A physical scale model of a mangrove canopy over different backgrounds was used in the laboratory to investigate the relationships between a number of spectral vegetation indices and LAI and percent canopy cover and the sensitivity of these indices to variations in background reflectance properties. High spectral resolution reflectance data were acquired from the experimental canopy and these were used to simulate the response in the red and NIR wavebands of the Landsat TM sensor. These data were then used to calculate NDVI, RVI, DVI, PVI, SAVI, SAVI2, and TSAVI. Three derivative-based indices (1DL_DGVI, 1DZ_DGVI and 2DZ_DGVI) that measure the amplitude of the chlorophyll red edge were also calculated. Based on the correlation coefficients for both LAI and percent canopy cover, the effects of background variations were most pronounced for NDVI, SAVI and TSAVI, whereas SAVI2 and RVI were moderately affected. The least affected spectral indices were DVI, PVI, 1DL_DGVI, 1DZ_DGVI and 2DZ_DGVI. The DVI appears to be the optimal spectral vegetation index for estimating the biophysical properties of mangroves which have variable background conditions because it had robust linear relationships with LAI and percent cover and it can be easily derived from commonly available broad band remotely sensed data.