Radiometric Comparison of Sentinel 2A, Sentinel 2B and

Landsat-8: Lifetime Trending, Cross Calibration and

Absolute Calibration Assessment Over the Libya 4 PICS

JACIE WorkshopSept 17-19, 2018College Park, MD

by

Morakot Kaewmanee, Esad Micijevic,

Dennis Helder, Md Obaidul Haque, Julia Barsi

1

Topics• Overview

– Sensor Properties

– Sensor Band Comparison

– Sensor RSR Comparison

• Lifetime Cross Calibration Trends– Cross Calibration Methodology

– SBAF Calculation

– TOA Reflectance Calculations

– MSI-A/MSI-B vs OLI Comparison

– MSI-B vs MSI-A Comparison

– Overall TOA Reflectance Comparison

• Refined SDSU APICS Calibration Model– Model Overview

– Model Equation

– Analysis Methodology

– OLI Observations vs Model Predictions

– MSI-A Observations vs Model Predictions

– MSI-B Observations vs Model Predictions

– Comparison of Model Performance Across Sensors

• Summary 2

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Sentinel-2A, 2B

• Sentinel-2 mission is developed by

European Space Agency (ESA).

• comprises a constellation of two

polar-orbiting satellites placed in the

same orbit, phased at 180° to each

other ( 5 days apart).

• S2A Launch date: 23 June 2015

• S2B Launch date: 7 March 2017

• Revisit time: 10 days

• Main instrument: MSI

• Provides 13 bands in the visible, near

infra-red, and short wave infra-red

part of the spectrum, at different

ground resolution.

Image courtesy: ESA

S2A, S2B Spectral bands

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Landsat 8

• Landsat 8 is a US Earth observation satellite which is the eighth satellite in the Landsat program; the seventh to reach orbit successfully. Originally called the Landsat Data Continuity Mission (LDCM), it is a collaboration between NASA and the United States Geological Survey (USGS).

• Launch date: February 11, 2013.

• Revisit time: 16 days

• Two Instruments:

– OLI : Coastal Aerosol, VNIR, SWIRs bands (9 bands)

– TIRS: 2 Thermal Infrared Bands (TIRS)

Image courtesy: NASA

BandsWavelength

(micrometers)

Resolution

(meters)

Band 1 - Ultra Blue

(coastal/aerosol)0.435 - 0.451 30

Band 2 - Blue 0.452 - 0.512 30

Band 3 - Green 0.533 - 0.590 30

Band 4 - Red 0.636 - 0.673 30

Band 5 - Near

Infrared (NIR)0.851 - 0.879 30

Band 6 -

Shortwave

Infrared (SWIR) 1

1.566 - 1.651 30

Band 7 -

Shortwave

Infrared (SWIR) 2

2.107 - 2.294 30

Band 8 -

Panchromatic0.503 - 0.676 15

Band 9 - Cirrus 1.363 - 1.384 30

Band 10 - Thermal

Infrared (TIRS) 110.60 - 11.19 100 * (30)

Band 11 - Thermal

Infrared (TIRS) 211.50 - 12.51 100 * (30)

Landsat 8 Spectral bands

Sensor Band Comparison

Courtesy: http://eros.usgs.gov/sentinel-2Source: http://landsat.gsfc.nasa.gov/wp-content/uploads/2015/06/Landsat.v.Sentinel-2.png

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CA, B, G, R NIR SWIR1 SWIR2

Sensor RSR Comparison

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Coastal Aerosol Blue Green Red

NIR SWIR-1 SWIR-2

Lifetime Cross Calibration Trends

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8/2/2015 GS2A_20150802T091216_000576_N02.04

