The Hyperspectral Thermal Emission Spectrometers - Characteristics and Performance

The HyTES instruments represent a new generation of airborne TIR pushbroom imaging spectrometers with much higher spectral resolution and a wide swath. HyTES-1 is operational and HyTES-2 is in development. The HyTES spectrometers include many enabling state-of-the-art technologies including a Dyson-inspired spectrometer and high-performance convex diffraction grating. The Dyson optical design allows for a very compact and optically fast system (F/1.6) and minimizes cooling requirements since a single monolithic prism-like grating design can be used which allows baffling for stray light suppression. The monolithic configuration eases mechanical tolerancing requirements which are a concern since the complete optical assembly is operated at cryogenic temperatures (≤100K). HyTES-1 has 512 cross track pixels over a 46-degree field of view. HyTES-1 originally used a Quantum Well Infrared Photodetector (QWIP) and had 256 spectral channels between 7.5μm to 12μm. In 2021 this was upgraded to a Barrier InfraRed Detector (BIRD) array with 284 spectral channels between 7.0μm to 12μm. The first science flights with the QWIP were conducted in 2013 and the first science flights with the BIRD in 2021. A second BIRD array with improved performance has now been completed and is being integrated into HyTES-1. Work is also underway on a second HyTES spectrometer referred to as HyTES-2. HyTES-2 has an extended wavelength coverage between 3-12μm and 512 spectral channels. HyTES-2 is expected to begin flights in 2027/8. Many flights have been conducted with HyTES-1, and the instrument can be deployed on a Twin Otter, Gulfstream or ER2 aircraft allowing a variety of pixel sizes depending on flight altitude. In 2023 a joint campaign was conducted with the European Space Agency to acquire data for simulating and evaluating data from several upcoming thermal infrared missions including the ASI/NASA SBG-TIR, the ESA LSTM and ISRO/CNES TRISHNA missions. This paper describes the instruments and their development together with some results.