Seasat synthetic aperture radar: ocean wave detection capabilities

A preliminary assessment has been made of the capability of the Seasat synthetic aperture radar to detect ocean waves. Comparison with surface and aircraft measurements from five passes of the satellite over the Gulf of Alaska indicates agreement to within about - 15 percent in wavelength and about +/- 25 degrees in wave direction. These results apply to waves 100 to 250 meters in length propagating in a direction predominantly across the satellite track, in sea states with significant wave height (H((1/3))) in a range of 2 to 3.5 meters.     

Shuttle imaging radar experiment

The shuttle imaging radar (SIR-A) acquired images of a variety of the earth's geologic areas covering about 10 million square kilometers. Structural and geomorphic features such as faults, folds, outcrops, and dunes are clearly visible in both tropical and arid regions. The combination of SIR-A and Seasat images provides additional information about the surface physical properties: topography and roughness. Ocean features were also observed, including large internal waves in the Andaman Sea.     

Seasat altimeter calibration: initial results

Preliminary analysis of radar altimeter data indicates that the instrument has met its specifications for measuring spacecraft height above the ocean surface (+/- 10 centimeters) and significant wave height (+/- 0.5 meter). There is ample evidence that the radar altimeter, having undergone development through three earth orbit missions [Skylab, Geodynamics Experimental Ocean Satellite 3 (GEOS-3), and Seasat], has reached a level of precision that now makes possible its use for important quantitative oceanographic investigations and practical applications.     

Spaceborne imaging radar: monitoring of ocean waves

A well-organized, very low energy ocean swell system off the East Coast of the United States was tracked with the Seasat synthetic aperture radar from deep water, across the continental shelf, and into shallow, water. The results indicate that spaceborne imaging radar may be used to accurately measure ocean wavelength and direction, even in coastal areas and in the presence of a mixed ocean.     

Seasat mission overview

During some 3 months of orbital operations, Seasat collected a unique set of global synoptic data on ocean winds, waves, temperature, and topography. All indications from a preliminary analysis of these data are that most of the mission's proof-of-concept objective-the demonstration of nearly all-weather microwave surveillance of the world's oceans-will be met.     

Surface observations for the evaluation of geophysical measurements from seasat

The surface observations used in the initial assessment of Seasat are discussed with emphasis on their ability to describe the synoptic-scale winds over the ocean.     

Ocean wave patterns under hurricane gloria: observation with an airborne synthetic-aperture radar

Surface imagery of ocean waves under Hurricane Gloria (September 1976) has been obtained with an airborne synthetic-aperture imaging radar. Observations were obtained over most of the area within a radius of 150 kilometers around the center of the eye. These direct observations made it possible to derive the wave patterns in the region around a hurricane eye.     

Temporal variability of the antarctic circumpolar current observed from satellite altimetry

Sea level measurements by the Seasat altimeter were used to study the temporal variability of the Antarctic Circumpolar Current between July and October 1978. Large-scale zonal coherence in the cross-stream sea level difference was observed, indicating a general increase in the surface geostrophic velocity of the current around the Southern Ocean. The result demonstrates the power of satellite altimetry to monitor the variability of large-scale ocean currents.     

Seasat scanning multichannel microwave radiometer: results of the gulf of alaska workshop

The scanning multichannel microwave radiometer results for the Gulf of Alaska Seasat Experiment Workshop are quite encouraging, especially in view of the immaturity of the data-processing algorithms. For open ocean, rain-free cells of highest-quality surface truth wind determinations exhibit standard deviations of 3 meters per second about a bias of 1.5 meters per second. The sea-surface temperature shows a standard deviation of approximately 1.5 degrees C about a bias of 3 degrees to 5 degrees C under a variety of changing meteorological conditions.     

Remote sensing of the fram strait marginal ice zone

Sequential remote sensing images of the Fram Strait marginal ice zone played a key role in elucidating the complex interactions of the atmosphere, ocean, and sea ice. Analysis of a subset of these images covering a 1-week period provided quantitative data on the mesoscale ice morphology, including ice edge positions, ice concentrations, floe size distribution, and ice kinematics. The analysis showed that, under light to moderate wind conditions, the morphology of the marginal ice zone reflects the underlying ocean circulation. High-resolution radar observations showed the location and size of ocean eddies near the ice edge. Ice kinematics from sequential radar images revealed an ocean eddy beneath the interior pack ice that was verified by in situ oceanographic measurements.     

Seasat visible and infrared radiometer

Visual and infrared images produced by the Seasat visible and infrared radiometer (VIRR) are adequate for the identification of cloud, land, and water features. A statistical comparison of VIRR-derived sea-surface temperatures in a cloud-free region with a National Oceanic and Atmospheric Administration analysis based on various surface measurements taken in the same region showed agreement to +/- 1.7 degrees K root-mean-square.     

Satellite measurements reveal persistent small-scale features in ocean winds

Four-year averages of 25-kilometer-resolution measurements of near-surface wind speed and direction over the global ocean from the QuikSCAT satellite radar scatterometer reveal the existence of surprisingly persistent small-scale features in the dynamically and thermodynamically important curl and divergence of the wind stress. Air-sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields, as are the influences of islands and coastal mountains. Ocean currents such as the Gulf Stream generate distinctive patterns in the curl field. These previously unresolved features have important implications for oceanographic and air-sea interaction research.     

