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| Titel |
Optimization of vegetation parameters through sequential assimilation of surface albedo observations |
| VerfasserIn |
G. Geppert, A. Loew |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068288
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| Zusammenfassung |
| The dynamic global vegetation model JSBACH, which is the land surface model of the
MPIÂ Earth System Model, uses cover fractions of 21 plant functional types (PFT) to
represent the vegetation in a grid box. Each PFT is described by a set of parameters and the
global distribution of PFTs allows for a spatially differentiated description of the land surface.
However, the PFT parameters are constant over time and thus neglect seasonal changes of the
described properties.
A comparison of land surface albedo estimated by JSBACH and observed land surface
albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS) shows a lack of
seasonal variability within the model results. Additionally, an analysis of leaf reflectance and
leaf transmittance in the products of the Joint Research Center Two-stream Inversion Package
indicates a seasonal cycle of these quantities which is not reflected by the constant canopy
albedo parameters of JSBACH.
To derive an appropriate set of seasonally varying canopy albedo parameters, we have set
up a flexible, sequential data assimilation framework that allows us to estimate a time series
of parameter values.
A standalone version of JSBACH including a phenology model (spatial resolution T63,
~ 1.9°; time step 30 minutes) is forced with ERA-Interim reanalysis data. The visible and
near-infrared canopy albedo parameters are perturbed to generate an ensemble that represents
their uncertainty. The Ensemble Kalman Filter is then used to update the combined state
and parameter vector according to observations every time a new observation is
available.
To configure the assimilation system and evaluate its performance, we use synthetic
observations from a control run of JSBACH with seasonally varying canopy albedo
parameters. The simulated land surface albedo of the control run is perturbed and
subsets of the data are used for the assimilation. Different subsets are generated to
represent global remote sensing and local station measurements and the results of the
assimilation are compared with respect to reproducing the parameters of the control run. |
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