Download - Mat Disney and Shaun Quegan
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Mat Disney and Shaun Quegan
EO data assimilation in land process models
No one trusts a model except the man who wrote it; everyone trusts an observation except the man who made it (Harlow Shapley)
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Ciais et al. 2003 IGOS-P Integrated Global Carbon Observing Strategy
Geo-referenced emissions inventories
Geo-referenced emissions inventories
Atmospheric measurements
Atmospheric measurements
Remote sensing of atmospheric CO2
Remote sensing of Remote sensing of atmospheric COatmospheric CO22
Atmospheric Transport Model
Atmospheric Transport Model
Ocean Carbon Model
Ocean Carbon Model Terrestrial
Carbon ModelTerrestrial
Carbon Model
Remote sensing of vegetation properties
Growth cycleFires
BiomassRadiation
Land cover/use
Ocean remote sensingOcean colour
AltimetryWindsSSTSSS
Water column inventories
Ocean time seriesBiogeochemical
pCO2
Surface observation
pCO2
nutrients
Optimised model
parameters
Optimised model
parameters
Optimised fluxes
Optimised fluxes
Ecological studies
Biomass soil carbon
inventories
Eddy-covariance flux towers
Coastal studiesCoastal studies
rivers
Lateral fluxes
Data assimilation
link
Climate and weather fields
Geo-referenced emissions inventories
Geo-referenced emissions inventories
Atmospheric measurements
Atmospheric measurements
Remote sensing of atmospheric CO2
Remote sensing of Remote sensing of atmospheric COatmospheric CO22
Atmospheric Transport Model
Atmospheric Transport Model
Ocean Carbon Model
Ocean Carbon Model Terrestrial
Carbon ModelTerrestrial
Carbon Model
Remote sensing of vegetation properties
Growth cycleFires
BiomassRadiation
Land cover/use
Ocean remote sensingOcean colour
AltimetryWindsSSTSSS
Water column inventories
Ocean time seriesBiogeochemical
pCO2
Surface observation
pCO2
nutrients
Optimised model
parameters
Optimised model
parameters
Optimised fluxes
Optimised fluxes
Ecological studies
Biomass soil carbon
inventories
Eddy-covariance flux towers
Coastal studiesCoastal studies
rivers
Lateral fluxes
Data assimilation
link
Climate and weather fields
Concept for Global Carbon Data Assimilation System
NB carbon and water are inextricably linked, so this is a more generalised vegetation – soil – water- atmosphere scheme
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Remote sensing of atmospheric CO2
Remote sensing of Remote sensing of atmospheric COatmospheric CO22
Atmospheric Transport Model
Atmospheric Transport Model
Terrestrial Carbon Model
Terrestrial Carbon Model
Remote sensing of vegetation properties
Growth cycleFires
BiomassRadiation
Land cover/use
Optimised model
parameters
Optimised model
parameters
Optimised fluxes
Optimised fluxes
Ecological studies
Biomass soil carbon
inventories
Eddy-covariance flux towers
rivers
Lateral fluxes
Climate and weather fields
Remote sensing of atmospheric CO2
Remote sensing of Remote sensing of atmospheric COatmospheric CO22
Atmospheric Transport Model
Atmospheric Transport Model
Terrestrial Carbon Model
Terrestrial Carbon Model
Remote sensing of vegetation properties
Growth cycleFires
BiomassRadiation
Land cover/use
Optimised model
parameters
Optimised model
parameters
Optimised fluxes
Optimised fluxes
Ecological studies
Biomass soil carbon
inventories
Eddy-covariance flux towers
rivers
Lateral fluxes
Climate and weather fields
Terrestrial Component
+ Water components: SWEsoil moisture
Which model(s) should go here?
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Land process models
Land models need to deal with transfers of
- energy
- matter
- momentum
between the land surface and the atmosphere.
Three classes of land (coupled carbon-water) models: Models driven by radiation (light use efficiency models) Dynamic Vegetation Models: climate driven Simple box models
Some models emphasise hydrology (not discussed here)
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∑=
=365
1
..day
PARfAPARLUENPP
Light Use Efficiency Light Use Efficiency modelsmodels
IncomingPAR CO2
GPP
LUELUEAbsorptionfAPAR
Photo-synthesis
Respiration
NPP
The LUE may depend on biome, soil moisture, temperature, nutrients, age,
Efficiency coefficient: LUE
Measured by satellites
Modeled or measured by satellites
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Notes on LUE models
Models built by ecologists tend to focus on leaves as the functional element (e.g. Leaf Area Index).
