Henry Buijs

ACE-FTS instrument: after five years on-orbit

The Atmospheric Chemistry Experiment (ACE) is the mission on-board Canadian Space Agencys science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, a grating spectrometer named MAESTRO, provides spectrographic data from the near ultra-violet to the near infrared, including the visible spectral range. With all instruments combined, the payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature are being made by solar occultation from this satellite in low earth orbit. The ACE mission measures and analyses the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (74°), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions. The ACE/SciSat-1 spacecraft was launched by NASA on August 12th, 2003. This paper presents the status of the ACE-FTS instrument, after nearly five years on-orbit. On-orbit SNR and some telemetry signals are presented. The health status of the instrument is discussed.

The University of Wisconsin Space Science and Engineering Center Absolute Radiance Interferometer (ARI)

A summary of the development of the Absolute Radiance Interferometer (ARI) at the University of Wisconsin Space Science and Engineering Center (UW-SSEC) will be presented. At the heart of the sensor is the ABB CLARREO Interferometer Test-Bed (CITB), based directly on the ABB Generic Flight Interferometer (GFI). This effort is funded under the NASA Instrument Incubator Program (IIP).

On-orbit performance of the ACE-FTS instrument

The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency (CSA) for its science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, MAESTRO, provides spectrographic data from the near ultra-violet to the near infrared, including the visible spectral range. In combination the instrument payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature are made by solar occultation from a satellite in low earth orbit. The ACE mission measures and analyses the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (74 degrees), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions. The ACE/SciSat-1 spacecraft was launched by NASA on August 12th, 2003. This paper presents the on-orbit performance of the ACE-FTS instrument. The commissioning activities allowed the activation of the various elements of the instrument and the optimization of several parameters such as gains, integration times, pointing offsets, etc. The performance validation was the last phase of the instrument hardware commissioning activities. The results of the performance validation are presented in terms of on-orbit instrument performance with respect to instrument requirements such as signal-to-noise ratio, transmittance accuracy, and spectral resolution. Results are also compared to ground validation tests performed during the thermal-vacuum campaigns. Performance is presented in terms of validation of instrument from an engineering perspective.

The University of Wisconsin Space Science and Engineering Center Absolute Radiance Interferometer (ARI): instrument overview and radiometric performance

Spectrally resolved infrared (IR) and far infrared (FIR) radiances measured from orbit with extremely high absolute accuracy (< 0.1 K, k = 3, brightness temperature at scene temperature) constitute a critical observation for future climate benchmark missions. The challenge in the IR/FIR Fourier Transform Spectrometer (FTS) sensor development for a climate benchmark measurement mission is to achieve the required ultra-high accuracy with a design that can be flight qualified, has long design life, and is reasonably small, simple, and affordable. In this area, our approach is to make use of components with strong spaceflight heritage (direct analogs with high TRL) combined into a functional package for detailed performance testing. The required simplicity is achievable due to the large differences in the sampling and noise requirements for the benchmark climate measurement from those of the typical remote sensing infrared sounders for weather research or operations. A summary of the instrument design and development, and the radiometric performance of the Absolute Radiance Interferometer (ARI) at the University of Wisconsin Space Science and Engineering Center (UW-SSEC) will be presented.

Evolution of FTIR technology as applied to chemical detection and quantification

Both Fourier Transform Infrared (FTIR) spectrometers and sampling techniques have seen a paradigm shift over the past 20 years. Infrared (IR) spectroscopy using the mid IR “fingerprint” region shows excellent specificity for determining the presence and quantity of well over 50000 organic chemical species. Tiny amounts of sample suffice for identification using a chemically inert scratch resistant diamond micro internal reflection crystal. For air quality, FTIR can be used as a point monitor, sniffing air samples in an IR cell or using a long open-air path with a remote reflector or direct passive remote sensing. This makes IR ideal for first responders and haz/mat professionals provided the FTIR is compact, rugged and easy to use in the field. Already FTIR is widely used in industrial plants often directly at the process. In parallel FTIR is increasingly used in mobile field environments including airborne platforms as well as for satellite-based sounders. This paper presents a resume of the evolution of FTIR and sampling technology and the boundaries of applicability of field deployed FTIR chemical sensors for the assessment of suspect substances as well as air pollution at the site of an emergency situation.

PCW/PHEOS-WCA: Quasi-geostationary Arctic measurements for weather, climate and air quality from highly eccentric orbits

The PCW (Polar Communications and Weather) mission is a dual satellite mission with each satellite in a highly eccentric orbit with apogee ~42,000 km and a period (to be decided) in the 12–24 hour range to deliver continuous communications and meteorological data over the Arctic and environs. Such as satellite duo can give 24×7 coverage over the Arctic. The operational meteorological instrument is a 21-channel spectral imager similar to the Advanced Baseline Imager (ABI). The PHEOS-WCA (weather, climate and air quality) mission is intended as an atmospheric science complement to the operational PCW mission. The target PHEOS-WCA instrument package considered optimal to meet the full suite of science team objectives consists of FTS and UVS imaging sounders with viewing range of ~4.5° or a Field of Regard (FoR) ~ 3400×3400 km2 from near apogee. The goal for the spatial resolution at apogee of each imaging sounder is 10×10 km2 or better and the goal for the image repeat time is targeted at ~2 hours or better. The FTS has 4 bands that span the MIR and NIR with a spectral resolution of 0.25 cm−1. They should provide vertical tropospheric profiles of temperature and water vapour in addition to partial columns of many other gases of interest for air quality. The two NIR bands target columns of CO2, CH4 and aerosol optical depth (OD). The UVS is an imaging spectrometer that covers the spectral range of 280–650 nm with 0.9 nm resolution and targets the tropospheric column densities of O3 and NO2 and several other Air Quality (AQ) gases as well the Aerosol Index (AI).