8/12/2015 GS2A_20150812T091216_000719_N02.04

8/22/2015 GS2A_20150822T090006_000862_N02.04

9/11/2015 GS2A_20150911T085736_001148_N02.04

10/1/2015 GS2A_20151001T085756_001434_N02.04

12/23/2015 GS2A_20151223T091412_002621_N02.01

12/30/2015 GS2A_20151230T090402_002721_N02.01

1/9/2016 GS2A_20160109T090342_002864_N02.01

1/29/2016 GS2A_20160129T090222_003150_N02.01

2/8/2016 GS2A_20160208T090822_003293_N02.01

5/18/2016 GS2A_20160518T085602_004723_N02.02

5/28/2016 GS2A_20160528T090022_004866_N02.02

6/7/2016 GS2A_20160607T085602_005009_N02.02

6/17/2016 GS2A_20160617T090022_005152_N02.04

6/27/2016 GS2A_20160627T085602_005295_N02.04

4/3/2017 GS2A_20170403T090021_009299_N02.04

4/13/2017 GS2A_20170413T085551_009442_N02.04

4/23/2017 GS2A_20170423T090021_009585_N02.04

5/3/2017 GS2A_20170503T085601_009728_N02.05

5/13/2017 GS2A_20170513T090021_009871_N02.05

5/23/2017 GS2A_20170523T085601_010014_N02.05

9/20/2017 GS2A_20170920T085631_011730_N02.05

9/30/2017 GS2A_20170930T090021_011873_N02.05

10/10/2017 GS2A_20171010T085901_012016_N02.05

10/20/2017 GS2A_20171020T090021_012159_N02.05

10/30/2017 GS2A_20171030T090111_012302_N02.06

11/9/2017 GS2A_20171109T090201_012445_N02.06

11/19/2017 GS2A_20171119T090251_012588_N02.06

6/7/2018 GS2A_20180607T085601_015448_N02.06

6/17/2018 GS2A_20180617T085551_015591_N02.06

6/27/2018 GS2A_20180627T085601_015734_N02.06

7/7/2018 GS2A_20180707T085601_015877_N02.06

Sentinel 2A- data: August 15 – July 18

Sentinel 2B- data: July 17 – July 18S2A Date of

Image Acquisition

All S2A , S2B data downloaded from: https://scihub.copernicus.eu/dhus/#/homeLandsat 8 downloaded from:https://earthexplorer.usgs.gov/

Processing

Version

8

2.01

2.02

2.04

2.04

ROI Extent (aka CNES Site):UTM, WGS84UL: 731565, 3189885

LR: 797445, 3143865

Geographic Coordinates

UL: Lat 29.75 , Lon 23.12

LR: Lat 27.99, Lon 24.28

2.05

2.06

Libya4

ROI

S2A, S2B

L8

Cross Calibration Methodology

– Use Sentinel 2A/2B MSI and Landsat 8 OLI

(Collection1) images over Libya4 PICS

– Calculate and apply spectral band adjustment

factors (SBAF)• 5 Hyperion images ( EO-1 & L8 co-incident pairs)

– Compute TOA reflectance from selected ROIs

– Compare TOA reflectance for MSI and OLI CA,

Blue, Green, Red, NIR, SWIR1 and SWIR2 bands

– Datasets:

Near-simultaneous acquisitions (up to 6 days apart) OLI: 44 images

S2A MSI: 37 images

S2B MSI: 9 images

Same day acquisitions OLI-S2A MSI: 10 images

S2A, S2B near-simultaneous acquisitions (5 days apart)

S2A MSI: 33 images

S2B MSI: 29 images

– Selected ROI: having temporal stability within 3%

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S2A-2B 34RGS

Landsat8P181/R40

Hyperion

ROI Extent (aka CNES Site):UTM, WGS84UL: 731565, 3189885

LR: 797445, 3143865

Geographic Coordinates

UL: Lat 29.75 , Lon 23.12

LR: Lat 27.99, Lon 24.28

SBAF Calculation

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Hyperion data over the test area were used to estimate Spectral Band Adjustment Factors (SBAF)

where

Note : Hyperion TOA reflectance is calculated using ESUN values derived from the CHKUR model

❖ 𝜌𝑇(𝜆) is the Hyperion TOA reflectance of the target area

❖ 𝑅𝑆𝑅𝐿8(𝜆) and 𝑅𝑆𝑅𝑆2𝐴(𝜆) are the relative spectral responses of OLI and MSI, respectively

