LOW POWER POLYPHASE FAST-FOURIER TRANSFORM SPECTROMETER FOR SPACEBORNE INSTRUMENTS

K. Kempe¹, M. Krus¹, O. Auriacombe¹

¹Omnisys Instruments AB

AAC Omnisys is a world leader in spectrometer back-end systems for radiometers, with a strong heritage in both spaceborne and ground-based instrumentation. Its autocorrelation spectrometer technology has been deployed in missions such as ODIN, the Submillimetre Wave Instrument onboard ESA’s Jupiter Icy Moon Explorer (JUICE), and NASA’s balloon mission GUSTO. The last two use the latest available ICs; HIFAS: 8 GHz 1024 channels [1]

In parallel, Omnisys has developed a Fast Fourier Transform (FFT) spectrometer implemented on FPGA technology, featuring 5 GHz instantaneous bandwidth, 16k channels, and 40 W power consumption, successfully deployed in ground-based water vapour radiometers and in the first airborne hyperspectral microwave sounder demonstrator [2–5].

Building on this experience, a new member of our FPGA based spectrometer family has been developed focusing on a reduction in power consumption at the expense of a slightly reduced frequency coverage. It is assembled into a 1U stackable cubesat compatible structure (100 x 100 x 25 mm) with a mass of 200 grams.

Two RF inputs can be used either individually or combined through IQ-mixing to achieve a maximum of 1500 MHz instantaneous bandwidth at a typical spectral resolution of less than 100 kHz (16384 channels).

The firmware design also includes double buffering capable of reading one buffer while integrating to the other.

The unit is powered from a single wide range 8-16 V input power line and performing all subsequent power conditioning locally inside the box.

A SpaceWire / RMAP interface is used as the nominal communication interface, but custom solutions including UART, SPI, I2C, etc can be developed on request, both single ended and LVDS differential.

For customization, a separate general purpose I/O connector can be used for direct and digital control of specific features.

This development addresses the growing demand for compact, power-efficient, high-resolution digital back-ends in future Earth Observation hyperspectral missions. The performance and characteristics of this next-generation spectrometer will be presented.

1. Christopher Walker, Craig Kulesa, Abram Young, William Verts, Jian-Rong Gao, Qing Hu, Jose Silva, Behnam Mirzaei, Wouter Laauwen, Jeffrey Hesler, Christopher Groppi, Anders Emrich, “Gal/Xgal U/LDB Spectroscopic/Stratospheric THz Observatory: GUSTO,” Proc. SPIE 12190, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI, 121900E (31 August 2022);

2. O. Auriacombe et al., “High Spectral Resolution Airborne Microwave Sounder (HiSRAMS),” 2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), Delft, Netherlands, 2022, pp. 1-2, doi: 10.1109/IRMMW-THz50927.2022.9895768.

3. N. Bliankinshtein et al., “Airborne Validation of HiSRAMS Atmospheric Soundings,” IGARSS 2023 – 2023 IEEE International Geoscience and Remote Sensing Symposium, Pasadena, CA, USA, 2023, pp. 4372-4375, doi: 10.1109/IGARSS52108.2023.10281883.

4. S. Xu et al., “Low-Level Processing of Passive Hyperspectral Microwave Measurements from Hisrams,” IGARSS 2023 – 2023 IEEE International Geoscience and Remote Sensing Symposium, Pasadena, CA, USA, 2023, pp. 1096-1099, doi: 10.1109/IGARSS52108.2023.10283050.

5. N. Bliankinshtein et al., “Radiometric Calibration of a Hyperspectral Microwave Sounder,” 2023 48th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Montreal, QC, Canada, 2023, pp. 1-2, doi: 10.1109/IRMMW-THz57677.2023.10299101.