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In recent decades, theoretical studies and numerical models of thermal tides have gained attention. It has been recognized that tides have a significant influence on the dynamics of the middle and upper atmosphere; as they grow in amplitude and propagate upward, they transport energy and momentum from the lower to the upper atmosphere, contributing to the vertical coupling between atmospheric layers. The superposition of tides with other atmospheric waves leads to non-linear wave–wave interactions. However, direct measurements of thermal tides in the middle atmosphere are challenging and are often limited to satellite measurements in the tropics and at low latitudes. Due to orbit geometry, such observations provide only a reduced insight into the short-term variability in atmospheric tides. In this paper, we present tidal analysis from 5 years of continuous observations of middle-atmospheric temperatures. The measurements were performed with the ground-based temperature radiometer TEMPERA (TEMPErature RAdiometer), which was developed at the University of Bern in 2013 and was located in Bern (46.95° N, 7.45° E) and Payerne (46.82° N, 6.94° E). TEMPERA achieves a temporal resolution of 1–3 h and covers the altitude range between 25–50 km. Using an adaptive spectral filter with a vertical regularization (ASF2D) for the tidal analysis, we found maximum amplitudes for the diurnal tide of approximately 2.4 K, accompanied by seasonal variability. The maximum amplitude was reached on average at an altitude of 43 km, which also reflected some seasonal characteristics. We demonstrate that TEMPERA is suitable for providing continuous temperature soundings in the stratosphere and lower mesosphere with a sufficient cadence to infer tidal amplitudes and phases for the dominating tidal modes. Furthermore, our measurements exhibit a dominating diurnal tide and smaller amplitudes for the semidiurnal and terdiurnal tides in the stratosphere. [ABSTRACT FROM AUTHOR]

The Institute of Applied Physics (IAP) of the University of Bern is active in the field of remote sensing of middle atmospheric trace gases such as ozone and water vapor by microwave radiometry. From the measured pressure broadened spectral lines, it is possible to retrieve the vertical distribution of the observed species. The vertical range is dependent on the bandwidth and resolution of the spectrometers. The radiometers from the IAP perform ground-based and airborne measurements. For the spectral analysis, they used acoustooptical spectrometers (AOS) or low-resolution filterbanks until recently. Unfortunately, AOS proved to be deficient under conditions encountered in an aircraft. For this reason, the approach of using novel real-time digital fast Fourier transform (FFT) spectrometers of bandwidth 1 GHz was chosen. In this paper, we present measurements of atmospheric trace constituents using digital FFT spectrometers and compare the results with measurements from the AOS and filterbank. The FFT spectrometer is superior in resolution and system stability as well as in the linearity and stability of the frequency axis. An important point is also the lower costs per bandwidth and resolution. The measured intensities of emitted radiation from the atmosphere from all spectrometer types were in good agreement. Index Terms--Discrete Fourier transforms, microwave radiometry, microwave spectroscopy, remote sensing, terrestrial atmosphere.

The design, fabrication, and characterization of a 500-GHz electromagnetic bandgap (EBG) based heterodyne receiver array is presented. The array contained seven planar dipole antennas that were photolithographically defined on a common 20-[micro]m-thick quartz substrate. Each antenna incorporated a Schottky diode and was connected to coplanar transmission lines that conveyed the down-converted 500-GHz signals to detectors. The quartz substrate was backed by a silicon EBG woodpile structure, which reduced antenna crosstalk and increased directivity. An off-axis parabolic mirror completed the beam-forming network. Index Terms--Electromagnetic bandgap (EBG) technology, imaging array, millimeter-wave technology.

The Scanning Polarimetric Imaging Radiometer (SPIRA) is a versatile fully polarimetric imager operating at 91 GHz. It is designed for measurements of polarimetric signatures of the Earth's surface and man-made objects. SPIRA combines a method for the measurement of the complete polarization state with a relatively fast high-resolution imager, which is suitable for a range of applications. The instrument measures all four Stokes parameters simultaneously and delivers images by mechanically scanning the scene with an elevation over azimuth scanner and an offset parabolic antenna. A two-channel heterodyne receiver is used for the reception of polarized radiation. The Stokes parameters are obtained by correlating two linear orthogonal-polarization components in a broadband analog adding correlator. In this paper, we present the design of the instrument and analyze its radiometric and polarimetric characteristics. The polarimetric calibration and a method for the characterization of the polarimetric calibration device are described. First polarimetric measurements are presented and discussed. Index Terms--Four Stokes parameters, imaging, millimeterwave, passive remote sensing, polarimeter.

