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SBUV/2 Flight Model 8 Radiometric Calibration Data Review

SBUV/2 Flight Model 8 Radiometric Calibration Data Review. Kevin Kelly Zongying Wei Test Engineer Optical Engineer (303) 939-5839 (303) 939-6898 kkelly@ball.com zwei@ball.com. Agenda. Welcome Introduction to FM8 radiometric calibration

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SBUV/2 Flight Model 8 Radiometric Calibration Data Review

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  1. SBUV/2 Flight Model 8Radiometric Calibration Data Review Kevin Kelly Zongying Wei Test Engineer Optical Engineer (303) 939-5839 (303) 939-6898 kkelly@ball.com zwei@ball.com

  2. Agenda • Welcome • Introduction to FM8 radiometric calibration • Comparison of calibration constants on the PTF in 2000 and 2001 • Calibrations in 2004 • PTF irradiance calibration • VTF irradiance calibration • Normalization of vacuum irradiance calibration • Radiance calibration on the PTF • Radiance calibrations on USSF and NITF • Comparison with PTF • Comparison of radiometric calibration in 2004 and 2001 • Radiometric calibration constants for FM8 • Lunch

  3. Agenda (continued) • Actual meeting agenda will be presented on-screen

  4. Absolute Radiometric Accuracy • The GSFC specification for SBUV/2 requires: • “Quartz iodide, argon arc or other standard sources of spectral irradiance used for preflight calibration shall be the best sources that can be provided by the National Bureau of Standards” • Absolute radiometric accuracy for the instrument as shown in the charts below (on the following slide) • Irradiance errors assume lamp calibration accuracy of • 6% for argon mini-arc lamps 200-250 nm • We use deuterium lamps in this wavelength range • 1.5% to 2.6% for FEL (quartz iodine) lamps 250-400 nm • Radiance errors assume test diffuser calibration accuracy of • 5.5% at 200-250 nm • 3% at 250-400 nm • No requirement for radiometric accuracy below 200 nm

  5. Radiometric Accuracy Requirements from GSFC S-480-31C

  6. Radiometric Accuracy for SBUV/2 Instruments • Irradiance calibration “output” is instrument response to a known source of irradiance (the irradiance of our test fixture) • The “inputs” are lamp irradiance and collimating mirror reflectance • Redundancy in sources and test fixtures ensure irradiance calibration accuracy • See backup slides for lamp and mirror trend data • Radiance calibration “output” is instrument response to a known radiance target • The “inputs” are the test fixture irradiance (above) and test diffuser BRDF • Bidirectional Reflectance Distribution Function • Redundant radiance targets ensure radiance calibration accuracy • See backup slides for diffuser BRDF trend data • The ratio of radiance calibration to irradiance calibration on our Primary Test Fixture (PTF) cancels any test fixture irradiance uncertainty • We devised a method of calculating radiance calibration constants, in order to maximize this advantage of the PTF • We call this method “Instrument BRDF” • Multiple data sets ensure accuracy of irradiance to radiance ratio

  7. Radiometric Precision for FM8

  8. Radiometric Calibration Repeatability • Evaluation of calibration precision is straightforward • Based on the standard deviation of calibration data sets • Evaluation of absolute accuracy is more difficult • Generally dependent on calibration standards • We can take a look at SBUV/2 calibration repeatability over time • Requirement in GSFC S-480-31C for SBUV/2 long-term stability is no more than 3% change in radiometric response over six months • FM8 shows extremely good repeatability 2000-2002 because the same calibration standards were used for both instrument calibrations • In 2001-2004, the relative difference between radiance and irradiance response is most likely due to a change in the instrument (solar) diffuser angle • New goniometric calibration in Jan-05 for FM8 eliminates errors caused by any change in the diffuser mechanism • Following charts show FM8 radiance repeatability over time is comparable to FM6 (NOAA-17) and FM7 (NOAA-18) instruments • Test data show that FM8 meets all calibration requirements

  9. Radiometric Repeatability for FM8

  10. Radiometric Repeatability for FM6 & FM7

  11. Radiance Calibration RepeatabilityFM6, FM7 & FM8

  12. FM8 Radiometric Calibration A Brief Introduction to SBUV/2 Radiometric Calibrations Section 5.1 of the Calibration Data Book (Rev.A) “Radiometric Calibration Methods” And a Quick Summary of Previous FM8 Radiometric Calibrations

