presentation xu - copy

Analysing Phenological Patterns in Boreal

Forests Using MODIS Time-Series-Derived & Eddy-Covariance Flux

DataXu Teo

MSc Earth Observation & Geoinformation Management

Why?

Introduction

…and what is phenology?• Plant phenology

“..is the study of the timing of recurring biological events in plants...” (Leith, 1974)

• Allows us to assess how trees are responding to climate change through timing.

• Determined via:• Ground measurements of CO2

• Satellite measurements of Normalised Difference Vegetation Index (NDVI)

IntroductionPhenology | TimingCO2

NDVI

Research Question

How reliable are satellite derived vegetation indices (VIs) in observing forest phenological

change?

IntroductionPhenology | TimingCO2

NDVI

AimAscertain the reliability of using satellite-derived proxy indicators, together with ground-based CO2 flux data, to identify the beginning and end of the growing season as accurately as possible.

ObjectivesDetermine the Growing Season Start Date (GSSD) and Growing Season End Date (GSED) via CO2 and NDVI data.

Compare both sets of data to obtain a statistical comparison of the viability of using satellite data.

IntroductionPhenology | TimingCO2

NDVI

Where?

IntroductionMethods

Phenology | TimingCO2

NDVI

Hyytiälä, FinlandIntroductionMethods

Phenology | TimingCO2

NDVI

How?

IntroductionMethods

Phenology | TimingCO2

NDVI

Eddy Covariance: CO2

IntroductionMethods

• Measure of turbulent gas fluxes

• 10-year dataset: 2003 – 2012

• Altitude: 23 m

• Sampled at 30 minute intervals

Fine temporal resolution

Phenology | TimingCO2 | Eddy CovarianceNDVI

MODIS: NDVIIntroductionMethods

• Highly correlated to absorbed fraction of photosynthetically active radiation (PAR).

• 10-year dataset: 2003 – 2012

• 16-day intervals

• Altitude: 700 km

• Pixel resolution: 250 m

Coarse spatial resolution

Phenology | TimingCO2 | Eddy CovarianceNDVI | MODIS

250 m

250 m

IntroductionMethods

Phenology | TimingCO2 | Eddy CovarianceNDVI | MODIS

Hypothetical Flux Footprint

Tower Pixel

250 m

IntroductionMethodsResults

The story thus far?

IntroductionMethodsResults

2003 2004 2005 2006 2007

IntroductionMethodsResults

2003 2004 2005 2006 2007

IntroductionMethodsResults

Example Start:7 April (DoY: 97)

Example End:16 Oct (DoY: 289)

Start here? End here?

IntroductionMethodsResultsDiscussion

So what’s next?

Phenology | TimingCO2 | Eddy CovarianceNDVI | MODIS

What’s next?Further research to define start/end date.

Other proxy indicators:• Normalised Difference Water Index• Surface Albedo

Phenology | TimingCO2 | Eddy CovarianceNDVI | MODIS

IntroductionMethodsResultsDiscussion

To concludePhenology | TimingCO2 | Eddy CovarianceNDVI | MODIS

IntroductionMethodsResultsDiscussionConclusion

• Phenology change timing central to understanding changing climate.

• In-situ measurements (EC) and proxy indicators (NDVI) are complementary to each other.

• Challenge in identifying transition timing.

• Other possible methods available.