HVRM: a second generation ACE-FTS instrument concept

The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) is the main instrument on-board the SCISAT-1 satellite, a mission mainly supported by the Canadian Space Agency [1]. It is in Low- Earth Orbit at an altitude of 650 km with an inclination of 74E. Its data has been used to track the vertical profile of more than 30 atmospheric species in the high troposphere and in the stratosphere with the main goal of providing crucial information for the comprehension of chemical and physical processes controlling the ozone life cycle. These atmospheric species are detected using high-resolution (0.02 cm-1) spectra in the 750-4400 cm-1 spectral region. This leads to more than 170 000 spectral channels being acquired in the IR every two seconds. It also measures aerosols and clouds to reduce the uncertainty in their effects on the global energy balance. It is currently the only instrument providing such in-orbit high resolution measurements of the atmospheric chemistry and is often used by international scientists as a unique data set for climate understanding. The satellite is in operation since 2003, exceeding its initially planned lifetime of 2 years by more than a factor of 5. Given its success, its usefulness and the uniqueness of the data it provides, the Canadian Space Agency has founded the development of technologies enabling the second generation of ACE-FTS instruments through the High Vertical Resolution Measurement (HVRM) project but is still waiting for the funding for a mission. This project addresses three major improvements over the ACE-FTS. The first one aims at improving the vertical instantaneous field-of-view (iFoV) from 4.0 km to 1.5 km without affecting the SNR and temporal precision. The second aims at providing precise knowledge on the tangent height of the limb observation from an external method instead of that used in SCISAT-1 where the altitude is typically inferred from the monotonic CO2 concentration seen in the spectra. The last item pertains to reaching lower altitude down to 5 km for the retrieved gas species, an altitude at which the spectra are very crowded in terms of absorption. These objectives are attained through a series of modification in the optical train such as the inclusion of a field converter and a series of dedicated real-time and post-acquisition algorithms processing the Sun images as it hides behind the Earth. This paper presents the concepts, the prototypes that were made, their tests and the results obtained in this Technology Readiness Level (TRL) improvement project.

Interferometer scanning mechanisms and metrology at ABB: recent developments and future perspectives

Interferometers are devices meant to create an interference pattern between photons emitted from a given target of interest. In most cases, this interference pattern must be scanned over time or space to reveal useful information about the target (ex.: radiance spectra or a star diameter). This scanning is typically achieved by moving mirrors at a precision a few orders of magnitude smaller than the wavelength under study. This sometimes leads to mechanism requirements of especially high dynamic range equivalent to 30 bits or more (ex. Sub-nanometer precision over stoke of tens of cms for spectroscopy or tens of meters for astronomical spatial interferometry). On top of this mechanical challenge, the servo control of the mirror position involves obtaining relative distance measurement between distant optical elements with similar if not better dynamic range. The feedback information for such servo-control loop is usually the optical path difference (OPD) measured with a metrology laser beam injected in the interferometer. Over the years since the establishement of the Fourier Transform Spectrometers (FTS) in the 60’s as a standard spectroscopic tools, many different approaches have been used to accomplish this task. When it comes to space however, not all approaches are successful. The design challenge can be viewed as analogous to that of scene scanning modules with the exception that the sensitivity and precision are much finer. These mechanisms must move freely to allow fine corrections while remaining stiff to reject external perturbations with frequencies outside of the servo control system reach. Space also brings the additional challenges of implementing as much redundancy as possible and offering protection during launch for these sub-systems viewed as critical single point failures of the payloads they serve.

The University of Wisconsin Space Science and Engineering Center Absolute Radiance Interferometer (ARI): Demonstrated Radiometric Performance

A summary of the Absolute Radiance Interferometer (ARI) radiometric performance demonstrated during vacuum testing at the University of Wisconsin Space Science and Engineering Center (UW-SSEC) is presented.

ACE-FTS on SCISAT: 10th year on-orbit anniversary

The Atmospheric Chemistry Experiment (ACE) is a mission on-board the Canadian Space Agency’s (CSA) SCISAT-1. ACE is composed of a suite of instruments consisting of an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary imager monitoring aerosols based on the extinction of solar radiation using two filtered detectors (visible and near infrared). A suntracker is also included to provide fine pointing during occultation. A second instrument, MAESTRO, is a spectrophotometer covering the near ultra-violet to the near infrared. In combination, the instrument payload covers the spectral range from 0.25 to 13.3 μm. The ACE mission came about from a need to better understand the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere, with particular emphasis on the Arctic region. Measurement of the vertical distribution of molecular species in these portions of the atmosphere permits elucidation of the key chemical and dynamical processes. The ACE-FTS measures the vertical distributions of trace gases as well as polar stratospheric clouds, aerosols, and temperature by a solar occultation technique from low earth orbit. By measuring solar radiation at high spectral resolution as it passes through different layers of the atmosphere, the absorption thus measured provides information on vertical profiles of atmospheric constituents, temperature, and pressure. Detailed and sensitive vertical distribution of trace gases help to better understand the chemical processes not only for ozone formation and destruction but also for other dynamic processes in the atmosphere. The ACE/SCISAT-1 satellite was successfully launched by NASA on August 12, 2003, and has been successfully operating since, now celebrating its 10th year on-orbit anniversary. This paper presents a summary of the heritage and development history of the ACE-FTS instrument. Design challenges and solutions are related. The actual on-orbit performance is presented, and the health status of the instrument payload is discussed. Potential future follow-on missions are finally introduced.