  13. Primary Test Fixture (PTF)

  14. SBUV/2 Radiance Calibration Equation for Primary Test Fixture KE is the instrument irradiance calibration constant (inverse sensitivity) E is the source irradiance on-axis εsis the weighted goniometric map of the source Over bar signifies mean goniometric factor calculated from weighted values εmis the collimating mirror reflectance CCE is the instrument irradiance signal • “Corrected Counts” • KE is directly proportional to lamp and mirror calibrations

  15. FM8 Discrete Mode Irradiance Calibration on the PTF in November 2000 • Lamps • FEL190 and FEL257 (black data points) • Deuterium RC876 and YE959 (white) • NIST calibration data for all lamps • Dec-99 • Jul-01 • Collimating Mirror ‘C’ • Ball optics lab measurements • Aug-98 • Sep-99 • Dec-99 • Jun-01 • Incidence Angle • Instrument coordinate system • Elevation 1° 37' 06" • Azimuth -34° 22' 24.1"

  16. FM8 Discrete Mode Irradiance Calibration on the PTF in 2001 • Lamps • FEL190 • NIST data Dec-99 and Jul-01 • FEL191 • NIST data Nov-00 and Jul-01 • FEL192 • NIST data Mar-97 and Jul-01 • Deuterium RC876 and YE959 • NIST data Dec-99 and Jul-01 • Deuterium YE964 • NIST data Nov-00 and Jul-01 • Collimating Mirror ‘C’ • Same measurements as previous slide • Incidence Angle • Instrument coordinate system • Elevation 1° 37' 38" • Azimuth -34° 21' 36.5"

  17. FM8 Sweep Mode Irradiance Calibration on the PTF in 2000 and 2001 • Sweep Mode Irradiance calibrations have two segments • FEL lamp data for long wavelengths (thick black line) • Deuterium lamp data for short wavelengths (red line) • Crossover at 261.762 nm in 2000, and 259.992 nm in 2001 • Deuterium lamp data are normalized to FEL lamp data • As recommended by NIST • Normalization Factor 1.001098 in 2000 • Normalization Factor 1.004931 in 2001

  18. FM8 Vacuum Irradiance Calibration on the VTF in 2000 • Irradiance calibration in vacuum extends Sweep Mode to shorter wavelengths • FEL190 and FEL257 data for long wavelengths (thick black line) • Lamps calibrated at NIST in Dec-99 and Jul-01 • Argon mini-arc Ball I for short wavelengths (red line) NIST calibration Jul-96 and Feb-97 • Lamps cross over at 265.015 nm in 2000, normalization factor of 1.036513 • Spectral emission lines in the mini-arc lamp are removed by spline fits • VTF included collimating mirror D and vacuum window #3 • VTF calibration constants adjusted to remove fixture effects, not vacuum effects • Accomplished by collecting VTF data in air for normalization to the PTF

  19. The following slide compares all 2000 and 2001 irradiance calibrations Very good agreement Sweep Mode calibration constants are on a true scale Same as the previous slide Discrete Mode calibration constants have been adjusted by the nominal ratio between integration times The integration time in Discrete Mode is 1.25 s The integration time in Sweep Mode is 0.1 s Expected signal ratio during initial instrument testing is 12.5 ±1% (12.38 to 12.63) FM8 measurements in 2004 test were 12.49 to 12.50 Sweep-Discrete Signal Ratio Ratios between Sweep Mode signals and Discrete Mode signals are not significant to instrument radiometric calibrations Both modes are calibrated during the same test, with the same calibration standards, but with separate data sets Calibration Constants for both modes are calculated separately Discrete Mode means are computed in real time by EGSE software and recorded manually in data sheets Sweep Mode data are stored in EGSE history files, extracted by off-line utilities, and means are calculated by IDL analysis software FM8 Sweep & Discrete Mode Irradiance Calibrations on the PTF in 2000 & 2001

  20. FM8 Mode & Discrete Mode Irradiance Calibrations on the PTF in 2000 & 2001

  21. 2001/2000 Ratios of Sweep Mode & Discrete Mode Irradiance Calibrations on the PTF

