MODIS On-orbit Calibration Methodologies Jack Xiong and Bill Barnes NASA/GSFC, Greenbelt, MD 20771, USA University of Maryland, Baltimore County, Baltimore MD, 21250, USA (Support provided by entire MCST Analysts Team) CEOS-IVOS at ESA / ESTEC, Noordwijk, Netherlands (12-14 October, 2004)
Outline Introduction Instrument background MODIS On-orbit Calibration Methodologies (performance examples included) Overview of MODIS on-orbit calibration and characterization Radiometric calibration of reflective solar bands (RSB) Radiometric calibration of thermal emissive bands (TEB) Spectral characterization (RSB only) Spatial characterization (RSB and TEB) Challenging Issues Summary Page 2
Introduction The MODerate Resolution Imaging Spectroradiometer (MODIS) is the keystone instrument for the NASA s Earth Observing System (EOS) MODIS is on both Terra and Aqua spacecraft. Terra (EOS-AM) launched on 12/18/99; Aqua (EOS-PM) launched on 05/04/02 http://terra.nasa.gov/ http://eos-pm.gsfc.nasa.gov/ Broad range of applications Land, oceans, atmosphere Close to daily global coverage Morning & afternoon observations Page 3
MODIS Characterization Support Team MODIS Science Team Leader: Vince Salomonson Land, Ocean, and Atmospheric Groups MODIS Support Teams MODIS Characterization Support Team (MCST) Science Data Support Team (SDST) MODIS Administration Support Team (MAST) MCST Responsibilities Support MODIS instrument operations Maintain and update L1B code and LUTs Design and improve algorithms; perform instrument calibration and data analysis; provide science support on instrument issues MCST Calibration Workshops (starting from pre-launch) MsWG (MODIS Sensor Working Group) Science Group Representatives and Instrument Vendor Page 4
Instrument Background Velocity Vector 2-sided Paddle Wheel Scan Mirror (10km by 2330 km swath per 1.478 sec) Day data rate = 10.6 Mbps, night data rate = 3.3 Mbps (100% duty cycle, 50% day and 50% night) 36 spectral bands Reflective solar bands (1-19, and 26) Thermal emissive bands (20-25, 27-36) 3 nadir spatial resolutions 250m (1-2), 500m (3-7), and 1km (8-36) On-Board Calibrators: Solar diffuser (SD) SD stability monitor (SDSM) Blackbody (BB) Spectroradiometric calibration assembly (SRCA) Space View (SV) Page 5
MODIS Optics System OPTICAL SYSTEM SCAN TRACK BAND 12 11 9 3 4 7 15 VIS VIS FOCAL PLANE 14 SWIR/MWIR FOCAL PLANE SCAN SCAN 19.371 TRACK TRACK BAND 12 11 9 3 4 7 15 15 15 15 BAND 12 11 9 3 4 7 15 15 15 15 LWIR FOCAL PLANE 5.5 14 TRACK SCAN BAND 19 14 12 2 1 14 15 16 17 19.371 NIR FOCAL PLANE S W TRACK N SCAN E Page 6
MODIS Key Specifications Primary Use Band Bandwidth 1 Spectral Land/Cloud/Aerosols Boundaries Land/Cloud/Aerosols Properties Ocean Color/ Phytoplankton/ B iogeochemistry R adiance 2 R equired Primary Use Band Bandwidth 1 Spectral SNR 3 R adiance 2 1 620-670 21.8 128 Surface/Cloud 20 3.660-3.840 0.45 (300K) 0.05 Temperature 2 841-876 24.7 201 21 3.929-3.989 2.38 (335K) 0.2 3 459-479 35.3 243 22 3.929-3.989 0.67 (300K) 0.07 4 545-565 29 228 23 4.020-4.080 0.79 (300K) 0.07 5 1230-1250 5.4 74 Atmospheric 24 4.433-4.498 0.17 (250K) 0.25 Temperature 6 1628-1652 7.3 275 25 4.482-4.549 0.59 (275K) 0.25 7 2105-2155 1 110 Cirrus Clouds Water Vapor 26 1.360-1.390 6 150 3 8 405-420 44.9 880 27 6.535-6.895 1.16 (240K) 0.25 9 438-448 41.9 838 28 7.175-7.475 2.18 (250K) 0.25 10 483-493 32.1 802 Cloud Properties 29 8.400-8.700 9.58 (300K) 0.05 11 526-536 27.9 754 Ozone 30 9.580-9.880 3.69 (250K) 0.25 12 546-556 21 750 Surface/Cloud 31 10.780-11.280 9.55 (300K) 0.05 Temperature 13 662-672 9.5 910 32 11.770-12.270 8.94 (300K) 0.05 14 673-683 8.7 1087 Cloud Top Altitude 33 13.185-13.485 4.52 (260K) 0.25 15 743-753 10.2 586 34 13.485-13.785 3.76 (250K) 0.25 R equired NE!T(K) 4 Atmospheric Water Vapor 16 862-877 6.2 516 35 13.785-14.085 3.11 (240K) 0.25 17 890-920 10 167 36 14.085-14.385 2.08 (220K) 0.35 18 931-941 3.6 57 1 Bands 1 to 19 are in nm; Bands 20 to 36 are in µm 19 915-965 15 250 2 Spectral R adiance values are (W/m 2 -µm-sr) 3 SNR = Signal-to-noise ratio 4 NE! T = Noise-equivalent temperature difference Page 7
MODIS On-orbit Calibration Methodologies and Performance Overview of MODIS on-orbit calibration and characterization On-orbit calibration schematic Page 8
On-orbit Calibration Schematic SDSM Solar Diffuser SDSM SRCA Blackbody Scan Mirror Space View Moon BB w arm-up/cool-dow n, quarterly SD/SDSM, w eekly (bi-w eekly) SRC A radiometric, monthly Lunar calibration, monthly (S/C roll maneuvers) Page 9
MODIS On-orbit Calibration Methodologies and Performance Overview of MODIS on-orbit calibration and characterization On-orbit calibration schematic Radiometric calibration of reflective solar bands (RSB) On-board solar diffuser (SD) and solar diffuser stability monitor (SDSM) Lunar observations Page 10
RSB Calibration Using SD/SDSM Reflectance factor *! EV " cos (# EV ) = m 1 " dn EV Sun 2 "d Earth$Sun 1.44% Screen Optional 7.8% Screen! = SD dc dc SD Sun SDSM m 1 = ( ) BRF SD!cos " SD * 2! $ < dn SD >!d SD! % SD Earth # Sun Δ SD : SD degradation factor; Γ SD : SD screen vignetting function d: Earth-Sun distance dn*: Corrected digital number dc: Digital count of SDSM Scan Mirror SD Page 11
MODIS RSB Calibration Using the Moon m 1 = SD Calibration ( ) BRF SD!cos " SD * 2! $ < dn SD >!d SD! % SD Earth # Sun m 1 = Moon Calibration f (view _ geometry) * < dn Moon > Why and How? f = f phase!angle " f libration " f over! sampling 2 2 d Sun!Moon " d Modis!Moon Page 12
Terra RSB (B9 and B17) Response Trending Band (wavelength), Detector, and Mirror Side Dependent Calibration 9 % MS1 12 % MS2 Page 13
Terra and Aqua RSB Response Trending Wavelength dependent B8 at 412nm, B17 at 905nm 11.2 38 Noticeable mirror side difference (Terra) 50.2 AOI dependent Aqua MODIS: less degradation Little mirror side difference (Terra) Page 14
Terra and Aqua SD degradation Trending m 1 = ( ) BRF SD!cos " SD * 2! $ < dn SD >!d SD! % SD Earth # Sun! = SD dc dc SD Sun SD door fixed at open with SD screen in place Similar SD Degradation for Both Terra and Aqua MODIS Page 15
MODIS On-orbit Calibration Methodologies and Performance Overview of MODIS on-orbit calibration and characterization On-orbit calibration schematic Radiometric calibration of reflective solar bands (RSB) On-board solar diffuser (SD) and solar diffuser stability monitor (SDSM) Lunar observations Radiometric calibration of thermal emissive bands (TEB) On-board Blackbody (BB) Page 16
