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Chapter 8

Chapter 8. Satellite Data of Ocean Color Remote Sensing of Ocean Color Instructor: Dr. Cheng-Chien Liu Department of Earth Sciences National Cheng-Kung University Last updated: 27 April 2003. 8.1 Introduction. Outline Level Type Format Parameters Name convention Access.

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Chapter 8

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  1. Chapter 8 Satellite Data of Ocean Color Remote Sensing of Ocean Color Instructor: Dr. Cheng-Chien Liu Department of Earth Sciences National Cheng-Kung University Last updated: 27 April 2003

  2. 8.1 Introduction • Outline • Level • Type • Format • Parameters • Name convention • Access

  3. 8.1 Introduction (cont.) • Links • CZCS • Getting Started with Coastal Zone Color Scanner (CZCS) Datahttp://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/OCDST/CZCS_Starter_kit.html • SeaWiFS • Summary and Samples of SeaWiFS Operational Data Productshttp://seawifs.gsfc.nasa.gov/SEAWIFS/SOFTWARE/DATA_PRODUCTS.html • SeaWiFS Archive Product Specifications - version 4.1 - updated October 2002 http://seawifs.gsfc.nasa.gov/SEAWIFS/SOFTWARE/specs.4.1.pdf

  4. 8.1 Introduction (cont.) • Links (cont.) • MODIS • An overview of the MODIS Ocean Data productshttp://modis-ocean.gsfc.nasa.gov/dataprod.html • Ocean product informationhttp://daac.gsfc.nasa.gov/daac-bin/whom/infoscript.pl?cfg=MODIS/ocean/info.cfg

  5. 8.2 Data Level • Raw data • Data in their original packets, as received from the observer • Level 0 • Raw instrument data at original resolution, time ordered, with duplicate packets removed

  6. 8.2 Data Level (cont.) • Level 1A • Reconstructed unprocessed instrument/payload data at full resolution; any and all communications artifacts (e.g. synchronization frames, communications headers) removed • Primary output of the L1A process contains • Unconverted radiances for all detectors at all sources; • Decommutated instrument engineering and memory information; • Spacecraft ancillary data; • EOS standard metadata; • Granule-specific metadata; • Data quality information.

  7. 8.2 Data Level (cont.) • Level 1B • Level 1A data that have been processed to sensor units and radiometrically corrected and geolocated • Only Channels 1 and 2 (primary use is land/cloud boundaries) have 250-m resolution, Channels 3-7 (primary use is land/cloud properties) have 500-m resolution, and the rest have 1-km resolution. • This MODIS data product consists of: • 250 m bands calibrated data aggregated to 1 km resolution and their uncertainties • 500 m bands calibrated data aggregated to 1 km resolution and their uncertainties • 1 km bands calibrated data and their uncertainties • Subset of geolocation data • Quality Assurance and Instrument Status Metadata.

  8. 8.2 Data Level (cont.) • Level 2 • Derived geophysical variables at the same resolution and location as the Level 1 source data. • Level 3 • Variables mapped on uniform space-time grid scales, usually with some completeness and consistency.

  9. Fig 8.2.1 Fig. 8.2.1 An example of MODIS MODOCL2 Browse Image and Coordinates for 2003-APR-21 03:25:00 to 2003-APR-21 03:30:00Source: http://acdisx.gsfc.nasa.gov/data/dataset/MODIS/03_Ocean/01_Level2/index.html

  10. 8.2 Data Level (cont.) • Level 4 • Model output or results from analyses of lower level data (i.e., variables derived from multiple measurements).

  11. 8.3 Data Type • GAC (Global area coverage) • LAC (Local area coverage) • Browse

  12. 8.4 Data Format: HDF • HDF • A self-describing data format • All of the information necessary to examine the data in an HDF file is contained within the file • Developed by the National Center for Supercomputing Applications (NCSA) at the University of Illinois • To help scientists reduce the time they were spending trying to convert data sets to familiar formats and instead have more time available for actually analyzing data

  13. 8.4 Data Format: HDF (cont.) • Advantages • portability to multiple machines (i.e. platform independent) • self documented files • efficient storage of and access to large data sets • capability of storing multiple data structures or types within the same file • extensibility for future enhancements

  14. 8.4 Data Format: HDF (cont.) • Example of HDF format:

  15. 8.5 Parameters • Introduction • Three categories • Ocean color • 36 parameters, six sub-groups • Optical properties (12=5+7) • Aerosol models (2) • Fluorescence (3) • Concentrations (8) • Chlorophyll (3) • Absorption coefficients (8=3+5) • Sea surface temperature (SST) • 4 parameters • SST bulk or skin temperature of the ocean during the day or at night (4) • Ocean productivity