We propose a new quasi-optical setup for a nulling interferometer at short millimeter and submillimeter wavelengths employing a single Martin-Puplett interferometer (MPI) for side-band separation. The new design allows the simultaneous use of both sidebands, thus avoiding the loss of sensitivity from conventional sideband filters. Although intended for solar flare observations, the quasi-optical setup can be applied to cancel any extended circular source, while at the same time preserving the full sensitivity toward a point-like source on or near the extended one. Numerical simulations show that the sinusoidal transmission characteristic of the MPI limits the usable relative bandwidth to one-third of the IF. Compared to an instrument employing lossless sideband filters, an increase of the response to a point-like continuum source by a factor of ~ 1.6-2 is expected, depending on the source position and relative bandwidth. Index Terms--Interferometry, radio astronomy, solar radiation, submillimeter-wave receivers, submillimeter-wave technology.

In the first half of this paper, an efficient method to calculate transmission and reflection characteristics of wire-grids consisting of periodic arrays of cylindrical conductors for arbitrary directions of incidence is presented by extending exact theory of wire-grids proposed by Yasumoto et al. In the latter half of this paper, an approximate calculation method for wire-grids with slight random irregularity in their spacings between wires is proposed by treating the irregularity as a small perturbation to the theory for regular grids. A comparison with preliminary measurements for actual wire-grids in millimeter- and submillimeter-wave regions demonstrated that this method is effectively applicable to wire-grids whose irregularity is not too much. Index Terms--Electromagnetic reflection, electromagnetic scattering by periodic structures, submillimeter wave devices, submillimeter wave measurements, wire grids.

This paper presents a new configuration of quasi-optical polarization-rotating dual-beam interferometer, which uses a pair of frequency-selective polarizers (FSPs) consisting of a wire-grid placed in front of a flat mirror, and has a function similar to the conventional Martin-Puplett interferometer (MPI). Advantages of this new configuration over the conventional MPI are lower residual reflection at the input and output ports and suitability to fixed-tuned applications. An experiment has shown it to have an MPI-like frequency characteristic as calculated. Careful machining was successful in achieving accuracy needed for a specified filter characteristic. This FSP-based quasi-optical device is to be used as a sideband separator in a space-borne submillimeter receiver for atmospheric research. Index Terms--Martin-Puplett interferometers (MPIs), polarization-rotating dual-beam interferometers, quasi-optical filters, sideband separators.

Continuous temperature observations at the stratosphere and lower mesosphere are rare. Radiometry opens the possibility by observing microwave emissions from two oxygen lines to retrieve temperature profiles at all altitudes. In this study, we present observations performed with a temperature radiometer (TEMPERA) at the Meteoswiss station at Payerne for the period from 2014 to 2017. We reanalyzed these observations with a recently developed and improved retrieval algorithm accounting for the Zeeman line splitting in the line center of both oxygen emission lines at 52.5424 and 53.0669 GHz. The new temperature retrievals were validated against MERRA2 reanalysis and the meteorological analysis NAVGEM-HA. The comparison confirmed that the new algorithm yields an increased measurement response up to an altitude of 53-55 km, which extends the altitude coverage by 8-10 km compared to previous retrievals without considering the Zeeman effect. Furthermore, we found correlation coefficients comparing the TEMPERA temperatures with MERRA2 and NAVGEM-HA for monthly mean profiles to be in the range of 0.8-0.96. In addition, mean temperature biases of 1 K and -2 K were found between TEMPERA and both models (MERRA2 and NAVGEM-HA), respectively. We also identified systematic altitude-dependent cold and warm biases compared to both model data sets. [ABSTRACT FROM AUTHOR]