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The compact scientific research device allows observing the Earth’s surface in multichannel spectral imaging, revealing objects on the planet and their properties that are invisible to conventional means of observation. Hyper-spectrometers help conducting environmental monitoring more efficiently, observing the condition of forests and agricultural crops, monitoring forest fires occurrence and performing other tasks.
The Samara development is installed on board the SXC3-219 ISO nanosatellite, launched into orbit in August 2022, as part of the launch from the Baikonur Сosmodrome of the Soyuz-2.1b launch vehicle with the “Fregat” upper stage with 16 Russian satellites and the Iranian “Khayyam” satellite. Previously, hyper-spectrometers on domestic spacecrafts of this class – standard CubeSat 3U nanosatellites (consisting of three “cubes”, each measuring 10x10x10 cm) – were not installed due to the difficulties of creating a sufficiently compact device with the parameters required for hyperspectral imaging from outer space.
“Our hyper-spectrometer for cubesats has passed the flight test program, successfully completing the tasks assigned to it. During the flight, high-quality hyperspectral images of various territories of Eurasia, Australia, Africa, and North America were obtained. There are only two continents – South America and Antarctica – left outside the lens. However, the main result of these tests is not the number of images taken and transmitted, but the fact that operability of the scheme of internal fastening of elements of such a hyper-spectrometer, invented by us in 2020, has been confirmed in practice. Unlike the foreign scheme of the elements, ours allows achieving greater image clarity with less design complexity and lower energy consumption,” said Roman Skidanov, Doctor of Physical and Mathematical Sciences, Professor of Samara University’s Department of Engineering Cybernetics.
Operating in orbit, the hyper-spectrometer is constantly exposed to significant temperature changes: the satellite is either heated by the Sun, or cooled in the shadow of the Earth. Temperature fluctuations cause deformation of the lens material and other structural elements, which leads to distortion and fuzziness of the resulting “image”. Usually, for avoiding such distortions, the space hyper-spectrometer is equipped with the special thermal stabilization system – a kind of “thermos” or “refrigerator”. However, this “refrigerator” not only takes up a lot of space on the satellite, but also consumes a lot of electricity.
In 2020, Samara scientists proposed an innovative approach – to change the traditional scheme of the fasteners of the hyper-spectrometer optics. The experiments conducted at that time showed that if the fasteners were placed radially, then the optical system could be regulated – adjusted, sharpened – using only two compact stepper motors. These engines are about an order of magnitude lighter than the conventional thermal stabilization system (which can now be dispensed with), moreover, they need less space (which means that another payload can also be installed on board), and have minimal power consumption, turning on only at the time of adjustment.
“The experimental results obtained at that time allowed us to make a reasonable assumption that such a hyper-spectrometer would be able to operate with high efficiency over a wide temperature range without using the thermal stabilization system to maintain a certain temperature. Flight tests of our hyper-spectrometer have fully confirmed this idea, and now we can confidently say that our proposed approach is very promising for use in outer space and the stratosphere,” noted Roman Skidanov.
The capacity of such technology is also clearly indicated by the difference between the quality of images made by the Samara device and its “classmates” – comparable in size and class hyper-spectrometers installed on foreign nanosatellites according to the traditional scheme with the thermal stabilization system, for example, on NASA NACHOS nanosatellites launched in the same year of 2022. Although there are not very many publicly available images from such nanosatellites, but from what we have, we can see that the quality of our “hyper-image” is much better.
Unfortunately, the first Russian hyper-spectrometer for cubesats will not return to the Earth. The orbit of the satellite it is on board slowly but surely decreases, and in about a year and a half, scientists predict for the satellite to burn up in the atmosphere. However, the test results and the space-proven technology will remain, on the basis of which new, more advanced compact hyperspectrometers will be created to solve a wide variety of tasks.
“This optical scheme makes it possible to reduce the design without significant deterioration in quality, since all the changes taking place there are almost linear, so it will be possible to design an even more compact hyper-spectrometer,” stressed Roman Skidanov.
About the hyper-spectrometer
This hyper-spectrometer is developed on the basis of the Offner’s method. The device shoots in the visible and near infrared ranges. The number of spectral channels is from 150 to 300, spectral resolution is from 2 to 4 nm. The hyper-spectrometer mass is 1.6 kg, its dimensions are 13x9.4x9.4 cm, that is, it occupies less than half of the internal space of the CubeSat 3U nanosatellite with dimensions 10x10x30 cm.
Despite the fact that the satellite was launched as part of the scientific and educational project “Space π”, the hyper-spectrometer installed on it is a full-fledged research device that allows conducting hyperspectral remote sensing of the Earth. Thus, during tests in outer space, the hyper-spectrometer demonstrated its capabilities to obtain data for determining spectral vegetation indices used in agriculture to solve problems of smart farming.
In total, there are more than 150 vegetation indices to be calculated on the basis of spectral data, show various plant parameters and properties necessary for agricultural producers to properly care for their crops. Depending on their condition, amounts of vitamins and moisture, ambient temperature and other factors, plants differently absorb and reflect electromagnetic waves in various ranges, and spectra. By comparing these data in the single complex with applying multi- or hyperspectral imaging, it is possible to remotely, quickly and more accurately assess the particular crop condition, without selectively sending individual plants or soil samples for laboratory analysis.
Images obtained in course of the experiment from the Samara hyper-spectrometer made it possible, for example, to identify areas of winter crops with the largest green mass, with high amount of chlorophyll, as well as to check farmlands that fell into the hyper-spectrometer lens for problematic crops. The data showed the level of moisture reserves in plants and helped to calculate the vegetation index that models the future productivity of plants, that is, gives the preliminary forecast of yield.
Another calculated index assessed the physiological condition of plants in terms of their stress. As it is known, plants are also subject to stress that can be caused by adverse phenomena – drought or overabundance of moisture, strong wind, temperature changes, sudden frosts, invasion of pest insects. Due to stress, metabolic changes occur in plants, and the hyper-spectrometer can detect them even from outer space.
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* Samara University is one of the world leaders in photonics. More than 40 years ago, the scientific School of Computer Optics and Image Processing was established and has been successfully operating at the University, headed by Viktor Soyfer, Academician of the RAS and the President of Samara University. The University scientists have developed innovative diffraction optics, which has found its application in a variety of fields, such as outer space, medicine, and agriculture.
** “Space π” is the science-and-education project for development and production of small CubeSat-format spacecrafts on domestic satellite platforms, aimed at forming a grouping of about 100 3U CubeSats in orbit for several years, to create the infrastructure for involving schoolchildren in research and technical creativity in the field of space technologies.
