) NASA Sea. Wi. FS Project Science (Chuck Mc. Clain) NOAA/NESDIS (Dennis Clark, Eric Bayler, Steve Kirkner) Others: DOE, DOD, IPO, USDA, Scripps Sea. Wi. FS Intl. Workshop on Radiometric & Geometric Calibration Dec 2003 Page 28 C. Johnson