Spectral Solar Irradiance Requirements for Earth Observing Sensors - PowerPoint PPT Presentation

Spectral Solar Irradiance Requirements for Earth Observing Sensors Operating in the Ultraviolet to Shortwave Infrared Jim Butler NASA Goddard Space Flight Center Code 618 Biospheric Sciences Laboratory Greenbelt, MD 20771 Ph: 301-614-5942 E-mail: James.J.Butler@nasa.gov 2015 Sun-Climate Symposium Savannah, GA November 11, 2015

Presentation Outline • Reflectance and radiance products from satellite instruments operating from the uv through swir (i.e. the reflected solar wavelength region) – UV: BUV instruments (e.g. TOMS, SBUV/2, OMI, GOME-2) – Vis/NIR/SWIR: MODIS/VIIRS • Challenges in the solar diffuser-based on-orbit calibration of reflected solar instruments • Spectral Solar irradiance in instrument intercomparisons, vicarious calibration, and production of long-term consistent datasets • Reflectance and radiance products: SI and traceability • Developing climate benchmark instruments and Spectral Solar irradiance • Brief summary of discussions and recommendations from the 2014 SORCE Spectral Solar Irradiance Review

Reflectance and radiance products from satellite instruments operating in the UV: BUV instruments •The BUV technique measures the Earth’s directional reflectance (top of the atmosphere) through comparison to a solar reflector with known directional reflectance      L ( , t ) k ( ) C ( , t ) r r      E ( , t ) k ( ) C ( , t ) i i E( λ , t)   L t k C t C t ( , ) ( ) ( ) ( )      Α r r r ( )   E ( t , ) k ( ) C ( t ) C ( t ) i i i   A BRF cos SD i L( λ ,t) L( λ , t): Backscattered Earth radiance E( λ , t): Solar irradiance k r ( λ ): Radiance calibration constant k i ( λ ): Irradiance calibration constant C r (t): Earth view signal C i (t): Solar view signal SD: Solar diffuser BRF SD : Bidirectional Reflectance Factor of SD Θ i : Solar incident angle A: Albedo calibration Goal: Detect column O 3 changes to within 1%/decade

Reflectance and radiance products from satellite instruments operating in the Vis through SWIR: MODIS •MODIS (primary) Level 1 SDR reflectance •MODIS Level 1 SDR radiance product: product:      m 1  dn EV * 2      EV  cos  EV  d Earth  Sun E cos  Sun EV EV L   EV 2 d     Earth _ Sun EV ( ) BRF cos dc        SD SD SD m E      1 SDS SD SD Sun * 2 m dn dn d dc   1 EV SD Earth Sun Sun Sun where E SUN is the spectral solar irradiance E SUN for MODIS: -0.4-0.8  m Thuillier et al., 1998; -0.8-1.1  m Neckel and Labs, 1984; -above 1.1  m Smith and Gottlieb, 1974 SD Screen (SDS) needed for high gain ocean color bands SD: Solar Diffuser SDSM: Solar Diffuser Stability Monitor SDSM SDS: Solar Diffuser Screen EV: Earth View M 1 : SD calibration coefficient BRF SD : Bidirectional Reflectance Factor of SD Δ SD : SD degradation factor; Γ SDS : SDS vignetting function Scan Mirror d Earth-Sun : Earth-Sun distance dn*: Corrected digital number (SD or EV) dc: Digital counts from SDSM (SD or Sun) Θ EV : Solar zenith angle SD Θ SD : Solar incident angle on SD

Reflectance and radiance products from satellite instruments operating in the Vis through SWIR: VIIRS •VIIRS Level 1 SDR reflectance product: •VIIRS (primary) Level 1 SDR radiance product: 2 2 𝑀 EV = 𝐺 ∙ 𝑑 0 + 𝑑 1 ∙ 𝑒𝑜 EV + 𝑑 2 ∙ 𝑒𝑜 EV 𝜌 ∙ 𝐺 ∙ 𝑑 0 + 𝑑 1 ∙ 𝑒𝑜 EV + 𝑑 2 ∙ 𝑒𝑜 E 𝑊 𝜍 EV = cos 𝜄 EV ∙ 𝐹 Sun 2 𝑀 SD ∙ 𝑑𝑝𝑡 𝜄 SD 1 𝐺 = ∙ where E SUN is the spectral solar irradiance 2 𝑒 Earth−Sun 𝑑 0 + 𝑑 1 ∙ 𝑒𝑜 SD + 𝑑 2 ∙ 𝑒𝑜 SD E SUN for VIIRS: -MODTRAN 4.3 𝑀 SD = 𝐹 Sun ∙ BRF SD ∙ 𝛥 SDS ∙ Δ 𝑇𝐸 𝜌 𝑀 EV 𝐹 Sun ∙ BRF SD ∙ 𝑑𝑝𝑡 𝜄 SD ∙ 𝛥 SD ∙ Δ SD 2 = ∙ 2 ∙ 𝑑 0 + 𝑑 1 ∙ 𝑒𝑜 EV + 𝑑 2 ∙ 𝑒𝑜 EV 2 ∙ 𝑑 0 + 𝑑 1 ∙ 𝑒𝑜 SD + 𝑑 2 ∙ 𝑒𝑜 SD 𝜌 ∙ 𝑒 Earth−Sun SD: Solar Diffuser c 0 , c 1 , c 2 : Non-linearity coefficients SDSM: Solar Diffuser Stability Monitor F: Radiance calibration coefficient SDS: Solar Diffuser Screen L SD : SD spectral radiance EV: Earth View Θ EV : Solar zenith angle BRF SD : Bidirectional Reflectance Factor of SD Θ SD : Solar incident angle on SD Δ SD : SD degradation factor; dn: Corrected digital number (SD or EV) Γ SDS : SDS vignetting function d Earth-Sun : Earth-Sun distance

