Optical design of wide-angle lens for LWIR earth sensors

Infrared Earth sensors with large-field-of-view (FOV) cameras are widely used in low-Earth-orbit satellites. To improve the accuracy and speed of Earth sensors, an algorithm based on modified random sample consensus (RANSAC) and weighted total least squares (WTLS) is proposed. Firstly, the modified RANSAC with a pre-verification step was used to remove the noisy points efficiently. Then, the Earth’s oblateness was taken into consideration and the Earth’s horizon was projected onto a unit sphere as a three-dimensional (3D) curve. Finally, the TLS and WTLS were used to fit the projection of the Earth horizon. With the help of TLS and WTLS, the accuracy of the Earth sensor was greatly improved. Simulated images and on-orbit infrared images obtained via the satellite Tianping-2B were used to assess the performance of the algorithm. The experimental results demonstrate that the method outperforms RANSAC, M-estimator sample consensus (MLESAC), and Hough transformation in terms of speed. The accuracy of the algorithm for nadir estimation is approximately 0.04° (root-mean-square error) when Earth is fully visible and 0.16° when the off-nadir angle is 120°, which is a significant improvement upon other nadir estimation algorithms

Section: Introductionmentioning

confidence: 99%

An Efficient Algorithm for Infrared Earth Sensor with a Large Field of View

Wang

Jin

2022

“…To the best of our knowledge, there is no commercial off-the-shelf (COTS) compact camera that operates in the [8–14] µm wavelength range and that features a FOV of 140° for the characterization of the OLR. State-of-the-art thermal cameras include either imaging designs operating in this wavelength range but with a smaller FOV (51° × 40°) [ 13 ], or cameras with the required FOV but in another and smaller wavelength range ([14–16] µm) [ 14 ], or systems that both operate in a different wavelength range and feature a smaller FOV, e.g., in [ 15 ]. Considering the required wavelength range, the maximal FOV that is currently published is obtained with a catadioptric objective and equals to 125° × 96° [ 16 ], which is still significantly smaller than our targeted value of 140° (circular full FOV).…”

Section: Introductionmentioning

confidence: 99%

Wide-Field-of-View Longwave Camera for the Characterization of the Earth’s Outgoing Longwave Radiation

Schifano

Smeesters

Berghmans

et al. 2021

The measurement of the Earth’s Outgoing Longwave Radiation plays a key role in climate change monitoring. This measurement requires a compact wide-field-of-view camera, covering the 8–14 µm wavelength range, which is not commercially available. Therefore, we present a novel thermal wide-field-of-view camera optimized for space applications, featuring a field of view of 140° to image the Earth from limb to limb, while enabling a high spatial resolution of 4.455 km at nadir. Our cost-effective design comprises three germanium lenses, of which only one has a single aspherical surface. It delivers a very good image quality, as shown by the nearly-diffraction-limited performance. Radiative transfer simulations indicate excellent performance of our camera design, enabling an estimate of the broadband Outgoing Longwave Radiation with a random relative error of 4.8%.

Wide-Field-of-View Multispectral Camera Design for Continuous Turfgrass Monitoring

Smeesters

Verbaenen

Schifano

et al. 2023

Sustainably using resources, while reducing the use of chemicals, is of major importance in agriculture, including turfgrass monitoring. Today, crop monitoring often uses camera-based drone sensing, offering an accurate evaluation but typically requiring a technical operator. To enable autonomous and continuous monitoring, we propose a novel five-channel multispectral camera design suitable for integrating it inside lighting fixtures and enabling the sensing of a multitude of vegetation indices by covering visible, near-infrared and thermal wavelength bands. To limit the number of cameras, and in contrast to the drone-sensing systems that show a small field of view, a novel wide-field-of-view imaging design is proposed, featuring a field of view exceeding 164°. This paper presents the development of the five-channel wide-field-of-view imaging design, starting from the optimization of the design parameters and moving toward a demonstrator setup and optical characterization. All imaging channels show an excellent image quality, indicated by an MTF exceeding 0.5 at a spatial frequency of 72 lp/mm for the visible and near-infrared imaging designs and 27 lp/mm for the thermal channel. Consequently, we believe our novel five-channel imaging design paves the way toward autonomous crop monitoring while optimizing resource usage.