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1.
Microwave scattering signatures of the ocean have been measured over a range of surface wind speeds from 3 m/s to 23.6 m/s using the AAFE RADSCAT scatterometer in an aircraft. Normalized scattering coefficients are presented for vertical and horizontal polarizations as a function of incidence angle (nadir to55deg ) and radar azimuth angle (0deg to360deg ) relative to surface wind direction. For a given radar polarization, incidence angle, and azimuth angle relative to the wind direction, these scattering data exhibit a power law dependence on surface wind speed. The relation of the scattering coefficient to azimuth angle obtained during aircraft circles (antenna conical scans) is anisotropic and suggests that microwave scatterometers can be used to infer both wind speed and direction. These results have been used for the design of the Seasat-A Satellite Scatterometer (SASS) to be flown in 1978 on this first NASA oceanographic satellite. 相似文献
2.
The measurement of internal-wave signatures using synthetic aperture radar (SAR) or real aperture radar (RAR) techniques is an emerging technology that offers a viable means of locating and tracking surface ship wakes by their unique signatures. Under the assumption that the image measured by the radar is dominated by the underlying dynamics of the internal wave, we develop model-based techniques for enhancement based on a recently developed generic dispersive-wave processor. Using images synthesized by a sophisticated propagation model, it is shown that the processor not only offers a unique approach compared to the more traditional image-processing techniques that do not incorporate the propagation model, but is also capable of providing reasonable enhancement of the noisy measurements 相似文献
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4.
Three- dimensional vector modeling and restoration of flat finite wave tank radiometric measurements
In this paper, a three-dimensional Fourier transform inversion method describing the interaction between water surface emitted radiation from a flat finite wave tank and antenna radiation characteristics is reported. The transform technique represents the scanning of the antenna mathematically as a correlation. Computation time is reduced by using the efficient and economical fast Fourier transform algorithm. To verify the inversion method, computations have been made and compared with known data and other available results. The technique has been used to restore data of the finite wave tank system and other available antenna temperature measurements made at the Cape Cod Canal. The restored brightness temperatures serve as better representations of the emitted radiation than the measured antenna temperatures. 相似文献
5.
The brightness reversal of submarine sand waves appearing in the small satellite constellation for environment and disaster monitoring and forecasting("HJ-1A/B") CCD sun glitter images can affect the observation and depth inversion of sand wave topography. The simulations of the normalized sun glitter radiance on the submarine sand waves confirm that the reversal would happen at a specific sensor viewing angle, defined as the critical angle. The difference between the calculated critical angle position and the reversal position in the image is about 1, which is excellent in agreement. Both the simulation and actual image show that sand wave crests would be indistinct at the reversal position, which may cause problems when using these sun glitter images to analyze spatial characteristics and migration of sand waves. When using the sun glitter image to obtain the depth inversion, one should take the advantage of image properties of sand waves and choose the location in between the reversal position and the brightest position. It is also necessary to pay attention to the brightness reversal when using "HJ-1A/B" CCD images to analyze other oceanic features, such as internal waves, oil slicks, eddies, and ship wakes. 相似文献
6.
In this paper, image processing technique that reduces video images of buoy motion to yield time series of image coordinates
of buoy objects will be investigated. The buoy motion images are noisy due to time-varying brightness as well as non-uniform
background illumination. The occurrence of boats, wakes, and wind-induced white caps interferes significantly in recognition
of buoy objects. Thus, semiautomated procedures consisting of object recognition and image measurement aspects will be conducted.
These offer more satisfactory results than a manual process. Spectral analysis shows that the image coordinates of buoy objects
represent wave motion well, indicating its usefulness in the analysis of wave characteristics. 相似文献
7.
A computer simulation is used to analyze errors in high-frequency (HF) radar ocean surface current measurements. Two pointing algorithms used for current extraction, a direction finding approach using MUltiple SIgnal Characterization (MUSIC) developed by Schmidt (1986), and conventional beam forming, are compared in terms of the effect of variations in sea state parameters on current measurement error. The radar system parameters used in the simulation were taken from the University of Michigan's multi-frequency coastal radar (MCR), which operates on four frequencies from 4.8 to 21.8 MHz and employs an eight-element linear phased array for its receive antenna. Results show MUSIC direction finding to be applicable to phased array systems and to have a better sensitivity to sharp current features, but larger random error than traditional beam forming methods. Also, for cases where beam forming errors are dominated by beam width or low signal to noise ratio, results show MUSIC to be a viable alternative to beam forming 相似文献
8.
