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Initial Assessment of VIIRS VI product with respect to heritage MODIS and AVHRR data records

Initial Assessment of VIIRS VI product with respect to heritage MODIS and AVHRR data records. prepared by Nikolay Shabanov NOAA-NESDIS-STAR, May, 2012. Contents. Product Specifications Data in this study Product analysis TOA NDVI comparison VIIRS vs. AVHRR

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Initial Assessment of VIIRS VI product with respect to heritage MODIS and AVHRR data records

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  1. Initial Assessment of VIIRS VI product with respect to heritageMODIS and AVHRR data records • prepared by NikolayShabanov NOAA-NESDIS-STAR, May, 2012

  2. Contents • Product Specifications • Data in this study • Product analysis • TOA NDVI comparison VIIRS vs. AVHRR • TOC NDVI comparison VIIRS vs. MODIS • TOC EVI comparion VIIRS vs. MODIS • Summary

  3. Data • VIIRS daily products for month of April 1-30, 2012 • Vegetation Index (VIVIO) • Surface Reflectance (IVISR) • Geolocation (GIMGO) • MODIS Terra 16 days VI composites (MOD13A2) • MODIS Terra Land cover product (MOD12Q1), LAI/FPAR 8-biomes • NOAA-18 AVHRR 7 days TOA NDVI composites • All data were gridded to common LATLON projection at 10 km resolution

  4. VIIRS VI product Quality Monitor at STAR • Intercompason of VI VIIRS-MODIS-AVHRR • Monitoring TOA NDVI, TOC NDVI and TOC EVI • Multiple metrics (TBD- maps, histograms, statistics) http://www.star.nesdis.noaa.gov/smcd/viirs_vi/Monitor.htm

  5. MODIS LAI/FPAR 8-biome Land Cover

  6. Break-up of VIIRS Overall TOC EVI QC Overall TOC EVI is “Good” if: Conf. Clear + No Glint + SZA <70deg and other misc conditions

  7. Cloud Mask

  8. Observation Geometry Extreme View/Illumination conditions degrade VI product. Example: SZA~85deg at Northern High latitudes causes unrealistic TOC EVI > 1 (cf. slide 18)

  9. TOA NDVI analysis

  10. TOA NDVI- comparison between VIIRS and NOAA-18 AVHRR Biased high VIIRS NDVI is seen both on map of difference and scatter plot

  11. TOA NDVI- comparison between VIIRS and NOAA-18 AVHRR- Time Series

  12. Clear+Pr Clear Clear+Pr Clear Needleleleaf Forests Grasses TOA NDVI as function of Biome and Cloud Mask Broadleaf Forests Savannah

  13. TOC NDVI analysis

  14. TOC NDVI- comparison between VIIRS and Terra MODIS Difference plot here Biased low VIIRS NDVI over Ndl. Forest (snow/cloud)- horizontal branch on the scatter plot (cf. slide 15)

  15. TOC NDVI- comparison between VIIRS and Terra MODIS- Time Series

  16. Clear+Pr Clear Clear+Pr Clear Needleleleaf Forests Grasses VIIRS Cloud Mask for TOC NDVI screening Broadleaf Forests Savannah

  17. Relationship between VIIRS TOA and TOC NDVI Ratio plot here Second peak on histogram corresponds to anomalously low TOC NDVI over Ndl. Forest (snow/cloud, cf. slide 13)

  18. TOC EVI analysis

  19. TOC EVI- comparison VIIRS and MODIS Difference plot here At Northern High latitudes VIIRS EVI is biased low, or have spots with anomalously high positive EVI (SZA~85deg, cf. 7)

  20. TOC EVI- comparison between VIIRS and Terra MODIS- Time Series

  21. Clear+Pr Clear Clear+Pr Clear Needleleleaf Forests Grasses VIIRS Cloud Mask for TOC EVI screening Broadleaf Forests Savannah

  22. In Red: 70<SZA<85 Impact of high SZA on TOC EVI No SZA screening With SZA screening Pixels Screened-out Difference plot here

  23. Summary • 1. Consistency VIIRS VI product with historical MODIS and AVHRR data records on a global scale through month of April, 2012: • VIIRS TOA NDVI is biased high wrt NOAA-18 AVHRR data (Mean/STD/r^2=+0.04/0.14/0.5) • VIIRS TOC NDVI is biased low wrt Terra MODIS data (Mean/STD/r^2=-0.07/0.21/0.6) • VIIRS TOC EVI is also biased low wrt Terra MODIS data (Mean/STD/r^2=-0.06/0.17/0.55) • 2. The discrepancy between products increases with value of VI- highest for Broadleaf Forest and Savannah with dense canopy cover • 3. Screening capabilities of VIIRS Cloud Mask: • 1. Daily global composites provide 60% of Confidently Clear, 20% Probably and remaining Confidently Cloudy • 2. Impact of CM is product and biome dependent: conservative screening has impact on Needle leaf Forests (all products) and Grasses (TOC NDVI only) • Indication of Cloud leakage were observed at biome level analysis of Daily Composites. However Cloud coverage overestimation is not possible to evaluate as product is set to fill values over Confidently Cloudy pixels. • 4. VI and View/Illumination Conditions: • 1. It was detected that under extreme SZA (~85deg) TOC EVI takes on unrealistic values, TOC EVI> 1 at Northern High latitudes

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