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Terrestrial and Astronomical Applications of Uncooled Infrared Technology

Rashman, M (2020) Terrestrial and Astronomical Applications of Uncooled Infrared Technology. Doctoral thesis, Liverpool John Moores University.

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Abstract

This thesis provides an account of the application of uncooled microbolometer technology in two different fields; astronomy and conservation ecology. Uncooled microbolometers are readily available as low-cost, commercial detectors for imaging in the 7.5 − 13.5μm spectral region. Their affordable price and coverage of the wavelengths at which the the spectral energy distribution of animals that use metabolic heat to maintain a stable internal temperature peaks, has popularised these systems for use in ecology. However, their use as the primary detectors in conservation surveys suffers from a data analysis bottleneck due to the large volumes of data and the manual approach to detecting and identifying animal species. As a result, the efficiency and efficacy of these systems is limited by the volume of data and the lack of resources and experience in handling infrared imagery. In contrast, astronomical techniques are well developed for infrared wavelengths and the analysis of large quantities of data has been successfully automated for many years. Apart from observations of solar system objects with very small (<200mm aperture) telescopes and some high altitude experiments, microbolometers have not been deployed in astronomy for ground-based observing. Although observing in this spectral region is key to understanding the cold, dusty and distant universe, resources for mid-IR observing are not as readily available as those for other wavelengths due to the very high thermal background and the requirement for specialist detector systems. Through our work, we attempt to discern whether microbolometers, and standard astronomical infrared observing and data analysis techniques, can be applied successfully in these two fields. In part I three analogous, standard astronomical instrumentation techniques are applied to characterise the random and spatial noise present in a FLIR Tau 2 Core microbolometer to determine the systematics and sources of statistical noise that limit read-out accuracy. Flat fielding, stacking and binning are used to determine that the focal plane array is dominated by large structure noise, and demonstrate how this can be corrected. An NEdT of < 60mK is isolated and recorded for the system. Part II introduces Astro-Ecology, a field that couples microbolometers and astronomy instrumentation techniques for application in conservation biology to monitor vulnerable species. Several investigations are presented to determine the feasibility of developing an astronomy based, fully automated reduction pipeline for mid-IR data collected using unmanned aerial vehicle (UAV) technology From these investigations the efficacy of microbolometers for animal surveys was found to be highly dependent on ground and ambient air temperatures, and to fully automate a pipeline would require more than standard astronomical techniques and software. In part III, a small, passively cooled, prototype, N -band (∼ 10μm) instrument is developed and tested. The optical and mechanical design of the instrument is described, with the instrument constructed from commercially available components and an uncooled microbolometer focal-plane array. The incorporation of adjustable germanium reimaging optics rescale the image to the appropriate plate scale for the 2-m diameter Liverpool Telescope on La Palma. A week-long programme of observations was conducted to test the system sensitivity and stability, and the feasibility of using this technology in ‘facility’ class instruments for small telescopes. From observations of bright solar system and stellar sources, a plate scale of 0.75′′ per pixel is measured, with this confirming that the optical design allows diffraction limited imaging. A photometric stability of ∼ 10% is recorded with this largely due to sky variability. A 3σ sensitivity of 7 × 103 Jy for a single, ∼ 0.11 second exposure is measured, which corresponds to a sensitivity limit of 3 × 102 Jy for a 60 second total integration. Recognising the need for improved sensitivity, the instrument was upgraded to be optimised for mid-IR observations using a chopping system. The instrument was deployed for a week on the 1.52m Carlos Sanchez Telescope on Tenerife alongside a regime of chopping and nodding. Observations of several very bright mid-IR sources with catalogue fluxes down to ∼ 600 Jy are presented. A sensitivity improvement of ∼ 4 magnitudes over previous unchopped observations is recorded, in line with sensitivity predictions.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: infrared; microbolometer; instrumentation; astronomy; ecology
Subjects: Q Science > QB Astronomy
Q Science > QH Natural history > QH301 Biology
Divisions: Astrophysics Research Institute
Date Deposited: 17 Jun 2020 22:03
Last Modified: 17 Jun 2020 22:04
DOI or Identification number: 10.24377/LJMU.t.00013093
Supervisors: Longmore, S, Wich, S and Steele, I
URI: https://researchonline.ljmu.ac.uk/id/eprint/13093

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