A Self-Calibration Method for Boresight Error of Mobile Mapping System

The boresight error is one of the main error sources of the Mobile Mapping System(MMS), which directly affects the overall accuracy and quality of the laser point cloud. Unideal boresight error estimation seriously reduces the point cloud registration accuracy. When there is a feature place in the laser point cloud, the boresight error will cause the feature plane to deviate from the real plane. In order to solve the above problems, a visual axis calibration method for a mobile surveying and mapping system based on known feature planes is proposed. According to the plane features of 3D scene, the Gauss-Helmert adjustment model is established, and the normal equation for calculating the boresight error is derived. This is a simple and reliable calibration method.

Feedforward Control Based on Error and Disturbance Observation for the CCD and Fiber-Optic Gyroscope-Based Mobile Optoelectronic Tracking System

In the mobile optoelectronic tracking system (MOTS) based on charge-coupled device (CCD) and fiber-optic gyroscope (FOG), the tracking performance (TP) and anti-disturbance ability (ADA) characterized by boresight error are of equal importance. Generally, the position tracking loop, limited by the image integration time of CCD, would be subject to a non-negligible delay and low-sampling rate, which could not minimize the boresight error. Although the FOG-based velocity loop could enhance the ADA of the system, it is still insufficient in the case of some uncertain disturbances. In this paper, a feedforward control method based on the results of error and disturbance observation was proposed. The error observer (EOB) based on the CCD data and model output essentially combined the low-frequency tracking feedforward and closed-loop disturbance observer (DOB), which could simultaneously enhance the low-frequency TP and ADA. In addition, in view of the poor low-frequency performance of the FOG due to drift and noise that may result in the inaccuracy of the observed low-frequency disturbance, the FOG-based DOB was used to improve the relatively high-frequency ADA. The proposed method could make EOB and DOB complementary and help to obtain a high-precision MOTS, for in practical engineering, we give more attention to the low-frequency TP and full-band ADA. Simulations and experiments demonstrated that the proposed method was valid and had a much better performance than the traditional velocity and position double-loop control (VPDC).

Multidisciplinary design optimization of sandwich-structured radomes

A multidisciplinary design optimization framework is proposed for sandwich-structured radomes. Radomes ensure the functional operation of antenna systems in adverse environment catering for aerodynamic stresses and payload requirements. The existence of radomes can partially degrade the electromagnetic performance of antenna systems. The electromagnetic performance and mechanical responses are taken into account simultaneously in the optimization design. This is more time-saving and economical compared to the traditional separate considerations on these two aspects. Coupled with multi-island genetic algorithm, transmission coefficient and boresight error are identified as the objectives. Lateral deformation, material failure, and structural stability are included in mechanical analysis. Three-dimensional ray-tracing technique and physical optics based aperture integration method are employed to address interactions between the antenna and radome. Tsai–Wu and maximum stress criteria are used to predict material failure. Structural stability is analyzed using the linear perturbation of stiffness matrices. The applicability of the electromagnetic model is validated using examples of a hemispheric air and single-layered radome. A numerical experiment is conducted to investigate the utility and feasibility of the multidisciplinary design optimization model. Results show that the optimal section profile brings about considerable improvement in transmission coefficient and boresight error. Mechanical constrains are reasonably subjected to the preset limits. Hence, the proposed multidisciplinary design optimization model is an effective and feasible alternative in the environment of radome design.