The Spatial Heterodyne Observations of Water instrument (SHOW) is a limb imaging instrument that is being developed to provide accurate, dense, high vertical resolution measurements of water vapour in the upper troposphere and lower stratosphere. SHOW utilizes a field widened spatial heterodyne spectrometer operating in the limb viewing configuration to observe limb scattered sunlight in a small ~3 nm spectral window centered near 1365 nm. Vertically resolved images of the limb absorption spectrum are obtained with each frame that are inverted using non-linear optimal estimation to extract the vertical distribution of water vapour. The large throughput and high spectral resolution (0.02 nm unapodized) provided by the field widened SHS allows vertical profiles with a target vertical resolution of < 500 m to be obtained with rapid along track sampling (~50 km below 20 km and between 100 km – 300 km above 20 km) from a low earth orbit satellite. In this paper, we present the SHOW measurement concept and examine the practical considerations that influence design tradeoffs. We discuss the challenges and solutions that have been identified to optimize the instrument configuration and present an end-to-end simulation of the level 0 measurements, calibrations and level 2 water vapour product.

Isentropic mixing across and above the subtropical jet is a significant mechanism for stratosphere–troposphere exchange. In this work, we show new observational evidence on the role of this process in moistening the lowermost stratosphere. The new measurement, obtained from the Spatial Heterodyne Observations of Water (SHOW) instrument during a demonstration flight on the NASA's ER-2 high-altitude research aircraft, captured an event of poleward water vapour transport, including a fine-scale (vertically <∼1 km) moist filament above the local tropopause in a high-spatial-resolution two-dimensional cross section of the water vapour distribution. Analysis of these measurements combined with ERA5 reanalysis data reveals that this poleward mixing of air with enhanced water vapour occurred in the region of a double tropopause following a large Rossby wave-breaking event. These new observations highlight the importance of high-resolution measurements in resolving processes that are important to the lowermost-stratosphere water vapour budget.

The Spatial Heterodyne Observations of Water instrument (SHOW) is a limb-sounding satellite prototype that utilizes the Spatial Heterodyne Spectroscopy (SHS) technique, operating in a limb-viewing configuration, to observe limb-scattered sunlight in a vibrational band of water vapour within a spectral window from 1363 to 1366 nm. The goal is to retrieve high vertical and horizontal resolution measurements of water vapour in the upper troposphere and lower stratosphere. The prototype instrument has been configured for observations from NASA's ER-2 high-altitude airborne remote science airplane. Flying at a maximum altitude of ∼21.34 km with a maximum speed of ∼760 km h−1, the ER-2 provides a stable platform to simulate observations from a low-earth orbit satellite. Demonstration flights were performed from the ER-2 during an observation campaign from 15 to 22 July 2017. In this paper, we present the laboratory characterization work and the level 0 to level 1 processing of flight data that were obtained during an engineering flight performed on 18 July 2017. Water vapour profile retrievals are presented and compared to in situ radiosonde measurements made of the same approximate column of air. These measurements are used to validate the SHOW measurement concept and examine the sensitivity of the technique.

A CubeSat-sized limb sounder utilizing a Spatial Heterodyne Spectrometer for the detection of the O2 Atmospheric A-Band is presented. The purpose of the instrument is to measure vertical profiles of temperature in the middle atmosphere.

A highly miniaturized limb sounder for the observation of the O2 A-band to derive temperatures in the mesosphere and lower thermosphere is presented. The instrument consists of a monolithic spatial heterodyne spectrometer, which is able to resolve the rotational structure of that band. The SHS operates at a Littrow wavelength of 762 nm with a resolving power in the order of 10.000. Complemented by a front optics with an acceptance angle of less than ±1 degree and a detector optics, the entire optical system fits into a volume of about 1.5 liters. This allows this instrument to be flown on a three or six unit CubeSat. In this paper, we introduce the optical design and computer simulations on the expected performance of the instrument. The laboratory characterization of a prototype instrument, which has been built on university level, and the lessons learned are discussed.

