A three-frequency scatterometer technique for the measurement ofocean wave spectra

A microwave technique for the measurement of ocean wave spectra has been compared with wave gauge output during extensive field testing. The method is based on the dual-frequency technique for detecting long ocean waves by matching the modulation of short waves with the beat wavelength between two transmitted microwave frequencies. The new method, however, utilizes three microwave frequencies in order to reduce mean backscatter not related to short-wave modulation. Two prototype scatterometers have been built using three frequencies at L-band and at K_u-band. Wave spectra have been measured by both radar systems which, when properly normalized, agree well with simultaneous in situ measurements taken by conventional wave gauges at the pier site. Thirteen sets of spectra have been computed, five of which correspond to a situation in which a local wind sea was generated and then decayed. The present experiment does not demonstrate the directionality of this new technique     

A DISAGGREGATE STORE-CHOICE MODEL OF SPATIAL DECISION-MAKING

Empirical testing of a decision model yields insights concerning the ways in which shoppers process information about grocery stores. Confirming hypotheses from the literature on consumer preferences, the results show that respondents are primarily concerned with quality and price of merchandise and that behavior is directly linked to derived utility measures. Clustering of the subjects discloses subtle differences among consumer groups in their approaches to evaluating the attributes of grocery stores.     

From a mountain-rural to a plains-urban society: implications of the 1981 Nepalese Census

Preliminary results of the 1981 Nepal census are analyzed as to urbanization and population movement to the Terai. Noting the substantial shift in the pattern of Nepal's population distribution occurring between 1971-81, and projecting these rates of change for the future, the paper reports a process of transformation wherein Nepal is shifting from a rural hill and mountain society to an urban-subtropical plains (Terai) state. While the flow of migrants to urban areas and the Terai region is well known, the increase in rate of change poses a serious challenge for the Nepalese government. Economic development planning must readjust its goals and assumptions to take into account the massive metamorphosis that is occurring in Nepal. Development efforts aimed at rural hill and mountain areas may need to be reevaluated in light of the changing distribution of population.     

An experimental study of a pulse compression scatterometer system

The ideal scatterometer, operating from either an aircraft or a satellite platform, should be capable of making rapid, accurate estimates of the sea backscatter cross sectionsigmaover as wide a range of grazing anglespsias possible. Efficient operation over a large range of grazing angles is desirable because 1)sigmabehavior for90deg geq psi geq 70degyields rms gravity wave slope information and is an indicator of sea state and 2)sigmabehavior for70deg geq psi geq 0degyields data on surface wind magnitude and direction as well as information about the power spectrum of the sea. A "hybrid" estimation procedure has been developed for pulse compression radars which uses both frequency and spatially decorrelated samples ofsigmato provide an unbiased estimate ofsigmahaving minimum variance over the entire range of grazing angles for which radar reception is not noise-limited.     

Using Wavelet Coherence to Characterize Surface Water Infiltration into a Low-Lying Karst Aquifer

Karstified carbonate aquifers may receive significant recharge contributions from losing streams, hence, the knowledge about surface water-groundwater (SW-GW) interactions is crucial with regard to water management (e.g., source protection zone delineation). The dynamics of SW-GW interactions may depend on factors such as the relative water levels between streams and aquifers, resulting in a temporal variation of exchange, which imposes complexity to the understanding of such dynamics. This study highlights the use of high-resolution time series and multiresolution analysis to help to gain insights into such complex dynamics. Wavelet coherence is applied on hourly time series of rainfall, stream, and spring discharges of a low-lying karstified spring catchment to yield a correlation in the time-frequency domain. This analysis provides comprehensive information on the overall impact of the river on the spring, which is supported by the cross-correlation function, as well as by more detailed information, including time-variant influences such as a threshold level of influence. Field observations of turbidity sampling at the spring appear to support this interpretation. This innovative approach relies on basic hydrological parameters, water level, or discharge, and is therefore applicable to many other systems with such existing time series.     

