Vegetation and Biochemical Indices Retrieved from Airborne MIVIS and VIRS Hyperspectral Images of Conifer and Hardwood Forest Stands

摘要

On June 21st, 2000 the Multispectral Infrared and Visible Imaging Spectrometer (MIVIS) and the Visible Infrared Spectrometer (VIRS-200) have been mounted on a Casa 212 aircraft in order to compare the two sensors for environmental monitoring. This study relates the hyperspectral data collected over San Rossore Reserve (Pisa, Italy) by the two airborne imaging spectrometers to ground measurements of forest structure and biochemical status. The images were acquired on a total of 122 channels with a spectral resolution of up to 2.5 nm and a spatial resolution of 2.5 and 5 meters for overflights at 1500 and 3000 m, respectively. After correction for atmospheric effects, a good agreement was found between the spectra acquired by the two imaging spectrometers and at the two altitudes. An extensive field measurement campaign was carried out contextually to the flight to provide a ground truth for the airborne data. Measurements focused on 11 stands of various age, comprising both natural hardwoods and pine plantations (Pinus pinea and P. pinaster). Biophysical (stand density, basal area, height, green canopy depth and leaf area index, together with specific leaf area) and biochemical parameters (leaf water content, foliar nitrogen, carotenoids and chlorophyll concentration) were measured for each stand. Vegetation indices (VI) taken from the literature were computed from airborne reflectances and related to each parameter. Very good relationships were found between vegetation indices and biochemical compounds. Biochemical concentrations (g g~(-1)) were better correlated to VIs than biochemical contents (g m~(-2)). Pearson coefficients higher than 0.9 were found for chlorophyll, carotenoids and nitrogen concentration and for carbon-to-nitrogen ratio, whilst tissue carbon and water content had R~2 higher than 0.8.