Challenges in On-orbit Calibration of Reflected Solar Satellite Instruments (1 of 2) •Current challenges in the on -orbit calibration of satellite instruments operating in the reflected solar wavelength regions are largely identical to those experienced in the EOS era 1. Evolution of solar diffuser materials: Instrument Instrument: SD material Operating Wavelength Range Quartz Volume Diffuser Roughened Al 250-425nm -BUV & SBUV: roughened aluminum -TOMS Meteor-3/ADEOS/EP/QuikTOMS: roughened aluminum -OMI: quartz volume diffuser -SNPP OMPS: roughened aluminum Mie Diffuser -JPSS OMPS: quartz volume diffuser (exptl.) -TEMPO & GEMS: roughened transmissive quartz 400-2500nm -SeaWiFS: YB-71 IITRI thermal control paint -MODIS Terra & Aqua: spacegrade Spectralon -MISR: spacegrade Spectralon -MERIS: spacegrade Spectralon -SNPP & JPSS VIIRS: spacegrade Spectralon -Landsat-7: YB-71 IITRI paint -Landsat-8: spacegrade Spectralon Spacegrade Spectralon

Challenges in On-orbit Calibration of Reflected Solar Satellite Instruments (2 of 2) 2. Monitoring solar diffuser (and by inference, instrument) degradation: a. On-orbit monitoring hardware b. Multiple diffusers with varying (e.g. SDSM on MODIS & VIIRS) solar exposure times (e.g. SNPP OMPS) OMPS diffuser measurement trends: Working diffuser Reference diffuser

Challenges in On-orbit Calibration of Reflected Solar Satellite Instruments (3 of 3) 3. Comparison of SD-based and lunar-based instrument degradation predictions (e.g. SNPP VIIRS) Line: Solar Diffuser measurement Symbol: Lunar measurement 1.05 M1 M2 1 M3 Gain Ratio to Initial Measurement M4 0.95 I1 M5 0.9 M6 I2 0.85 M7 M1 Lunar 0.8 M2 Lunar M3 Lunar 0.75 M4 Lunar I1 Lunar 0.7 M5 Lunar M6 Lunar 0.65 I2 Lunar M7 Lunar 0.6 0 300 600 900 1200 1500 Days Since Launch

Effect of Solar Spectral Irradiance on Reflected Solar Instrument Inter-comparisons: MODIS and VIIRS • Instrument inter-comparisons are critical to the production of long-term satellite data records -Differences in comparison results can be due to spatial registration effects, spectral differences, temporal changes in atmosphere and surface between sensor data collects 1.1 MODIS Esun VIIRS Esun 1.05 VIIRS to MODIS radiance ratios determined using sensor-based 1 Esun models (MODIS and VIIRS) and RSR for their spectrally 0.95 matched bands 0.9 M1/B8 M2/B9 M3/B10 M4/B4 M5/B1 M6/B15 M7/B2 I1/B1 I2/B2

Effect of Solar Spectral Irradiance on Reflected Solar Instrument Inter-comparisons: MODIS, ALI, ASTER, ETM+, and MASTER •In addition to the satellite instrument requirement on the use of a solar irradiance spectrum to derive a radiance product in the on-board solar diffuser approach, vicarious calibration methods of instrument inter-comparison all require the use of a solar irradiance spectrum. -EOS era comparison of the WRC and MODTRAN-4 spectral solar irradiance models: 20 5 10-nm block average 50-nm average 15 Percent Difference Percent Difference 100-nm average 0 10 -5 5 0 -10 -5 -15 -10 0.5 1 1.5 2 0.5 1 1.5 2 2.5 Wavelength (micrometers) Center Wavelength Percent difference between the WRC model Percent difference between the WRC model originally chosen as the EOS standard and the originally chosen as the EOS standard and the Chance-Kurucz model embedded in MODTRAN Chance-Kurucz model embedded in MODTRAN for the ALI, ASTER, ETM+, MASTER, and Terra -K. Thome, et al., Proc. SPIE, 4540, 260-269 MODIS spectral bands (2001)

Reflectance and radiance products: SI and traceability, (1 of 3) -NIST: the U.S. National Metrology Institute (NMI) responsible for developing, maintaining, and disseminating national standards used to realize the SI. -SI: an internationally accepted coherent system of physical units, derived from the MKSA (meter-kilogram-second-ampere) system, using the meter, kilogram, second, ampere, kelvin, mole, and candela as the basic units (SI units) respectively of the fundamental quantities of length, mass, time, electric current, temperature, amount of substance, and luminous intensity. -Traceability : The property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties. International Vocabulary of Basic and General Terms in Metrology, VIM 2 nd ed., Geneva: International Organization for Standardization, Sec. 6.10 (1993). Traceability: (1) establishes a common reference base for measurements (2) provides a quantitative measure of assessing the agreement of results from different sensors at different times. Note: It is the responsibility of the instrument calibrator to establish and support their claim of traceability and the responsibility of instrument data users to assess the validity of that claim