A highly miniaturized limb sounder for the observation of the O-2 A-band to derive temperatures in the mesosphere and lower thermosphere is presented. The instrument consists of a monolithic spatial heterodyne spectrometer (SHS), which is able to resolve the rotational structure of the R-branch of that band. The relative intensities of the emission lines follow a Boltzmann distribution and the ratio of the lines can be used to derive the kinetic temperature. The SHS operates at a Littrow wavelength of 761.8 nm and heterodynes a wavelength regime between 761.9 and 765.3 nm with a resolving power of about 8000 considering apodization effects. The size of the SHS is 38 x 38 x 27 mm(3) and its acceptance angle is +/- 5 degrees. It has an etendue of 0.01 cm(2) sr. Complemented by front optics with an acceptance angle of +/- 0.65 degrees and detector optics, the entire optical system fits into a volume of about 1.5 L. This allows us to fly this instrument on a 3- or 6-unit CubeSat. The vertical field of view of the instrument is about 60 km at the Earth's limb when operated in a typical low Earth orbit. Integration times to obtain an entire altitude profile of nighttime temperatures are on the order of 1 min for a vertical resolution of 1.5 km and a random noise level of about 1.5 K. Daytime integration times are 1 order of magnitude shorter. This work presents the design parameters of the optics and a radiometric assessment of the instrument. Furthermore, it gives an overview of the required characterization and calibration steps. This includes the characterization of image distortions in the different parts of the optics, visibility, and phase determination as well as flat fielding.

The Spatial Heterodyne Observations of Water instrument (SHOW) is a limb-sounding satellite prototype that is being developed to provide high spatial resolution measurements of water vapour in the upper troposphere and lower stratosphere region. In 2017, SHOW flew several flights on NASA's ER-2 airplane, allowing for sub-orbital demonstration of the measurement technique. Here, we present the results from the measurement campaign and examine the sampling capabilities of the instrument.

The auroral green-line emission at 557.7nm wavelength as arising from the atomic oxygen O(S-1 -> D-1) transition typically peaks at an altitude of similar to 100km specifically in the nightside oval, induced by auroral electrons within an energy range of similar to 100eV-30keV. Intense aurora is known as being suppressed by sunlight in summer daytime but usually occurs in low electrical background conductivity. However, in the present study in summer (July) sunlit condition, enhancements of O(S-1) emission rates observed by using the Wind Imaging Interferometer/UARS were frequently observed at low altitudes below 90km, where ice particles are created initially as subvisible and detected as polar mesosphere summer echoes, emerging to be an optical phenomenon of polar mesospheric clouds. The intense O(S-1) emission occurring in summer exceeds those occurring in the daytime in other seasons both in occurrence and in intensity, frequently accompanied by occurrences of supersonic neutral velocity (300-1500ms(-1)). In the mesosphere, ion motion is controlled by electric field and the momentum is transferred to neutrals. The intense O(S-1) emission is well associated with high-energy electron precipitation as observed during an event of high-speed solar wind streams. Meanwhile, since the minimum occurrences of O(S-1) emission and supersonic velocity are maintained even in the low precipitation flux, the mechanism responsible is not only related to high-energy electron precipitation but also presumably to the local conditions, including the composition of meteoric-charged ice particles and charge separation expected in extremely low temperatures (<150K).

The SHOW instrument is designed to vertically resolve water profiles from limb scattered sunlight absorption in the atmosphere. The technical design of the instrument will be presented along with how it will be integrated onto a NASA Lockheed ER-2 airplane for planned flight test evaluations.

The Spatial Heterodyne Observations of Water (SHOW) instrument is a prototype Canadian satellite instrument specifically designed to make high spatial resolution measurements of water vapor in the upper troposphere and lower stratosphere through vertical imaging of the limb scattered sunlight in a near infrared vibrational absorption band. The spatial heterodyne approach provides sufficient spectral resolution and signal-to-noise performance such that when combined with a multiple scattering forward model and a non-linear inversion, the SHOW measurements can be used to tomographically reconstruct the two dimensional water vapour distribution, i.e. in altitude along the satellite track. Here we present the motivation for the measurement, the instrument concept, prototype specifications and results from simulated measurements and retrievals.

