Improvements in Calibration and Validation of the Absolute

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Improvements in Calibration, and Validation of the Absolute Radiometric Response of MAXAR Earth-Observing Sensors Michele Kuester and Tina Ochoa

Joint Agency Commercial Imagery Evaluation (JACIE) Workshop-2019, Reston, VA, USA, 9/24 – 9/26, 2019 OVERVIEW . New facility in Fort Lupton, CO, USA . 2018v0 Calibration – updates to methodology & validation . Stability of MAXAR sensors over Libya-4 in Saharan Desert . Comparisons to Landsat & Sentinel

. Located in Fort Lupton, CO, USA . 3 acres – plenty of room for tarps . Very rural location (less pollution, less adjacency from nearby neighborhoods) . A laboratory space for instrument maintenance and on-site work . Web-enabled weather stations alert us to non-ideal deploy conditions (clouds, wet soil, winds, temperatures)

. Surface reflectance measured at sensor view angles . NASA GODDARD AERONET linked Cimel Sun Photometer − Aerosol optical depth − Column water vapor, ozone and carbon dioxide − Single scattering albedo − Asymmetry parameter . Online weather station − Temperature − Pressure − UV and VNIR solar irradiance Thuillier in 2003 as recommended by the Committee on Earth − Observation Satellites (CEOS) Wind velocity used for the top-of-atmosphere solar irradiance (ChKur and WRC − Rain bucket and soil moisture probes are available upon request) − All-sky camera 4 © 2019 Maxar Technologies 4 2018v0 Calibration Improvements . Five years of ground truth on calibration tarps . A more robust surface reflectance measurement that uses angle dependent calibration (derived from measurements at UofA) of the reference Spectralon panel . What solar curve is being used makes a big difference (particularly in SWIR) . Automation software employed to decrease human error . Employ statistics to remove outlier data (versus by hand) . *.IMD abscalFactors checked for inconsistencies

When using imagery with other datasets or performing atmospheric correction it is advised to match

The aim of Absolute radiometric calibration is to assign absolute scientific units to pixels based on radiometric parameters such as scan direction, scan rate, TDI level, and DN value. For World-View class sensors, the absolute radiometric calibration product specification for ninety-five percent of products is: • < 10% of dynamic range there shall be no specification • Between 10% and 85% of the dynamic range the absolute radiometric response specifications shall not exceed +/- 10% uncertainty for VNIR sensors and +/- 15% for SWIR sensors • > 85% of dynamic range there shall be no specification

. We now have enough coincident data over Railroad Valley, NV, USA (RVUS) to create meaningful validation plots . Only imagery with < 20-deg off-nadir angle are used . Next slides show pre-launch, 2016v0 and 2018v0 absolute radiometric calibrations on MAXAR sensor imagery compared to RadCalNet Truth

* Committee on Earth Observation Satellites Radiometric Calibration Network portal: radcalnet.org

© 2019 Maxar Technologies 6 2018v0 AbsRadCal GE01 within 5% difference of RVUS RadCalNet* Thuillier Solar Curve Pre-Launch 2016v0 2018v0 *Note that pre- %Dif to On-orbit Cal %Dif to On-orbit Cal %Dif to launch No On-orbit Cal RadCalNet Adjustment RadCalNet Adjustment RadCalNet calibration could Gain Offset RVUS Gain Offset RVUS GAIN OFFSET RVUS also be PAN 1.000 0.000 0.942 -2.704 1.001 0.000 considered good BLUE 1.000 0.000 -1.246 0.988 -5.736 -6.288 1.041 0.000 2.480 for GE01 – GREEN 1.000 0.000 2.869 0.936 -3.546 -6.012 0.972 0.000 0.343 compares < 5% RED 1.000 0.000 4.252 0.952 -2.512 -2.484 0.979 0.000 2.868 NIR 1.000 0.000 2.321 0.961 -3.300 -4.930 0.951 0.000 -1.978 to RadCalNet

