Extracting information about vegetation seasons in Africa from pathfinder AVHRR NDVI imagery using temporal filtering and least-squares fits to asymmetric Gaussian functions

Lars Eklundh, Per Jönsson

Research output: Chapter in Book/Report/Conference proceedingPaper in conference proceedingpeer-review

3 Citations (SciVal)

Abstract

Time-series of NASA/NOAA Pathfinder AVHRR Land (PAL) data have been analysed to extract parameters describing the seasonality of vegetation in Africa. Two methods have been developed to fit smooth curves to the time-series. The first method is based on an adaptive Savitzky-Golay filtering technique, and the second on non-linear least-squares fits of asymmetric Gaussian model functions. Both processing methods involve a preliminary definition of the number and timing of growing seasons using a least-squares fit of sinusoidal functions and a second order polynomial. The fit to the sinusoidal functions is used to determine the type of seasonal pattern (uni-modal or bi-modal) and to obtain starting values for the non-linear Gaussian function fits to the data. The processing incorporates qualitative information on cloudiness from the CLAVR dataset. The resulting smooth curves are used for defining parameters describing the growing seasons. The method has been applied to PAL NDVI data, and resulting imagery have been generated that show parameters such as beginnings and ends of seasons, seasonal integrated NDVI, seasonal amplitudes etc. The results indicate that the two methods complement each other and that they may be suitable in different areas depending on the behaviour of the NDVI signal.
Original languageEnglish
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
PublisherSPIE
Pages215-225
Volume4885
DOIs
Publication statusPublished - 2003
EventImage and Signal Processing for Remote Sensing VII - Agia Pelagia, Greece
Duration: 2002 Sep 242002 Sep 27

Publication series

Name
Volume4885
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferenceImage and Signal Processing for Remote Sensing VII
Country/TerritoryGreece
CityAgia Pelagia
Period2002/09/242002/09/27

Subject classification (UKÄ)

  • Physical Geography

Keywords

  • Temporal filtering
  • Seasonality
  • Gaussian functions

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