Offner Scheme Research Articles

Spectral-spatial neural network classification of hyperspectral vegetation images

The paper presents the results of a study of the method of classification of vegetation types based on hyperspectral survey data. A hyperspectrometer based on the Offner scheme was used as a shooting equipment. The spatial-spectral architecture of a convolutional neural network is used as a classifier. The experiments performed show the effectiveness of the proposed approach for the classification of vegetation types.

Negatively chirped pulse compressor with internal telescope for 1.4 µm range

The peculiarities analysis in design of compressors for negatively chirped optical pulses parametrically amplified in double-chirped regime up to 1 J in multi-cascade system is done. A comparative analysis of the spatio-temporal distribution of the pulses at the output of various compressor schemes with an internal telescope has been performed. The analysis has been carried out using two methods: calculating additional compressor dispersion using the Seidel aberration coefficients of the internal telescope and the ray tracing method. A ray-tracing algorithm has been developed that allows to calculate the spatiotemporal and spatiospectral pulse intensity distributions at the output of compressors with an internal telescope. The on-axis and off-axis Offner schemes, Martinez scheme compressor and compressor scheme with a single-lens internal telescope are analyzed. It is shown, that the ray tracing method more accurately takes into account system aberrations, including high-order aberrations, while the calculation with the Seidel aberration coefficients takes into account only primary aberrations. According to the analysis, the optimal scheme of a grating compressor with an internal telescope for compressing negatively chirped pulses in the range of 1410 nm to a duration of less than 40 fs and energies up to ~ 0.8 J is the off-plane Offner scheme.

Offner型连续变焦中波红外光谱成像系统设计

In order to adapt to the application requirements of different field of view spectrometers, a continuous zoom medium-wave infrared spectrum imaging system based on offner scheme was designed. The front zoom system to achieve continuous zoom in the range of 60-300 mm was introduced in the system, and a grating-type offner concentric structure was used for spectral splitting and imaging. The working band was 3-5 m, the cooled medium-wave infrared detector was used, the F#=4.0 in this system. According to the object image exchange principle and the power distribution principle, the initial structure of the front zoom system and the relay system were calculated, and the zemax software was used to optimize each subsystem to meet the design parameters. The modulation transfer function of the final continuous zoom medium-wave infrared spectrum imaging system based on offner scheme was close to the diffraction limit at a spatial frequency of 33 lp/mm, and the root mean square radius of the spot was smaller than one pixel. The design results show that the system structure is simple, and the image quality is good and meets the design indicator requirements at each focal length position and each spectral segment.

A dual-range diffraction grating for imaging hyperspectrometer based on the Offner scheme

The paper presents the results of a study of the feasibility of using a dual-range diffraction reflecting grating applied to a convex mirror in a imaging hyperspectrometer based on the Offner scheme. The parameters of a small diffraction grating are chosen and large for operation in the spectral ranges of visible and middle infrared regions. The results of modeling the work of the proposed configuration of the diffraction grating are presented, which showed a negligibly small effect of a large diffraction grating on the work of small and vice versa, and the negligibly small effect of a small grating on the work of a large grating. A method is proposed for increasing the diffraction efficiency of a dual-range grating for operation in the +1 order in the visible range and in the −1 near IR range. The results of modeling using the software package Zemax

Experimental study and calibration of the imaging hyperspectrometer based on the Offner scheme

In this paper, a hyperspectrometer based on the Offner scheme is described. Experimental testing of the hyperspectrometer model was carried out. The spectral characteristics of the imaging hyperspectrometr are investigated. With the help of a tunable laser, calibration data of the experimental design of the hyperspectrometer were obtained, which allowed each channel of the hyperspectral image to correspond to a specific wavelength. The spectral sensitivity of the imaging hyperspectrometer was experimentally obtained. The software for obtaining hypercubes is presented. Using the example of calculating the NDVI and WBI indices, the technical capabilities of the prototype is showed.

Offner型消热差中波红外成像光谱仪设计

Offner型消热差中波红外成像光谱仪设计

The study of the basic operating parameters of a hyperspectrometer based on the Offner scheme

In this article, the comparing of mathematical modelling results of a hyperspectrometer based on the Offner’s scheme is considered. This modelling was carried on within geometric optics. The goal of this comparing was a confirmation of mathematical model correctness, which was developed. The dependences of point spread function size and coordinate of beam center from wavelength was obtained. All results shows that developed mathematical model describes quiet well a hyperspectrometer behaviour.

Alignment and study of prototypes of the Offner hyperspectrometer

A prototype of the hyperspectrometer based on the Offner scheme has been tested. Drawings have been produced and the main mirror elements of the hyperspectrometer including diffraction grating on a convex spherical surface have been fabricated. The profile of the grating groove has been measured and light energy distribution in diffraction orders has been modeled as a function of wavelength. Optomechanical elements for the necessary alignments of the hyperspectrometer elements have been designed and manufactured. Adjustment of the optical prototyping scheme has been implemented and point images for three wavelengths of monochromatic radiation have been obtained. Distribution of light energy in diffraction orders and maxima positions are in an agreement with the simulation results. The spectrometer has also been tested on test images in polychromatic radiation under the control of the developed software.

A dual-range spectrometer based on the Offner scheme

We considered the feasibility of using a dual-range diffraction grating on the convex mirror in an imaging hyperspectrometer based on the Offner scheme. We conducted modeling in Zemax software. It is shown that the use of a dual-range grating allows one to use the hyperspectrometer based on the Offner scheme in two spectral ranges: the visible and mid-infrared.

Modeling the performance of a spaceborne hyperspectrometer based on the offner scheme

This article deals with modeling of a hyperspectrometer based on the Offner scheme within geometric optics. We show that at a certain set of parameters, the geometric aberrations are small compared with the size of a conventional CCD matrix sensor. An integral equation for the reconstruction of spectral components of the signal under the overlapping of spectral orders is derived.

Simulation model of a multichannel Offner hyperspectrometer

We study an advanced airborne hyperspectral system based on the Offner scheme for Earth remote sensing that has the advantages of compact size and high spatial and spectral resolution. An algorithm that enables choosing the most effective design parameters is developed. A schematic design and a simulation model of the multichannel hyperspectrometer are discussed.

Modeling action of a hyperspectrometer based on the offner scheme within geometric optics

We considered comparative modeling action of a hyperspectrometer based on the Offner scheme including prisms or a diffraction grating within the geometrical optics. It is shown that the use of a diffraction grating instead of a prism results in a more uniform spread of the spectral components of the dispersed image.