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Remote Sensing and Image Processing: 9
Dr. Hassan J. Eghbali
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• Application– Remote sensing of terrestrial vegetation and the global
carbon cycle
Today…..
Dr. Hassan J. Eghbali
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Why carbon?
CO2, CH4 etc.greenhouse gasesImportance for understanding (and Kyoto etc...)Lots in oceans of course, but less dynamic AND less prone to anthropogenic disturbance
de/afforestationland use change (HUGE impact on dynamics)Impact on us more direct
Dr. Hassan J. Eghbali
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The Global Carbon Cycle (Pg C and Pg C/yr)
Atmosphere 730Accumulation + 3.2
Fossil fuels &cement production 6.3
Net terrestrialuptake 1.4
Net oceanuptake 1.7
Fossil organic carbon and minerals
Ocean store 38,000
Vegetation 500Soils & detritus 1,500
Runoff 0.8
Atmosphere ocean exchange 90
Atmosphere land exchange 120
Burial 0.2
(1 Pg = 1015 g)Dr. Hassan J. Eghbali
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CO2 – The missing sink
Dr. Hassan J. Eghbali
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CO2 – The Mauna Loa record
Dr. Hassan J. Eghbali
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Why carbon??
Thousands of Years (x1000)
180 ppm
280 ppm
Dr. Hassan J. Eghbali
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Why carbon?
• Cox et al., 2000 – suggests land could become huge source of carbon to atmosphere • see http://www.grida.no/climate/ipcc_tar/wg1/121.htm
Dr. Hassan J. Eghbali
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Why vegetation?
• Important part of terrestrial carbon cycle• Small amount BUT dynamic and of major
importance for humans – vegetation type (classification) (various) – vegetation amount (various) – primary production (C-fixation, food) – SW absorption (various) – temperature (growth limitation, water) – structure/height (radiation interception, roughness -
momentum transfer)
Dr. Hassan J. Eghbali
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Appropriate scales for monitoring
• spatial: – global land surface: ~143 x 106 km – 1km data sets = ~143 x 106 pixels – GCM can currently deal with 0.25o - 0.1o
grids (25-30km - 10km grid)
• temporal: – depends on dynamics – 1 month sampling required e.g. for crops
Dr. Hassan J. Eghbali
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So…… • Terrestrial carbon cycle is global• Temporal dynamics from seconds to millenia• Primary impact on surface is vegetation / soil system• So need monitoring at large scales, regularly, and
some way of monitoring vegetation……• Hence remote sensing….
– in conjunction with in situ measurement and modelling
Dr. Hassan J. Eghbali
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Back to carbon cycle Seen importance of vegetation
Can monitor from remote sensing using VIs (vegetation indices) for example
Relate to LAI (amount) and dynamics
BUT not directly measuring carbon at all…. So how do we combine with other measures
Dr. Hassan J. Eghbali
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Vegetation and carbon We can use complex models of carbon cycle
Driven by climate, land use, vegetation type and dynamics, soil etc.
Dynamic Global Vegetation Models (DGVMS)
Use EO data to provide…. Land cover Estimates of “phenology” veg. dynamics (e.g. LAI) Gross and net primary productivity (GPP/NPP)
Dr. Hassan J. Eghbali
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Basic carbon flux equations
• GPP = Gross Primary Production – Carbon acquired from photosynthesis
• NPP = Net Primary Production– NPP = GPP – plant respiration
• NEP = Net Ecosystem Production– NEP = NPP – soil respiration
Dr. Hassan J. Eghbali
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Basic carbon flux equations
• Units: mass/area/time– e.g. g/m2/day or mol/m2/s
• Sign: +ve = uptake – but not always!– GPP can only have one sign
Dr. Hassan J. Eghbali
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Dynamic Vegetation Models (DVMs)
• Assess impact of changing climate and land use scenarios on surface vegetation at global scale
• Couple with GCMs to provide predictive tool
• Very broad assumptions about vegetation behaviour (type, dynamics)
Dr. Hassan J. Eghbali
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Max Evaporation
Soil Moisture
Litter
Transpiration
Soil Moisture
LAI
Soil C & N NPPSoil
Moisture H2O30
Phenology
Hydrology NPP
Century Growth
e.g. SDGVM (Sheffield Dynamic Global Veg. Model – Woodward et al.)
Dr. Hassan J. Eghbali
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Potentials for integrating EO data• Driving model
– Vegetation dynamics i.e. phenology
• Parameter/state initialisation– E.g. land cover and vegetation type
• Comparison with model outputs– Compare NPP, GPP
• Data assimilation– Update model estimates and recalculate
Dr. Hassan J. Eghbali
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Parameter initialisation: land cover
EO derived land cover products are used to constrain the relative proportions of plant functional types that the
model predicts
evergreen forest
deciduous forest
shrubsgrasses crops
Land cover
PFTs
Dr. Hassan J. Eghbali
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Parameter initialisation: phenology
Day of year of
green-upSpring crops
Green up
Senescence
green-up occurs when the sum of growing degree days above some threshold temperature t is equal to n
Dr. Hassan J. Eghbali
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•MODIS Phenology 2001 (Zhang et al., RSE)
•Dynam. global veg. models driven by phenology
•This phenol. Based on NDVI trajectory....
greenup maturity
senescence dormancy
DOY 0
DOY 365
Dr. Hassan J. Eghbali
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Model/EO comparisons: GPPSimple models of carbon fluxes from EO data exist and thus provide a point of comparison between more complex models (e.g. SDGVM) and EO data e.g. for
GPP = e.fAPAR.PAR
e = photosynthetic efficiency of the canopy
PAR = photosynthetically active radiation
fAPAR = the fraction of PAR absorbed by the canopy (PAR.fAPAR=APAR)
Dr. Hassan J. Eghbali
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Model/EO comparisons: GPP
Dr. Hassan J. Eghbali
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Model/EO comparisons: NPP
Dr. Hassan J. Eghbali
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Summary: Current EO data Use global capability of MODIS, MISR,
AVHRR, SPOT-VGT...etc. Estimate vegetation cover (LAI) Dynamics (phenology, land use change etc.) Productivity (NPP) Disturbance (fire, deforestation etc.)
Compare with models and measurements AND/OR use to constrain/drive models
Dr. Hassan J. Eghbali
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Dr. Hassan J. Eghbali
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Future? OCO, NASA 2007
•Orbiting Carbon Observatory – measure global atmospheric columnar CO2 to 1ppm at 1x1 every 16-30 days
•http://oco.jpl.nasa.gov/index.html
Dr. Hassan J. Eghbali
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Future? Carbon3D 2009?
http://www.carbon3d.uni-jena.de/index.html
Dr. Hassan J. Eghbali
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Future? Carbon3D? 2009?
Dr. Hassan J. Eghbali
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