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Focus Area on Phenology Product Validation


Joshua Gray, North Carolina State University, USA
Víctor Rodríguez-Galiano, University of Seville, Spain

 

Phenology Definition

Satellite-based land surface phenology (LSP) products describe the seasonal changes in vegetation greenness and photosynthetic leaf area at the landscape scale, including canopy greenup date (start of season), peak date, senescence date (end of season) and season length. The phenology metrics, however, vary from product to product and are generally based on curve-fitting and/or threshold techniques applied to a vegetation index time-series. The phenology sub-group is currently working to develop standardized definitions of these metrics that are biome-specific and both applicable and traceable to well-defined vegetation states.

Units: start of season, end of season [day of year], season length [days]


Highest Validation Stage Currently Reached for Satellite-Derived Phenology Products

Validation stage 2 (LPV validation stage hierarchy) - Independent studies have demonstrated that these products are in good agreement with in-situ measurements and metrics derived from phenology cameras. However, validation efforts thus far are limited in scope and would greatly benefit from comprehensive efforts across a globally distributed range of biomes. The phenology sub-group is working to establish a core set of sites: Type A sites with detailed spatial and temporal ground phenological observations incorporating multiple resolution scaling opportunities; and Type B sites with phenocams and good representation of measurements of citizen observations within national phenological networks.


Validation Good Practices

Land surface phenology products currently are based on various algorithms for calculating start and end of season, and seasonal length. Next steps towards the development of a validation good practices protocol include the preparation of a golden standard phenology validation database using species level field observations, in situ phenology camera observations with a standard algorithm across sites, the comparison of this golden standard with satellite-derived products, as well as applying different algorithms to the same satellite vegetation indices data series. Additionally, new products based on fluorescence signal might lead to a more concise definition of land surface phenology.


Phenology Metrics

phenology metrics slide1 phenology metrics slide2 phenology metrics slide3

 
 

Phenology Validation Reference Data Sets

Best currently available in situ reference data for satellite-derived land surface phenology product validation are provided by networks based on the following measurements:

  1. Species-specific phenological observations of bud-burst, flowering, etc.:
  2. Ground-based imaging/ continuous spectral measurements

Phenology References | Phenology Products | Phenology Collaboration

LPV Focus Areas

 

Meetings

Land Product Validation and Evolution, June 12 -14, 2023 ESA/ESRIN, Italy.

IGARRS 2023, 16-21 July 2023, Pasadena, CA. Abstract submission due 18 Nov 2022.

EGU 2023, 23-28 April 2023, Vienna, Austria. Abstract submission due 10 Jan 2023.

Phenology 2022, Phenology at the crossroads, 20-24 June 2022, Avignon, France.


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