Multi-beam techniques for deriving wind fields from airborne doppler radars
Multi-beam techniques for deriving wind fields from airborne doppler radars
复制标题
从机载多普勒雷达获取风场的多波束技术
DOI：
10.1007/bf01032002
复制
发表时间：
1996
影响因子：
2
通讯作者：
J. D. DuGranrut
中科院分区：
文献类型：
--
作者：
D. Jorgensen;T. Matejka;J. D. DuGranrut
摘要提出并讨论了两种使用垂直扫描机载多普勒雷达数据导出水平和垂直空气运动的技术。这些技术利用 NOAA P-3 尾装雷达天线的扫描能力，在直线飞行轨迹中从至少两个有利位置观察空间区域。该扫描方法被称为“前/后扫描技术”或 FAST，因为天线交替扫描飞行轨迹的前部和后部。与在两条准正交飞行轨迹上飞行（天线扫描垂直于飞行轨迹）相比，FAST 的主要优点是，数据收集时间大约为一半，并且飞机不必执行直角转弯。然而，由于波束交叉角从 90° 减小到约 50°，因此所得到的风场的精度略有下降。还讨论了由于大漂移角而导致覆盖面积的减少。可以使用来自 FAST 数据的双多普勒方程，使用两个径向速度估计和连续性方程的垂直积分（在云顶和地球表面无垂直运动的边界条件下）构建三维风场。为了使计算的风的误差保持在可接受的小范围内，仰角通常限制在水平方向的±45°范围内，以最大限度地减少终端下降速度对水平风的污染。可以使用第二种技术导出不同的、也许更可信的垂直速度，该技术利用两架（或更多）机载多普勒雷达装备的飞机，每架飞机都使用 FAST 来观察公共点处的回波顶部垂直速度（例如，两架飞机平行飞行、路径，或通过使用具有单个飞行路径的 L 形飞行轨迹）飞机）。该技术在每个点产生 4 个（或更多）径向速度估计（因此称为“四多普勒”技术）。可以使用超定三方程解或超定双多普勒解（以更准确者为准）导出水平风。为了计算垂直速度，提出了一种新方法，利用云顶附近垂直粒子运动的超定三重多普勒解，减去终端坠落速度的估计，作为向下垂直发散积分的顶部边界条件，以导出域中其他地方的垂直空气速度。此外，这种方法允许在陡峭的仰角处进行测量，从而在给定范围内获得更大的覆盖深度。为了展示该方法的实用性，我们将使用 FAST 收集的数据分析与根据 S 波段地面多普勒雷达同时收集的数据构建的传统双多普勒风场进行了比较。最近完成的热带海洋/全球大气耦合海洋/大气响应实验（TOGA/COARE）也提供了四多普勒技术的示例。将四多普勒垂直速度与 NASA DC-8 收集的原位垂直空气运动进行比较，以判断进近的质量。
SummaryTwo techniques for deriving horizontal and vertical air motions using vertically scanning airborne Doppler radar data are presented and discussed. These techniques make use of the scanning ability of the NOAA P-3 tail-mounted radar antenna to view a region of space from at least two vantage points during a straight-line flight track. The scanning methodology is termed the “Fore/Aft Scanning Technique” or FAST because the antenna is alternately scanning forward and then aft of the flight track. The major advantages of FAST over flying two quasi-orthogonal flight tracks with the antenna scanning normal to the flight track are that the data are collected in roughly half the time and the aircraft does not have to execute a right-angle turn. However, accuracy of the resulting wind field is compromised slightly because the beam intersection angle is reduced from 90° to about 50°. The reduction of area covered because of large drift angles is also discussed.A three-dimensional wind field can be constructed using the dual-Doppler equations from FAST data using the two radial velocity estimates and vertical integration of the continuity equation with a boundary condition of no vertical motion at cloud top and the Earth's surface. To keep errors in the calculated winds acceptably small, the elevation angles are typically restricted to ±45° from the horizontal to minimize contamination of the horizontal wind by terminal fallspeeds.A different, and perhaps more believable vertical velocity, can be derived using a second technique that utilizes two (or more) airborne Doppler radar equipped aircraft each using FAST to observe the echo-top vertical velocity at common point (e.g., two aircraft flying parallel flight, paths, or by using an L-shaped flight track with a single aircraft). This technique results in 4 (or more) radial velocity estimates at each point (hence is called the “quad-Doppler” technique). Horizontal winds can be derived using either an overdetermined three-equation solution or an overdetermined dual-Doppler solution, whichever is more accurate. For the calculation of vertical velocity a new approach is proposed that utilizes the overdetermined triple-Doppler solution for vertical particle motion near cloud top, minus an estimate of terminal fallspeeds, as a top boundary condition for the downward vertical divergence integration to derive vertical air velocity elsewhere in the domain. In addition, this approach allows measurements at steep elevation angles allowing for more depth of coverage for a given range.To show the utility of the method, analyses of data collected using FAST are compared to conventional dual-Doppler-derived wind fields constructed from data collected simultaneously by S-band ground-based Doppler radars. An example of the quad-Doppler technique is also presented from the recently completed Tropical Oceans/Global Atmospheres Coupled Ocean/Atmosphere Response Experiment (TOGA/COARE). Comparisons of quad-Doppler vertical velocity are made with in-situ derived vertical air motions collected by the NASA DC-8 to judge the quality of the approach.