Passive wind measurements using Doppler shifts from atmospheric emissions were well demonstrated by the Wind Imaging Interferometer (WINDII) and the High Resolution Doppler Imager (HRDI) instruments on the National Aeronautics and Space Administration's (NASA's) Upper Atmosphere Research Satellite, operated from 1991 to 2005. For WINDII these emissions were from visible region upper atmospheric airglow in the altitude range from 80 to 300 km. Application of the same technique in the stratosphere requires using thermal emission from a minor constituent, and an ozone line near 1133 cm(-1) (about 8.8 mu m) has been identified as a suitable target line. The WINDII method employed a Doppler Michelson Interferometer, in which the wind is measured from phase shifts of a single spectral line. Isolating a single ozone spectral line is a major challenge but using Spatial Heterodyne Spectroscopy (SHS) offers a way to resolve a number of interferogram spectral components (fringes) within a narrow spectral range. The instrument is a Michelson interferometer similar to WINDII but one in which the two mirrors are replaced by diffraction gratings. A developmental instrument capable of measuring the phase shifts from several ozone lines within a spectral range of 4 cm(-1) has been designed, built, and operated in the laboratory. Simulated retrievals using the measurement parameters of this instrument demonstrate the capability of wind measurement with an accuracy better than 3 m s(-1) over an altitude range of 24 to 60 km. The retrieval employs four spectral lines for wind and three fringe frequencies for ozone concentration (of about 30 possible), each of which provides an optimal measurement for a particular altitude range. Ozone concentrations are also provided with an accuracy better than 10% from 20 to 50 km. Further detailed tests of this instrument are planned for the future. This work is supported by the Canadian Space Agency.

SHOW is a Spatial Heterodyne Spectrometer designed to vertically resolve water profiles from limb scattered sunlight in the upper troposphere - lower stratosphere region of the atmosphere. Studying water profiles is critical to understanding its impact on climate. The instrument successfully flew over Ontario (Canada) on September 19th 2014 at 35 km float altitude. We present an overview of the instrument and preliminary flight data results.

We describe the development of a waveguide Fourier-transform spectrometer for space-borne high-resolution sensing. A prototype device is designed to monitor the water vapor absorption band near 1,364 nm with a resolution of 0.05 nm. It has no moving parts and is based on a unique concept of arrayed interferometers implemented in silicon-on-insulator planar waveguide chip. The optical input is formed by many independent waveguides, providing a significantly increased light gathering capability (étendue) compared to single-waveguide input configurations. Enhancements of the spectrometer capabilities are achieved by stacking planar waveguide layers and by using surface gratings to couple light into the waveguides.

The concept and design of a new type of waveguide device, a multiaperture Fourier-transform planar waveguide spectrometer, implemented as a prototype instrument is presented. The spectrometer's objective is to demonstrate the ability of the new slab waveguide technology for application in remote-sensing instruments. The spectrometer will use a limb-viewing configuration to detect the 1.36µm waveband allowing the concentrations of water vapor in Earth's atmosphere to be measured. The most challenging aspects of the design, assembly, and calibration are presented. Focus will be given to the effects of packaging the spectrometer and interfacing to the detector array. Stress-induced birefringence will affect the performance of the waveguides, therefore, the design of a stress-free mounting over a range of temperatures is important. Spectral retrieval algorithms will have to correct for expected fabrication errors in the waveguides. Data-processing algorithms will also be developed to correct for nonuniformities of input brightness through the array, making use of multimode interference output couplers to capture both the in-phase and anti-phase interferometer outputs. A performance assessment of an existing breadboard spectrometer will demonstrate the capability of the instrument.

This invited talk presents the evolution of the planar waveguide dispersive devices developed in our laboratory for spatial heterodyne spectroscopy. The basic concepts are introduced and then applied to a Mach-Zehnder interferometer array capable of a resolution of 0.1 nm over a bandwidth of 2.5 nm.

We present development of a compact, robust, waveguide Fourier-transform microspectrometer for high-resolution and high-throughput spectroscopy in space-based applications. The prototype device is being developed to monitor water vapor in the atmosphere from a micro-satellite platform. The instrument is based on a unique slab waveguide spatial heterodyne spectrometer (SHS) chip fabricated at the National Research Council Canada in silicon-on-insulator (SOI) technology.

We present multiaperture stationary spectrometers in planar optical waveguides. The devices are based on the spatial heterodyning technique, do not require moving parts, and use Fourier transformation for spectra retrieval. The design is based on arrays of waveguide interferometers with linearly increasing optical path delay. The spectrometers have increased optical throughput due to multiple input waveguides. We discuss design, fabrication, and first experimental results for these multiaperture spectrometers implemented in silicon-on-insulator (SOI) ridge waveguides.

We present a novel micro-interferometer implemented using arrays of single-mode planar optical waveguides. The spatial heterodyne waveguide spectrometer offers high resolution and increased optical throughput (etendue) and is compatible with a microsatellite platform. A stationary Fourier technique is employed to reconstruct the input spectrum from the array of outputs. Calibration mitigates waveguide fabrication errors and input illumination non-uniformities and can be readily implemented in the spectral retrieval algorithm. Signal to noise performance is estimated for a remote sensing application using a classical telescope front end with comparison to classical techniques.