RadCalNet (excepting Red Band at 6%) Thuillier Solar Curve Pre-Launch 2016v0 2018v0 %Dif to On-orbit Cal %Dif to On-orbit Cal %Dif to No On-orbit Cal RadCalNet Adjustment RadCalNet Adjustment RadCalNet Gain Offset RVUS Gain Offset RVUS Gain Offset RVUS PAN 1.000 0.000 0.942 -2.704 0.949 -5.523 COASTAL 1.000 0.000 -4.351 1.151 -7.478 3.908 1.203 -11.839 2.788 BLUE 1.000 0.000 11.141 0.988 -5.736 5.927 1.002 -9.835 4.108 GREEN 1.000 0.000 14.995 0.936 -3.546 5.316 0.953 -7.218 4.401 YELLOW 1.000 0.000 15.403 0.949 -3.564 7.175 0.946 -5.675 3.876 RED 1.000 0.000 14.308 0.952 -2.512 7.094 0.955 -5.046 6.056 REDEDGE 1.000 0.000 10.974 0.974 -4.120 4.854 0.980 -6.114 2.592 NIR1 1.000 0.000 10.906 0.961 -3.300 3.474 0.966 -5.096 2.675 NIR2 1.000 0.000 8.796 1.002 -2.891 4.886 1.010 -4.059 2.168

RVUS uncertainty reported as 5.3% @400nm and 3.8% @850nm 12 Images © 2019 Maxar Technologies 8 2018v0 AbsRadCal WV03 VNIR within 3.5% difference of RVUS RadCalNet Thuillier Solar Curve Pre-Launch 2016v0 2018v0 %Dif to On-orbit Cal %Dif to On-orbit Cal %Dif to No On-orbit Cal RadCalNet Adjustment RadCalNet Adjustment RadCalNet Gain Offset RVUS Gain Offset RVUS Gain Offset RVUS PAN 1.000 0.000 0.950 -3.629 0.955 -5.505 COASTAL 1.000 0.000 20.544 0.905 -8.604 2.517 0.938 -13.099 0.471 BLUE 1.000 0.000 12.189 0.940 -5.809 1.872 0.946 -9.409 1.264 GREEN 1.000 0.000 11.723 0.938 -4.996 1.768 0.958 -7.771 1.276 YELLOW 1.000 0.000 9.806 0.962 -3.649 3.409 0.979 -5.489 2.064 RED 1.000 0.000 9.821 0.964 -3.021 3.947 0.969 -4.579 3.446 REDEDGE 1.000 0.000 5.807 1.000 -4.521 2.530 1.027 -5.552 2.575 NIR1 1.000 0.000 11.701 0.961 -5.522 2.536 0.977 -6.508 2.328 NIR2 1.000 0.000 10.009 0.978 -2.992 3.679 1.007 -3.699 3.289

RVUS uncertainty reported as 5.3% @400nm and 3.8% @850nm 10 Images © 2019 Maxar Technologies 9 2019v0 AbsRadCal WV03 SWIR within 5.5% difference of RVUS RadCalNet 2019v0 Pre-Launch 2016v0 Thuillier* %Dif to %Dif to %Dif to RadCal On-orbit Cal RadCal On-orbit Cal RadCal No On-orbit Cal Net Adjustment Net Adjustment Net BAND Gain Offset RVUS Gain Offset RVUS GAIN OFFSET RVUS SWIR1 1.000 0.000 0.360 1.200 -5.546 8.5413 1.030 0.000 3.371 SWIR2 1.000 0.000 0.276 1.227 -2.600 14.334 1.052 0.000 5.491 SWIR3 1.000 0.000 -0.687 1.199 -2.309 10.269 0.992 0.000 -1.482 SWIR4 1.000 0.000 -0.906 1.196 -1.676 10.462 1.014 0.000 0.481 SWIR5 1.000 0.000 -3.001 1.262 -0.705 14.255 1.012 0.000 -1.837 SWIR6 1.000 0.000 -5.813 1.314 -0.669 14.510 1.082 0.000 1.910 SWIR7 1.000 0.000 -6.348 1.346 -0.512 17.909 1.056 0.000 -1.103 SWIR8 1.000 0.000 -7.103 1.376 -0.372 19.328 1.101 0.000 2.279

Recall that RVUS data uses Thuillier

. TOA Reflectance of the green band for GE01, WV02, WV03 and L8 shown over Pseudo- invariant site Libya4, Saharan Desert . Libya4 can achieve variabilities as low as 2- 3% in the visible and near infrared (VNIR)* . Data from 2013 – 2019 has no discernable slope

