Land Data Assimilation

1. Land Data Assimilation Tristan Quaife, Emily Lines, Philip Lewis, Jon Styles.

2. Last 6 month highlights Implemented vertical heterogeneity in vegetation structure for land surface model RT schemes and observation operators Implemented a particle filter for JULES

3. Task 2.2: Vegetation Structure Task 2.3: Optical RT modelling Canopy structure

4. Typical observation operator Very simple canopy structure: Vertical homogeneity in leaf size, arrangement and reflective properties 1D-RT model of the canopy

5. PROSAIL • Calculates the diffuse and direct reflectance and transmittance of the whole canopy using: • Solar/viewing angle • Leaf area index (m2/m2) • Leaf angle distribution • Soil reflectance • Leaf reflectance/transmittance (Verhoef et al. 2007) with leaf optics model PROSPECT • Calculates the reflectance and transmittance of a single leaf using a plate model dependent on: • Internal leaf mesophyll structure • Chlorphylla+b and carotenoid content (μg/cm2) • Dry matter content (g/cm2) • Equivalent water thickness (cm) • Brown pigment (Jacquemoud & Ustin 2008) Combines 4-stream canopy model SAIL

6. Factors affecting reflectance Leaf chlorophyll concentration Leaf angle Photosynthetically active radiation (PAR) 400-700 nm Simulations using PROSAIL Leaf area index (LAI)

7. Observed vertical structure Leaves are often more upright at the top of the canopy and flatter at the bottom Higher proportion of LAI found higher in the canopy, and leaves have higher mass/unit leaf area (LMA) Leaf chlorophyll and water concentrations highest at the top of the canopy Within-crown measurements from a temperate evergreen broadleaf species Coomes et al. 2012 Whole-stand measurements from a temperate evergreen broadleaf forest Holdaway et al. 2008 Whole-stand measurements from an temperate broadleaf forest Wang & Li 2013 Assuming vertical homogeneity is often not valid for real canopies:

8. Multi-layered PROSAIL Canopy structural properties and leaf optical properties are constant within a layer Properties vary between layers to represent vertical heterogeneity SOIL

9. Multi-layered PROSAIL Rt,1 z=0 Reflectance/transmittance of two layers combined: Td,1 Tu,1 Tu,1 layer 1 Rt,2 Rt,2 Rb,1 Rb,1 Td,2 Td,2 layer 2 z=-1

10. Vertical variation in leaf angle homogeneous canopy structure decline in leaf angle with height Top of canopy Bottom of canopy

11. Variation in leaf chlorophyll homogeneous canopy structure decline in leaf chlorophyll with height Top of canopy Bottom of canopy Small decrease in reflectance in PAR region

12. Does this matter for LS models? fAPAR is key biophysical variable for calculating primary productivity Vertical structural heterogeneity affects light levels through the canopy Land surface schemes (e.g. JULES) typically account for variable nitrogen, but not leaf angle or pigment properties

13. Task 2.1: Process model development Da assimilation with jules

14. JULES

15. JULES: Carbon Budget

16. Fluxnet

17. Flux tower observations

18. Resampling Particle Filter • We have implemented a resampling particle filter for JULES • Uses the Metropolis-Hasting’s algorithm to perform the resampling • Implementation is very flexible • Requires no modification to the JULES code • Easy to adapt for different observations and different model configurations

19. Stochastic forcing • Add noise into desired state vector elements • In following examples: • Daily stochastic forcing (JULES time step = 30min) • Truncated normal distribution • Soil carbon • Soil moisture (4 vertical levels) • Easy to change all of the above characteristics

20. Resampling step α = min 1, Loop over all particles, x x* = random particle y = observations L(y|x*) L(y|x) Draw z from U(0,1) x* if z≤α xif z> α x=

21. Particle Filter

22. Non-assimilated variables

23. Pros/Cons Pros: • Fully non linear • Robust to changes in JULES • Easy to switch to other analysis schemes • e.g. Ensemble Kalman Filter Cons: • Slow: approx 5 mins/particle/year • but algorithm is inherently parallelisable

24. Next 6 months

25. Immediate Finish experiments on vertical structure and implement in JULES Write up JULES Particle Filter experiments with Fluxnetdata Initial experiments against EO data

26. Next 6 months • Further modify JULES Sellers scheme to predict viewed crown and ground (for assimilation of long wavelength data) • Build 2-stage Data Assimilation algorithm: • EOLDAS for Leaf Area temporal trajectory and other slow processes (optical data) • Particle Filter for assimilating observations related to diurnal cycle (thermal, passive microwave)

27. EOLDAS & JULES phenology • JULES phenology routine is effectively separate from the rest of the model • Used to prescribe LAI profile, but not influenced by other parts of the model state • Consequently can be optimised stand-alone • Ideal application for EOLDAS • Use modified Sellers scheme as observation operator