This article examines visitors’ normative acceptance of encounters with boats at a marine protected area and the extent that the number of boats, size of boats, and size of boat on which individuals were traveling influences these encounter norms. Data were obtained from a survey of 439 people visiting Molokini Shoal Marine Life Conservation District in Hawai’i, and photographs depicting four levels of boat use and three proportions of boat size measured encounter norms. Number of boats most strongly influenced encounter norms, boat size was less influential, and the size of boats on which respondents were traveling had little influence. Visitors wanted fewer boats at this site and a majority would not accept encountering more than 15 or 16 boats at one time. When the impact of boat size was considered, they would not accept encountering more than 12 large boats to 17 small boats. Implications for future research and managing standards of quality and social carrying capacity indicators at this marine protected area are discussed. 相似文献
9.
星载微波辐射计外定标的关键问题是通过辐射传输方程计算天线入瞳处亮温。根据辐射传输方程,海面成份对亮温的影响包括海面的微波辐射和对下行大气辐射的反射,其中的关键参数分别为海面发射率ep和海表面反射率R。文中对平静海面Fresnel反射率模式和粗糙海面反射率模式进行了研究分析,在此基础上着重研究了海面温度TS、海面盐度SS、海面风速W、以及观测角度θ等物理参数对海面发射率ep的影响,进而分析了这些物理参数的测量误差对亮温的计算精度的影响。 相似文献
10.
A joint airborne measurement program is being pursued by NRL and NASA Wallops Flight Center to determine the extent to which wind speed and sea surface significant wave height (SWH) can be measured quantitatively and remotely with a short pulse (2 ns), wide-beam (60deg ), nadir-looking 3-cm radar. The concept involves relative power measurements only and does not need a scanning antenna, doppler filters, or absolute power calibration. The slopes of the leading and trailing edges of the averaged received power for the pulse limited altimeter are used to infer SWH and surface wind speed. The interpretation is based on theoretical models of the effects of SWH on the leading edge shape and rms sea-surface slope on the trailing-edge shape. The models include the radar system parameters of antenna beam width and pulsewidth. Preliminary experimental results look promising and indicate that it may be possible to design a relatively compact airborne radar to infer, in real-time, the sea surface SWH and surface wind speed. 相似文献
11.
Calibration and Validation of Direction-Finding High-Frequency Radar Ocean Surface Current Observations 总被引：1，自引：0，他引：1
Jeffrey D. Paduan Kyung Cheol Kim Michael S. Cook Francisco P. Chavez 《Oceanic Engineering, IEEE Journal of》2006,31(4):862-875
This paper focuses on the validation of remotely sensed ocean surface currents from SeaSonde-type high-frequency (HF) radar systems. Hourly observations during the period July 22, 2003 through September 9, 2003 are used from four separate radar sites deployed around the shores of Monterey Bay, CA. Calibration of direction-finding techniques is addressed through the comparisons of results obtained using measured and ideal (i.e., perfect) antenna patterns. Radial currents are compared with observations from a moored current meter and from 16 surface drifter trajectories. In addition, four overwater baselines are used for radar-to-radar comparisons. Use of measured antenna patterns improves system performance in almost all cases. Antenna-pattern measurements repeated one year later at three of the four radar locations exhibit only minor changes indicating that pattern distortions are stable. Calibrated results show root-mean-square (rms) radial velocity differences in the range of 9.8-13.0 cm/s, which suggest radar observation error levels in the range of 6.9-9.2 cm/s. In most cases, clear evidence of bearing errors can be seen, which range up to 30deg for uncalibrated radar-derived radial currents and up to 15deg for currents obtained using measured antenna patterns. Bearing errors are not, however, constant with angle. The results recommend use of measured antenna patterns in all SeaSonde-type applications. They also recommend an expanded simulation effort to better describe the effects of antenna-pattern distortions on bearing determination under a variety of ocean conditions 相似文献
12.
