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The incorporation of polarisation sensitive optics offers considerable potential for improving the utility of remote sensing imaging systems operating within the visible or infrared wavebands. Systems now exist allowing measurement of the four components of Stokes vector arising from each pixel in the image. In order to develop the interpretation of polarimetric images, knowledge is required of the polarised directional reflectance properties of the materials in the scene, which determine the radiation reaching the sensor. Natural vegetation forms a significant element of many scenes observed with remote sensing systems. Although the size of a leaf may be below the spatial resolution of a system, the reflectance properties of individual leaves will affect the polarimetric data observed. This paper will report the results of measurements of the linear polarised bidirectional reflectance distribution function (BRDF) from two examples of leaves. The polarimetric properties of the directional reflectance from an individual leaf will depend on the surface and volume scattering properties. We report data on two leaves representing extreme cases of the leaf structure. Laurel (prunus laurecatious) has a nacreous surface creating a gloss finish to the leaf. Mullein (verbascum thapsus) has a highly pubescent surface, creating a highly diffuse surface reflectance. Measurements of the linear polarisation BRDF are reported at 632.8nm, 1064nm, 3.39pm and 10.6µm as a function of the polar scatter angles. These wavelengths characterise the polarised reflectance from the leaves under different conditions of absorption and scattering. In both cases the body of the leaf acts a highly diffuse reflector through multiple scattering, but this mechanism is only important when the absorption by the leaf constituents is low. In the spectral regions of moderate and high absorption the surface reflectance dominates. In the case of laurel the surface is relatively smooth, with an associated Brewster angle, whereas the data suggests the layer of hair covering a mullein leaf acts as an array of scattering sources.

Since the launch of the first Sputnik in 1957, the number of space debris in orbit is progressively increasing, up to a point that is today considered serious. Scientists quickly became aware of this phenomena and started studying the evolution, mitigation, and characterization of space debris. But jurists are today confronted with a situation that the United Nations Outer Space Treaties did not foresee. The purpose of the presentation is to look at the existing international public law and examine how it may help to characterize and/or mitigate the space debris population. After having briefly described the problem caused by space debris, the first part will study the United Nations Space Treaties and in particular the principles of responsibility and liability as laid down in the 1967 Outer Space Treaty and the 1972 Liability Convention, which should allow us to conclude that there is an urgent need for a new international convention of space debris. The second part will then focus on the several proposals made concerning space debris and will lay down a set of general principles of the legislation on space debris.