MODIS TEB Calibration Using Blackbody Radiance (TOA), L EV RVS EV! L EV + ( RVS SV " RVS EV )! L SM 2 = a 0 + b 1! dn EV + a 2! dn EV RVS: Response Versus Scan-angle ε: Emissivity L: Spectral band averaged radiance dn: Digital count with background corrected Calibration coefficient, b1, from BB RVS BB!" BB! L BB + RVS SV # RVS BB 2 = a 0 + b 1! dn BB + a 2! dn BB ( )! L SM + RVS BB!( 1 # " BB )!" cav! L cav b 1 Page 17
MODIS TEB Calibration Using Blackbody BB from 270-315K provides a0 and a2 BB at T_BB provides b1 on a scan-by-scan basis Page 18
Terra MODIS TEB Response Trending Page 19
Aqua MODIS TEB Response Trending Page 20
MODIS On-orbit Calibration Methodologies and Performance Overview of MODIS on-orbit calibration and characterization On-orbit calibration schematic Radiometric calibration of reflective solar bands (RSB) On-board solar diffuser (SD) and solar diffuser stability monitor (SDSM) Lunar observations Radiometric calibration of thermal emissive bands (TEB) On-board Blackbody (BB) Spectral characterization (RSB only) On-board Spectro-radiometric calibration assembly (SRCA) Page 21
MODIS Spectral Calibration Using SRCA Exit slit Didymium filter SRCA COLLIMATOR Calibration SiPD Reference SiPD Focusing mirror Collimating mirror Grating Motor MONOCHROMATOR Entrance slit Integration sphere Filter wheel LIGHT SOURCE To MODIS scan mirror Grating Equation 2A! = $ sin( " + " ) $ cos # m grating offset half _ angle Self-calibration using didymium filter peaks Page 22
On-orbit Terra MODIS (B3, B4, B8, and B9) Relative Spectral Response (RSR) Terra MODIS, Band 3 Terra MODIS, Band 4 RSR 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.450 0.455 0.460 0.465 0.470 0.475 0.480 0.485 Prelaunch 2000061 2001099 2002109 2003125 2004028 RSR 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.535 0.540 0.545 0.550 0.555 0.560 0.565 0.570 Prelaunch 2000061 2001099 2002109 2003125 2004028 Wavelength ( µ m) Wavelength ( µ m) RSR Terra MODIS, Band 8 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.398 0.402 0.406 0.410 0.414 0.418 0.422 0.426 Wavelength ( µ m) Prelaunch 2000061 2001099 2002109 2003125 2004028 RSR 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Terra MODIS, Band 9 0.432 0.436 0.440 0.444 0.448 0.452 Wavelength ( µ m) Prelaunch 2000061 2001099 2002109 2003125 2004028 Page 23
Terra and Aqua MODIS RSB (λ<1µm) On-orbit Band Center Wavelength Shift Terra Aqua yyyyddd Band Cneter wavelength ( µm) 2000061 2001099 2002109 2003125 2004112 2002171 2003118 2004118 1 0.6463 0.4 0.2 0.2 0.2 0.2 0.2 0.5 0.4 2 0.8564 0.5 0.0 0.2 0.0-0.1 0.8 1.2 1.2 3 0.4657 0.2 0.0 0.0-0.1-0.1 0.1 0.0 0.0 4 0.5537 0.2-0.1 0.0-0.1-0.1 0.0 0.1 0.1 8 0.4119-0.5-0.7-0.6-0.5-0.5 0.1 0.3 0.3 9 0.4422-0.2-0.4-0.5-0.5-0.5 0.1 0.1 0.2 10 0.487-0.2-0.3-0.4-0.5-0.4 0.1 0.1 0.1 11 0.5298 0.0-0.2-0.3-0.3-0.3 0.0 0.1 0.0 12 0.5469 0.2-0.1-0.1-0.2-0.2 0.1 0.2 0.1 13 0.6657 0.1-0.1-0.3-0.3-0.2 0.1 0.1 0.2 14 0.6769 0.3 0.0-0.1-0.1-0.1 0.2 0.2 0.2 15 0.7465 0.0-0.2-0.3-0.3-0.2 0.1 0.2 0.1 16 0.8664-0.1-0.4-0.5-0.4-0.4 0.1 0.1 0.1 17 0.9042 0.1-0.1-0.1-0.1 0.0 0.2 0.2 0.1 18 0.9357-0.1-0.4-0.6-0.6-0.4 0.1 0.0 0.1 19 0.9363 0.1 0.0-0.2-0.4-0.1 0.2 0.5 0.4 Page 24
