Assessment of the performance of a compact concentric spectrometer system for Atmospheric Differential Optical Absorption Spectroscopy

Abstract

Abstract.A breadboard demonstrator of a novel UV/VIS grating spectrometer has been developed based upon a concentric arrangement of a spherical meniscus lens, concave spherical mirror and curved diffraction grating suitable for a range of atmospheric remote sensing applications from the ground or space. The spectrometer is compact and provides high optical efficiency and performance benefits over traditional instruments. The concentric design is capable of handling high relative apertures, owing to spherical aberration and comma being near zero at all surfaces. The design also provides correction for transverse chromatic aberration and distortion, in addition to correcting for the distortion called "smile", the curvature of the slit image formed at each wavelength. These properties render this design capable of superior spectral and spatial performance with size and weight budgets significantly lower than standard configurations. This form of spectrometer design offers the potential for exceptionally compact instrument for differential optical absorption spectroscopy (DOAS) applications from LEO, GEO, HAP or ground-based platforms. The breadboard demonstrator has been shown to offer high throughput and a stable Gaussian line shape with a spectral range from 300 to 450 nm at 0.5 nm resolution, suitable for a number of typical DOAS applications.

High-resolution measurements from the airborne Atmospheric Nitrogen Dioxide Imager (ANDI)

“…To gain perspective on the distribution of NO 2 around urban environments, a remote sensing instrument known as the Atmospheric Nitrogen Dioxide Imager (ANDI) was developed at the University of Leicester. The main component of the ANDI instrument is a compact imaging spectrometer known as CompAQS (Whyte et al, 2009), which was installed in a light aircraft alongside a series of ancillary systems and flown in a push-broom nadir configuration on the 28 February 2013. When flown at 900 m altitude the ANDI system produces maps of NO 2 differential slant column densities (dSCDs) beneath the aircraft across swaths approximately 600 m wide with an across-swath resolution of approximately 5 m (see Sect.…”

High-resolution measurements from the airborne Atmospheric Nitrogen Dioxide Imager (ANDI)

“…The components include a CompAQS spectrometer (Whyte et al, 2009), the Global Positioning System (GPS), an inertial monitoring unit (IMU), a digital single-lens reflex (DSLR) camera and a power system to condition and convert the 28 V provided by the aircraft's generators into the 12 and 19 V used by the ANDI instruments. The ANDI system design is shown in Fig.…”

“…The CompAQS spectrometer was originally built as a technology readiness improvement exercise towards the development of a compact grating spectrometer suitable for a small satellite mission (Whyte et al, 2009;Leigh et al, 2015). For application in the ANDI system the optical bench of CompAQS was modified and strengthened to allow for a vertical (nadir) configuration.…”

“…The original design had a UV optimised grating (2350 grooves mm −1 ), while in ANDI a grating of 1800 grooves mm −1 was used for the fitting window specified in Table 2. Additionally, in the Whyte et al (2009) breadboard design a fold mirror was incorporated, which was removed in the ANDI iteration to simplify the design and to reduce internal stray light. It is most likely that the degradation in the instrument line shape has occurred as a result of the build of the airborne version.…”

“…The main component of the ANDI instrument is a compact imaging spectrometer known as CompAQS (Whyte et al, 2009), which was installed in a light aircraft alongside a series of ancillary systems and flown in a push-broom nadir configuration on the 28 February 2013. When flown at 900 m altitude the ANDI system produces maps of NO 2 differential slant column densities (dSCDs) beneath the aircraft across swaths approximately 600 m wide with an across-swath resolution of approximately 5 m (see Sect.…”