Update on VIIRS Lunar Calibration Using ROLO Thomas C StoneU S Geologi - PDF document

1 Update on VIIRS Lunar Calibration Using
Update on VIIRS Lunar Calibration Using ROLO Thomas C. StoneU. S. Geological Survey, Flagstaff, AZMODIS/VIIRS Calibration Workshop26 February 2021 MODIS/VIIRS Calibration Workshop, 26 February 2021 VIIRS Observations of the MoonSNPP and NOAA20 execute roll maneuvers each month to capture the Moon in the Earthview sector at phase angle ~51before Full Moonwhen the Moon is observable, typically October through Juneas the spacecraft traverses its orbit, the Moon passes through the field of viewroll angle specified to center the Moon disk in Earth view: SNPP VIIRS image d20170604_t1934579, band M7, scan 12 2 MODIS/VIIRS Calibration Workshop, 26 February 2021 VIIRS Observations of the MoonSNPP and NOAA20 execute roll maneuvers each month to capture the Moon in the Earthview sector at phase angle ~51before Full Moonwhen the Moon is o

2 bservable, typically October through Jun
bservable, typically October through Juneas the spacecraft traverses its orbit, the Moon passes through the field of viewroll angle specified to center the Moon disk in Earth view:centering avoids stray light, seen by stretching the display level: SNPP VIIRS image d20170604_t1934579, band M7, scan 12 3 MODIS/VIIRS Calibration Workshop, 26 February 2021 Lunar CalibrationUSGS lunar calibration works with lunar irradiances, comparing sensor measurements to corresponding referencevaluesthe ROLO model. Irradiance measurements from Moon images involves spatial integration of pixels on the lunar disk: • Reference irradiances are generated for the photometric geometry of each Moon observation: 4 MODIS/VIIRS Calibration Workshop, 26 February 2021 Lunar Calibration Application Typical usage : tracking sensor response changes on or

3 bit the Moon is an exceptionally stable
bit the Moon is an exceptionally stable solar diffusertime series of measurement/ROLratios reveal sensor response trendsfound to be particularly useful for onorbit calibration for ocean color X. XiongNASA GSFC MODIS/VIIRS Calibration Workshop, 26 February 2021 USGS Results for VIIRS Lunar CalibrationLunar irradiance ratios (measureROLO) not normalizedVIIRS Moon image processing by USGS:RDRs from NOAA CLASS; ADLtemporal trends removed using SD ffactors (thanks to VCST) Notable plot features : • discrepancies (offsets)16% for M1 to M6• bandcorrelatedoscillation pattern��6&#x/BBo;&#xx [4;.27;5 8;�.84; 31;.72;$ 1;V.2; ;&#x]/Su;typ; /F;&#xoote;&#xr /T;&#xype ;&#x/Pag;&#xinat;&#xion ;&#x/BBo;&#xx [4;.27;5 8;�.84; 31;.72;$ 1;V.2; ;&#x]/

4 Su;typ; /F;&#xoote;&#xr /T;&#xyp
Su;typ; /F;&#xoote;&#xr /T;&#xype ;&#x/Pag;&#xinat;&#xion ;Uncertainty in the ROLO model is typically quoted as 5 MODIS/VIIRS Calibration Workshop, 26 February 2021 USGS Results for VIIRS Lunar CalibrationLunar irradiance ratios (measureROLO) not normalizedVIIRS Moon image processing by USGS: RDRs from NOAA CLASS; ADLtemporal trends removed using SD ffactors (thanks to VCST) Uncertainty in the ROLO model is typically quoted as 5• highlighting shows the effect of 510% offset in ROLO values• bands M1 and M6 fall outside this range MODIS/VIIRS Calibration Workshop, 26 February 2021 USGS Results for VIIRS Lunar CalibrationLunar irradiance ratios (measureROLO) not normalizedVIIRS Moon image processing by USGS: RDRs from NOAA CLASS; ADLtemporal trends removed using SD ffactors (thanks to VCST)Uncertainty in the

5 ROLO model is typically quoted as 5
ROLO model is typically quoted as 5• highlighting shows the effect of 510% offset in ROLO values• bands M9, M10, M11 fall outside this range MODIS/VIIRS Calibration Workshop, 26 February 2021 Impact of the MeasurementROLO Discrepancies The cause(s) of these discrepancies need to be understood to realize the important potential benefits of lunar calibration : Absolute calibration against a potentially SItraceable referencereduced time to converge and stabilize onorbit calibrationInterconsistent calibration to the same reference standardsupports interoperability of sensors, for aggregation into climate recordssupports a constellation approach for future Earth remote sensing programsAbility to bridge a gap in an otherwise continuous measurement seriesthe accuracy of the bridge calibration depends on the accuracy of the

6 lunar referenceTransfer of prelaunch ca
lunar referenceTransfer of prelaunch calibration to onorbit operations Addressing this discrepancy issue requires a 2pronged approach:An improved lunar irradiance model the calibration referenceRevised techniques for extracting irradiance measurements from sensor Moon images MODIS/VIIRS Calibration Workshop, 26 February 2021 Lunar Irradiance Measurements from ImagesIrradiance is measured by summing radiance pixels:pixel radiance i this is the only term where sensor calibration is accountednet radiance, above background levelinadequate background evaluation leads to phase angle dependence in measurementspixel IFOV effective detector spatial response (different from GSD)oversampling factor oversampling of the Moon disk (different from slew/sampling ratio) 10 ��Each factor has an associated uncertainty ��

