Abstract
An accurate and cost-effective micro sun sensor based on the extraction of the sun vector using a phenomenon called the “black sun” is presented. Unlike conventional image-based sun sensors where there is difficulty in accurately detecting the sun center, the black sun effect allows the sun center to be accurately extracted even with the sun image appearing irregular and noisy due to glare. This allows the proposed micro sun sensor to achieve high accuracy even when a 1 mm × 1 mm CMOS image sensor with a resolution of 250 × 250 pixels is used. The proposed micro sun sensor is implemented in two application modes: (1) a stationary mode targeted at tracking the sun for heliostats or solar panels with a fixed pose of single image sensor of 1 mm × 1 mm × 1.74 mm in size and (2) a non-stationary mode targeted at determining the orientation of moving platforms with six sensors on the platform, which is configured in an icosahedron geometry of 23 mm × 23 mm × 12 mm in size. For the stationary mode, we obtained an accuracy of 0.013° by applying Kalman filter to the sun sensor measurement for a particular sensor orientation. For the non-stationary mode, we obtained an improved accuracy of 0.05° by fusing the measurements from three sun sensors available at any instant of time. Furthermore, experiments indicate that the black sun effect makes the precision of sun vector extraction independent of the sun location captured on the image plane.
Highlights
One of the challenges in astrophysics, while capturing the images of a celestial star, is the optical phenomenon called limb darkening [1]
Unlike other conventional image-based sun sensors, we observed that we the location of the sun captured on the image plane
We explained in depth how we took advantage of the phenomenon in CMOS image sensors known as the “black sun” caused by electron overspill at an oversaturated pixel
Summary
One of the challenges in astrophysics, while capturing the images of a celestial star, is the optical phenomenon called limb darkening [1]. MEMS and camera-based the blooming of the to their the advantage using blooming to supplement thesun sun vector sun sensors by CCD supplementing simplicity,by cost-effectiveness, and lines wide FOV of camera-based sensors with the accuracy and small size of the MEMS-based sun sensors. Wesun achieve thisis bycaptured proposingat image extraction They observed that error increases when image an approach for extracting the sun vector that will result in a wide-FOV, cost-efficient, and boundaries due to increased distortion effect or when two blooming lines are closeaccurate together; their sun sensor that uses off-the-shelf components for easy deployment. Additional performance comparison the centroid algorithm withor the conventional centroid of observed that our black sun effect based sunofvector measurement error variance is independent method was conducted.
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