Measuring the effect of helicopter rotors on GPS reception
Measuring the effect of helicopter rotors on GPS reception
复制标题
测量直升机旋翼对 GPS 接收的影响
作者：
G. Brodin;J. Cooper;J. Stevens
摘要本文描述了利用海上运输直升机进行的一项实验，以研究旋翼叶片对全球定位系统(GPS)接收的影响。测试飞机安装了两个独立的GPS天线，它们的位置是为了隔离主旋翼和尾旋翼造成的影响。飞机在地面上进行了测试，这使得能够在不同的旋翼速度下进行评估，并精确控制天线、旋翼和卫星之间的相对几何形状。对包含三个不同GPS接收器(包括符合技术标准订单(TSO)-C129())的航空单元和定制研究接收器的测量系统的记录数据进行了分析，以确定旋翼在相关器一级的影响，并确定对测距精度、测距测量的可用性和接收器的信号电平估计的影响。相关数据表明，旋翼叶片既能产生破坏性干扰效应，又能产生相长干扰效应，并且这些振动的周期性直接对应于叶片通过频率。据确认，信号退化并不局限于与转子盘相交的卫星信号路径。没有发现因转子干扰而增加代码测量误差的证据，但已证明这可能会对接收器保持对卫星信号的连续跟踪的能力产生重大影响。这一可用性问题对某一特定安装和操作类型的总体影响将取决于卫星几何形状和本研究范围以外的其他因素。通过检查载噪比估计，研究了接收器识别转子干扰存在的能力，这表明不同接收器的结果不一致，这意味着所采用的估计算法不同。还指出，在存在转子干扰的情况下，两种替代的“教科书”估计器不会给出相同的结果，因此建议应谨慎解释这类数据。
Abstract This paper describes an experiment which was performed using an offshore transport helicopter to investigate the impact of the rotor blades upon Global Positioning System (GPS) reception. The test aircraft was fitted with two separate GPS antennas which were positioned to isolate the effects caused by the main and tail rotors. Testing was undertaken with the aircraft on the ground and this allowed an assessment to be performed at different rotor speeds with accurate control over the relative geometry between the antenna, rotors and satellites. Recorded data from a measurement system incorporating three dissimilar GPS receivers (including a technical standard order (TSO)-C129() compliant aviation unit and a custom research receiver) was analysed to identify the effect of the rotors at the correlator level and to determine the impacts upon ranging accuracy, the availability of ranging measurements, and the receivers’ signal level estimates. Correlation data was used to demonstrate that the rotor blades were capable of generating both destructive and constructive interference effects, and the periodic nature of these oscillations was shown to correspond directly to the blade passing frequency. It was identified that signal degradation was not limited to satellite signal paths which intersected the rotor discs. No evidence was found for any increase in code measurement error due to the rotor interference, but it was demonstrated that there could be a significant impact upon a receiver’s ability to maintain continuous tracking of the satellite signals. The overall effect of this availability problem for a given installation and type of operation will be dependent upon satellite geometry and other factors which are beyond the scope of this study. The ability of a receiver to identify the presence of rotor interference was investigated by examining estimates of carrier-to-noise, and this revealed inconsistencies between the results from different receivers implying differences in the estimation algorithms employed. It was also identified that two alternative ‘textbook’ estimators do not give identical results in the presence of rotor interference and it is suggested that such data should therefore be interpreted with caution.