摘要:

Extensive experimental work has been performed in recent years involving the dual-frequency microwave scatterometer. This system can selectively measure the modulated return from a very narrow band of ocean wavenumbers. By varying the difference in transmitted frequencies a directional modulation spectrum may be obtained. Theories have been developed to explain the output of the dual-frequency spectrometer in quantitative terms. Because of the complexity of the measurements involved, these theories have, heretofore, only been partially tested. The experiments reported here independently evaluate both sides of a theoretical equation for χ(κ), the basic signal/background ratio for the technique, using single- and dual-frequency signals backscattered at low grazing angles. The experimental results agree well with the theoretical expression and provide evidence that composite surface theory is viable at quite low grazing angles.

ISSN:0143-1161    

DOI:10.1080/01431168208948409

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

In the sky-wave radar technique, the parameters of sea waves beyond the horizon are deduced from the Doppler spectra of ionospherically propagated sea echoes. Ionospheric movements and multipath can contaminate the sea echo spectrum from a given location. Measurements of die multipath and Doppler spread for a 700 km ionospheric path during MARSEN are reported. For one hop by way of the F2 layer, a typical r.m.s. Doppler shift over 10 min was 0·005 Hz and Doppler spread, to — 10 dB, was 0·08Hz. Multihop and side-scatter modes of propagation and their Doppler structure were identified. The possible use of side scatter at the sea surface is analysed.

ISSN:0143-1161    

DOI:10.1080/01431168208948410

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

This paper reports on the results of a two-frequency (Δκ) microwave radar experiment for measuring the spectral characteristics of the large-scale ocean surface gravity waves from an aircraft. The experiment was conducted as part of the 1979 Maritime Remote Sensing (MARSEN) project. A coherent Ku-band radar was used to study the Bragg type resonance matching of the electromagnetic wavelength at the difference frequency (Δƒ) to the length of the surface waves. The spatial spectrum of the surface reflectivity modulation was then computed from the measurements as the value of Δƒ was varied over a matching range of 15-300 m in surface wavelength. The strength and Doppler behaviour of individual resonances has been evaluated and modulation spectra have been produced from two data flights, with different surface conditions, at three altitudes, and for three flight paths—upwave, downwave and crosswave. Aircraft laser measurements of the one-dimensional surface profile spectrum were used in interpreting the radar data. In addition, a one-dimensional theoretical analysis of the Δκ resonance response that includes the effects of the antenna gain pattern and surface illumination parameters has been developed. The MARSEN results show strong resonances with consistent Doppler features and modulation spectra that agree well with the theory, surface truth and earlier stationary platform experimental results.

ISSN:0143-1161    

DOI:10.1080/01431168208948411

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

An analysis of remote measurements of sea surface currents during MARSEN is presented. Remote measurements were made by high-frequency (HF) radars in the German Bight from September to October.1979. Moored current meters made concurrentin situmeasurements several metres below the surface. Comparisons of instantaneous data sets show differences, which may be explained by vertical current shear. The computed tidal coefficients from HF and current meter measurements agree well.

ISSN:0143-1161    

DOI:10.1080/01431168208948412

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The high wavenumber detection cut-off is determined above which the spectrum of ocean waves imaged by a synthetic aperture radar (SAR) is lost in the background noise spectrum consisting of the clutter noise associated with the Rayleigh statistics of the backscattering surface and the thermal noise originating in the SAR system itself. For given power, the maximum detection cut-off wavenumber is attained if the SAR resolution is chosen such that the clutter and noise spectra are equal at the cut-off wavenumber. Assuming a constant modulation transfer function relating the image modulation and wave slope spectra, the cut-off wavenumber is in this case proportional to (ρaρg)−1/2, where ρaand ρgrepresent the full bandwidth (single look) azimuthal and ground range resolutions, respectively. The same proportionality holds (but with a cut-off wavenumber increased by a factor √2) for a clutter limited cut-off, the normal operating condition of an SAR. To first order, incoherent multilook averaging has no influence on the signal-to-background detection cut-off wavenumber, provided the reduced Nyquist cut-off wavenumber resulting from the reduced multilook spatial resolution remains greater than the signal-to-background cut-off wavenumber. Estimates of the detection cut-off wave-numbers are given for the Seasat SAR and the SAR proposed for the European Remote Sensing Satellite ERS-1.

ISSN:0143-1161    

DOI:10.1080/01431168208948413

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The location of oceanic fronts became important to the ocean community because sonar transmissions were distorted and disrupted at those locations.

ISSN:0143-1161    

DOI:10.1080/01431168208948414

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Airborne microwave radiometer measurements at 1·43 and 2·65 GHz over a sea surface covered with a monomolecular oleyl alcohol surface film and over adjacent slick sea surfaces are presented. The measurements show that at 2·65 GHz the brightness temperatureTBis not affected by the slick, while at 1·43 GHz it drops from 93 K to a minimum value of almost O K. This implies that at 1·43 GHz the emissivity of the slick-covered sea surface is extremely small, similar to a metallic layer, and that this resonant-type phenomenon is confined to a narrow frequency band of width δƒ/ ƒ<0·6.

ISSN:0143-1161    

DOI:10.1080/01431168208948415

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The acquisition and application of airborne laser induced emission spectra from German Bight water during the 1979 MARSEN experiment is detailed for the synoptic location of estuarine fronts. The NASA Airborne Oceanographic Lidar (AOL) was operated in the fluorosensing mode. A nitrogen laser transmitter at 3371 nm was used to stimulate the water column to obtain Gelbstoff or organic material fluorescence spectra together with water Raman backscatter. Maps showing the location and relative strength of estuarine fronts are presented. The distribution of the fronts indicates that mixing within the German Bight takes place across a relatively large area. Reasonable agreement between the patterns observed by the AOL and published results are obtained. The limitations and constraints of this technique are indicated and improvements to the AOL fluorosensor are discussed with respect to future ocean mapping applications.

ISSN:0143-1161    

DOI:10.1080/01431168208948416

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431168208948417

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor