Retrieval of forest leaf functional traits from HySpex imagery using radiative transfer models and continuous wavelet analysis

Abebe Mohammed Ali*, Andrew K. Skidmore, Roshanak Darvishzadeh, Iris van Duren, Stefanie Holzwarth, Joerg Mueller

*Corresponding author for this work

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

Quantification of vegetation properties plays an important role in the assessment of ecosystem functions with leaf dry mater content (LDMC) and specific leaf area (SLA) being two key functional traits. For the first time, these two leaf traits have been estimated from the airborne images (HySpex) using the INFORM radiative transfer model and Continuous Wavelet Analysis (CWA). Ground truth data, were collected for 33 sample plots during a field campaign in July 2013 in the Bavarian Forest National Park, Germany, concurrent with the hyperspectral overflight. The INFORM model was used to simulate the canopy reflectance of the test site and the simulated spectra were transformed to wavelet features by applying CWA. Next, the top 1% strongly correlated wavelet features with the LDMC and SLA were used to develop predictive (regression) models. The two leaf traits were then retrieved using the CWA transformed HySpex imagery and the predictive models. The results were validated using R2 and the RMSE of the estimated and measured variables.

Our results revealed strong correlations between six wavelet features and LDMC, as well as between four wavelet features and SLA. The wavelet features at 1741 nm (scale 5) and 2281 nm (scale 4) were the two most strongly correlated with LDMC and SLA respectively. The combination of all the identified wavelet features for LDMC yielded the most accurate prediction (R2 = 0.59 and RMSE = 4.39%). However, for SLA the most accurate prediction was obtained from the single most correlated feature: 2281 nm, scale 4 (R2 = 0.85 and RMSE = 4.90). Our results demonstrate the applicability of Continuous Wavelet Analysis (CWA) when inverting radiative transfer models, for accurate mapping of forest leaf functional traits.

Original languageEnglish
Pages (from-to)68-80
Number of pages13
JournalISPRS Journal of Photogrammetry and Remote Sensing
Volume122
DOIs
Publication statusPublished - Dec 2016
Externally publishedYes

Keywords

  • Continuous wavelet analysis
  • INFORM
  • LDMC
  • SLA
  • Leaf traits

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