❖ 𝜌𝐿8(𝜆) and 𝜌𝑆2𝐴(𝜆) are the simulated TOA reflectances of OLI and MSI, respectively

TOA Reflectance Calculations• OLI TOA Reflectance

– where

• 𝜌𝜆= Top-of-Atmosphere Reflectance

• 𝑀𝜌= Band-specific reflectance multiplicative scaling factor

(REFLECTANCE_MULT_BAND_N metadata parameter)

• 𝐴𝜌= Band-specific reflectance additive scaling factor

(REFLECTANCE_ADD_BAND_N metadata parameter)

• 𝑄𝑐𝑎𝑙= Level 1 pixel value in (calibrated) DN

• 𝜃 = Solar Zenith Angle (90-SUN_ELEVATION metadata parameter)

• MSI TOA Reflectance

– where

• 𝜌𝜆= Top-of-Atmosphere Reflectance

• 𝑄𝑐𝑎𝑙= L1C pixel value in DN

• QUANTIFICATION_VALUE is a metadata parameter

• Convert MSI TOA reflectance to OLI equivalent reflectance′𝑀𝑆𝐼 = 𝑀𝑆𝐼 ∗ 𝑆𝐵𝐴𝐹 11

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MSI-A/MSI-B vs OLI Comparison

Comparison %DiffOLI vs MSI-SBAF CA Blue Green Red NIR SWIR1 SWIR2

OLI vs S2A-SBAF (6 days)1.91% -1.05% 0.29% 1.14% 0.93% 0.98% 0.32%

OLI vs S2B-SBAF (6 days)0.43% -0.84% 0.30% 0.35% -0.14% 1.09% -0.63%

OLI vs S2A-SBAFCo-incident pairs

2.15% -0.84% 0.49% 1.24% 1.03% 1.03% -0.02%

SBAF CA Blue Green Red NIR SWIR1 SWIR2

SBAF-S2AL8 1.0015 0.9580 1.0061 0.9783 0.9992 0.9985 0.9990

SBAF-S2BL8 0.9995 0.9630 1.0079 0.9772 0.9967 1.0023 0.9804

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MSI-B vs MSI-A Comparison

ComparisonS2B-SBAF vs S2A

CA Blue Green Red NIR SWIR1 SWIR2

Relative Diff% Near Co-incident pairs

-1.16% 0.31% 0.23% -0.84% -0.91% 0.00% -0.90%

SBAF CA Blue Green Red NIR SWIR1 SWIR2

SBAF-S2B2A 0.9981 1.0033 1.0024 0.9977 0.9986 1.0037 0.9820

Overall TOA Reflectance Comparison

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• Near simultaneous acquisition up to 6 days apart( OLI-44 images, S2A 37 images, S2B 9 images)

• Same day acquisition ( OLI-S2A, 10 images)

• S2A agrees very well with OLI for both cases i.e. within 2% for CA and, 1% for Blue, Green and SWIR2, and within 1.4% for Red, NIR and SWIR1 bands

• S2B agrees very well with OLI, within 1% all bands

• S2B agrees very well with S2A, within 1% all bands, except CA with 1.1%

0% Difference

Refined SDSU Absolute PICS

Calibration Model (APICS)

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Introduction

• The potential exists to use Libya4-PICS for absolute

calibration of optical satellite sensors.

• The sensor can view Libya4-PICS as it would view a

calibration panel in the laboratory during pre-launch

testing.

• SDSU began development of an algorithm in 2012:

• Initial development used ETM+ and Hyperion datasets;

Terra MODIS was used as a transfer radiometer

• MODIS datasets were used to generate an SZA BRDF

model.

• Hyperion datasets were used to generate a VZA BRDF

model and spectral profile of Libya4

• Results were published in two papers in 2012 and 2014.

