Modeling inertial sensors errors using Allan variance

Abstract

It is well known that Inertial Navigation Systems (INS) can provide high accuracy information on the position, velocity, and attitude over a short time period. However, their accuracy degrades rapidly with time. The requirements for accurate estimation of navigation information necessitate the modeling of the sensors' noise components. Several methods have been devised for stochastic modeling of inertial sensors noise. Each of them is useful but each has its own disadvantage. The Adaptive Kalman filter is one of the mostly used methods to estimate inertial sensor noise, but the form of the model needs to be known first. Frequency domain approaching uses the power spectral density to estimate transfer functions. It is straightforward but it is difficult for non­system analysts to understand. In the time domain methods, the correlation function approach is very model sensitive. Variance techniques are basically very similar, and primarily differ only in that various signal processing, by way of weighting functions, window functions, etc., are incorporated into the analysis algorithms in order to achieve a particular desired result for improving the model characterizations. The simplest technique is the Allan variance method. Allan variance is a method of representing root mean square (RMS) random drift error as a function of average time. It is simple to compute and relatively simple to interpret and understand. Allan variance method can be used to determine the character of the underlying random processes that give rise to the data noise. This technique can be used to characterize various types of noise terms in the inertial sensor data by performing certain operations on the entire length of data. In this thesis, the Allan variance technique is used in noise analysis of different grade Inertial Measurement Units (IMU), which include: • Navigation grade IMU: The Honeywell Commercial IMU (CIMU); • Tactical grade IMU: The Honeywell HG 1700; and ■ Consumer grade MEMS based IMU: The Systron Donner MotionPak II-3g By performing a simple operation on the entire length of data, a characteristic curve is obtained whose inspection provides a systematic characterization of various random errors contained in the inertial sensor output data. Being a directly measurable quantity, Allan variance can provide information on the types and magnitude of various noise terms. The research work will cover both the theoretical basis for Allan Variance for modeling inertial sensors noise terms, and its implementation in modeling different noise terms existing in the different grade inertial sensors. Simple implementation and ease of interpretation make the Allan variance method suitable in inertial sensor noise identification and stochastic modeling.