Borehole study of compressional and shear attenuation of basalt flows penetrated by the Brugdan and William wells on the Faroes shelf

We investigated the seismic attenuation of compressional (P‐) and converted shear (S‐) waves through stacked basalt flows using short‐offset vertical seismic profile (VSP) recordings from the Brugdan (6104/21–1) and William (6005/13–1A) wells in the Faroe‐Shetland Trough. The seismic quality factors (Q) were evaluated with the classical spectral ratio method and a root‐mean‐square time‐domain amplitude technique. We found the latter method showed more robust results when analysing signals within the basalt sequence. For the Brugdan well we calculated effective Q estimates of 22–26 and 13–17 for P‐ and S‐waves, respectively, and 25–33 for P‐waves in the William well. An effective Q_S/Q_P ratio of 0.50–0.77 was found from a depth interval in the basalt flow sequence where we expect fully saturated rocks. P‐wave quality factor estimates are consistent with results from other VSP experiments in the North Atlantic Margin, while the S‐wave quality factor is one of the first estimates from a stacked basalt formation using VSP data. Synthetic modelling demonstrates that seismic attenuation for P‐ and S‐waves in the stacked basalt flow sequence is mainly caused by one‐dimensional scattering, while intrinsic absorption is small.     

Polarimetric analysis and modeling of multifrequency SAR signaturesfrom Gulf Stream fronts

Using airborne synthetic aperture radar data from the 1990 Gulf Stream Experiment, this paper investigates the polarization and wavelength dependence of radar signatures for narrow fronts with converging flows occurring within the Gulf Stream. The signal-to-background ratios of the cross-polarization backscatter return from a convergent front were found much higher than those of copolarization returns, when the flight path is crossing the front. However, a second convergent front, imaged at 45°, showed that the signal-to-background ratios are nearly equal for co- and cross-polarizations. A polarimetric procedure, which has been successfully used to measure terrain slopes and to generate elevation maps, is applied to the convergent front to explain the polarization and imaging geometry dependence of these radar responses. A theoretical modeling of radar modulation using an ocean wave model and a composite-Bragg scattering model, which incorporates the effect of breaking waves, was developed. Calculations with the model agree reasonably well with the radar measurements at various polarizations for three radar frequencies: P-band (68 cm in wavelength), L-band (24 cm), and C-band (5.7 cm)     

Characterization of organic-rich material in an evaporitic environment: the Lower Oligocene of the Mulhouse basin (Alsace,France)

Evaporitic sediments from the Max borehole (Mulhouse Potash Basin, southern Rhine Graben) were studied over an interval of about 40 m in the vicinity of sylvite beds. Total organic carbon (TOC) analyses of 450 samples showed that marly layers interbedded within the evaporites have TOC values that fluctuate in a rhythmic manner; the highest values are found near the top of the clay—anhydrite layers and the lowest values are recorded near the top of the halite-rich beds. Geochemical (elemental analysis of kerogen, gas chromatography of bitumen) and palynological studies of 26 samples showed that the organic matter is mainly of algal origin (A and B groups). A third category of organic material (C group) may have been derived from a mixture of continental supply and in situ bacterial productivity.     

Flow separation on Zongo Glacier,Cordillera Real,Bolivia

Meltwaters collected from the proglacial stream escaping from Zongo Glacier (2·1 km²), Bolivia (16°S), have been monitored in order to analyse the internal drainage system of an Andean glacier. Electrical conductivity has been measured sporadically between February 1995 and March 1996, during 16 one-day field surveys, under various meteorological conditions in summer and winter. The mixing-model technique based on the electrical conductivity is used for a quantitative separation of discharge which is derived from continuous water level registration. Tracer experiments (mainly uranine dye and NaCl salt) have been carried out from March to June 1997 to obtain information about the internal drainage system. In the tropical Andes, accumulation only occurs in austral summer, whereas ablation occurs throughout the year and is higher during the accumulation season, between November and March. The assumptions involved in the use of mixing models for analysis of glacial drainage structure are applicable for tropical glaciers because glacial conduits do not suffer complete closure, and are permanently supplied by meltwaters, even in wintertime. Two components of discharge are separated: an englacial flow originating from surface meltwater which is routed without chemical enrichment, and offering low electrical conductivity; and a subglacial one routed in contact with bedrock or sediments showing high ionic concentrations. Electrical conductivity of meltwater varies diurnally, inversely to discharge fluctuations. According to this behaviour, total discharge is mainly formed by the englacial component. The drainage structures for englacial and subglacial flow have to be widely interconnected, as indicated by diurnal variations of the subglacial discharge. Comparison of hydrograph separation based on conductivity and on ¹⁸O isotope confirms that the subglacial flow is influenced by surface melting. A hydrograph separation of the subglacial flow is proposed, between a diurnal variable component, composed of water coming from the englacial network, and a base flow, which may vary seasonally. The dye tracing experiments confirm the drainage complexity of Zongo Glacier and demonstrate the interest of identifying three main drainage components. © 1998 John Wiley & Sons, Ltd.