Assessment of ionosphere spatial decorrelation for global positioning system-based aircraft landing systems
Assessment of ionosphere spatial decorrelation for global positioning system-based aircraft landing systems
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DOI：
10.2514/1.28199
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发表时间：
2007-09-01
影响因子：
2.2
通讯作者：
Enge, Per
中科院分区：
文献类型：
--
作者：
Lee, Jiyun;Pullen, Sam;Enge, Per
全球定位系统的地面增强功能需要保证完整性，以支持飞机精确进场和着陆导航。为了定量评估导航完整性，飞机使用电离层空间去相关的标准偏差将垂直和横向保护水平计算为位置误差界限。因此，有必要估计标称天数的典型电离层梯度并确定适当的上限以充分覆盖由于电离层空间去相关而导致的微分误差。站对和时间步长方法都用于评估垂直（或天顶）电离层梯度（sigma(vig)）的标准偏差。站对方法比较两个不同参考站与单个卫星的同时天顶延迟，并观察已知电离层穿透点间隔的延迟差异。由于这些电离层穿透点间隔限制了站对方法的可观测性，因此时间步长方法也可用于更好地了解短距离尺度（10-40 km）的电离层梯度。时间步长方法将单个视线在一个历元的电离层延迟与同一视线在短时间内（几分钟到几十分钟）后在另一历元的延迟进行比较。该方法的优点是消除了不同卫星和接收机上的频间偏差校准误差，同时可能引入由于时间电离层梯度而引起的估计误差。本研究的结果表明，对于非暴风雨电离层条件，sigma(vig) 的典型值约为 1-3 mm/,km。因此，4 mm/ km 的 sigma(vig) 足够保守，足以限制标称天数的电离层空间去相关，并且仍然为更活跃的天数和非高斯尾部行为留下足够的余量。
Ground-based augmentations of the global positioning system demand guaranteed integrity to support aircraft precision approach and landing navigation. To quantitatively evaluate navigation integrity, an aircraft computes vertical and lateral protection levels as position-error bounds using the standard deviation of ionosphere spatial decorrelation. Thus, it is necessary to estimate typical ionospheric gradients for nominal days and to determine an appropriate upper bound to sufficiently cover the differential error due to the ionosphere spatial decorrelation. Both station-pair and time-step methods are used to assess the standard deviation of vertical (or zenith) ionospheric gradients (sigma(vig)). The station-pair method compares the simultaneous zenith delays from two different reference stations to a single satellite and observes the difference in delay across the known ionosphere pierce point separation. Because these ionosphere pierce point separations limit the observability of the station-pair method, the time-step method is also used to better understand ionospheric gradients at short distance scales (10-40 km). The time-step method compares the ionospheric delay of a single line of sight at one epoch with the delay for the same line of sight at another epoch a short time (a few to tens of minutes) later. This method has the advantage of removing interfrequency bias calibration errors on different satellites and receivers while possibly introducing an estimation error due to temporal ionospheric gradients. The results of this study demonstrate that typical values of sigma(vig) are on the order of 1-3 mm/,km for nonstormy ionospheric conditions. As a result, sigma(vig) of 4 mm/ k m is conservative enough to bound ionosphere spatial decorrelation for nominal days and still leave enough margin for more active days and for non-Gaussian tail behavior.