PROSPECT Leaf Optical Properties Model

The PROSPECT model is a simple but effective radiative transfer model that simulates directional–hemispherical reflectance and transmittance of various green monocotyledon and dicotyledon species, as well as senescent leaves, over the solar spectrum from 400 nm to 2500 nm. It is based on the representation of the leaf as one or several absorbing plates with rough surfaces giving rise to isotropic scattering. The model uses four classes of input variables: the leaf structure parameter N (the number of compact layers specifying the average number of air/cell walls interfaces within the mesophyll); the chlorophyll a+b concentration Cab (mg cm-2), the equivalent water thickness EWT noted Cw (cm or g cm-2); and the dry matter content.

PROSPECT has been validated by iterative inversion of the model on reflectance and transmittance spectra of about sixty leaves of various species from the LOPEX database, and fourteen leaves of cereal crops (Newnham and Burt, 2001). LOPEX, an experiment conducted in summer of 1993 at the Joint Research Centre (Ispra, Italy), associated visible / infrared spectra of dry and fresh vegetation elements (leaves, conifer needles, stems, etc.) with physical measurements (thickness, water content, specific leaf area) and biochemical analyses (chlorophyll a+b, proteins, cellulose, lignin, etc.) (Hosgood et al., 1995). LOPEX was used to introduce the full leaf biochemistry into PROSPECT (Jacquemoud et al., 1996). PROSPECT generally performs well in terms of spectrum, reconstruction. The comparison between measured and estimated values of Cab, Cw, and Cm also gives satisfactory results on fresh leaves.

Hosgood, B., Jacquemoud, S., Andreoli, G., Verdebout, J., Pedrini, G. & Schmuck, G. 1995. Leaf Optical Properties EXperiment 93 (LOPEX93). European Commission, Joint Research Centre, Institute for Remote Sensing Applications, Report EUR 16095 EN.

Jacquemoud, S. & Baret, F. 1990. PROSPECT: a model of leaf optical properties spectra. Remote Sensing of Environment, 34:75-91.

Jacquemoud, S., Ustin, S.L., Verdebout, J., Schmuck, G., Andreoli, G. & Hosgood, B. 1996. Estimating leaf biochemistry using the PROSPECT leaf optical properties model. Remote Sensing of Environment, 56:194-202.

Jacquemoud, S., Bacour, C., Poilve, H. & Frangi, J.P. 2000. Comparison of four radiative transfer models to simulate plant canopies reflectance – Direct and inverse mode. Remote Sensing of Environmnent, 74:471-481.

Jacquemoud, S., Verhoef, W., Baret, F., Bacour, C., Zarco-Tejada, P.J., Asner, G.P., François, C., & Ustin, S.L. 2008. PROSPECT + SAIL models: a review of use for vegetation characterization. Remote Sensing of Environment, in press.

Recent studies based on statistical methods permitted the quantification of the contribution of each of the input parameters to the model outputs, as well as their interactions. Variation in transmittance values – it would be similar with reflectance values - are exclusively influenced by N, Cw and Cm in the near and middle infrared. As expected, water has the greatest influence with 80-90% of contribution in the absorption peaks, but N and Cm also significantly affect transmittance values within this range.