  16. 8.5 Parameters (cont.) • Introduction (cont.) • Resolution • Each of the forty (40) ocean color and SST parameters is associated with Products that have several time and spatial resolutions • Temporal resolution • Level 2 data are 5-minute granules • level 3 data are associated with daily, 8-daily and monthly data • Spatial resolution (4) • 1 km, 4.6-km, 36-km or 1-degree • Ocean productivity consists of two Level 4 products: weekly and yearly ocean primary productivity at 5-km spatial resolution

  17. 8.5 Parameters (cont.) • Optical properties • 12 parameters • Tau Aerosol (at 865 microns) • Epsilon (765/865) • Epsilon for Clear Water (at 531 microns) • Instantaneous PAR • Diffuse Attenuation (K 490) • Normalized Water-leaving Radiances (in seven bands from 412 to 678 microns)

  18. 8.5 Parameters (cont.) • Optical properties (cont.) • Tau aerosol, t865 • t865 atmospheric correction  LWN • Dimensionless • Only provided for cloud-free pixels (with Sun glitter below a threshold) • All valid pixels are outside a distance threshold from land

  19. 8.5 Parameters (cont.) • Optical properties (cont.) • Epsilon e78 (t765/t865) • e78t765/t865 • Dimensionless (0 ~ 1.5)

  20. 8.5 Parameters (cont.) • Optical properties (cont.) • Epsilon for clear water eclearwater • eclearwater LWN(531)/ LWN(667) • Dimensionless • Objectives • Estimate aerosol iron content • Flag suspicious LWN retrievals • Check on the Angstrom exponent

  21. 8.5 Parameters (cont.) • Optical properties (cont.) • Instantaneous PAR, Ed,PAR • Photosynthetically Available Radiation (PAR) • The total downwelling flux of photons (0-, 400-700nm) • mW cm-2 micron-1 sr-1 • Objectives of Ed,PAR • photosynthetic rate of growth of phytoplankton • primary ocean production. • LWN  Rrs  Chl-a

  22. 8.5 Parameters (cont.) • Optical properties (cont.) • Diffuse attenuation K490 • Unit: m-1 • AOP • K490 = K490 (l,z)

  23. 8.5 Parameters (cont.) • Optical properties (cont.) • Normalized water-leaving radiances LWN • 7 bands (412, 443, 490, 531, 551, 667, 678 nm) • Unit: mW cm-2 micron-1 sr-1 • LWN  Rrs  Chl-a  primary productivity • The fundamental parameters for recovering most of the MODIS ocean products

  24. 8.5 Parameters (cont.) • Aerosol Models • Two models • atmospheric correction  removal of aerosols (difficult) • A set of candidate aerosol models. • aerosol size distribution, aerosol index of refraction, assumption of spherical particle… • Two models from 16 candidate models

  25. 8.5 Parameters (cont.) • Fluorescence • Mechanism of light reaction • Application • Estimate chlorophyll concentrations and primary productivity

  26. 8.5 Parameters (cont.) • Fluorescence (cont.) • Fluorescence baseline • Unit: mW cm-2 micron-1 sr-1 • linear • Places on either side of the fluorescence peak. Created from Channel 13: LWN(667) and Channel 15: LWN(748)

  27. 8.5 Parameters (cont.) • Fluorescence (cont.) • Fluorescence line height (FLH) • The intensity of Channel 14: LWN(678) above the baseline • Unit: mW cm-2 micron-1 sr-1 • Solar-stimulated chlorophyll fluorescence  current photophysiology of phytoplankton estimate primary productivity

  28. 8.5 Parameters (cont.) • Fluorescence (cont.) • Fluorescence efficiency (FE) • Dimensionless • Quantifies the level of photosynthesis by phytoplankton

  29. 8.5 Parameters (cont.) • Application of FLH and FE • FLHChl • FEphotosynthesislevels of nutrient availability • Fig. 8.5.1 • Top vortex  spinning counterclockwise  draw nutrient-rich water upward • Bottom vortex  spinning clockwise  force water downward

  30. Fig. 8.5.1 Fig. 8.5.1 FLH and FE from the northwestern portion of the Arabian Sea, collected by MODIS on Dec. 2, 2000. Source: http://modis.gsfc.nasa.gov/about/modis_brochure.pdfImage credit: MODIS Ocean Team/Ocean Fluorescence Product, Mark Abbott, Principal Investigator, Oregon State University.

