# Presentation: 265862

## Radiometric Measurement Comparisons at NASA’s Goddard Space Flight Center’s Radiance Calibration FacilityJames J. Butler, Brian L. Markham, and Scott J. Janz-NASA’s GSFCB. Carol Johnson, Steven W. Brown, Edward A. Early, and David W. Allen-NISTStuart F. Biggar and Edward F. Zalewski-University of ArizonaDonald F. Heath-Research Support Instruments, Inc.Gerhard Meister-Futuretech Corporation-SIMBIOS ProjectEdward Kaita and Milton G. Hom-Science Systems and ApplicationsJohn W. Cooper, Gilbert R. Smith, and John E. Marketon-Raytheon Information Technology and Scientific ServicesSteven J. Schiller-South Dakota State UniversityPavel Hajek and Robert A. Barnes-Science Applications International Corporation

## Comparison Dates:
March 30 to April 9, 2001
Comparison Location:
GSFC’s Radiance Calibration Facility’s class 10,000 cleanroom
Comparison Goals:
Validate the radiance scales assigned by GSFC calibration labs to its 180cm and 50.8cm diameter integrating spheres
Examine GSFC sphere operation, radiometric stability and repeatability
Validate the radiance calibrations of a number of radiometers used in the vicarious calibration of EOS satellite instruments

- March 30 to April 9, 2001
**Comparison Location:**
- GSFC’s Radiance Calibration Facility’s class 10,000 cleanroom
**Comparison Goals:**
- Validate the radiance scales assigned by GSFC calibration labs to its 180cm and 50.8cm diameter integrating spheres
- Examine GSFC sphere operation, radiometric stability and repeatability
- Validate the radiance calibrations of a number of radiometers used in the vicarious calibration of EOS satellite instruments

## Radiometers Participating in the GSFC Radiometric Measurement Comparison

**Radiometers Participating in the GSFC Radiometric Measurement Comparison**

## Slide 4

## Slide 5

## Slide 6

## Slide 7

## Radiance Comparison Approach
Compute band averaged spectral radiance, LB, using a radiance spectrum, Lλ, and the relative spectral response functions, Rλ, from the radiometers
Compare the percent difference of the radiometer measurements, LR, from the computed radiance, LB, via

		% Difference = ((LR – LB)/LB) x 100

Calculated for all filter radiometers
LB:
Hardy sphere: 746/ISIC calibration from 400 to 2400nm on 3/28/01
50.8cm sphere: SSBUV calibration from 230 to 400nm on 4/1/01; 746/ISIC calibration from 400 to 2400nm on 4/6/01
NPR: FASCAL calibration from 300 to 2400nm (4 lamps) and 300 to 1100nm (1 lamp) on 3/29/01

- Compute band averaged spectral radiance, LB, using a radiance spectrum, Lλ, and the relative spectral response functions, Rλ, from the radiometers
- Compare the percent difference of the radiometer measurements, LR, from the computed radiance, LB, via
- 		% Difference = ((LR – LB)/LB) x 100
- Calculated for all filter radiometers
- LB:
- Hardy sphere: 746/ISIC calibration from 400 to 2400nm on 3/28/01
- 50.8cm sphere: SSBUV calibration from 230 to 400nm on 4/1/01; 746/ISIC calibration from 400 to 2400nm on 4/6/01
- NPR: FASCAL calibration from 300 to 2400nm (4 lamps) and 300 to 1100nm (1 lamp) on 3/29/01

## Sources Measured
180cm Diameter Integrating Sphere (a.k.a. Hardy)
Integrating sphere source located in GSFC’s Radiance Calibration Facility’s class 10,000 cleanroom
Calibrated for spectral radiance from 400 to 2400nm by the GSFC 746/ISIC using NIST standards of spectral irradiance
Specifications
Material: Fiberglass shell with BaSO4 interior coating
Diameter: 180cm
Aperture diameter: 25.4cm
Lamps: 16 baffled 200W quartz tungsten halogen
Monitor: Filter Radiometer Monitoring System (FRMS) at 410, 440, 460, 640, 840, and 1050nm
Recent user programs
Aeronet calibration
EOS Validation (eg. MODIS, CERES, ETM+)
SIMBIOS Validation
DOE/ARM Validation

- 180cm Diameter Integrating Sphere (a.k.a. Hardy)
- Integrating sphere source located in GSFC’s Radiance Calibration Facility’s class 10,000 cleanroom
- Calibrated for spectral radiance from 400 to 2400nm by the GSFC 746/ISIC using NIST standards of spectral irradiance
- Specifications
- Material: Fiberglass shell with BaSO4 interior coating
- Diameter: 180cm
- Aperture diameter: 25.4cm
- Lamps: 16 baffled 200W quartz tungsten halogen
- Monitor: Filter Radiometer Monitoring System (FRMS) at 410, 440, 460, 640, 840, and 1050nm
- Recent user programs
- Aeronet calibration
- EOS Validation (eg. MODIS, CERES, ETM+)
- SIMBIOS Validation
- DOE/ARM Validation