• Model refinements/improvements implemented in 2017

• Results published / presented at PECORA20 (2017):– Improvement of the SDSU APICS Model: 7 spectral bands

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Libya4 - ()

SDSU Model

The model predicts the TOA reflectance as a function of wavelength over Libya 4 for given solar zenith angle and sensor view zenith angle (SZA, VZA)

PredictedMeasured

SDSU Absolute Calibration Model: APICS Model

Model Overview

• 2014: developed model using Landsat 7, Terra MODIS, Hyperion

6 spectral bands

Validated to ~2-3% precision using Terra/Aqua MODIS, ETM+, OLI, UK-2 DMC, and MERIS data

• 2017: Improvement on the K(): including CA band to the model Removed atmospheric correction parameters

• Evaluated the refined APICS Model with Sentinel 2A, 2B and Landsat7, 8

Collection1 data

With Angle information extracted from ROI over the Angle files

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Existing APICS %Difference :Model vs Measure

Refined APICS %Difference : Model vs Measure

Bands L7 L8 S2A L7 L8 S2A S2B

CA -3.20 0.72 -1.78 0.31 -1.15

Blue 2.62 1.17 0.12 3.04 1.00 1.06 0.92

Green 0.49 -0.40 0.52 0.58 -0.47 0.31 0.39

Red 0.22 1.91 3.93 -0.46 1.31 2.81 1.85

NIR 2.68 0.34 0.85 1.78 0.91 1.14 -0.17

SWIR1 -2.35 -0.44 0.06 -2.65 -0.70 -0.26 -1.07

SWIR2 0.63 -0.06 0.03 0.75 1.00 0.64 0.66

PECORA20 Slide @ November 2017

Using Blue band default K()

Model Equation

• The absolute calibration model is of the form

where

(***Nischal Mishra, Dennis Helder, Amit Angal, Jason Choi, Xiaoxiong Xiong, Absolute Calibration of Optical Satellite Sensors Using Libya 4 Pseudo Invariant Calibration Site , Remote Sensing, ISSN 2072-4292,2014)

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K() is the scaling factor, to place ρh() on MODIS- calibrated scale

SZA and VZA are the solar and view zenith angles (degrees) ρh() is the hyperspectral TOA reflectance derived from co-incident pairs of

MODIS and Hyperion image data, with SZA < 35° and VZA of ± 5°

m1 is the BRDF model coefficient for solar zenith angle derived from Terra MODIS, scaled to a 30° solar zenith angle

m2 and m3 are the BRDF model coefficients for view zenith angle derived from Hyperion (±15°)

fA(t) = atmospheric model parameters (can be negligible)

Analysis Methodology

• Use Sentinel data from Libya 4 PICS - CNES ROI

– Landsat8: WRS2 Path/Row 181/040 (Apr 2013 – July 2018)

– Sentinel-2A: Tile 34RGS, (Aug 2015 – July 2018),

– Sentinel-2B: Tile 34RGS, (July 2017 – July 2018),

– ROI size: ~25x24km

• 5 Hyperion spectral profile over Libya4

• Compute the TOA reflectance difference between

observed and predicted model values

S2A,S2B

L8

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OLI Observations vs Model Predictions

Landsat8- OLI CA Blue Green Red NIR SWIR1 SWIR2

Avg, Measure 0.2294 0.2472 0.3366 0.4599 0.5827 0.6748 0.5959

Avg, Model 0.2329 0.2443 0.3382 0.4542 0.5774 0.6800 0.5911

Diff% Meas-Model -1.52% 1.22% -0.45% 1.25% 0.91% -0.79% 0.81%

STD. of Residuals 1.28% 1.15% 1.19% 1.40% 1.48% 2.27% 2.52%

SDSU Refined APICS model shows that

the OLI absolute calibration is well within 1.5% across all bands*** Better than 1% for Green and longer wavelength bands

All available data from April 2013 – July 2018: 109 images: Landsat8 Collection1 data

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MSI-A Observations vs Model Predictions

• RSR-S2A: Obviously not an ideal RSR shape!! This results

in a predicted TOA reflectance value less than the

other sensors.

