Abstract
The airborne area camera has received broad application in aerial reconnaissance, land resource surveying, environmental monitoring, photogrammetry mapping, and natural disaster information acquisition. A three-axis, inertially stabilized platform with a large rotation range for the roll axis is designed, which is based on the cantilever structure, in order to realize a large-angle sweep imaging function for airborne area cameras. An image attitude control algorithm in the inertial space is proposed, which can regulate the line of sight (LOS) as well as the image orientation. The area camera image motion calculation model and image motion compensation residual computing method are proposed, utilizing space position and velocity vector transformation mathematics and derivations. The variation of linear velocity of the image motion in the sensor frame is analyzed, and the changing laws of the maximum deviation of image motion with the image attitude are studied. Flight tests imply that the vertical imaging technique correctly regulates the LOS along the local geodetic vertical. The along-flight overlap rate is greater than 65%, which meets the stereo mapping requirement. The sweep imaging technique considerably enlarges the cross-flight angle of view. The LOS and image orientation during sweep imaging are correctly controlled, and gap-free coverage of the survey area is maintained. The image’s azimuth or roll deviation is less than 0.1°, and the image pitch deviation is less than 0.35°. The quality of the test images is superior. Black and white line pairs for evaluation can be clearly distinguished. The image’s motion is well compensated, and the image motion compensation residual is well constrained. These verify the validity of the proposed imaging technique and the image motion analysis model.
Highlights
The area camera is one of the most important visible light sensors for aerial remote sensing
A three-axis inertially stabilized platform (ISP) based on a cantilever structure was designed which supported a rolling range from −85◦ to +85◦ in sweep imaging mode
The techniques were developed for airborne area camera vertical imaging and sweep imaging based on a threeaxis platform
Summary
The area camera is one of the most important visible light sensors for aerial remote sensing. In accordance with the rotation coupling laws of the three gimbal axes and the space vector decomposition and transformation theorems, an image attitude control algorithm for a three-axis ISP is proposed in this paper. The image motion calculation model for analyzing IMV and the IMC residual computing method for area cameras are proposed, utilizing space position and velocity vector transformation mathematics and derivations. The IMC Calculation module computes the angular rate ωF (refer to Section 4.1), the Imaging Controller module changes the servo state of the pitch axis to the velocity model, and the Servo Control module makes the pitch axis rotate at angular velocity ωF. The uncertain disturbances of the aircraft can be sensed by the gyro and will be compensated by the closed loop of the velocity control of the servo system This frame has its origin at the local horizontal plane. According to Equations (2) and (5), κ, φ, and ω can be solved as follows:
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