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LAI estimation of wheat fields from MERIS and ASAR data

Giuseppe Satalino(1), Francesco Mattia(1), Anna Balenzano(1), Laura Dente(2) and Michele Rinaldi(3)

(1) CNR-ISSIA, Via Amendola, 122/D, 70126 Bari, Italy
(2) ITC, Hengelosestraat 99, 7511AA Enschede, Netherlands
(3) CRA-SCA, Via Celsio Ulpiani, 5, 70125 Bari, Italy

Abstract

The possibility of estimating Leaf Area Index (LAI) over large areas and at relatively low costs by remote sensing techniques is appealing for a variety of applications. For example, the monitoring of LAI during the crop growth cycle is crucial to obtain improved yield predictions (Dente et al., 2008). To date, LAI is principally estimated by relationships with vegetation indexes extracted from visible and near-infrared (VIS-NIR) remote sensed data (Mynemi et al., 1995). However one important inconvenient of using VIS-NIR data is that the presence of clouds over the area of interest prevents to obtain LAI estimates. This is particularly troublesome for winter crops when the lack of data can occur during the growth stages. Synthetic Aperture Radar (SAR) sensors may circumvent this problem because, at microwave frequencies, the surface backscatter is independent on cloud cover, though it is sensitive to vegetation canopy and soil parameters. For instance, in recent works (Mattia et al., 2003; Brown et al., 2003) strong relationships between the radar HH/VV backscatter ratio, acquired at C-band and 40ยบ incidence angle, and wheat fresh biomass and LAI were found. Using this approach, maps of LAI at watershed scale were obtained on the Matera site, Southern Italy, and validated through in situ measurements at field scale (Dente et al., 2005).

The objective of this work is to assess the accuracy of LAI maps derived from ENVISAT MERIS and ASAR data over two agricultural areas, mainly devoted to wheat cultivation. The methodology consists of comparing wheat LAI maps, retrieved from MERIS data, with those retrieved from ASAR Alternating Polarization (AP) data. The latter were preliminary validated, at field scale, by means of in situ data. LAI maps derived from MERIS data were estimated by the algorithm referred to as TOA_VEG (Baret et al., 2005), implemented in the BEAM software (Brockmann, 2005), whereas LAI maps derived from ASAR data were obtained by means of the empirical expression found in (Mattia et al., 2005).

The experimental sites are two agricultural areas located in the Basilicata and Puglia region, respectively. On these areas, temporal series of ENVISAT MERIS and ASAR Alternating Polarization data were acquired during the 2004, 2006, and 2007 growing seasons. Moreover, coincidentally with remote sensing acquisitions, ground data were intensively collected in the framework of two experimental campaigns (Dente et al., 2008; Rinaldi et al., 2007).

Acknowledgment: The authors wish to thank ESA for supply of MERIS and ASAR data in the framework of ENVISAT AO 662.

References

- Baret F., K. Pavageau, C. Bacour, D. Beal, M. Weiss, V. Bruniquel, and P. Regner (2005), Algorithm Theoretical Basis Document for MERIS Top of Atosphere Land Products (TOA_VEG), Feb. 2005, INRA-Novelties, on http://www.brockmann-consult.de/beam/plugins.html.

- Brockmann C. (2005), BEAM software, http://www.brockmann-consult.de/beam.

- Brown S. C. M., S. Quegan, K. Morrison, J. C. Bennett, G. Cookmartin (2003), High-Resolution Measurements of Scattering in Wheat Canopies: Implications for Crop Parameter Retrieval, IEEE Transaction on Geoscience and Remote Sensing, vol. 41 (7), 1602-1610.

- Dente L., G. Satalino, F. Mattia, M. Rinaldi, (2008), Assimilation of ASAR and MERIS data into CERES-Wheat model to estimate yield maps, Remote Sensing of Environment, 112 (2008), pp. 1395-1407, doi:10.1016/j.rse.2007.05.023.

- Dente L., M. Rinaldi, F. Mattia, G. Satalino (2005), Retrieval of Wheat LAI and Yield Maps from ENVISAT ASAR AP Data: Matera Case Study, Proceedings of The International Conference on Earth Observation for vegetation monitoring and water management, Napoli, 10-11 November 2005.

- Mattia F., L. Dente, G. Satalino, T. Le Toan (2005) Sensitivity of ASAR AP data to wheat crop parameters, Proc. of 2004 ENVISAT & ERS Symposium, Salzburg, Austria, ESA SP-572, CDROM, 2005.

- Mattia F., T. Le Toan, Ghislain Picard, F. Posa, A. D'Alessio, C. Notarnicola, A. M. Gatti, M. Rinaldi, G. Satalino, G. Pasquariello (2003), Multitemporal C-Band Radar Measurements on Wheat Fields, IEEE Trans. on Geosc. and Rem. Sens.,41, (7), 1551-1560.

- Mynemi R. B., F. G. Hall, P. J. Sellers, and A. L. Marshak (1995), The interpretation of spectral vegetation indexes, IEEE Trans. on Geosc. and Rem. Sens., 33 (2), 481-486.

- Rinaldi M., P. Campi, M. Castellini, R. M. Ferrara, C. Fiorentino, P. Garofalo, G. Satalino, "AQUATER Project: the Measurement Campaign in Capitanata Plain of Soil-Plant-Atmosphere Continuum," Proc. of the 5th Int. Symp. on Retrieval of Bio- and Geophysical Parameters from SAR Data for Land Applications, Bari, Italy, Sept. 25-28, 2007.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry