Development of an Optical System Based on Spectral Imaging Used for a Slug Control Robot

The state-of-the-art technique to control slug pests in agriculture is the spreading of slug pellets. This method has some downsides, because slug pellets also harm beneficials and often fail because their efficiency depends on the prevailing weather conditions. This study is part of a research project which is developing a pest control robot to monitor the field, detect slugs, and eliminate them. Robots represent a promising alternative to slug pellets. They work independent of weather conditions and can distinguish between pests and beneficials. As a prerequisite, a robot must be able to reliably identify slugs irrespective of the characteristics of the surrounding conditions. In this context, the utilization of computer vision and image analysis methods are challenging, because slugs look very similar to the soil, particularly in color images. Therefore, the goal of this study was to develop an optical filter-based system that distinguishes between slugs and soil. In this context, the spectral characteristics of both slugs and soil in the visible and visible near-infrared (VNIR) wavebands were measured. Conspicuous maxima followed by conspicuous local minima were found for the reflection spectra of slugs in the near infrared range from 850 nm to 990 nm]. Thus, this enabled differentiation between slugs and soils; soils showed a monotonic increase in the intensity of the relative reflection for this wavelength. The extrema determined in the reflection spectra of slugs were used to develop and set up a slug detector device consisting of a monochromatic camera, a filter changer and two narrow bandpass filters with nominal wavelengths of 925 nm and 975 nm. The developed optical system takes two photographs of the target area at night. By subtracting the pixel values of the images, the slugs are highlighted, and the soil is removed in the image due to the properties of the reflection spectra of soils and slugs. In the resulting image, the pixels of slugs were, on average, 12.4 times brighter than pixels of soil. This enabled the detection of slugs by a threshold method.

Rotational varifocal moiré metalens made of single-crystal silicon meta-atoms for visible wavelengths

Metasurface lenses (metalenses) offer an ultrathin and simple optical system with dynamic functions that include focal length tuning. In this study, a rotational varifocal (i.e., moiré) metalens based on octagonal single-crystal silicon pillars was designed and fabricated to realize a high transmittance, whole 2π phase coverage, and polarization insensitivity for visible wavelengths. The moiré metalens consists of a pair of cascaded metasurface-based phase lattices and the focal length can be adjusted from negative to positive by mutual rotation. The fabricated moiré metalens demonstrated a focal length that can be tuned from −36 mm to −2 mm and from 2 to 12 mm by mutual rotation from −90° to 90°, and the experimental measurements agreed well with theoretical values at the design wavelength of 633 nm. Imaging was demonstrated at three distinct wavelengths of 633, 532, and 440 nm.

Design of 3D Imaging Lidar Optical System for Large Field of View Scanning

3D lidar has been widely used in various fields. The MEMS scanning system is one of its most important components, while the limitation of scanning angle is the main obstacle for its application in various fields to improve the demerit. In this paper, a folded large field of view scanning optical system is proposed. The structure and parameters of the system are determined by theoretical derivation of ray tracing. The optical design software Zemax is used to design the system. After optimization, the final structure performs well in collimation and beam expansion. The results show that the scan angle can be expanded from ±5° to ±26.5°, and finally parallel light scanning is realized. The spot diagram at a distance of 100 mm from the exit surface shows that the maximum radius of the spot is 0.506 mm with a uniformly distributed spot. The maximum radius of the spot at 100 m is 19 cm, and the diffusion angle is less than 2 mrad. The energy concentration in the spot range is greater than 90% with a high system energy concentration, and the parallelism is good. This design overcomes the shortcoming of the small mechanical scanning angle of the MEMS lidar, and has good performance in collimation and beam expansion. It provides a design method for large-scale application of MEMS lidar.

Design Simulation of Czerny–Turner Configuration-Based Raman Spectrometer Using Physical Optics Propagation Algorithm

We report the design simulation of the Raman spectrometer using Zemax optical system design software. The design is based on the Czerny–Turner configuration, which includes an optical system consisting of an entrance slit, two concave mirrors, reflecting type diffraction grating and an image detector. The system’s modeling approach is suggested by introducing the corresponding relationship between detector pixels and wavelength, linear CCD receiving surface length and image surface dimension. The simulations were carried out using the POP (physical optics propagation) algorithm. Spot diagram, relative illumination, irradiance plot, modulation transfer function (MTF), geometric and encircled energy were simulated for designing the Raman spectrometer. The simulation results of the Raman spectrometer using a 527 nm wavelength laser as an excitation light source are presented. The present optical system was designed in sequential mode and a Raman spectrum was observed from 530 nm to 630 nm. The analysis shows that the system’s image efficiency was quite good, predicting that it could build an efficient and cost-effective Raman spectrometer for optical diagnostics.

OPTICAL SYSTEM DESIGN OF THE DETECTOR FOR SOLAR TERAHERTZ EMISSION MEASUREMENTS

The objectives and scientific tasks of the planned space experiment “Solntse-Terahertz” to be performed onboard the ISS Russian Segment are briefly described in the paper. In particular, the aim of the experiment is to study uninvestigated solar electromagnetic emission in the terahertz domain, in ~ 1012 – 1013 Hz (300-30 µm) frequency range. It is expected to obtain new data on solar active region emission including solar flare emission. These data are necessary to clarify the nature of solar activity and construct physical model of charged particle acceleration in active regions during solar flares and other astrophysical objects. We focus on the telescope optical system design and evaluation of main characteristics of this system. Results of simulations and comparison with the experimental verification of obtained characteristics are presented. A close correlation of the estimations and experimental results was obtained. As a result, main parameters of the telescope optical system of experimental hardware “Solntse-Terahertz” were determined. Key words: Sun, solar flares, terahertz emission, optical system.

Autonomous Streaming Space Objects Detection Based on a Remote Optical System

Traditional image processing techniques provide sustainable efficiency in the astrometry of deep space objects and in applied problems of determining the parameters of artificial satellite orbits. But the speed of the computing architecture and the functions of small optical systems are rapidly developing thus contribute to the use of a dynamic video stream for detecting and initializing space objects. The purpose of this paper is to automate the processing of optical measurement data during detecting space objects and numerical methods for the initial orbit determination.This article provided the implementation of a low-cost autonomous optical system for detecting of space objects with remote control elements. The basic algorithm model had developed and tested within the framework of remote control of a simplified optical system based on a Raspberry Pi 4 single-board computer with a modular camera. Under laboratory conditions, the satellite trajectory had simulated for an initial assessment of the compiled algorithmic modules of the computer vision library OpenCV.Based on the simulation results, dynamic detection of the International Space Station in real-time from the observation site with coordinates longitude 25o41′49″ East, latitude 53o52′36″ North in the interval 00:54:00–00:54:30 17.07.2021 (UTC + 03:00) had performed. The video processing result of the pass had demonstrated in the form of centroid coordinates of the International Space Station in the image plane with a timestamps interval of which is 0.2 s.This approach provides an autonomous raw data extraction of a space object for numerical methods for the initial determination of its orbit.