With Shannon sampling rates at the sensors of a linear antenna, it is not always possible to achieve a beam system with complete azimuth coverage. Furthermore, it is not possible to compensate an antenna system platform's own motion in such a way as to be able to build up a beam system fixed in space. Even the method of increasing the sampling rate for the sensors to an impracticably high value would only solve these problems to a limited extent. On the other hand, a solution which is easily put into practice is offered by time interpolation between adjacent sample points of the sensor signals. Therefore we have investigated this method in detail. The beam patterns are formed by special linear combination of the autocorrelation function (ACF) of the sensor signals. This kind of linear combination is applicable to all types of interpolation between adjacent sample points. For one special type of interpolation, namely linear interpolation, an azimuthal level-distribution function which specifies the maximum antenna reception sensitivity for all steering angles is stated for a linear antenna havingN sensors. With this function, it is possible to estimate the influence of the sampling frequency, Signal center frequency, signal bandwidth, and antenna dimensions on the antenna/beamformer performance. 相似文献
13.
Kangseok Hwang Eun-A Yoon Sukyung Kang Hyungkee Cha Kyounghoon Lee 《Ocean Science Journal》2017,52(4):563-571
The present study focuses on the influence of target strength (TS) changes in the swimming angle of the hairtail (Trichiurus lepturus). We measured in-situ TS at 38 and 120 kHz with luring lamps at a fishing ground for jigging boats near the coastal waters of Jeju-do in Korea. Swimming angle and size of hairtails were measured using an acoustic camera. Results showed that mean preanal length was estimated to be 13.5 cm (SD = 2.7 cm) and mean swimming tilt angle was estimated to be 43.9° (SD = 17.6°). The mean TS values were ?35.7 and ?41.2 dB at 38 and 120 kHz, respectively. The results will assist in understanding the influence of swimming angle on the TS of hairtails and, thus, improve the accuracy of biomass estimates. 相似文献
14.
Bishwajit Chakraborty Hans Werner Schenke Vijay Kodagali Rick Hagen 《Marine Geodesy》2013,36(1-2):19-26
Utilizing a hull-mounted, multinarrow beam echosounder onboard RV Polarstern, we measured variation of acoustic backscatter with incidence angles at two different sites in the Southern Oceans (Agulhas Plateau and the Riiser Larsen Sea). We modeled the data, using a composite roughness model, including water-sediment interface roughness and sediment volume roughness parameters. The model effectively uses the near normal incidence angle backscatter to determine the seafloor interface roughness parameters employing Helmholtz-Kirchhoff theory. Beyond 20° incidence angles, an application of Rayleigh-Rice theory is made by using a necessary splicing technique (combining both of the theories at 20° incidence angle). The estimated interface and volume roughness parameters are found to be in accordance with the known area geology. 相似文献
15.
Bishwajit Chakraborty Hans Werner Schenke Vijay Kodagali Rick Hagen 《Marine Geodesy》2002,25(1):19-26
Utilizing a hull-mounted, multinarrow beam echosounder onboard RV Polarstern, we measured variation of acoustic backscatter with incidence angles at two different sites in the Southern Oceans (Agulhas Plateau and the Riiser Larsen Sea). We modeled the data, using a composite roughness model, including water-sediment interface roughness and sediment volume roughness parameters. The model effectively uses the near normal incidence angle backscatter to determine the seafloor interface roughness parameters employing Helmholtz-Kirchhoff theory. Beyond 20° incidence angles, an application of Rayleigh-Rice theory is made by using a necessary splicing technique (combining both of the theories at 20° incidence angle). The estimated interface and volume roughness parameters are found to be in accordance with the known area geology. 相似文献
16.
The underwater acoustic noise of five representative whale-watching boats used in the waters of west Maui was measured in order to study the effects of boat noise on humpback whales. The first set of measurements were performed on 9 and 10 March, close to the peak of the whale season. The ambient noise was relatively high with the major contribution from many chorusing humpback whales. Measurements of boat sounds were contaminated by this high ambient background noise. A second set of measurements was performed on 28 and 29 April, towards the end of the humpback whale season. In both sets of measurements, two of the boats were inflatables with outboard engines, two were larger coastal boats with twin inboard diesel engines and the fifth was a small water plane area twin hull (SWATH) ship with inter-island cruise capabilities. The inflatable boats with outboard engines produced very complex sounds with many bands of tonal-like components. The boats with inboard engines produced less intense sounds with fewer tonal bands. One-third octave band measurements of ambient noise measured on 9 March indicated a maximum sound pressure level of about 123 dB re 1 microPa at 315 Hz. The maximum sound pressure level of 127 dB at 315 Hz was measured for the SWATH ship. One of the boats with outboard engines produced sounds between 2 and 4 kHz that were about 8-10 dB greater than the level of background humpback whale sounds at the peak of the whale season. We concluded that it is unlikely that the levels of sounds produced by the boats in our study would have any grave effects on the auditory system of humpback whales. 相似文献
17.
