Philippe Baron

At the Dawn of a New Era in Terahertz Technology

The National Institute of Information and Communications Technology (NICT, Japan) started the Terahertz Project in April 2006. Its fundamental purpose in the next five years is to enable a nationwide technical infrastructure to be created for diverse applications of terahertz technology. The technical infrastructure includes the development of semiconductor devices such as terahertz quantum cascade lasers, terahertz-range quantum well photodetectors, and high-precision tunable continuous wave sources. It also includes pulsed terahertz measurement systems, modeling and measurement of atmospheric propagation, and the establishment of a framework to construct a materials database in the terahertz range including standardization of the measurement protocol. These are common technical infrastructure even in any terahertz systems. In this article, we report the current status of developments in these fields such as terahertz quantum cascade lasers (THz-QCLs) (with peak power of 30 mW, 3.1 THz), terahertz-range quantum well photodetectors (THz-QWPs) (tuned at 3 THz) an ultrawideband terahertz time domain spectroscopy (THz-TDS) system (with measurement range of from 0.1 to 15 THz), an example of a database for materials of fine art, and results obtained from measuring atmospheric propagation.

A ground‐based microwave radiometer dedicated to stratospheric ozone monitoring

A microwave radiometer has been developed for long-term measurements of strato-mesospheric ozone profiles at midlatitudes. The instrument located at the Bordeaux Observatory, France (45°N) is operated in the framework of the French atmospheric station, of the European Alpine station belonging to the Network for the Detection of Stratospheric Change. The instrument detects an ozone spectral line at 110.836 GHz, enabling the retrieval of ozone profiles from ∼25 to ∼75 km. The technical parameters are described as the observing technique, calibration procedures, and data acquisition. Two retrieval methods are used: the Backus-Gilbert method and the optimal estimation method. Strong emphasis is placed on the error analysis including a detailed characterization of errors. To improve the retrieval, we discuss which errors have to be taken into account in the retrieval process. Three cases have been selected for which retrieval errors due to time stochastic and time systematic errors are calculated. First, only the thermal noise is introduced in the retrieval code; second, all errors are introduced; and finally, a selection among errors is searched in order to provide a good compromise between the retrieval error and the vertical resolution. Diurnal variations of mesospheric O3 are compared with results from a photochemical model. The agreement is within 5–10%. During the February-March 1996 period the temporal evolution of ozone at an altitude of 30 km is in good agreement with both satellite and three-dimensional model data. There is a good correlation with the potential vorticity field calculated at the 850 K isentropic temperature. A crossing of the polar vortex over the site is associated with an O3 decrease observed in the three data sets.

Partial CO2 Column-Averaged Dry-Air Mixing Ratio from Measurements by Coherent 2-μm Differential Absorption and Wind Lidar with Laser Frequency Offset Locking

AbstractA coherent 2-μm differential absorption and wind lidar (Co2DiaWiL) with a 2-μm single-frequency Q-switched laser with laser frequency offset locking was used for long-range CO2 measurement. The frequency stabilization of the single-frequency λ on pulsed laser was 1.0 MHz. Experimental horizontal CO2 measurement over a column range of 2.6–5.6 km and 900 shot pairs (1-min integration time) was conducted on 22 October 2009 to examine the detection sensitivity of the Co2DiaWiL. The achieved precision was less than 2.1%. The root-mean-square of the differences between the 30-min CO2 averages measured by the Co2DiaWiL and a ground-based in situ instrument was 0.9% (3.5 ppm). Experimental vertical CO2 measurements were conducted in February 2010 and January and February 2011. The partial CO2 column-averaged dry-air mixing ratios (XCO2) for an altitude between 0.4 and 1.0 km in 2010 and 2011 were 403.2 ± 4.2 and 405.6 ± 3.4 ppm, respectively. In the paper, the Co2DiaWiL results were well validated careful...

European Minor Constituent Radiometer: A New Millimeter Wave Receiver for Atmospheric Research

EMCOR is a heterodyne receiver for the frequency range of 201 to 210 GHz. It has been designed for ground-based measurements of various minor constituents of the stratosphere involved in ozone chemistry. Since the aim was the detection of faint spectral lines, a superconducting tunnel junction has been chosen as mixer element and special care has been taken in developing the calibration unit of the system. The front-end is completed by a quasi-optical system, a solid state local oscillator with electronic tuning and a HEMT pre-amplifier. In the back-end an acousto-optical spectrometer is employed to analyse the signal. A PC controls the whole system. The instrument has been installed at a high mountain site in the Swiss Alps.

HO2 measurements in the stratosphere and the mesosphere from the sub-millimetre limb sounder Odin/SMR

This paper presents observations of the hydroperoxy radical (HO2) performed by the Odin/SMR instrument from the middle stratosphere to the upper mesosphere (35–90 km). The data set covers the period from October 2003 to December 2005 on a basis of one observation period of 24 hours each month. Odin/SMR can provide two zonal maps of HO2 per day, with a vertical resolution of 10 km. The non-standard processing applied to the retrievals is described. The consistency between HO2 observations from three periods in August 2004 demonstrates the robustness of the retrieval method. It also shows that the measurements are sensitive enough to detect changes in the middle and upper mesosphere. The retrieval needs further improvements for studying stratospheric variations.

Studying the Potential of Terahertz Radiation for Deriving Ice Cloud Microphysical Information

With wavelengths in the order of the size of typical ice cloud particles and therefore being sensitive to ice clouds, the Terahertz (THz) region is expected to bear a high potential concerning measuring ice cloud properties, in particular microphysical parameters. In this paper we give an introduction to the characteristics of atmospheric THz radiation between 0-5THz (wavelengths >60 μm and wavenumber<170 cm-1 respectively) as well as ice cloud optical properties and cloud effects in the THz region. Using radiative transfer model simulations we analyze the sensitivity of THz spectra to ice content and particle size. For tropical cases cloud effects in the order of 0.1 K/(g/m2) are found. Assuming instrumental sensitivities of typically around 1K these effects allow for detection of clouds with columnar ice content of 10 g/m2. It is demonstrated that submillimeter (SMM) instruments are sensitive to particles with sizes larger than 100 μm, while THz observations potentially can measure particles as small as 10 μm.

Measurement of stratospheric and mesospheric winds with a submillimeter wave limb sounder: results from JEM/SMILES and simulation study for SMILES-2

Satellite missions for measuring winds in the troposphere and thermosphere will be launched in a near future. There is no plan to observe winds in the altitude range between 30-90 km, though middle atmospheric winds are recognized as an essential parameter in various atmospheric research areas. Sub-millimetre limb sounders have the capability to fill this altitude gap. In this paper, we summarize the wind retrievals obtained from the Japanese Superconducting Submillimeter Wave Limb Emission Sounder (SMILES) which operated from the International Space Station between September 2009 and April 2010. The results illustrate the potential of such instruments to measure winds. They also show the need of improving the wind representation in the models in the Tropics, and globally in the mesosphere. A wind measurement sensitivity study has been conducted for its successor, SMILES-2, which is being studied in Japan. If it is realized, sub-millimeter and terahertz molecular lines suitable to determine line-of-sight winds will be measured. It is shown that with the current instrument definition, line-of-sight winds can be observed from 20 km up to more than 160 km. Winds can be retrieved with a precision better than 5 ms-1 and a vertical resolution of 2-3 km between 35-90 km. Above 90 km, the precision is better than 10 ms-1 with a vertical resolution of 3-5 km. Measurements can be performed day and night with a similar sensitivity. Requirements on observation parameters such as the antenna size, the satellite altitude are discussed. An alternative setting for the spectral bands is examined. The new setting is compatible with the general scientific objectives of the mission and the instrument design. It allows to improve the wind measurement sensitivity between 35 to 90 km by a factor 2. It is also shown that retrievals can be performed with a vertical resolution of 1 km and a precision of 5-10 ms-1 between 50 and 90 km.

Future Doppler lidar wind measurement from space in Japan

Wind profile is fundamental in many atmospheric phenomena. Radiosonde, windprofiler, and Doppler lidar, have been developed for the wind measurement. Radiosonde and windprofiler are used to obtain wind profiles. About 1,300 weather stations launch radiosondes to obtain profiles of pressure, wind, temperature, and humidity. Most of the weather stations are on land, while the stations on the sea are very sparse. Spaceborne visible and infrared imagers and microwave scatterometers can obtain wind data only at a specific altitude. Current wind observations are not enough and their reliability in the global climate model and weather prediction must be improved. Many scientific groups anticipate the realization of a global observation system for three-dimensional wind measurements. The spaceborne Doppler lidar is regarded as one of the candidate sensors for the global wind measurements. The working group on Japanese spaceborne Doppler Lidar has been established to realize for wind measurements from space. In this paper, we describe the activities and goals of this working group.

Sensitivity study of SMILES-2 for chemical species

Sensitivity studies of temperature and chemical species (Observed by ISS/JEM/SMILES: O3, HCl, ClO, HO2, BrO, HNO3, CH3CN, and Not observed by SMILES: Temperature, H2O, N2O, NO2, NO, CH3Cl, CO, H2CO, OH and O-atom) was carried out for the SMILES-2 proposal, a sub-mm and THz observation of limb emission from space over the spectral region from 400 GHz to 2.5 THz. Tentative but optimal candidate of frequency bands to cover these species was selected with 3 SIS (Superconductor-Insulator-Superconductor) mixers; SIS-1 (485-489 GHz + 523-527 GHz), SIS-2 (623-627 GHz + 648-652 GHz), SIS-3 (557 GHz + 576.3 GHz) and 2 HEB (Hot Electron Bolometer); HEB-1 (1.8 THz OH) and HEB-2 (2.06 THz O-atom). Temperature can be retrieved with 1 K precision and 1 km vertical resolution from 15 to 120 km. Other chemical species also showed very high single scan precision (random error) comparable to statistical standard error of previous satellite measurements.

Gain nonlinearity calibration of the SMILES receiver

The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) was launched in September 2009 and has successfully observed the stratosphere for half a year. Before launch we measured the receiver gain nonlinearity. The gain compression of the SMILES receiver is estimated to be 2.6 to 4.3% from the measurement. The nonlinearity correction is applied to the observed data in space. Data are satisfactory corrected in the stratosphere but not in the higher altitude. The reason of the unsuccessful correction is discussed and attributed to our overestimation of the broadband nonlinearity.