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A new semiempirical model to describe the bidirectional reflectance of arbitrary natural surfaces using only three parameters has been developed. This model successfully accounts for the observed variability of reflectance measurements in laboratory and field conditions, ranging from bare soil to full canopy cover, in both the visible and the near-infrared bands. Coupled with a simple atmospheric radiation transfer model, this model has been inverted against actual NOAA/advanced very high resolution radiometer (AVHRR) data from several desert sites in northern Africa. This procedure allows the retrieval of surface properties and average amounts of atmospheric constituents (aerosol optical thickness and water vapor) for the duration of the measurement period. Further work is required to expand the usability of the coupled model to other locations and shorter periods of time, but the paper demonstrates the feasibility of inverting a coupled surface-atmosphere model against existing AVHRR data and documents the current limits of this approach.1.

Absorption and scattering processes in the atmosphere affect the transfer of solar radiation along its double path between the Sun, the Earth's surface, and the satellite sensor. These effects must be taken into account if reliable and accurate information on the surface must be retrieved from satellite remote sensing data. One approach consists in characterizing the state of the atmosphere from independent observations and correcting the data with the help of radiation transfer models. This approach requires a detailed and accurate description of the composition of the atmosphere (e.g., aerosol and water vapor profiles in the case of advanced very high resolution radiometer data) at the time of the satellite overpass and requires significant computer resources. An alternative method is to attempt to simultaneously retrieve surface and atmospheric parameters by inverting a coupled surfaceatmosphere model against remote sensing data. This study describes such a coupled model and the results of its inversion against synthetic data, using a nonlinear inversion technique. The results obtained are encouraging in that realistic directional reflectances at the top of the atmosphere can be produced, and the inversion of the model against these synthetic data is capable of estimating surface and atmospheric variables. The accuracy of the retrieval is studied as a function of the amount of noise added to the data. It is shown that some surface or atmospheric parameters are easier to retrieve than others with such a coupled model, and that although it appears to be difficult to accurately and reliably estimate the water vapor amount from channel 2, there is a definite possibility of retrieving the aerosol loading from simulated channel 1 data, if the type of aerosol can be assumed.The scale, intensity, and persistence with which human activities have affected the environment and changed the composition of the atmosphere have raised questions about the sensitivity of the climate system to these perturbations and, in particular, about the likelihood of large-scale and long-term effects [Houghton et al., 1990;Jiiger and Ferguson, 1991]. The widespread concern results from the fact that these changes may be unpredictable and largely undesirable. No consensus has been reached yet in the political arena on the need to take action, or even on the extent and severity of the measures that might be adopted, except that there is general agreement on the need for a much better understanding of the processes involved and for a reduction in the uncertainties associated with current predictions.The most significant worldwide effort in this area is coordinated under aegis of the International Geosphere Biosphere Program (IGBP), also known as the Global

The effect of exogenously applied putrescine (Put) on salt stress tolerance was investigated in Panax ginseng. Thirty-day-old ginseng sprouts were grown in salinized nutrient solution (150 mM NaCl) for five days, while the control sprouts were grown in nutrients solution. Putrescine (0.3, 0.6, and 0.9 mM) was sprayed on the plants once at the onset of salinity treatment, whereas control plants were sprayed with water only. Ginseng seedlings tested under salinity exhibited reduced plant growth and biomass production, which was directly interlinked with reduced chlorophyll and chlorophyll fluorescence due to higher reactive oxygen species (hydrogen peroxide; H2O2) and lipid peroxidation (malondialdehyde; MDA) production. Application of Put enhanced accumulation of proline, total soluble carbohydrate, total soluble sugar and total soluble protein. At the same time, activities of antioxidant enzymes like superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase in leaves, stems, and roots of ginseng seedlings were increased. Such modulation of physio-biochemical processes reduced the level of H2O2 and MDA, which indicates a successful adaptation of ginseng seedlings to salinity stress. Moreover, protopanaxadiol (PPD) ginsenosides enhanced by both salinity stress and exogenous Put treatment. On the other hand, protopanaxatriol (PPT) ginsenosides enhanced in roots and reduced in leaves and stems under salinity stress condition. In contrast, they enhanced by exogenous Put application in all parts of the plants for most cases, also evidenced by principal component analysis. Collectively, our findings provide an important prospect for the use of Put in modulating salinity tolerance and ginsenosides content in ginseng sprouts.