ONA < 40 AVERAGE STDEV PERCENT UNC # IMAGERY USED GeoEye-1 0.331 0.009 2.7% 60 . Variability up to 4% with WorldView-2 if view WorldView-2 0.342 0.013 3.9% 96 WorldView-3 0.332 0.011 3.4% 83 angle is not restricted. Restricting sensor off- Landsat-8 0.338 0.003 0.7% 8 nadir angle to < 20 deg shows all sensors ONA < 20 AVERAGE STDEV PERCENT UNC # IMAGERY USED GeoEye-1 0.332 0.008 2.5% 37 within uncertainty of the site reflectance WorldView-2 0.338 0.009 2.6% 61 WorldView-3 0.329 0.007 2.2% 40 variability Landsat-8 0.338 0.003 0.7% 8 *L. Helder, Dennis & Basnet, Bikash & L. Morstad, Daniel. (2010). Optimized identification of worldwide radiometric pseudo- invariant calibration sites. Canadian Journal of Remote Sensing. 36. 527-539. 10.5589/m10-085. © 2019 Maxar Technologies 13 WorldView-2 & WorldView-3 radiometrically stable as shown over Libya-4

WV03 2018v0 WV02 2018v0 TOA Reflectance TOA

WorldView-3 (2014 -2019) WorldView-2 (2014 -2019) Band Slope Intercept Average StdDev Band Slope Intercept Average StdDev Coastal -1.04E-05 0.286748 0.27368 0.047889 Coastal -8.61E-06 0.232 0.218 0.011 Blue -3.69E-06 0.290769 0.28615 0.012965 Blue -3.86E-06 0.280 0.274 0.010 Green -2.96E-06 0.366388 0.36268 0.010547 Green -2.25E-06 0.371 0.368 0.009 Yellow -1.58E-06 0.449422 0.44745 0.009573 Yellow -2.13E-06 0.473 0.470 0.010 Red 7.76E-07 0.506627 0.5076 0.009948 Red -3.61E-06 0.525 0.520 0.015 RedEdge 1.21E-05 0.478172 0.49336 0.019277 RedEdge 5.95E-06 0.507 0.516 0.020 NIR1 1.40E-05 0.565498 0.58307 0.026085 NIR1 -2.74E-06 0.586 0.582 0.028 NIR2 7.74E-06 0.455639 0.46534 0.083162 NIR2 1.07E-05 0.457 0.474 0.029

© 2019 Maxar Technologies 14 MAXAR sensors show good agreement with Landsat and Sentinel over RadCalNet site Railroad Valley, NV . RadCalNet data are given at Nadir. MAXAR sensors will typically have an ONA of 5 - 30 degrees. Variation in ONA will increase the variability in MAXAR data due to surface BRDF and longer atmospheric path and < 10% is considered good. . WV02 is showing a relative difference of < 6%, and WV03 and GE01 are < 5% (Right). Comparable Landsat bands are within 5% (Left).

Landsat and Sentinel plot on this slide from Xin Jing, Larry Leigh, Cibele Pinto, and Dennis Helder, “Evaluation of RadCalNet Output Data Using Landsat 7, Landsat 8, Sentinel 2A, and Sentinel 2B Sensors,” Remote Sens. 2019, 11(5), 541; https://doi.org/10.3390/rs11050541

© 2019 Maxar Technologies 15 MAXAR sensors are radiometrically accurate, reliable and stable . New absolute radiometric vicarious calibration employs improvements that tighten uncertainties and falls within specifications . MAXAR compares to RadCalNet RVUS at +/- 5% . MAXAR sensors are shown to be radiometrically stable throughout their lifetime . MAXAR radiometry is comparable to Landsat 8 and Sentinel at +/- 5% . We continue to investigate our atmospheric model and include more measured data to improve derived TOA radiance for truth . Future Plans: − Update Libya-4 BRDF model and transfer 2018 calibration to CAVIS − Validate data collected at new calibration range in Fort Lupton, CO, USA − Step back and work on further automation − Preparation for next generation of sensors − Perform sensitivity analysis across system and look for more places to improve