PRESENTATION XU - Copy
Transcript of 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.