7 00;All contributeto the total uncertaint
00;All contributeto the total uncertainty in irradiance measurements MODIS/VIIRS Calibration Workshop, 26 February 2021 Improving the Lunar Reference: ROLOThe ROLO observational dataset is still an indispensable characterization of the Moon’s brightness variations with phase angle and librationsi.e.time and observer location), but its absolute accuracy can be improved.Current USGS efforts to refine irradiance measurements from ROLO imagesgroundbased measurements require correction for observing through the atmospheree.g.Moon image edge spread patterns are azimuthally asymmetric: ��ROLO Moon image acquired 06 May 2001 phase = 17.1Same image stretched and with Moon disk blanked MODIS/VIIRS Calibration Workshop, 26 February 2021 Improving the Lunar Reference: Modeling EffortsSeveral projects worldwide to devel

8 op lunar irradiance models, including:Lu
op lunar irradiance models, including:Lunar Irradiance Model ESA (LIME)calibrated aerosol photometer at Pico Teide, Izaña, TenerifeSpacecraft and Earthbased Aggregate Lunar Irradiance Model (SLIM)effort by Hugh Kieffer, using ROLO and multiple spacecraft measurement setsLunar Extended Satellite Simulation Solar Reflectance(LESSSR)development done under contract to EUMETSATbased on spectrally resolved Moon observations taken by SCIAMACHYPresentations on the above given at the GSICS virtual Lunar Calibration Workshop, 19 November 2020 http://gsics.atmos.umd.edu/bin/view/Development/LunarCalibrationWS2020��12&#x/BBo;&#xx [3;.44; 54;&#x.672;&#x 857;&#x.470; 11;�.59; ]/;&#xSubt;&#xype ;&#x/Foo;&#xter ;&#x/Typ; /P; gin; tio;&#xn 00;&#x/BBo;&#xx [3;.44; 54;&#x.672;&#x 857;&#x.470;

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11;�.59; ]/;&#xSubt;&#xype ;&#x/Foo;&#xter ;&#x/Typ; /P; gin; tio;&#xn 00;This community of modelers have agreed on the need for a “ground truth” lunar irradiance scale, requiring new highaccuracy measurements MODIS/VIIRS Calibration Workshop, 26 February 2021 Improving the Lunar Reference: New Measurements airborne Lunar Spectral Irradiance (airLUSI) 13 ��Lunar irradiance measurements taken from the NASA ER2 aircraft��•flight altitude: 70,000 feet (21.6 km), above �90% of the atmosphere��A collaborative project with NASA, NIST, USGS, Univ. of Guelph (Canada)��•details to be presented in the next talk, by Kevin Turpie(airLUSI PI)��Status:��•Successful 5night campaign: 1317 November 2019�&

10 #x0000;•operational ready for futur
#x0000;•operational ready for future flightsphotos: K. Turpie MODIS/VIIRS Calibration Workshop, 26 February 2021 Improving the Lunar Reference: New Measurements Lunar Spectral Irradiance at Mauna Loa Observatory (MLOLUSI) ��14&#x/BBo;&#xx [7;�.14; 34;.38; 59;.50;
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15 tarting midlate 2021 MODIS/VIIRS Calibra
tarting midlate 2021 MODIS/VIIRS Calibration Workshop, 26 February 2021 Improving the Lunar Reference: New Measurements ARCSTONE 15 NASA Langleyled effort to measure lunar spectral reflectance from a 6U CubeSat in LEO ��•fulldisk Moon and Sun acquisitions with no change of opticssinglepixel FOV ~0.7, no scanning�7 orders of magnitude intensity difference accommodated by spatial and temporal integrations��•absolute scale and SI traceability tied to TSIS��Formfit grating spectrograph with cooled HgCdTe array detector��•spectral range: 3502300 nm, 4 nm sampling��•target absolute accuracy for reflectance: 0.5% (k=1) uncertainty&#x-1 0;&#x-1 0;Status:&#x-1 0;&#x-1 0;•development on track for TRL 5 by June 2021&#x-1 0;&#x-1 0;•

16 ;potential inflight validation measureme
;potential inflight validation measurements in 2024 timeframe MODIS/VIIRS Calibration Workshop, 26 February 2021 Summary and ConclusionsComparisons of VIIRS lunar irradiance measurements to ROLO reference values show discrepancies larger than the absolute uncertainties in ROLOthese discrepancies need to be addressed to derive full benefits of lunar calibrationNew highaccuracy lunar irradiance measurements will allow to constrain the absolute scale of the ROLO modelterm: airLUSI, MLOLUSI; future: ARCSTONEother, nonU.S. projects are acquiring measurements to redevelop the lunar referenceFuture work:examine spatial aspects of VIIRS Moon imaging pertinent to deriving lunar irradiance measurements:the presumed 1.0 oversampling factormotion of the Moon relative to the line of sight during scanspotential effects of pixel aggregation