  22. SBUV/2 Radiance Calibration Equation for Primary Test Fixture KL is the instrument radiance calibration constant (inverse sensitivity) [ ] encloses “Instrument BRDF” value εdis the weighted BRDF map of the diffuser Over bar indicates mean BRDF calculated from weighted values iis the diffuser angle of incidence CCL is the instrument radiance signal • KL is directly proportional to test diffuser BRDF calibration

  23. FM8 Discrete Mode Radiance Calibration on the PTF in November 2000 • Test Diffuser • Spectralon Plate H1 • BRDF data from GSFC physics lab • Oct-00 • Jul-01 • Test Diffuser Angle • Angle of incidence from diffuser normal • 54° 17' 35" • “Instrument BRDF” • PTF radiance calibrations are computed by the Instrument BRDF method • This method relies on the ratio of signals from irradiance and radiance calibrations • Two FEL lamps provide signal data for long wavelengths (black) • Two D2 lamps provide signals at the 252 nm wavelength (white)

  24. FM8 Discrete Mode Radiance Calibration on the PTF in 2001 • Test Diffuser • Spectralon Plate H1 • BRDF data from GSFC physics lab • Oct-00 • Jul-01 • Test Diffuser Angle • Angle of incidence from diffuser normal • 54° 17' 24" • “Instrument BRDF” • Ratio of signals from irradiance and radiance calibrations • Three FEL lamps provide signal data for long wavelengths (black) • Three D2 lamps provide signals at the 252 nm wavelength (white)

  25. FM8 Sweep Mode Irradiance to Radiance Signal Ratio on the PTF in 2000 and 2001 • Sweep Mode Irradiance to Radiance signal ratios have two segments • FEL lamp data for long wavelengths (thick black line) • Deuterium lamp data for short wavelengths (red line) • Crossovers at 275.191 nm in 2000, and 275.299 nm in 2001 • These are natural crossover points • No normalization between data from different lamps

  26. FM8 Sweep Mode & Discrete Mode Radiance Calibrations on the PTF in 2000 & 2001

  27. 2001/2000 Ratios of Sweep Mode & Discrete Mode Radiance Calibrations on the PTF

  28. FM8 Radiometric Calibration SBUV/2 Calibration Data Processing Section 5.2 of the Calibration Data Book (Rev.A) “Radiometric Instrument Response” FM8 Data on the PTF in 2004

  29. 2004 Irradiance Data Processing • Raw counts are processed into Corrected Counts • Offsets removed by subtracting measured backgrounds for each range • Counts are corrected for temperature response at Discrete wavelengths • Nominal calibration temperature is 20 °C • Temperature coefficients based on testing in May-00 • A single coefficient (not wavelength dependent) used for Sweep data • Counts are corrected for linearity for each range • Linearity coefficients based on testing in May-00 • Counts are converted into Corrected Counts (CC) • In the past, sometimes called “Range 2 Equivalent” counts • Provides a common unit that is independent of PMT range • Range 1 counts are divided by the Inter-Range Ratio (IRR12) • IRR12 = 100.74 determined from Dec-04 test data • Range 3 counts are multiplied by IRR23 • Range 3 data only from the GSFC sphere (radiance calibration) • IRR23 = 99.14 determined from Dec-04 test data • Process is the same for Discrete Mode and Sweep Mode

  30. 2004 Irradiance Data Processing • We track changes in instrument wavelength calibration • Collect data from the Hg lamp before every set of radiometric data • Look for a shift from the original wavelength calibration • Shift is zero for radiometric calibration on the PTF in 2004 • Shift is 0.2 steps for the tests on the USSF and NITF (0.015 nm) • The A2 coefficient of the wavelength equation for Discrete Mode changed from -3481.6 to -3481.8 • Correction is applied to the sweep mode A2 coefficient in the same way, which is changed from -3482.2 to -3482.4 • No change in the instrument grating positions used to collect data during any tests • Change only in the effective wavelength at each position • All channels remain within specifications • Values loaded into the Flex Memory have not changed since 2001

  31. FM8 Sweep Mode Irradiance Signals on the PTF in 2004

  32. FM8 Radiometric Calibration PTF Irradiance Calibrations in 2004 Section 5.3 of the Calibration Data Book (Rev.A) “Irradiance Calibration in Air”