• The APICS model is sensitive to the shape of the RSR

profile

Sentinel 2A – MSI-A CA Blue Green Red NIR SWIR1 SWIR2

Avg, Measure 0.2329 0.2546 0.3349 0.4747 0.5873 0.6809 0.5963

Avg, Model 0.2316 0.2518 0.3344 0.4616 0.5807 0.6839 0.5906

Diff% Meas-Model 0.60% 1.12% 0.15% 2.85% 1.13% -0.45% 0.96%

STD. of Residuals 1.15% 1.21% 1.43% 1.64% 1.81% 2.38% 2.71%

SDSU Refined APICS model shows that the MSI-A absolute calibration is generally well within 1.0% for all bands except the Red, which is within ~2.85%.

All available data from Aug 2015 – July 2018: 82 images

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MSI-B Observations vs Model Predictions

Better shape of RSR-S2B, the model

gives accuracy to ~1.5%

in Red band,

SDSU Refined APICS model shows that the S2B Absolute Calibration is generally well within 1.0% for all bands, except Red band with 1.5%

All available data from July 2017 – July 2018: 29 images

Sentinel 2B – MSI-B CA Blue Green Red NIR SWIR1 SWIR2

Avg, Measure 0.2298 0.2543 0.3349 0.4724 0.5829 0.6789 0.6009

Avg, Model 0.2320 0.2520 0.3339 0.4652 0.5844 0.6838 0.6013

Diff% Meas-Model -0.93% 0.91% 0.31% 1.56% -0.27% -0.72% -0.08%

STD. of Residuals 2.25% 1.96% 1.21% 1.03% 0.92% 0.97% 2.43%

Comparison of Model Performance Across Sensors

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%Difference = 100%*(Observed - Predicted)

Predicted

• L8: all data available between April 2013 and July 2018

– OLI absolute calibration is generally within 2% for all bands

• S2A: all data available between August 2015 and July 2018

– MSI-A absolute calibration is generally within 1.2% except for Red (2.8%)

• S2B: all data available between July 2017 and July 2018

– MSI-B absolute calibration is generally within 1% for all bands except CA, Red with 1.6%

*** All 3 sensors agree very well with the APICS Model with differences between sensors are within 1% or better except Red band

*** Red band, L8 vs S2A, 1.6% difference,

L8 vs S2B, 0.3% difference,

S2A vs S2B, 1.3% difference

** Large disagreement between APICS and MSI-A Red band may be caused by the shape of RSR and narrow bandwidth when calculating TOA reflectance profile using Hyperion data.

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Summary

• S2A, S2B Processing data version 2.06 since end Nov 2017

• MSI-A and MSI-B temporal uncertainties are well within 2% for all bands.

• Cross Calibration – lifetime average (No BRDF Correction)

– Results between OLI, MSI-A and MSI-B varied on the order of 0.2% across all

comparable bands when using co-incident data and near-coincident pairs.

– The Libya4 site is “stable” with respect to a 6 day revisit period.

– Comparison between OLI and MSI-A TOA reflectance showing ~2.1% in CA band; all other bands are within 1.2% .

– Comparison between OLI and MSI-B TOA reflectance showing agreement well within 1% in all bands.

– Comparison between MSI-A and MSI-B TOA reflectance showing agreement well within 1% in all bands.

• Refined SDSU Absolute Calibration Model confirmed typical differences

on the order of 1.5% or less in nearly all bands across OLI, MSI-A and MSI-B

– Difference of approx. 2.8% observed with MSI-A Red band, due primarily to

characteristics of RSR profile.

25

Thank you!

26

ADDITIONAL SLIDES

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Landsat8 OLI: SDSU Absolute Calibration Model

109 Cloud Free scenes: from April 2013 to July 2018

CA Blue Green

Red NIR SWIR-1

28

SWIR-2

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Sentinel 2A: SDSU Absolute Calibration Model

82 Cloud Free scenes: from Aug 2015 to July 2018

CA Blue Green

SWIR2SWIR1

Red

NIR

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Sentinel 2B: SDSU Absolute Calibration Model

28 Cloud Free scenes: from July 2017 to July 2018

CA Blue Green Red

SWIR2SWIR1 NIR