Improved Estimates Of Turbulence From Mesosphere-Stratosphere-Troposphere (MST) Radars

改进的中间层-平流层-对流层 (MST) 雷达湍流估计

• 批准号: 0129464
• 负责人: Gregory Nastrom
• 金额: $ 14.77万
• 依托单位: St. Cloud State University
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-01 至 2006-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0129464&HistoricalAwards=false
• 关键词: Improved; Estimates; Turbulence; Mesosphere; Stratosphere

Doppler spectra measured by MST (mesosphere-stratosphere-troposphere) radars are broadened by turbulent velocity fluctuations of the scattering elements in the beam. Measuring the spectral spread is therefore one of the ways of using MST radar to estimate the intensity of turbulence. Because the beams of such radars are fairly broad (typically several degrees) there are additional contributions to the Doppler spread caused by the cross-beam wind (so-called beam broadening) and by shear of the radial wind component in the direction of the beam axis. Recent studies indicate that the methods currently used to correct for these effects are inaccurate. Such methods are usually based on the assumption that the contributing volume is uniformly filled with turbulence. In fact, the turbulence is often confined to one or more horizontal layers that are thinner than the vertical extent of the contributing volume. Corrections based on the assumption of a filled beam are then generally too large.The present award supports development of a new experimental technique that will enable improved radar estimates of turbulence. Called the dual-beamwidth technique, it has the advantage of obtaining the turbulence intensity directly, without the need for the usual corrections to the Doppler spectral width. The assumption underlying the method is that the (generally unknown) contribution of beam broadening to the Doppler spread is proportional to the beamwidth. Simultaneous measurements at the same range with two beamwidths, which is possible with advanced MST radars such as those in Japan and India, then make it possible to measure the contribution of beam-broadening to the total Doppler spread and to compensate for it in estimating the remaining spread due to turbulence. The turbulence intensities determined this way will be compared with those estimated from a single beam employing the concept of an "effective beamwidth," which is less than the geometric beamwidth to allow for the limited vertical extent of the turbulent layers. If the method employing a single effective beamwidth is proven accurate, it will then be applied to recompute turbulence intensities for radar data from Japan and White Sands, New Mexico, that have already been reported in the literature.

用MST（mesosphere-stratosphere-troposphere）雷达测量的多普勒谱会因波束中散射元素的湍流速度起伏而展宽。 因此，测量频谱扩展是使用MST雷达估计湍流强度的方法之一。 由于这种雷达的波束相当宽（通常为几度），因此由交叉波束风（所谓的波束展宽）和波束轴方向上的径向风分量的切变引起的多普勒扩展有额外的贡献。 最近的研究表明，目前用于纠正这些影响的方法是不准确的。 这种方法通常基于这样的假设，即贡献体积均匀地充满湍流。 事实上，湍流通常被限制在一个或多个水平层中，这些水平层比贡献体积的垂直范围更薄。 基于填充波束假设的修正通常太大。本奖项支持开发一种新的实验技术，该技术将能够改进湍流的雷达估计。 这种方法被称为双束宽技术，它的优点是直接获得湍流强度，而不需要对多普勒谱宽进行通常的校正。 该方法的基本假设是波束展宽对多普勒扩展的贡献（通常未知）与波束宽度成比例。 在同一距离上用两种波束宽度同时进行测量，这对于先进的MST雷达（如日本和印度的MST雷达）来说是可能的，这样就有可能测量波束展宽对总多普勒扩展的贡献，并在估计湍流引起的剩余扩展时对其进行补偿。 将用这种方法确定的湍流强度与采用“有效束宽”概念的单束估计的湍流强度进行比较，有效束宽小于几何束宽，以考虑湍流层的有限垂直范围。 如果采用一个单一的有效波束宽度的方法被证明是准确的，它将被应用到重新计算湍流强度的雷达数据从日本和白色沙滩，新墨西哥州，已经在文献中报道。