Models built by remote sensors tend to focus on radiation.
LUE models are driven by EO data, rather than geared to assimilating data.
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Properties of DVMs
DVMs originally designed to examine long-term trends under climate change so…
Data-independent, except for varying climate data and static soil texture data
Comprehensive description of biophysics All processes internalised, parameterised Complex, non-linear, non-differentiable,
(discontinuities, thresholds) Expensive to run
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Soil texture
The Structure of a Dynamic Vegetation Model
ParametersClimate
Sn Sn+1DVM
Processes Testing
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How EO data can affect DVM calculations
Parameters
DVM
Climate
Soils
Sn Sn+1
Processes
Observable
Land coverForest age
PhenologySnow waterBurnt area
Testing:RadiancefAPAR
Possible feedback
fAPAR
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Calibration– boreal budburst
Offline setting of global parameters can be thought of as a form of DA, but is better described as model calibration.
In the following e.g, we use new EO observations that are unaffected by snow-melt to parameterise the spring warming boreal phenology model.
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Start of budburst
T0
∑days
min(0, T – T0) > Threshold, budburst occurs.
The sum is the red area. Optimise over the 2 parameters, Threshold and T0 (minimum effective temperature).
When
The SDGVM budburst algorithm
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The Date of budburst derived from minimum NDWI (VGT sensor, 2000) N. Delbart, CESBIO
Day of year
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Testing SDGVM with EO data
SDGVM can predict satellite ‘observations’ since it contains a canopy model and the concept of radiation interception
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Model “skill”
SkillBad Good
1999
SDGVM fAPAR
AVHRR NDVI
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Are derived parameters the problem?
Is the problem the SDGVM or the derived parameter from the EO signal?
The next slide shows the fAPAR derived from Seawifs (JRC) and from MODIS for a site in the UK. The large bias between the two is a general feature of these two datasets.
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Biases in derived parameters
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Assimilating products
Data Assimilation Scheme(KF, EnKF, 4DVAR, etc)
MODEL
Assumptions
Observations
Observations
Assumptions
Assumptions
For example: soil moisture from SMOS, surface
temperature, LAI from MODIS
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Low-level vs derived products
similar products give substantially different values;
assumptions used to derive products usually inconsistent with biospheric models;
Product uncertainties are poorly known Can we use low-level products (Reflectance?
BOA radiance? TOA radiance?)
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Assimilating reflectance
Data Assimilation Scheme(KF, EnKF, 4DVAR, etc)
Observations
Observations
MODEL
Assumptions
Observation Operator
Assumptions
Assumptions in the observation operator are made to be consistent
with those in the model
e.g. reflectance, backscatter, etc…
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Observation operators
This approach needs observation operators: translate ecosystem model state vector into observable properties e.g.
reflectance data assimilated into DALEC; predicting radar coherence in ERS Tandem data from
the SPA model; relating snowpack properties to SSM/I radiometer data; recognising burnt area and severity of burn.
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Which is the right model?
Complex DVM-type models never designed for DA
So, pursuing another approach with a simplified box model designed from the start for DA
– DALEC
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The Structure of a Data Assimilation Model (DALEC)
Cf
Cr
Cw
Cl
Cs
GPP
WS1
WS2
WSn
ETPpt
Q
RhRa
Stocks and fluxes of carbon (left) and water (right)
EO data (e.g. LAI, VI, reflectance)
Observation model
Ensemble Kalman
Filter
Blue lines indicate integration of EO data with DALEC
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Observation operator: simple RT model + snow
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Canopy foliage results
No assimilation
Assimilating MODIS
(bands 1 and 2)
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Canopy foliage results
Assimilating MODIS
inc. snow
Assimilating MODIS
exc. snow
Quaife, Williams, Disney et al. RSE in press
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EO land cover and carbon
Quaife, Quegan, Disney et al.,
submitted
All EO land cover the same? DGVMs use land cover indirectly
– How do we translate land cover classes to PFTs?
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EO land cover and carbon
Quaife, Quegan, Disney et al., submitted
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How do we find best model-data framework?
Use ‘God’ models to test assumptions of simpler models
– DVMs + DALEC-type models Model-data fusion inter-comparison e.g. REFLEX:
Regional Flux Estimation Experiment – www.carbonfusion.org– Compare strengths/weaknesses of various model-
data fusion techniques– Quantify errors/biases introduced when
extrapolating fluxes in both space and time using a model constrained by model-data fusion methods.
