An Overview of MODIS Reflective Solar Bands Calibration and Performance Jack Xiong NASA / GSFC GRWG Web Meeting on Reference Instruments and Their Traceability (June 22, 2010)

Outline MODIS Instrument Background Reflective Solar Bands Calibration On-orbit Performance For more Information on MODIS Calibration and Characterization: http://mcst.gsfc.nasa.gov/ Page 2

MODIS On-board Terra and Aqua Spacecraft 36 Spectral Bands Terra launched in December 1999 and Aqua in May 2002 MODIS follow-on: VIIRS 36 Spectral Bands 20 reflective solar bands (RSB) in VIS, NIR, and SWIR covering wavelengths from 0.41 to 2.2mm 16 thermal emissive bands in MWIR and LWIR covering wavelengths from 3.7 to 14.4mm 3 Spatial Resolutions (nadir) 250m (bands 1-2), 500m (bands 3-7), and 1km (other bands) Broad Science Applications Nearly 40 science data products for studies of the Earth’s system of land, oceans, and atmosphere Page 3

MODIS Scan Cavity and On-Board Calibrators (OBC) SD SDSM BB SRCA SV (moon) SD/SDSM, SRCA, and Lunar Observations used for RSB Calibration Page 4

MODIS Reflective Solar Bands Calibration Calibration Requirements ±2% for reflectance factors and ±5% for radiances (at typical scene radiances (Ltyp) within a ±45º scan angle range) 1% additional uncertainty for scenes from 0.3Ltyp to 0.9Lmax Calibration Algorithm and Traceability Reflectance based calibration A simple linear approach (MODIS serving as a ratioing radiometer) Sensor response corrected for instrument temperature, background, and response versus scan angle (RVS) Calibration parameters from pre-launch and on-orbit characterizations On-orbit Calibration SD and SDSM observations SRCA (spectral characterization) Lunar observations Ground targets (long-term stability, cal inter-comparison) Page 5

Calibration Algorithm EV Reflectance Solar Diffuser SRCA SDSM Blackbody BRFSD: SD pre-launch BRF DSD: SD on-orbit degradation; GSD: SD screen vignetting function d: Earth-Sun distance dn*: Digital number corrected for RVS and inst. temperature dc: Digital count of SDSM Scan Mirror Space View Page 6

MODIS RSB Calibration Traceability Reflectance based calibration referenced to SD BRF Unbroken chain of comparisons (pre-launch and on-orbit) with stated uncertainties SD BRF Characterized pre-launch with traceability to NIST reflectance scale (a scale transfer process) Tracked on-orbit by the on-board SDSM Instrument temperature effect Characterized at 3 instrument temperatures Response versus scan angle (RVS) Characterized pre-launch Monitored relative changes on-orbit SD screen vignetting function characterization Derived from observations during spacecraft yaw maneuvers Other effects Page 7

SBRS: Santa Barbara Remote Sensing BRF Characterization NIST Standard Reference Lab Secondary Standard MODIS SD BRF % SD BRF characterized at limited wavelengths, angles, and panel locations SBRS: Santa Barbara Remote Sensing Page 8

On-orbit Performance Instrument performance Changes of sensor response Changes are detector, mirror side, and scan angle dependent Large changes in VIS spectral bands SD degradation Larger degradation at shorter wavelength Signal-to-noise ratio (SNR) Continue to meet design requirements for most RSB detectors A few exceptions (noisy detectors and detectors in band 8) Spatial and spectral performance Page 9

Terra MODIS Instrument and FPA Temperatures ~3.5K increase over 10 years Warm FPA ~3.5K increase over 10 years Cold FPA extremely stable

Aqua MODIS Instrument and FPA Temperatures ~1.5K increase over 8 years Warm FPA ~1.5K increase over 8 years Cold FPA 0.1-0.2K increase in last few years

Relative Gain Changes in Terra MODIS VIS/NIR Changes are mirror side and AOI dependent; monitored for individual detectors Page 12

Relative Gain Changes in Aqua MODIS VIS/NIR Changes are mirror side and AOI dependent; monitored for individual detectors Page 13

Terra and Aqua MODIS Bands 1 and 2 Responses SD and lunar observations are made at different AOI; larger differences in VIS Page 14

Terra MODIS SD Degradation SDSM covers wavelengths from 0.41 to 0.94mm SD Door Fixed at Open SDSM covers wavelengths from 0.41 to 0.94mm Page 15

Terra and Aqua MODIS SD Degradation Terra MODIS SD degradation is much faster with its SD door fixed at “open” position Page 16

Terra MODIS Spectral Characterization

Terra MODIS Spatial Characterization Cold FPA Cold FPA

Summary Both Terra and Aqua MODIS continue to operate with satisfactory performance On-board calibrators (OBC) continue to provide the “designed” functions RSB calibration uses SD/SDSM, lunar observations, and ground targets Large changes in VIS spectral bands Challenges Changes in RVS and polarization sensitivities for VIS spectral bands On-orbit spatial and spectral performance remains stable Dedicated effort from MODIS calibration support team with regular input from and communication with science team representatives Page 19

References: Xiong X, J. Sun, X. Xie, W. Barnes, and V. Salomonson, “On-Orbit Calibration and Performance of Aqua MODIS Reflective Solar Bands,” IEEE Transactions on Geoscience and Remote Sensing, Vol. 48 No. 1, 535-546, 2010 Xiong X, J. Sun, W. Barnes, V. Salomonson, J. Esposito, H. Erives, and B. Guenther, “Multi-year On-orbit Calibration and Performance of Terra MODIS Reflective Solar Bands,” IEEE Transactions on Geoscience and Remote Sensing, Vol. 45, No. 4, 879-889, 2007 Xiong X and J. Butler, “MODIS Solar Reflective Calibration Traceability,” Proceedings of SPIE - Earth Observing Systems XIV , Vol. 7452, 74520K, doi: 10.1117/12.824761, 2009 Xiong X, J. Sun, A. Wu, K. Chiang, J. Esposite, and W.L. Barnes, “Terra and Aqua MODIS Calibration Algorithms and Uncertainty Analysis,” Proceedings of SPIE – Sensors, Systems, and Next Generation of Satellites IX, 5978, 59780V, doi:10.1117/12.627637, 2005 Xiong X, N. Che, and W.L. Barnes, “Terra MODIS On-orbit Spectral Characterization and Performance”, IEEE Transactions on Geoscience and Remote Sensing, Vol. 44, No. 8, 2198-2206, 2006 Sun J, X. Xiong, W. Barnes, and B. Guenther, “MODIS Reflective Solar Bands On-orbit Lunar Calibration,” IEEE Transactions on Geoscience and Remote Sensing, Vol. 45, No. 7, 2383-2393, 2007 Page 20

Backup slides

MODIS Specifications and Applications 20 reflective solar bands (RSB: bands 1-19, and 26) from 0.41 - 2.2mm 16 thermal emissive bands (TEB: bands 20-25, 27-36) from 3.5 - 14.4mm Page 22

Spatial and spectral characterization Spatial mode Frame -> x Spectral mode Grating step -> q Page 23