Abstract
Accurate attitude information from a satellite image sensor is essential for accurate map projection and reducing computational cost for post-processing of image registration, which enhance image usability, such as change detection. We propose a robust attitude-determination method for pushbroom sensors onboard spacecraft by matching land features in well registered base-map images and in observed images, which extends the current method that derives satellite attitude using an image taken with 2-D image sensors. Unlike 2-D image sensors, a pushbroom sensor observes the ground by changing its position and attitude according to the trajectory of a satellite. To address pushbroom-sensor observation, the proposed method can trace the temporal variation in the sensor attitude by combining the robust matching technique for a 2-D image sensor and a non-linear least squares approach, which can express gradual time evolution of the sensor attitude. Experimental results using images taken from a visible and near infrared pushbroom sensor of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra as test image and Landsat-8/OLI images as a base map show that the proposed method can determine satellite attitude with an accuracy of 0.003° (corresponding to the 2-pixel scale of ASTER) in roll and pitch angles even for a scene in which there are many cloud patches, whereas the determination accuracy remains 0.05° in the yaw angle that does not affect accuracy of image registration compared with the other two axes. In addition to the achieved attitude accuracy that was better than that using star trackers (0.01°) regarding roll and pitch angles, the proposed method does not require any attitude information from onboard sensors. Therefore, the proposed method may contribute to validating and calibrating attitude sensors in space, at the same time better accuracy will contribute to reducing computational cost in post-processing for image registration.
Highlights
Pushbroom-type image sensors have been widely used in Earth observation missions such as Landsat series, Terra, and Aqua
Because a sensor onboard a satellite captures a target from space, a small error in attitude inevitably causes a large position error of a target on the surface (e.g., 1◦ error for a 700-km-altitude satellite causes a 10-km displacement on the surface), which leads to the necessity of a large search range for matching observed and reference images; huge computational cost is needed for the matching
We examined the derivation of sensor attitude with a combination of linear and quadratic equations for obtaining more accurate attitude information when the drift of a pushbroom sensor is not negligible
Summary
Pushbroom-type image sensors have been widely used in Earth observation missions such as Landsat series, Terra, and Aqua. Considering contamination of sunlight and reflected sunlight by solar panels and modules in an STT’s field of view, attitude information from STTs may not be available for a while To address this problem, we propose an attitude-determination method for pushbroom sensors that is only based on observed images with known satellite positions. We propose an attitude-determination method for pushbroom sensors that is only based on observed images with known satellite positions It does not require any attitude information from onboard sensors. We first provide the mathematical basis of satellite attitude determination from an observed image with known satellite position, discuss how we extract and match feature pairs from satellite and base-map images, how we determine sensor attitude including its temporal variation
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