Spectral Responses of Eucalyptus Trees Submitted to Natural Hydrocarbon Seepages: An Integrated Approach from Leaf- to Canopy- Scales

Transcription

1 State University of Campinas - UNICAMP Institute of Geosciences (IG) Spectral Responses of Eucalyptus Trees Submitted to Natural Hydrocarbon Seepages: An Integrated Approach from Leaf- to Canopy- Scales Lucíola Alves Magalhães Carlos Roberto de Souza Filho Wilson José Oliveira {luciola, beto@ige.unicamp.br} {wilsonjo@petrobras.com.br}

2 Introduction Objectives Conclusions Introduction The São Francisco Basin displays several gaseous hydrocarbon seeps. Among the most intensively investigated in recent years are those located in the Remanso do Fogo area (Minas Gerais State). The study area is situated between the São Francisco and Paracatu rivers and is covered by Eucalyptus spp. (Eucalyptus) plantations.

3 Introduction Objectives Conclusions Introduction Seepages at Paracatu River One of the first evidence of seeps in this region

4 Introduction Objectives Conclusions Objectives This study aims to characterize spectral modifications on eucalyptus trees induced by hydrocarbons gases at leaf and canopy scale using: Hyperspectral ProSpecTIR-VS images: collected in June 2010, 357 bands from 0.4 to 2.5 µm, 1 m spatial resolution, Portable spectrometer FieldSpec 3 Hi-Res: that formed a database of foliar spectral measurements acquired in July 2011, > 2000 bands, 0.4 to 2.5 µm. R(56)G(36)B(14) ProSpecTIR image superimposed on a Landsat image

5 Introduction Objectives Conclusions The employment of the chlorophyll a index (R807/R638) allowed the identification of spectrally anomalous areas related to geobotanical anomalies Spectir bands (b88/b53)

6 Field checking of these anomalies shows that eucalyptus trees in these areas are poorly developed, with foliage loss or simply do not tree growing. Foliage loss Not grow No stress

7 Additionally, three vegetation indices were tested: Moisture Stress Index (MSI): R1599/R819, SpecTIR bands (b221/b90) sensitive to increase leaf water content; Structure insensitive pigment index (SIPI): ((R800-R445) / (R800- R680)), SpecTIR bands (b87-b12)/(b87- b62) designed to maximize the sensitivity of the index to the ratio of carotenoids to chlorophyll, so an increase in SIPI indicate increased canopy stress; CSE: indicator of plant stress. R694/R760, Spectir bands (b65/b78).

8 A ternary composition of these indices demonstrated a lateral variation in photosynthetic pigments and leaf water content. The study area is dominated by healthy vegetation in contrast to the western portion, which showed high concentrations of gas and stressed vegetation. R(Chla) G(MSI) B(SIPI) R(Cse) G(MSI) B(SIPI)

9 An average of 256 pixels in ten points provides spectral signatures used after for a comparison with the leaf's signatures collected in situ. ROI

10 Spectral signature average of 256 pixels. Smothing at The Unscrambler X. Red: points situated in western stressed vegetation Green: points situated in eastern non-stressed vegetation.

11 Scores PCA Score Plots PC1 x PC2 PC-2 (6%) PC-1 (94%)

12 Even so that spectral responses is quite different, field observations do no show these changes as we can see in these photos Healthy Stressed

13 Scores PCA Score Plots PC1 x PC2 PC-2 (6%) PC-1 (94%)

14 PC1 Loadings - SWIR and VIS are keys to distinguish between stressed and non-to less-stressed vegetation 0,1 VIS NIR Loadings SWIR µm µm µm X-variables (PC-1) (94%) 0,3985 0,4701 0,5436 0,6197 0,6958 0,7729 0,851 0,9192 1,0075 1,1091 1,2096 1,3104 1,4098 1,5101 1,6106 1,711 1,7987 1,8992 1,9999 2,1003 2,2 2,2507 2,3516 2,4518

15 42 Leafs were analyzed in situ using the Leaf Clip: average of three leafs around each point

16 42 Spectra collected in image (ProSpecTIR data) Canopy scale. Average of 256 pixels in each point

17 Leaf Canopy

18 238% 112% Leaf Canopy Leaf spectra recorded an increase two times higher than at canopy scale when comparing the stressed vegetation with its healthy equivalent.

19 Leaf Canopy At near infrared, leaf spectra register no significant variations, while at canopy scale, a mild increase of 5% is recorded at 1.17 microns.

20 3% 73% 5% 8% 59% 172% 19% Leaf Canopy Throughout the SWIR, the increase in reflectance indicates a fall in leaf water content and biochemical compounds (lignin and cellulose) with chlorosis increasing. But changes in biochemical compounds could be observed just at leaf scale.

21 Conclusions The results derived at canopy scale were significantly similar to the spectral signatures at leaf scale, excluding the near infrared (NIR) and the end of the shortwave infrared (SWIR); The visible (VIS) region register the higher differences between stressed to non-stressed vegetation; Although the ATCOR radiometric calibration applies a non-linear interpolation at water absorption bands at canopy spectra, the results shows a high correlation with the reflectance values obtained in the field using a portable spectrometer. Changes in biochemical compounds could be registered just at leaf scale; These results support the efficient use of vegetation remote sensing in prospecting activities of hydrocarbon seepages.

22 Acknowledgements Financial support Lis Maria, Renato Rocha, Pedro Altoé Conrad Wright, Mark Landers, Chris Joyce, Rob Cushing Guilherme Brechbuhler de Pinho