We determined the fluxes and concentrations of atmospheric sulfur species at ground level and from aircraft over the Amazon Basin during the 1987 wet season, providing a comprehensive description of the sulfur cycle over a remote tropical region. The vertical profile of dimethylsulfide (DMS) during the wet season was found to be very similar to that measured during the dry season, suggesting little seasonal variation in DMS fluxes. The concentrations of hydrogen sulfide (H2S) were almost an order of magnitude higher than those of DMS, which makes H2S the most important biogenic source species in the atmospheric sulfur cycle over the Amazon Basin. Using the gradient-flux approach, we estimated the flux of DMS at the top of the tree canopy. The canopy was a source of DMS during the day, and a weak sink during the night. Measurements of sulfur gas emissions from soils, using the chamber method, showed very small fluxes, consistent with the hypothesis that the forest canopy is the major source of sulfur gases. The observed soil and canopy emission fluxes are similar to those measured in temperate regions. The concentrations of SO2 and sulfate aerosol in the wet season atmosphere were similar to dry season values. The sulfate concentration in rainwater, on the other hand, was lower by about a factor of 5 during the wet season. Due to the higher precipitation rate, however, the wet deposition flux of sulfate was not significantly different between the seasons. The measured fluxes and concentrations of DMS, H2S, and SO2 were consistent with a model describing transport and chemistry of these sulfur species in the boundary layer. The concentrations of aerosol and the sulfate deposition rate, on the other hand, could only be explained by import of significant amounts of marine and anthropogenic sulfate aerosol into the Amazon Basin.

Two new polyphase pulse compression codes and efficient digital implementation techniques are presented that are very Doppler tolerant and that can provide large pulse compression ratios. One of these codes is tolerant of precompression bandwidth limitations.In previous publications [1,2], the authors introduced a new class of polyphase pulse compression codes and techniques for use in digitally coded radars. Such codes and compressors can be employed to obtain much larger time-bandwidth products (pulse compression ratios) than are feasible with analog dispersive delay lines.It is the purpose of this paper to extend this class to include two new codes, one of which is tolerant of precompression bandwidth limitation that appears in radar receivers [2]. The availability of several different codes provides a radar designer with more flexibility.These new phase codes are conceptually derived from a linear frequency modulation waveform (LFMW) and are more Doppler tolerant than other phase codes derived from a step approximation to a LFMW. By Doppler tolerant, we mean that the compressed pulse does not degrade significantly with relatively large Doppler shifts on echoes. These new phase codes also have low range-time sidelobes without amplitude weighting. Also described is an efficient technique for implementing these new phase codes in a digital pulseexpander-compressor, and performance data is presented.It should be noted that these phase codes are designed to be used both on transmission and reception to insure that the receive filter matches the transmitted waveform independent of time differences between the leading edge of the echo and a sampling pulse, i.e., independent of target range. NEW PHASE CODESThe two new phase codes will be called the P3 and P4 codes to distinguish them from the P1 and P2 codes discussed in [2]. The P3 code is not precompression bandwidth limitation tolerant but is much more Doppler tolerant than the Frank [31 or P1 and P2 codes.The P4 code is a rearranged P3 code with the same Doppler tolerance and with better precompression bandwidth limitation tolerance. P3 CODEThe P3 code is conceptually derived by converting a linear frequency modulation waveform to baseband using a local oscillator on one end of the frequency sweep and sampling the inphase I and quadrature Q video at the Nyquist rate. Letting the waveform to be coherently detected have a pulse length T and frequency f = fo + kt (1) Manuscript

The temporal characteristics of radar backscatter from the sea depend on the pulse width for surface resolutions less than about 20 m. While low-resolution backscatter appears continuously noiselike, as the resolution is increased, the backscatter is punctuated by substantially quieter periods. This results in a noticeably 'spikey' characteristic. Measurements at 3 cm using several different pulse widths have been made near grazing incidence together with synchronized television views of the radar-illuminated surface. These observations confirm that the largest backscatter is due to whitecaps. However, even the quieter periods disclose spikes, although they are about 3 orders of magnitude lower in power. A simple model of the salient scattering regions consists of a random collection of effective scattering centers which change in number with whitecap growth or decay. By comparing modeled surface realization with radar data it is concluded that the decorrelation time of the surface and scatterers within the surface are each about 10 -2 s at X band.

I suppose that most textbooks of European history or of world history—which in European textbooks is much the same thing—contain a chapter called ‘The Age of the Discoveries’, or something of the kind, which deals with the period from the fifteenth century onwards when Western Europe set about discovering the rest of the world. My subject to-day is another and earlier discovery, in which the West European was not the explorer going forth to discover the barbarian, but the barbarian discovered by the explorer—the Muslim explorer. My purpose is to outline, very briefly, the sources, nature, and stages of growth of Muslim knowledge concerning Western Europe, first in the obscure centuries before the Crusades, then during that great offensive of Western Christendom against Islam, of which the expeditions to Palestine were the easternmost expression.

A new class of symmetric radar pulse compression polyphase codes is introduced which is compatible with digital signal processing. These codes share many of the useful properties of the Frank polyphase code. In contrast with the Frank code, the new codes are not subject to mainlobe to sidelobe ratio degradation caused by bandlimiting prior to sampling and digital pulse compression. It is shown that bandlimiting the new codes prior to pulse compression acts as a waveform amplitude weighting which has the effect of increasing the mainlobe to sidelobe ratios.