神舟四号高度计波形数据预处理和信息提取 总被引：1，自引：0，他引：1
神舟四号(SZ-4)高度计在国内首次提供了星载雷达高度计回波波形数据.本文中作者分析了SZ-4高度计回波波形的特点,完成波形数据的预处理,并在此基础上完成初步的信息提取.在数据预处理方面,通过SZ-4高度计水陆边界处波形的特点,提出了波形最大幅度控制的方法,筛选回波波形.在波形归一化处理过程中,发现SZ-4高度计波形中存在双峰现象,并指出第二个峰为异常波形区.在波形信息提取方面,利用波形重新跟踪得到的半功率点计算出SZ-4高度计高度跟踪补偿误差,并根据高度计天线指向角和回波波形下降沿斜率之间的关系,从波形后沿提取天线指向角信息.分析结果表明,SZ-4高度计天线指向比较平稳,而跟踪补偿由于变化较大,在计算海面高度时,应作为一项误差源被考虑到. 相似文献
18.
The paper summarizes the results of the long-term complex satellite monitoring of the Black and Baltic seas. Data from synthetic aperture radars (SARs) constitute the experimental basis for the investigation of satellite. In addition to radar data, the data of the visible and infrared bands from MODIS Terra/Aqua, MERIS Envisat, Landsat series sensors are used. The features of the manifestation of hydrodynamic processes, submesoscale eddies in particular, in satellite radar and optical images in a period of intense phytoplankton bloom are discussed. A relationship is established between the intensity and duration of the phytoplankton bloom in the regions of observation and the frequency of the appearance of long-lasting wakes behind moving ships in SAR images. These wakes appear as long narrow bright bands of enhanced backscattered signal extending for tens and sometimes hundreds of kilometers. It is proposed to consider the wakes of this type as indicators of the areas and duration of intense phytoplankton bloom. Satellite observations over the Black and Baltic Seas conducted for more than ten years have shown that long-lasting ship wakes are influenced by powerful jet streams, such as those associated with the passage of eddies that leads to shifts and deformations. By comparing the true route of a ship with its wake in the satellite image, it is possible to obtain detailed information about the parameters of currents. 相似文献
19.
相比于实孔径微波辐射计,一维综合孔径微波辐射计具有高空间分辨率和多入射角观测特点。本文提出采用观测频率为6.9,10.65,18.7,23.8和36.5 GHz,且入射角范围为0°~65°的一维综合孔径微波辐射计遥感大气海洋环境要素。基于构建的微波大气海洋辐射传输正演模型,分析了辐射计亮温对大气海洋环境要素的敏感性,为辐射计关键指标确定和大气海洋环境要素反演算法设计提供技术支撑。结果表明：一维综合孔径微波辐射计的垂直和水平极化亮温对大气海洋环境要素的敏感性表现出不同特性,且敏感性随入射角的改变而变化显著;6.9和10.65 GHz对海面温度的敏感性较大,且随着入射角的增大,垂直极化亮温的敏感性增大,水平极化亮温的敏感性减小;10.65和18.7 GHz对海面风速的敏感性相对较大,且敏感性最大的风速区间位于10~20 m/s;23.8 GHz对大气水汽含量最敏感,且水汽含量较低、入射角较大时,敏感性越大;36.5 GHz对云液态水含量最敏感,随着入射角的增大,垂直极化亮温的敏感性减小,水平极化的敏感性增大,但两者均在液态水含量较小时表现出较大的敏感性。 相似文献
20.
Chotiros N.P. Mautner A.M. Lovik A. Kristensen A. Bergem O. 《Oceanic Engineering, IEEE Journal of》1997,22(4):604-615
An experiment was performed to measure sediment penetrating acoustic waves to test a model of acoustic propagation, which is based on Biot's theory. Independent geophysical measurements provided model input parameters. A parametric sound source was used to project a narrow beam pulse into a silty sand sediment at a shallow grazing angle. The sediment acoustic waves were measured by an array of buried sensors and processed to measure wave directions and speeds. Two acoustic waves were observed, corresponding to the fast and slow waves predicted by Biot's theory. Discrepancies between model predictions and measured acoustic waves were examined, deficiencies in the model identified, and strategies for improvement postulated. The permeability and bulk modulus of the solid frame were of particular interest 相似文献