THz Instruments for Space

Terahertz technology has been driven largely by applications in astronomy and space science. For more than three decades cosmochemists, molecular spectroscopists, astrophysicists, and Earth and planetary scientists have used submillimeter-wave or terahertz sensors to identify, catalog and map lightweight gases, atoms and molecules in Earth and planetary atmospheres, in regions of interstellar dust and star formation, and in new and old galaxies, back to the earliest days of the universe, from both ground based and more recently, orbital platforms. The past ten years have witnessed the launch and successful deployment of three satellite instruments with spectral line heterodyne receivers above 300 GHz (SWAS, Odin, and MIRO) and a fourth platform, Aura MLS, that reaches to 2520 GHz, crossing the terahertz threshold from the microwave side for the first time. The former Soviet Union launched the first bolometric detectors for the submillimeter way back in 1974 and operated the first space based submillimeter wave telescope on the Salyut 6 station for four months in 1978. In addition, continuum, Fourier transform and spectrophotometer instruments on IRAS, ISO, COBE, the recent Spitzer Space Telescope and Japan's Akari satellite have all encroached into the submillimeter from the infrared using direct detection bolometers or photoconductors. At least two more major satellites carrying submillimeter wave instruments are nearing completion, Herschel and Planck, and many more are on the drawing boards in international and national space organizations such as NASA, ESA, DLR, CNES, and JAXA. This paper reviews some of the programs that have been proposed, completed and are still envisioned for space applications in the submillimeter and terahertz spectral range

Aqua: AIRS, AMSU, HSB, AMSR-E, CERES, MODIS

This brochure provides an overview of the Aqua spacecraft, instruments, science, and data products Aqua, Latin for water, is a NASA Earth Science satellite mission named for the large amount of information that the mission is collecting about the Earth's water cycle, including evaporation from the oceans, water vapor in the atmosphere, clouds, precipitation, soil moisture, sea ice, land ice, and snow cover on the land and ice. Additional variables also measured by Aqua include radiative energy fluxes, aerosols, vegetation cover on the land, phytoplankton and dissolved organic matter in the oceans, and air, land, and water temperatures. Note: this guide was produced before Aqua was launched; for the most recent information on Aqua, go to http://aqua.nasa.gov. Educational levels: Undergraduate lower division, Undergraduate upper division, Graduate or professional, Informal education

Frequency tunable electronic sources working at room temperature in the 1 to 3 THz band

Compact, room temperature terahertz sources are much needed in the 1 to 3 THz band for developing multi-pixel heterodyne receivers for astrophysics and planetary science or for building short-range high spatial resolution THz imaging systems able to see through low water content and non metallic materials, smoke or dust for a variety of applications ranging from the inspection of art artifacts to the detection of masked or concealed objects. All solid-sate electronic sources based on a W-band synthesizer followed by a high-power W-band amplifier and a cascade of Schottky diode based THz frequency multipliers are now capable of producing more than 1 mW at 0.9THz, 50 μW at 2 THz and 18 μW at 2.6 THz without the need of any cryogenic system. These sources are frequency agile and have a relative bandwidth of 10 to 15%, limited by the high power W-band amplifiers. The paper will present the latest developments of this technology and its perspective in terms of frequency range, bandwidth and power

Mission Operations Working Group (MOWG) Report to the OMI Science Team

This PowerPoint presentation will discuss Aura's current spacecraft and OMI insturment status, highlight any performance trends and impacts to OMI operations, identify any operational changes and express concerns or potential process improvements

Validation of Aura Microwave Limb Sounder OH measurements with Fourier Transform Ultra-Violet Spectrometer total OH column measurements at Table Mountain, California

The first seasonal and interannual validation of OH measurements from the Aura Microwave Limb Sounder (MLS) has been conducted using ground-based OH column measurements from the Fourier Transform Ultra-Violet Spectrometer (FTUVS) over the Jet Propulsion Laboratory's Table Mountain Facility (TMF) during 2004–2007. To compare with FTUVS total column measurements, MLS OH vertical profiles over TMF are integrated to obtain partial OH columns above 21.5 hPa, which covers nearly 90% of the total column. The tropospheric OH and the lower stratopheric OH not measured by MLS are estimated using GEOS (Goddard Earth Observing System)-Chem and a Harvard 2-D model implemented within GEOS-Chem, respectively. A number of field observations and calculations from a photochemical box model are compared to OH profiles from these models to estimate the variability in the lower atmospheric OH and thus the uncertainty in the combined total OH columns from MLS and models. In general, the combined total OH columns agree extremely well with TMF total OH columns, especially during seasons with high OH. In winter with low OH, the combined columns are often higher than TMF measurements. A slightly weaker seasonal variation is observed by MLS relative to TMF. OH columns from TMF and the combined total columns from MLS and models are highly correlated, resulting in a mean slope of 0.969 with a statistically insignificant intercept. This study therefore suggests that column abundances derived from MLS vertical profiles have been validated to within the mutual systematic uncertainties of the MLS and FTUVS measurements

Potential of Radiotelescopes for Atmospheric Line Observations: I. Observation Principles and Transmission Curves for Selected Sites

Existing and planned radiotelescopes working in the millimetre (mm) and sub-millimetre wavelengths range provide the possibility to be used for atmospheric line observations. To scrutinize this potential, we outline the differences and similarities in technical equipment and observing techniques between ground-based aeronomy mm-wave radiometers and radiotelescopes. Comprehensive tables summarizing the technical characteristics of existing and future (sub)-mm radiotelescopes are given. The advantages and disadvantages using radiotelescopes for atmospheric line observations are discussed. In view of the importance of exploring the sub-mm and far-infrared wavelengths range for astronomical observations and atmospheric sciences, we present model calculations of the atmospheric transmission for selected telescope sites (DOME-C/Antarctica, ALMA/Chajnantor, JCMT and CSO on Mauna Kea/Hawaii, KOSMA/Swiss Alpes) for frequencies between 0 and 2000 GHz (150 micron) and typical atmospheric conditions using the forward model MOLIERE (version~5). For the DOME-C site, the transmission over a larger range of up to 10 THz (30 micron) is calculated in order to demonstrate the quality of an earth-bound site for mid-IR observations. All results are available on a dedicated webpage (http://transmissioncurves.free.fr)Comment: Planetary and Space Science accepted (in press), see also website http://transmissioncurves.free.f

Resolving the model-observation discrepancy in the mesospheric and stratospheric HO_x chemistry

We examine the middle atmospheric odd-hydrogen (HO_x) chemistry by comparing the Aura Microwave Limb Sounder (MLS) OH and HO_2 measurements with a photochemical model simulation. The model underestimates mesospheric OH and HO_2 concentrations if the standard chemical kinetic rates are used, whether the model H_2O and O_3 are constrained with observations or not. To resolve the discrepancies, we adjust the kinetic rate coefficients of three key reactions (O + OH → O_2 + H, OH + HO_2 → H_2O + O_2, and H + O_2 + M → HO_2 + M) and the O2photo absorption cross section at Lyman-α (121.57 nm) using the Bayesian optimal estimation. A much better model-observation agreement can be achieved if the kinetic rate coefficients for H + O_2 + M → HO_2 + M is increased by 134–310%, and the O_2 photo absorption cross section at Lyman-α is reduced by 33–54%, while the kinetic rate coefficients for O + OH → O_2 + H and OH + HO_2 → H_2O + O_2 remain consistent with the current laboratory values. The kinetic rate coefficient for H + O_2 + M → HO_2 + M requires a very large adjustment beyond the uncertainty limits recommended in the NASA Data Evaluation, suggesting the need for future laboratory measurements. An alternative explanation is that the radiative association reaction, H + O_2 → HO_2 + hν, plays a significant role, which has never been measured. Our results demonstrate that high quality satellite observations can be used to constrain photochemical parameters and help improve our understanding of atmospheric chemistry

Validation of Stratospheric and Mesospheric Ozone Observed by SMILES from International Space Station

We observed ozone O3 in the vertical region between 250 and 0.0005 hPa (~ 12-96 km) using the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) between 12 October 2009 and 21 April 2010. The new 4K superconducting heterodyne receiver technology of SMILES allowed us to obtain a one order of magnitude better signal-to-noise ratio for the O3 line observation compared to past spaceborne microwave instruments. The non-sun-synchronous orbit of the ISS allowed us to observe O3 at various local times. We assessed the quality of the vertical profiles of O3 in the 100-0.001 hPa (~ 16-90 km) region for the SMILES NICT Level 2 product version 2.1.5. The evaluation is based on four components: error analysis; internal comparisons of observations targeting three different instrumental setups for the same O3 625.371 GHz transition; internal comparisons of two different retrieval algorithms; and external comparisons for various local times with ozonesonde, satellite and balloon observations (ENVISAT/MIPAS, SCISAT/ACE-FTS, Odin/OSIRIS, Odin/SMR, Aura/MLS, TELIS). SMILES O3 data have an estimated absolute accuracy of better than 0.3 ppmv (3%) with a vertical resolution of 3-4 km over the 60 to 8 hPa range. The random error for a single measurement is better than the estimated systematic error, being less than 1, 2, and 7%, in the 40-1, 80-0.1, and 100-0.004 hPa pressure regions, respectively. SMILES O-3 abundance was 10-20% lower than all other satellite measurements at 8-0.1 hPa due to an error arising from uncertainties of the tangent point information and the gain calibration for the intensity of the spectrum. SMILES O3 from observation frequency Band-B had better accuracy than that from Band-A. A two month period is required to accumulate measurements covering 24 h in local time of O3 profile. However such a dataset can also contain variation due to dynamical, seasonal, and latitudinal effects

Global and long-term comparison of SCIAMACHY limb ozone profiles with correlative satellite data (2002–2008)

SCIAMACHY limb scatter ozone profiles from 2002 to 2008 have been compared with MLS (2005–2008), SABER (2002–2008), SAGE II (2002–2005), HALOE (2002–2005) and ACE-FTS (2004–2008) measurements. The comparison is performed for global zonal averages and heights from 10 to 50 km in one km steps. The validation was performed by comparing monthly mean zonal means and by comparing averages over collocated profiles within a zonal band and month. Both approaches yield similar results. For most of the stratosphere SCIAMACHY agrees to within 10% or better with other correlative data. A systematic bias of SCIAMACHY ozone of up to 100% between 10 and 20 km in the tropics points to some remaining issues with regard to convective cloud interference. Statistical hypothesis testing reveals at which altitudes and in which region differences between SCIAMACHY and other satellite data are statistically significant. We also estimated linear trends from monthly mean data for different periods where SCIAMACHY has common observations with other satellite data using a classical trend model with QBO and seasonal terms in order to draw conclusions on potential instrumental drifts as a function of latitude and altitude. Since the time periods considered here are rather short these trend estimates are only used to identify potential instrumental issues with the SCIAMACHY data. As a result SCIAMACHY exhibits a statistically significant negative trend in the range of of about 1–3% per year depending on latitude during the period 2002–2005 (overlapping with HALOE and SAGE II) and somewhat less during 2002–2008 (overlapping with SABER) in the altitude range of 30–40 km, while in the period 2004–2008 (overlapping with MLS and ACE-FTS) no significant trends are observed. Since all correlative satellite instruments do not show to a very large extent statistically significant trends in any of the time periods considered here, the negative trends observed with SCIAMACHY data point at some remaining instrumental artifact which is most likely related to residual errors in the tangent height registration of SCIAMACHY