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Key issues for DA in land models 1
Models– Simple enough for effective DA but complex
enough to capture biophysics– Suitable interface with observation
operators– preferably differentiable
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Key issues for DA in land models 2
Data– Same meaning of observed parameters as used in
models– Proper characterisation of uncertainty i.e. PDFs– Use OOs to make best use of all available data e.g.
optical, LiDAR, RADAR, thermal ….
We are still searching for the best model-data structure.
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Key issues for DA in land models 3
DA through observation operators not only answer, for various practical reasons.
Also pursue general concepts of how EO data can reduce the uncertainty in land models
– Calibration, testing etc.
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Thank you
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Severity of disagreement – AVHRR/SDGVM
r > 0.497 OR r.m.s.e < 0.2
r < 0.497 AND r.m.s.e > 0.2
r < 0.497 AND r.m.s.e > 0.3
1998
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Severity of disagreement – example
Mid Europe
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Severity of disagreement – example
SW China
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Lesson
1. The DVM as currently formulated only supports a simple observation operator. This allows meaningful estimates of time series of observables; absolute values of the observables are of dubious value.
2. These time series permit the model to be interrogated with satellite data, and model failures to be identified.
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Detecting incorrect land cover
Pearson’s product moment
0.0 0.9
Crop class incorrectly set Crop class correctly set
Temporal correlation
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Lesson
Forward operators may prove a powerful tool in land cover mapping
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Impact on Carbon Calculations Impact on Carbon Calculations
Picard et al.,GCB, 2005
1 day advance: NPP increases by 10.1 gCm-2yr-1
15 days advance: 38% bias in annual NPP
Observations
Phenology modelDynamic Vegetation
Model
Carbon Calculation
calibrate
Calibrated model is unbiased,unlike methods based on NDVI
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Model needs to be region specific,Model needs to be region specific,here include chilling requirement ?here include chilling requirement ?
Comparison Model-EO: RMSE Comparison Model-EO: RMSE
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NDVI predicted by SDGVM
1998 1999
0 1 0 1
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NBP
LEACHED
Litter Disturbance
ATMOSPHERICCO2
BIOPHYSICS
Soil
Photosynthesis
GROWTH
Biomass
GPP
NPP
Thinning
Mortality
Fire
A Dynamic Vegetation Model (SDGVM)
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Assimilating reflectance
Data Assimilation Scheme(KF, EnKF, 4DVAR, etc)
MODEL
Observations
Assumptions
But how do we use a non-linear observation operator?
The real world
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May 99 August 99
Comparing model and measured fAPAR
Seawifs
SDGVM
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Model and predicted fAPAR
Average overthe whole of Europe for 1999 and 2000
Note: if SDGVM were driven by the Seawifs values, most model forests would die
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Experiments State and parameter estimation. DE1 and EV1 sites, 3
years driving data, all available obs As 1. but using synthetic data (DE2 and EV2) Within site forecasting. Another year of driving data for
DE1 and EV1, but no observations As 3. but using synthetic data (DE2 and EV2) Between site extrapolation. DE3 and EV3 sites, 4 years
driving data, MODIS LAI only
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Integrated flux predictions
Flux (gC.m-2)
Assimilated data Total
StandardDeviation
NEP
Assimilation exc. snow 373.0 151.3
Assimilation inc. snow 404.8 129.6
Williams et al. (2005) 406.0 27.8
GPP
Assimilation exc. snow 2620.3 96.8
Assimilation inc. snow 2525.6 42.7
Williams et al. (2005) 2170.3 18.1
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REFLEX data sets
“Paired” sites to test extrapolation/estimation– Brasschaat (DE2) and Vielsalm (EV2) (MF)– Hainich (DE3) and Hesse (DE1) (DBF)– Loobos (EV1) and Tharandt (EV3) (ENF)
Meteorological drivers, fluxes, MODIS LAI and stocks
– Attempting to estimate “uncertainty” in fluxes and MODIS LAI
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REgional Flux Estimation eXperiment (REFLEX)
FluxNet dataMODIS
MDF
Full analysisModel parameters
DALECmodel
Training Runs
Deciduous forest sites
Coniferous forest sites
Assimilation
Output
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REgional Flux Estimation eXperiment (REFLEX)
FluxNet dataMODIS
MDF
Full analysisModel parameters
DALECmodel
Testing site forecastswith limited EO data
MDF
MODIS
Analysis
FluxNet data
testing
Assimilation