## Hardy Sphere: 16 Lamps

## Hardy Sphere: 6 Lamps

## Hardy 16 and 6 Lamp Stability
Monitor data from the Filter Radiometer Monitoring System (FRMS)

- Monitor data from the Filter Radiometer Monitoring System (FRMS)

## 50.8cm Diameter Integrating Sphere
Integrating sphere located in GSFC’s Radiometric Calibration and Development Facility’s class 10,000 cleanroom
Calibrated for spectral radiance from 230 to 425nm by the Solar Backscatter UltraViolet instrument and from 400 to 2400nm by the GSFC 746/ISIC
Specifications
Material: aluminum shell with BaSO4 interior coating
Diameter: 50.8cm
Aperture diameter: 20.3cm
Lamps: 4 unbaffled 150W quartz tungsten halogen
Monitor: none
Recent user programs
Shuttle Ozone Limb Sounding Experiment/Limb Ozone Retrieval Experiment (SOLSE/LORE)
Optical Spectrograph and InfraRed Imaging System (OSIRIS)
SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY)
Ozone Monitoring Instrument (OMI)

- Integrating sphere located in GSFC’s Radiometric Calibration and Development Facility’s class 10,000 cleanroom
- Calibrated for spectral radiance from 230 to 425nm by the Solar Backscatter UltraViolet instrument and from 400 to 2400nm by the GSFC 746/ISIC
- Specifications
- Material: aluminum shell with BaSO4 interior coating
- Diameter: 50.8cm
- Aperture diameter: 20.3cm
- Lamps: 4 unbaffled 150W quartz tungsten halogen
- Monitor: none
- Recent user programs
- Shuttle Ozone Limb Sounding Experiment/Limb Ozone Retrieval Experiment (SOLSE/LORE)
- Optical Spectrograph and InfraRed Imaging System (OSIRIS)
- SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY)
- Ozone Monitoring Instrument (OMI)

## 50.8 cm Sphere: 4 Lamps

## Slide 15

## 50.8cm Sphere 4 Lamp Stability
Monitor data from the UVFR 388.03nm channel
April 3 turn-on time: 8:38am EST
April 4 turn-on time: 8:45am EST

- Monitor data from the UVFR 388.03nm channel
- April 3 turn-on time: 8:38am EST
- April 4 turn-on time: 8:45am EST

## NIST Portable Radiance Source (NPR)
Integrating sphere used at EOS calibration facilities in conjunction with transfer radiometers
Calibrated for spectral radiance from 300 to 2400nm at NIST’s Facility for Automated Spectral Irradiance and Radiance Calibrations (FASCAL)
Specifications
Material: aluminum shell with Spectralon interior
Diameter: 30.5cm
Aperture diameter: 10.2cm
Lamps: 4-30W quartz tungsten halogen
Monitors: Two Si photodiodes with a 365±10nm uv and a photoptic filter

- Integrating sphere used at EOS calibration facilities in conjunction with transfer radiometers
- Calibrated for spectral radiance from 300 to 2400nm at NIST’s Facility for Automated Spectral Irradiance and Radiance Calibrations (FASCAL)
- Specifications
- Material: aluminum shell with Spectralon interior
- Diameter: 30.5cm
- Aperture diameter: 10.2cm
- Lamps: 4-30W quartz tungsten halogen
- Monitors: Two Si photodiodes with a 365±10nm uv and a photoptic filter

## NPR Sphere: 4 Lamps

## NIST Irradiance Standards F496 and F512 + Spectralon Panel
Irradiance lamps used by GSFC’s Radiance Calibration Facility in the calibration of their integrating spheres
F496 and F512 are irradiance lamps calibrated against the NIST 1990/2 and 2000 scales, respectively

- Irradiance lamps used by GSFC’s Radiance Calibration Facility in the calibration of their integrating spheres
- F496 and F512 are irradiance lamps calibrated against the NIST 1990/2 and 2000 scales, respectively

## Lamp irradiance data fit with Planck + polynomial (8 terms)
F496

- F496

## F512

## Signal(F512)/E(F512) to Signal(F496)/E(496) Ratio

## Conclusions
Hardy Sphere
With the exceptions of wavelengths below 440nm and in the swir water vapor absorption bands, the transfer radiometers (ie. VXR, UAVNIR, LXR, SXR II, SWIXR, and UASWIR) validated the Hardy radiance scale at 16 and 6 lamps to within the measurement uncertainty (k=2) of the 746/ISIC.
Following a 3 hour warm-up, the Hardy sphere radiance changes at a rate of 0.6%/hr at 412nm, 0.5%/hr at 440nm, 0.33%/hr at 460nm, and negligibly at 640, 840, and 1050nm.
The Ames ASD and 746/ISIC radiance measurements of the sphere agreed to well within their combined measurement uncertainties for wavelengths above 420nm and outside the swir water vapor absorption regions.

- Hardy Sphere
- With the exceptions of wavelengths below 440nm and in the swir water vapor absorption bands, the transfer radiometers (ie. VXR, UAVNIR, LXR, SXR II, SWIXR, and UASWIR) validated the Hardy radiance scale at 16 and 6 lamps to within the measurement uncertainty (k=2) of the 746/ISIC.
- Following a 3 hour warm-up, the Hardy sphere radiance changes at a rate of 0.6%/hr at 412nm, 0.5%/hr at 440nm, 0.33%/hr at 460nm, and negligibly at 640, 840, and 1050nm.
- The Ames ASD and 746/ISIC radiance measurements of the sphere agreed to well within their combined measurement uncertainties for wavelengths above 420nm and outside the swir water vapor absorption regions.

## 50.8cm Sphere
With the exceptions of wavelengths above 2200nm and in the swir water vapor absorption bands, the transfer radiometers validated the 50.8cm sphere radiance scale at 4 lamps to within the measurement uncertainty (k=2) of the 746/ISIC.
According to the UVFR monitor data at 388.03nm, the 50.8cm sphere output stabilizes to ±0.15% approximately 4 hours after turn-on.
The SDSU ASD measurements of the 50.8cm sphere were systematically higher than the 746/ISIC calibration by 5 to 10%.
The CTSS measurements of the 50.8cm sphere agreed with the 746/ISIC calibration to within 0 to –3% in below 760nm.  At wavelengths above 900nm, the CTSS measured lower radiance values.
The UVFR and UVSR measured radiances in the uv agreed with the SSBUV measured radiances to within ±3.0%.  The CTSS agreed with the SSBUV measured radiances to within ±5.3%.

- With the exceptions of wavelengths above 2200nm and in the swir water vapor absorption bands, the transfer radiometers validated the 50.8cm sphere radiance scale at 4 lamps to within the measurement uncertainty (k=2) of the 746/ISIC.
- According to the UVFR monitor data at 388.03nm, the 50.8cm sphere output stabilizes to ±0.15% approximately 4 hours after turn-on.
- The SDSU ASD measurements of the 50.8cm sphere were systematically higher than the 746/ISIC calibration by 5 to 10%.
- The CTSS measurements of the 50.8cm sphere agreed with the 746/ISIC calibration to within 0 to –3% in below 760nm.  At wavelengths above 900nm, the CTSS measured lower radiance values.
- The UVFR and UVSR measured radiances in the uv agreed with the SSBUV measured radiances to within ±3.0%.  The CTSS agreed with the SSBUV measured radiances to within ±5.3%.

## NPR Sphere
The LXR, SXR 2, VXR, and UAVNIR radiance measurements agreed with the FASCAL calibration of the NPR to within the combined uncertainties of the two sets of measurements (k=2).
The CTSS radiance measurements were 0.8 to 4% lower than the FASCAL radiances below 800nm.  Above 800nm the CTSS radiances were 6 to 8% lower.
Outside of the water vapor absorption regions, the GSFC and SDSU ASDs measured radiances which were 0 to 4% and 4 to 8.5% higher, respectively, than the FASCAL radiances.
Outside of the water vapor absorption regions, the GSFC 746/ISIC and the UASWIR instruments measured radiances which were 0 to 5% lower than the FASCAL radiances.

- The LXR, SXR 2, VXR, and UAVNIR radiance measurements agreed with the FASCAL calibration of the NPR to within the combined uncertainties of the two sets of measurements (k=2).
- The CTSS radiance measurements were 0.8 to 4% lower than the FASCAL radiances below 800nm.  Above 800nm the CTSS radiances were 6 to 8% lower.
- Outside of the water vapor absorption regions, the GSFC and SDSU ASDs measured radiances which were 0 to 4% and 4 to 8.5% higher, respectively, than the FASCAL radiances.
- Outside of the water vapor absorption regions, the GSFC 746/ISIC and the UASWIR instruments measured radiances which were 0 to 5% lower than the FASCAL radiances.

## Lamps/Panel
The S/E “ratio of ratios” indicates that the 1990/2 and 2000 irradiance scales differ by 1.0% from 400 to 1300nm, by 1.0 to 2.0% from 1300 to 1700nm, and by 1.3 to 6.2% from 1700 to 2400nm.
The differences below 2300nm are within the combined k=2 NIST irradiance uncertainties of the lamps and the uncertainties of the radiometer measurements. 
The Planck + 8 term polynomial used in this analysis does not necessarily provide the best fit to the lamp irradiance data. Other fits will be explored.
These preliminary results reinforce the need for irradiance lamps to be recalibrated against the 2000 NIST detector-based irradiance scale.

- The S/E “ratio of ratios” indicates that the 1990/2 and 2000 irradiance scales differ by 1.0% from 400 to 1300nm, by 1.0 to 2.0% from 1300 to 1700nm, and by 1.3 to 6.2% from 1700 to 2400nm.
- The differences below 2300nm are within the combined k=2 NIST irradiance uncertainties of the lamps and the uncertainties of the radiometer measurements.
- The Planck + 8 term polynomial used in this analysis does not necessarily provide the best fit to the lamp irradiance data. Other fits will be explored.
- These preliminary results reinforce the need for irradiance lamps to be recalibrated against the 2000 NIST detector-based irradiance scale.