MODIS On-orbit Calibration Methodologies and Performance Overview of MODIS on-orbit calibration and characterization On-orbit calibration schematic Radiometric calibration of reflective solar bands (RSB) On-board solar diffuser (SD) and solar diffuser stability monitor (SDSM) Lunar observations Radiometric calibration of thermal emissive bands (TEB) On-board Blackbody (BB) Spectral characterization (RSB only) On-board Spectro-radiometric calibration assembly (SRCA) Spatial characterization (RSB and TEB) On-board Spectro-radiometric calibration assembly (SRCA) Page 25
MODIS Spatial Calibration Using SRCA Along-track Along-scan Reticles x( b, ch) = N x " x= 0 N dn( b, ch, x)! x x " x= 0 dn( b, ch, x) Mirror Entrance opening IR source To MODIS Integration sphere Beam -splitter in filter wheel Page 26
1 2 3 4 5 6 7 8 9 10 1 1 1 1 1 1 1 1 1 20 2 2 2 2 2 2 2 2 2 30 3 3 3 3 3 3 3 3 3 40 4 4 4 4 4 4 4 4 4 50 5 5 5 5 5 5 5 5 5 60 MODIS Spatial Calibration Using SRCA dn 400 350 300 250 200 150 100 50 0 Terra SRCA signal for each individual phase-delay Band 8 channel 5 PD_0 PD_1 PD_2 PD_3 PD_4 Not in use PD_5 Along-Scan Examples Phase-delay introduced dn 400 350 300 250 200 Terra SRCA signal combined from all phase-delays Band 8 channel 5 x( b, ch) = N x " x= 0 N dn( b, ch, x)! x x " x= 0 dn( b, ch, x) 150 100 50 0 0 1 2 3 4 5 6 7 8 9 10 11 X Page 27
Challenging Issues No valid pre-launch measurements for Terra MODIS TEB RVS At-launch RVS derived from witness sample reflectance and parameters from Aqua MODIS RVS measurements C-NAD relative RVS to improve imagery DSM RVS to improve radiometry SDSM sun view signal ripples caused by a design error Modeling and simulation Alternative approach Terra MODIS PC optical leak Lunar observation SWIR crosstalk (thermal leak and electronic crosstalk) Improvement with a linear correction algorithm Additional calibration error and striping Page 28
Challenging Issues Tracking RSB response change Mirror side, wavelength, AOI dependent (on-orbit RVS) SD calibration uncertainty (impact on ocean) RSB BRF pre-launch characterization uncertainty (spatial non-uniformity can cause annual oscillation in response trending) No SD vignetting function characterized pre-launch (Yaw maneuvers) Noisy detectors (additional error and striping) Earthshine impact (0.2%) MWIR crosstalk (electronic crosstalk) B21 calibration Polarization sensitivity change (ocean color) Page 29
Summary Instruments performed better than overall design specifications Terra (+4.5 years) and Aqua (+2.0 years) Constant calibration and characterization efforts Thermal Emissive Bands (16 bands and 160 detectors) Terra MODIS Stable short-term and long-term response trending (excluding sensor configuration change and instrument reset events) 20 (10 from pre-launch, B36) noise detectors and 0 inoperable detectors Aqua MODIS (similar and better) Better response trending than Terra MODIS 1 (1 from pre-launch) noise detectors and 0 inoperable detectors Page 30
Summary Reflective Solar Bands (20 bands and 330 detectors) Terra MODIS Noticeable optics degradation (wavelength dependent, mirror side, and AOI dependent) 21 (20 from pre-launch, band 7) noise detectors and 0 inoperable detectors Aqua MODIS (more stable) Noticeable optics degradation (wavelength dependent) 3 noise detectors and 15 (13 from pre-launch, band 6) inoperable detectors Stable Spectral and Spatial Performance for Both Terra and Aqua Useful Experience and Lessons Learned Terra MODIS => Aqua MODIS MODIS => NPOESS and NPP VIIRS Page 31