  33. Lamp Irradiance • NIST measures on-axis irradiance of FEL and deuterium lamps • Measurements at 10 nm intervals • We use new fitting functions to predict irradiance at FM8 wavelengths • “New” for the SBUV/2 program means less than 10 years old • NIST units of W/cm3 are equal to mW/(m2∙nm) • Lamp irradiance values are plotted on a log scale in the charts below • NIST measures goniometric response of the lamps • At the same time as the NIST irradiance measurements • Lamps are rotated ±9° in azimuth and ±7° in pitch, 1° increments • Lamp output is normalized to the center (on-axis) position • Goniometric map of the lamp is larger than it needs to be for the PTF • Goniometric corrections are also needed on USSF and NITF • On these fixtures, lamps illuminate a 12" x 12" diffuser plate • We use average of two NIST data sets for each lamp • Before and after calibration of the SBUV/2 instrument

  34. FEL Lamp Irradiance Curves

  35. D2 Lamp Irradiance Curves

  36. FEL Lamp Goniometric Map for PTF

  37. D2 Lamp Goniometric Map for PTF

  38. Reflectance of PTF Collimating Mirror • Mirror C reflectance data from 2003 to 2005 are used in all FM8 PTF calibrations • One data point at 410 nm was added from a measurement in 1999 • Data points with polynomial curve fits are shown on the following slide • Two fits are required • Curve for short wavelengths • 185 to 350 nm • Used for sweep mode calibrations with deuterium lamps • Curve for long wavelengths • 230 to 410 nm • Used for all discrete mode calibrations • Used for sweep mode calibrations with FEL lamps • As a result of uncertainties in recent Ball reflectivity measurements, GSFC also measured mirror C reflectivity • GSFC measurements were at a central spot • Ball measurements were at ten spots in two columns

  39. Ball & GSFC Reflectance Data for Mirror C

  40. FM8 Discrete Mode Irradiance Calibration on the PTF in 2004 • Lamps • FEL257 (excluded from data average) • NIST data Jul-01 and May-05 • FEL191, FEL192, and FEL564 • NIST data Jul-03 and May-05 • Deuterium RC876, YE959, and YE964 • NIST data Jul-03 and May-05 • Collimating Mirror ‘C’ • Ball optics lab measurements • Apr-03 • GSFC physics lab measurements • Sep-03 • May-05 • Incidence Angle • Instrument coordinate system • Elevation 1° 47' 51" • Azimuth -33° 55' 46.5"

  41. FM8 Discrete Mode Irradiance Calibration • The ratio of test fixture irradiance Edk to instrument counts CC is the calibration constant • Four FEL lamps were used in the PTF calibration: #191, #192, #564 and #257 • If given equal weight in the calibration, then deviations of the calibration constants from FEL191, FEL192 and FEL564 are less than 0.5% from the average • Calibration constants from FEL257 are different from the average of other three lamps by 1.5 – 2% • Lamp spectral irradiance may have changed after NIST measurement or during instrument calibration • We excluded data from FEL257 in composite calibration constants

  42. Irradiance Data from Four FEL Lamps

  43. FEL Lamps Used for Irradiance Calibration

  44. FM8 Discrete Mode Irradiance 252 nm • We also used data from three deuterium lamps to calculate a calibration constant for channel 1 • Multiplied by a normalization factor of 1.010002 • Derived in parallel as a part of our sweep mode data processing

  45. D2 Lamps Used for Irradiance Calibration

  46. Sweep Mode Irradiance Calibrations • PTF data produces 200–406 nm sweep mode calibrations • Method is similar to discrete mode calibration • Composite calibrations based on two types of lamps • FEL • Deuterium • Data from FEL257 are not included in the sweep mode calibration • Same as discrete mode

  47. FEL Lamp Sweep Mode Irradiance Data

  48. Sweep Mode Irradiance Calibrations • Data from FEL564 show spectral features • Located at 279 nm, 309 nm, and 396 nm • NIST now buys FEL lamps from Osram-Sylvania • Earlier SBUV/2 calibrations have only used lamps from GE • Data from FEL191 and FEL192 do not show these features • Features may be caused by FEL564 absorption and emission lines • If these features were not created by the SBUV/2 instrument then they must be removed from radiometric calibration curves • Features were removed from the FEL564 curve by using the IDL Spline function • This method has been used for all SBUV/2 instruments to remove spectral lines from mini-arc lamp data (vacuum irradiance calibration)

  49. New FEL Absorption and Emission Lines

  50. Method for Removing Lamp Features

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