Global reprocessed Leaf Area Index (LAI) from SPOT-VGT
The LAI products derived from SPOT-VGT data, (CYCLOPES and geoland2), are globally reprocessed to provide a spatiotemporally continuous time series (as ten day composites) in spatial resolution of 1 km.
The improved Leaf Area Index is processed from SPOT-VGT products provided by Medias France (CYCLOPES, 1999 2007) and VITO (geoland2, also using the CYCLOPES-algorithms, 2010 today). For time series analysis the method of Harmonic Analysis, HA, (Bittner, 1997), modified by Niklaus et al. (2011), is used. The HA describes the annual variability of the LAI signal as superposition of single sine waves. After the dominant oscillation of the annual data is found (this might be the growing season with wavelength of half a year), it is subtracted from the full set of data. From the residual the second dominant oscillation is computed and subtracted again, and so on. While fitting the second sine function the period, amplitude and phase of the first sine function also are free parameters. This causes an important reduction of the variance of the fitted time series. This is done for further oscillations until a minimum period of six data points, representing 60 days, is reached.
We produced a global dataset of ten-day composites for the available period 1999 2007 and the year 2010, in spatial resolution of the CYCLOPES products (1 km) (Fig. 1).
For validation the results are compared to a set of LAI reference maps, provided by the VALERI and BigFoot projects (Morisette et al., 2006; Cohen et al., 2006). It shows that reprocessed SPOT-VGT LAI data correlates slightly better (0.83) with the reference map data, than the original SPOT-VGT LAI data (0.82).
The data is available as 36 global ten-day composites for LAI and one global map for NRMSE for each year of the period 1999 2007 and the year 2010. Data for the year 2011 will be available end of January, 2012.
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Bittner, M., Value adding Produkte bei GOME. Technical Report 1997, DLR Oberpfaffenhofen, 1997.
Cohen, W. B., Maiersperger, T. K., & Pflugmacher, D. (2006). BigFoot Leaf Area Index Surfaces for North and South American Sites, 2000-2003. Data set. Available on-line from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/747
Morisette, J. T., Baret, F., Privette, J. L., Myneni, R. B., Nickeson, J. E., Garrigues, S., Shabanov, N. V., Weiss, M., Fernandes, R. A., Leblanc, S. G., Kalacska, M., Sanchez-Azofeifa, G. A., Chubey, M., Rivard, B., Stenberg, P., Rautiainen, M., Voipio, P., Manninen, T., Pilant, A. N., Lewis, T. E., Iiames, J. S., Colombo, R., Meroni, M., Busetto, L., Cohen, W. B., Turner, D. P., Warner, E. D., Petersen, G. W., Seufert, G., & Cook, R. (2006). Validation of global moderate-resolution LAI products: a framework proposed within the CEOS land product validation subgroup. IEEE Transactions on Geoscience and Remote Sensing, 44, 1804-1817.
Niklaus, M., Tum, M., Günther, K. P., Bittner, M., Generation of a global, gap-free SPOT-VGT LAI dataset using spectral analysis techniques, in prep.