Spectrometer
Optics for collecting electromagnetic radiation for the observation of earth and space
Far-field exploration by satellite systems has emerged as a special field of space technology. This analysis of the environment works with special instruments, complex spectrometers or sensors. Objectives of such projects include the investigation and monitoring of the climate and associated inspection of air pollution or pollutant formation within the atmosphere. Successful explorations require complex optical components designed to withstand extreme environmental conditions and to ensure the best possible imaging quality.
The electromagnetic spectrum
Electromagnetic radiation is emitted continuously or in pulses by objects as wave radiation and does not require a propagation medium. Consequently, it can take long distances, even in space. Far-field exploration uses this characteristic. The entirety of the wavelengths occurring in electromagnetic radiation ranges from short to long wavelengths and is called the electromagnetic spectrum. Depending on the individual material properties,
- Deflection, scattering or reflection,
- Absorption and
- Transmission
of electromagnetic radiation occurs at the interfaces of investigated objects or materials. To measure this radiation, complex systems and individually adapted optics are required. In addition to high-quality spheres, aspheres or mirror systems, high-performance sensors (e.g. within a spectrometer) are used to detect the electromagnetic radiation. Furthermore, a carrier (satellite), a placement and control unit are required. For data transmission, a far-reaching data transmission system is required too.
Figure 1: Simplified schematic structure of a spectrometer
Remote sensing of the earth’s atmosphere
Thanks to high-quality spectrometers mounted on satellites, remote sensing of the Earth’s atmosphere provides a wealth of new, useful and global information for various environmental analyses. The spectrometer acts as a sensor whose task is to analyze and measure sunlight (= electromagnetic radiation) scattered into the atmosphere and also reflected by the earth’s surface. For this purpose, the spectral components of incident light are decomposed by a prism and/or a grating structure (see Fig.1) and recorded by a multi-lens camera - a so-called multispectral camera. The obtained spectra contain specific information on the scattering and absorption behavior of the earth’s atmosphere as well as the reflection behavior of the earth’s surface. Thanks to the different spectral colors, aerosol particles, for example, can be distinguished from cloud particles. High data density and the associated complex calculations result in an extremely complex analysis.
Sentinel-4 and 5 as project examples
Spectrometers are used in missions such as Sentinel-4 and Sentinel-5, satellites of the Copernicus program, a joint project of EU and ESA. Both are designed for the ultraviolet, visible and near-infrared spectral range, the Sentinel-5 spectrometer additionally for short-wave infrared spectral range. Aims of these projects include monitoring air quality over regions of Europe and North Africa (Sentinel-4) and measurements of trace gases and aerosols (Sentinel-5). As project partner asphericon produced, among other things, various high-quality spheres and aspheres for the spectrometer of Sentinel-4. The manufactured optics are characterized by high-end surface shape, roughness and form deviation tolerances.
Learn more about the Sentinel-4 spectrometer in our reference story.
asphericon offers high-precision optics, such as aspheres and spheres, as well as other optical components for high-performance space spectrometers. In addition to extremely compact designs, which allow space for further components within a system, we guarantee best imaging qualities even for unusual geometries. Finishing processes, such as High-End Finishings, ensure lowest roughness values.
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