The conventional formulation of quantum electrodynamics in which the system develops from one spacelike hyperplane to the next is here replaced by one in which the development proceeds over null hyperplanes. For detailed study a quantized electromagnetic field Afi is chosen to interact with a quantized spin-0 particle field @ in an unquantized electromagnetic field A,& as background. If the latter is chosen to be a laser field, the @-A,& interaction permits exact closed-form solutions (Volkov) and allows the construction of wave packets which cannot be done in the usual formulation. The perturbation solution for the S matrix is thercfore conveniently based on the Furry picture. The null-plane formulation has various advantages. In particular, the gauge problem ~vhich causes difficulties in the usual theory is absent in the null-plane gauge chosen here. Since there are only two dynanlically independent components of AP, the commutation relations, field equations, gauge conditions, and vacuum definition are all mutually consistent. A natural nullplane gauge is used. Similarities and differences between this anti the conventional theory are pointed out. As an application the Compton scattering of a charged particle with a laser beam is shown to lead to an intensity-dependent frequency shift. The controversy on this issue is settled here without divergent phase factors, because our wave-packet description permits a clean separation of the particle beam from the laser.

Linear unmixing is a commonly used technique for the analysis of imaging spectrometer data. This procedure requires the use of 'endmember' spectra which represent pure target species. One of the methods under investigation at Canada Centre for Remote Sensing for the automatic extraction of endmembers from the image cube, is called the 'Iterative Error Analysis', (IEA) method. This procedure is described, and the results of its application to a data set acquired over Nevada are presented.

The optical constantsof synthetic 2H-MoS, have been determined over the range 0.05 to 3.75 eV. The absorption edge consists of two series of exciton bands due to direct allowed transitions. The Zeeman splitting and diamagnetic shift of these exciton lines are measured together with the effects of crystal confinement and temperature; the derived exciton parameters are different from those of molybdenite. Oscillatory magneto-absorption occurs a t the high energy side of each exciton series which gives a measure of the carrier masses.

The spectrum of light backscattered from the sea in the visible and near infrared and, in particular, the chlorophyll a fluorescence line at 685 nm have been observed from an aircraft under natural illumination by using a multichannel silicon diode spectrometer. The instrument was mounted in the aircraft so as to view the water surface at the Brewster angle by using a polarizer to reduce reflected skylight substantially, even under rough surface conditions. This and the relatively high red sensitivity of the silicon diode detectors explain why this line appears here but not in previous airborne observations. The observed line height has been compared with chlorophyll depth distribution measurements made from a launch and is shown to be proportional to an average of the chlorophyll concentration near the surface, weighted with depth to allow for absorption by the water of light at 685 nm. These observations were made at low (150 m) altitude, but it is shown that the observed line height is relatively insensitive to altitude up to 1200 m. Although the lowest chlorophyll concentration encountered was 2 mg/m 8, the technique is expected to be useful for airborne mapping of chlorophyll at concentrations several times smaller than this.

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