Skylab radar altimeter: short-wavelength perturbations detected in ocean surface profiles

Short-wavelength anomalies in sea surface topography, caused by the gravitational effects of major ocean bottom topographic features, have been detected by the radar altimeter aboard Skylab. Some features, such as deep ocean trenches, seamounts, and escarpments, displace the ocean surface by as much as 15 meters over 100-kilometer wavelengths. This experiment demonstrates the potential of satellite altimetry for determining the ocean geoid and for mapping major features of the ocean bottom.     

Phytoplankton pigments from the nimbus-7 coastal zone color scanner: comparisons with surface measurements

The removal of atmospheric effects from Nimbus-7 Coastal Zone Color Scanner (CZCS) images reveals eddy-like ocean turbidity patterns not apparent in the original calibrated images. Comparisons of the phytoplankton pigment concentrations derived from the corrected CZCS radiances with surface measurements agree to within less than 0.5 log C, where C is the sum of the concentrations of chlorophyll a plus phaeopigments a (in milligrams per cubic meter).     

Two-dimensional imaging of potential waves in electrochemical systems by surface plasmon microscopy

The potential dependence of resonance conditions for the excitation of surface plasmons was exploited to obtain two-dimensional images of the potential distribution of an electrode with high temporal resolution. This method allows the study of spatiotemporal patterns in electrochemical systems. Potential waves traveling across the electrode with a speed on the order of meters per second were observed in the bistable regime of an oscillatory electrochemical reaction. This velocity is close to that of excitation waves in nerve fibers and is far greater than the velocity of reaction-diffusion waves observed in other chemical systems.     

Microwave radiometric measurements of sea surface temperature from the seasat satellite: first results

Initial results from the Seasat scanning multichannel microwave radiometer indicate that the sea surface temperature can be measured with a root-mean-square sensitivity of 1.2 degrees C or better. The first microwave map of sea surface temperature for the entire Pacific has been produced.     

马尾松木材空洞开裂残损的雷达检测成像初探

本研究以木结构古建筑常用的马尾松木材为研究对象，采取人工模拟的方法在马尾松木段端部制作中心空洞及外缘开裂的残损，通过开展残损木材的雷达探测及成像影响因素研究，给出不同残损在雷达检测下的表现形态，实现木材内部空洞和外缘开裂残损的快速识别及表征。研究结果表明:利用雷达无损检测技术可以实现木材内部空洞和外缘开裂残损的快速检出，而对残损大小的评估，雷达检测面积与实际残损面积存在偏差；当雷达探测到木材内部空洞时，其交界面会出现强烈的黑-白-黑形态图像，对应的反射波形为谷-峰-谷；当雷达探测到木材外缘开裂等凹陷特征时，其图像上会出现不同于正常背景的纵向干扰条纹；木材外缘开裂并不严重影响内部空洞残损的检出，木材表面存在贴合紧密的树皮或保护性地仗对内部残损的识别也无明显影响；木材含水率对雷达检测结果影响较为显著，在其他条件一定时，木材含水率越高，其雷达检测残损面积越小；雷达检测结果受含水率等因素影响，其残损的检测边界可能会产生一定的偏移，因此，在实际检测中应根据雷达检测图像进行深度方向的延伸分析。通过本研究可知:雷达无损检测技术可以实现木材空洞和开裂残损的快速检出，但对于残损的定量评估有待于进一步研究。      

Deep ocean impact of a Madden-Julian oscillation observed by Argo floats

Using the new Argo array of profiling floats that gives unprecedented space-time coverage of the upper 2000 meters of the global ocean, we present definitive evidence of a deep tropical ocean component of the Madden-Julian Oscillation (MJO). The surface wind stress anomalies associated with the MJO force eastward-propagating oceanic equatorial Kelvin waves that extend downward to 1500 meters. The amplitude of the deep ocean anomalies is up to six times the amplitude of the observed annual cycle. This deep ocean sink of energy input from the wind is potentially important for understanding phenomena such as El Ni?o-Southern Oscillation and for interpreting deep ocean measurements made from ships.     

Satellite measurements of sea surface temperature through clouds

Measurements of sea surface temperature (SST) can be made by satellite microwave radiometry in all weather conditions except rain. Microwaves penetrate clouds with little attenuation, giving an uninterrupted view of the ocean surface. This is a distinct advantage over infrared measurements of SST, which are obstructed by clouds. Comparisons with ocean buoys show a root mean square difference of about 0.6 degrees C, which is partly due to the satellite-buoy spatial-temporal sampling mismatch and the difference between the ocean skin temperature and bulk temperature. Microwave SST retrievals provide insights in a number of areas, including tropical instability waves, marine boundary layer dynamics, and the prediction of hurricane intensity.     

基于不同风场的台风浪数值模拟

为了检验FVCOM海洋模式模拟台风浪的效果,分别以CCMP风场和WRF模式模拟风场构建驱动台风浪的海面风场模型,基于FVCOM海洋模式,以2010年的"凡比亚"台风为例进行台风浪数值模拟,并用站点浮标资料进行了模拟结果检验。结果表明,FVCOM海洋模式模拟的水位、有效波高结果与实际观测结果的整体误差较小,模拟效果较好;受到风场与地形的影响,最大增水与减水的区域分别位于台风中心的左侧沿岸和右侧沿岸;风场与表面流场的模拟结果也符合台风过程中的风生流分布特征,即风场与表面流场方向、大小存在一致性。此外,对比分析2种不同海面风场模型下的台风浪模拟结果发现,二者均能较好地模拟此次台风过程,但存在一定的差异,增加WRF模式模拟风场作为强迫驱动风场模拟的有效波高更接近观测值。