###### 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\({}^{\circ}\), and the image pitch deviation is less than 0.35\({}^{\circ}\). 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. airborne area camera; image attitude; line of sight (LOS); image motion variation; image motion compensation; three-axis platform; inertially stabilized platform; sweep imaging; gimbal angle; photogrammetry mapping +
Footnote †: journal: Applied Sciences  
ground resolution from a higher flight altitude and provide larger aerial coverage, resulting in higher aerial survey productivity. These advantages make area cameras very popular in the aerial reconnaissance and photogrammetry mapping fields. An inertially stabilized platform (ISP) is essential for airborne area cameras [4; 5; 6]. Its primary function is to isolate the aerial camera from aircraft vibrations and disturbances, regulate the line of sight (LOS), and compensate for image motion during the exposure process [7; 8; 9]. A platform with a two-axis platform is described in [10], which is designed for aerial imaging and tracking. In [11], an inertially stabilized two-axis airborne camera platform is presented, which is applied to object pointing and tracking. The two-axis platform has broad applications in searching and surveillance. However, the two-axis platform cannot control the image orientation, which is essential for photogrammetry mapping and surveying. Therefore, a three-axis ISP [12; 13] has been developed, which is equipped with a position and orientation system (POS) to control the LOS and image orientation in inertial space. In order to increase the efficiency of airborne area camera imaging and meet the urgent aerial sensing demand of natural disasters, the cross-flight angle of view should be enlarged. Sweep imaging through the roll axis is an effective way to enlarge the cross-flight angle of view. The rotation range of the roll axis for an available three-axis ISP, such as the PAV30, PAV80, and GSM3000, is usually within 30\({}^{\circ}\), which cannot support wide-range sweep imaging. A novel three-axis ISP based on the cantilever structure is designed, the rotation range of which is greater than 150\({}^{\circ}\). The aircraft's attitude will vary during imaging, and the gimbal angle for each axis should be adjusted so that the area camera can maintain the desired inertial attitude.