POS机上对准新方法：基于状态转移矩阵
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"基于状态转移矩阵的POS机上对准"
在现代航空遥感系统中，位置和定向系统（Position and Orientation System，简称POS）扮演着至关重要的角色。它被用来测量并补偿航空传感器在成像过程中的运动误差，以确保数据的精确性和可靠性。然而，传统的POS在飞行中的校准（In-flight Alignment）方法面临一个问题，即初始对准误差较大，导致必须使用非线性误差模型和非线性滤波器，这会显著增加系统的计算负担。
针对这一问题，这篇名为“基于状态转移矩阵的POS机上对准”的研究论文提出了一种新的、计算负载较少的在飞对准方法。该方法首先分析了POS的误差传播特性，利用状态转移矩阵来记录初始对准误差在每次计算步骤中的传播过程。状态转移矩阵是动态系统理论中的一个重要工具，它可以描述系统状态随时间的演化规律。
论文中进行了新方法的可观测性分析，这是确保校准有效性的关键步骤。可观测性是指通过系统的输出数据能否完全确定系统的状态。在对新方法进行可观测性分析后，根据导航误差和错误状态转移矩阵，可以进行在飞行中的实时校准。
此方法的核心在于减少了对非线性滤波器的依赖，转而依赖于状态转移矩阵来跟踪和纠正误差，从而降低了计算复杂性，提升了校准效率。这使得POS系统在校准过程中能更快地收敛到实际状态，提高了整个系统在运行周期中的精度和鲁棒性。
此外，这种基于状态转移矩阵的对准策略还可能适用于其他需要实时校准和误差补偿的精密导航系统，如自动驾驶车辆、无人机等，具有广泛的应用前景。通过简化计算流程，该方法有助于优化系统设计，提高整体性能，并且在资源有限的环境下更具优势。
这篇研究论文提供了一种创新的POS在飞对准解决方案，利用状态转移矩阵来有效地管理和减少初始对准误差，降低了系统的计算需求，对于提高航空遥感系统的性能有着积极的贡献。
3258 IEEE SENSORS JOURNAL, VOL. 15, NO. 6, JUNE 2015
In-Flight Alignment of POS Based
on State-Transition Matrix
Jiancheng Fang and Zhanchao Liu
Abstract—Position and orientation system (POS) is an
important part of airborne remote sensing system, it is used to
measure and compensate the motion errors of airborne sensors
in course of imaging. In-flight alignment is an effective way to
improve the accuracy and robustness of POS in its operating
cycles. In the traditional in-flight alignment methods, large initial
alignment errors result in the fact that nonlinear error models
and nonlinear filters must be used, which means much calculation
load will accompany the system. To avoid the large initial
alignment errors, in this paper, a new in-flight alignment method
with fewer calculation loads is proposed. The error propagate
characteristic of POS is analyzed first, and state transition matrix
is used to record the initial alignment errors propagate process
in every calculation step. After observability analysis of the new
method, the in-flight alignment is carried out according to the
navigation errors and the error state-transition matrix of POS.
To validate the proposed in-flight alignment method, car-mounted
experiment and flight test are carried out. Experiment results
show that, the proposed in-flight alignment method can improve
the accuracy and the robustness of POS with fewer calculation
loads.
Index Terms—Airborne remote sensing, position and
orientation system, in-flight alignment, error model,
observability, state transition matrix.
I. INTRODUCTION
T
HE Position and Orientation System (POS) is a kind of
integrated navigation system, it is mainly used to measure
and compensate the motion errors of airborne sensors. POS
consists of Inertial Measurement Unit (IMU), GPS receiver,
POS Computer System (PCS) and post-processing software
suite. IMU contains three gyroscopes and three accelerom-
eters, and it is usually embedded in airborne sensors to
measure angular and linear information. Global Positioning
System (GPS) receiver provides absolute position and
velocity of the airborne remote sensing system. PCS and
pos-processing software suite are used to integrate the IMU
data and GPS data online and offline respectively [1]–[4].
POS is different from traditional integrated navigation
system. The ability to align itself in dynamic environment
which called in-flight alignment (IFA) is important
Manuscript received July, 7, 2014; accepted December 22, 2014. Date of
publication January 7, 2015; date of current version April 22, 2015. This work
was supported in part by the National Basic Research Program of China
under Grant 2009CB724002 and in part by the Foundation for Innovative
Research Groups through the National Natural Science Foundation of China
under Grant 61121003. The associate editor coordinating the review of this
paper and approving it for publication was Dr. Thilo Sauter.
The authors are with Beihang University, Beijing 100191, China (e-mail:
fangjiancheng@buaa.edu.cn; liuzhanchao@hotmail.com).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/JSEN.2015.2388697
for POS [5]. There is short time for static alignment in
ground, as POS is just part of the whole airborne remote
sensing system. In many cases, POS is just powered on in
air when the airborne sensors start to work in consider of
energy conservation, operation convenience and safety of the
plane. Moreover, GPS output is easily affected by airborne
sensors and other factors [5], for example, the Synthetic
Aperture Radar (SAR) will interrupt the satellite signal of
GPS sometimes, in which case the system needs new in-flight
alignment. All the features aforementioned make the in-flight
alignment is key technology for POS to get a good
performance. But there are many features of POS we can
make full use of, for example, the typical trace of POS is
uniform rectilinear motion back and forth when the airborne
sensors work in imaging areas [6], [7].
During in-flight alignment, coarse alignment is carried out
firstly to provide initial attitude for fine alignment according
to the accelerometer outputs of IMU and GPS heading in
the past, and fine alignment will take the velocity errors
between Strapdown Inertial Navigation System (SINS) and
GPS into a filter to estimate the navigation errors [5], [8]. But
in most cases, the initial attitude error provided by the coarse
alignment is quite large, so that nonlinear error models and
nonlinear filters must be used for fine alignment in the past.
To overcome the large coarse alignment errors, large head-
ing error models [9], [10], extended kalman filter (EKF),
unscented kalman filter and predictive filter are used in the
in-flight alignment [11]–[15]. The EKF is used most widely
because of its better real-time performance [16]–[18], but
the EKF is sensitive to GPS signal when the GPS signal is
disturbed by airborne sensors, maneuver of the aircraft
and other factors. So adaptive kalman filtering algorithms
are proposed afterwards, and the innovation based adaptive
estimation (IAE) is most concentrated [5], the Innovation
Adaptive EKF method for airborne POS can reduce the
relay on prior knowledge of the filter with good real-time
performance, but it is still not robust enough with large initial
attitude errors, moreover, the Adaptive EKF filter will induce
much calculation loads.
In this paper, a new in-flight alignment method of POS
is presented, which can provide accurate initial attitude of
POS, and the new method is robust enough to avoid unstable
GPS outputs. After coarse alignment, the system start inertial
navigation instead of SINS/GPS integrated navigation, then
state transition matrix is used to estimate the initial attitude
errors analytically according to the inertial navigation results
relative to GPS outputs. The new in-flight alignment method
1530-437X © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
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