  31. 8.5 Parameters (cont.) • Concentrations • 8 parameters • CZCS pigment • Total pigment - case 1 • Suspended Solids Concentration • Pigment concentration in coccolith blooms • Coccolith concentration • Calcite concentration • Phycoerythrobilin (PEB) • Phycourobilin (PUB)

  32. 8.5 Parameters (cont.) • Concentrations (cont.) • CZCS pigment • CZCS pigment concentration • The sum of chlorophyll-a and associated degradation products. • Unit: mg m-3 • Based primarily on methods and algorithms developed for the CZCS program and refined and adapted to the MODIS bands

  33. 8.5 Parameters (cont.) • Concentrations (cont.) • Total pigment - case 1 • The sum of chlorophyll a and phaeopigment concentration • Case 1 waters: optical properties are dominated by chlorophyll and associated covarying detrital pigments • Case 2 waters: optical properties which may not covary with chlorophyll. • Other substance, such as gelbstoff, suspended sediments, coccolithophores, detritus and bacteria, change optical properties as well • Unit: mg m-3

  34. 8.5 Parameters (cont.) • Concentrations (cont.) • Suspended Solids Concentration • Ocean suspended sediments  analysis of complex bio-optical properties of coastal and estuarine regions/environments • Unit: mg m-3 • Ocean substance concentrations  productivity  global biogeochemical models  global climate models

  35. 8.5 Parameters (cont.) • Concentrations (cont.) • Pigment concentration in coccolith blooms • Unit: mg m-3 • Coccolithophores • Small marine phytoplankton • Form external calcium carbonate scales having diameters of a few microns and a thickness of 250 to 750 nm • The main source of calcium carbonate on Earth • An important part of the biogenic carbon cycle

  36. Fig. 8.5.2 Fig. 8.5.2 Two side-views of coccoliths.Source: http://www.soes.soton.ac.uk/staff/tt/eh/coccoliths.html

  37. Fig. 8.5.3 Fig. 8.5.3 Coccoliths in the Celtic SeaSource: http://earthobservatory.nasa.gov/Newsroom/NewImages/Images/PIA03441.jpg

  38. 8.5 Parameters (cont.) • Concentrations (cont.) • Coccolith concentration • This is the detached coccolith concentration • Unit: 1/m3

  39. 8.5 Parameters (cont.) • Concentrations (cont.) • Calcite concentration • This is the estimated calcite concentration due to coccoliths • Unit: mg m-3 of calcium carbonate

  40. 8.5 Parameters (cont.) • Concentrations (cont.) • Phycoerythrobilin (PEB) • Unit: mg m-3 • Phycoerythrins (藻紅素) • phycourobilin-rich (PUB) phycoerythrins • phycoerythrobilin-rich (PEB) phycoerythrins • The PUB and PEB parameters are retrieved by a sequential-convergent-iteration method, which uses five independent bands

  41. 8.5 Parameters (cont.) • Concentrations (cont.) • Phycourobilin (PUB) • Unit: mg m-3

  42. 8.5 Parameters (cont.) • Chlorophyll • Significance • A key input to the primary ocean production product • To trace oceanographic currents, jets, and plumes

  43. Fig. 8.5.4 Fig. 8.5.4 Eddies off the Queen Charlotte IslandsSource: http://earthobservatory.nasa.gov/Newsroom/NewImages/Images/QueenCharlotte_S2002164.jpg

  44. 8.5 Parameters (cont.) • Chlorophyll (cont.) • Chlorophyll MODIS • Unit: mg m-3 • The concentration of Case 1 chlorophyll in sea water • Derived using the Clark 3 or 4-band algorithm

  45. 8.5 Parameters (cont.) • Chlorophyll (cont.) • Chlorophyll-a (SeaWiFS) • Using the standard SeaWiFS "OC2" algorithm • It contains ocean chlorophyll a pigment concentration for Case 1 waters and Case 2 waters • Unit: mg m-3

  46. 8.5 Parameters (cont.) • Chlorophyll (cont.) • Chlorophyll-a (semi-analytic) • Using multiple bands in an analytic model • It contains ocean chlorophyll a pigment concentration for Case 1 waters and Case 2 waters • Unit: mg m-3

  47. 8.5 Parameters (cont.) • Absorption • Absorbed radiation by phytoplankton (ARP) • Averaged over the first optical depth • Unit: mW cm-2 micron-1 sr-1 • Critical for calculation of fluorescence efficiency (FE)

  48. 8.5 Parameters (cont.) • Absorption • Gelbstoff absorption coefficient • ag • Unit: m-1 • It is operationally defined as a of the material that can fit through a 0.2 micron filter • It is also known as yellow substance or colored dissolved organic material (CDOM) absorption

  49. 8.5 Parameters (cont.) • Absorption • Chlorophyll-a absorption • ac • Unit: m-1

  50. 8.5 Parameters (cont.) • Absorption • Total absorption • Total absorption includes absorption due to water, phytoplankton, detritus and gelbstoff • Wavelengths: 412, 433, 488, 531 and 551 nm • Valid data exist only for ocean cloud-free pixels • Unit: m-1

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