1,201 research outputs found

    A geostationary orbit microwave multi-channel radiometer

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    The geostationary orbit microwave multi-channel radiometer has the advantages of high real-time performance and large coverage, which plays an important role in typhoon, strong precipitation detection, and medium-to-short-term meteorological/oceanic forecasting. However, due to the difficulty in engineering development of the payload, its application on-orbit has not yet been achieved at present. To satisfy the requirements of fine and quantitative application of satellite observation data, a geostationary orbit microwave multi-channel radiometer with a 10-m-caliber is developed, in which the spatial resolution at horizontal polarization is better than 24 km at 54 GHz. In geostationary orbit microwave multi-channel radiometer, a quasi-optical feed network covering nearly 28 frequency octave bands and ranging from 23.8 to 664 GHz is proposed to solve the technical problem of multi-frequency sharing in the system. Meanwhile, a high-precision reflector preparation method and a high-precision unfolding scheme are proposed, which are considered as a solution for the large-diameter reflector with a high maintaining surface accuracy. A high-precision antenna prototype with 0.54-m is developed, and the tests are performed to verify the key technologies, such as the preparation of high-precision grating reflectors at the micron level, high surface accuracy detection, and sub-millimeter wave antenna electrical performance testing. The results indicate that measured main beam efficiency of the 664 GHz antenna is better than 95.5%. In addition, the system sensitivity is greater than 1.5 K, and the calibration accuracy is better than 1.8 K, according to the results of an analysis of the multi-channel radiometer’s essential parameters and calibration errors

    Polymer-based 3-D printing of G-band metal-pipe rectangular waveguide components

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    The objective of this thesis is to investigate the use of low-cost polymer-based 3-D printing for G-band (140 to 220 GHz) metal-pipe rectangular waveguide (MPRWG) components. First, various preliminary designs are investigated. Then, a successful ‘trough-and-lid’ assembly is demonstrated, which mitigates against the main design challenges for split-block waveguide construction at upper-millimeter-wave frequencies (ca. 100 GHz to 300 GHz), and can be realized using low-cost 3-D printing and conventional metal plating techniques. With this assembly, inexpensive masked stereolithographic apparatus (MSLA) 3-D printers and a standard commercial copper electroplating service are used. The trough-and-lid assembly is expected to provide a standard solution for the low-cost and low loss realization of most MPRWG implementations above 100 GHz; previously, this was infeasible without the use of high-cost, state-of-the-art 3-D printing and/or custom-developed metal plating techniques. Three different component types are successfully demonstrated: (i) straight thru lines; (ii) 90° twists; and (iii) bandpass filters (BPFs). Along with frequency-domain S-parameter measurements, a detailed time-domain reflectometry analysis is also included. For the more accurate characterization of these components, the additional insertion loss due to conductor surface roughness is investigated. Finally, the integration of an MPRWG component into a millimeter-wave subsystem, which is based on the design of a radiometer front-end, is presented.Open Acces

    Spaceborne sensors (1983-2000 AD): A forecast of technology

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    A technical review and forecast of space technology as it applies to spaceborne sensors for future NASA missions is presented. A format for categorization of sensor systems covering the entire electromagnetic spectrum, including particles and fields is developed. Major generic sensor systems are related to their subsystems, components, and to basic research and development. General supporting technologies such as cryogenics, optical design, and data processing electronics are addressed where appropriate. The dependence of many classes of instruments on common components, basic R&D and support technologies is also illustrated. A forecast of important system designs and instrument and component performance parameters is provided for the 1983-2000 AD time frame. Some insight into the scientific and applications capabilities and goals of the sensor systems is also given

    Millimeter and sub-millimeter wave radiometers for atmospheric remote sensing from CubeSat platforms

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    2018 Fall.Includes bibliographical references.To view the abstract, please see the full text of the document

    Preliminary submillimeter spectroscopic measurements using a submillimeter heterodyne radiometer

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    A submillimeter heterodyne radiometer uses a submillimeter laser, pumped by a CO2 laser, as a local oscillator and a room temperature Schottky barrier diode as the first IF mixer. The radiometer can resolve spectral lines in the submillimeter region of the spectrum (arising from pure rotational molecular transitions) to within 0.3 MHz, using acousto-optic spectrum analyzer which measures the power spectrum by simultaneously sampling 0.3 MHz wide channels over a 100 MHz bandwidth spanning the line. Preliminary observations of eight spectral lines of H2O2, CO, NH3 and H2O, all lying in the 434-524 micrometer wavelength range are described. All eight lines were observed using two local oscillator frequencies obtained by operating the submillimeter laser with either methyl fluoride (CH3F) or formic acid (HCOOH) as the lasing gas. Sample calculations of line parameters from the observed data show good agreement with established values. One development goal is the size and weight reduction of the package to make it suitable for balloon or shuttle experiments to detect trace gases in the upper atmosphere

    Three Dimensional Radiative Effects in Passive Millimeter/Sub-Millimeter All-sky Observations

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    This study was conducted to quantify the errors prompted by neglecting three-dimensional (3D) effects, i.e., beam-filling and horizontal photon transport effects, at millimeter/sub-millimeter wavelengths. This paper gives an overview of the 3D effects that impact ice cloud retrievals of both current and proposed (Ice Cloud Imager) satellite instruments operating at frequencies of approximate to 186.3 and approximate to 668 GHz. The 3D synthetic scenes were generated from two-dimensional (2D) CloudSat (Cloud Satellite) observations over the tropics and mid-latitudes using a stochastic approach. By means of the Atmospheric Radiative Transfer Simulator (ARTS), three radiative transfer simulations were carried out: one 3D, one independent beam approximation (IBA), and a one-dimensional (1D). The comparison between the 3D and IBA simulations revealed a small horizontal photon transport effect, with IBA simulations introducing mostly random errors and a slight overestimation (below 1 K). However, performing 1D radiative transfer simulations results in a significant beam-filling effect that increases primarily with frequency, and secondly, with footprint size. For a sensor footprint size of 15 km, the errors induced by neglecting domain heterogeneities yield root mean square errors of up to approximate to 4 K and approximate to 13 K at 186.3 GHz and 668 GHz, respectively. However, an instrument operating at the same frequencies, but with a much smaller footprint size, i.e., 6 km, is subject to smaller uncertainties, with a root mean square error of approximate to 2 K at 186.3 GHz and approximate to 7.1 K at 668 GHz. When designing future satellite instruments, this effect of footprint size on modeling uncertainties should be considered in the overall error budget. The smallest possible footprint size should be a priority for future sub-millimeter observations in light of these results

    3-D Printed Plug and Play Prototyping for Low-cost Sub-THz Subsystems

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    Polymer-based additive manufacturing using 3-D printing for upper-millimeter-wave ( ca. 100 to 300 GHz) frequency applications is now emerging. Building on our previous work, with metal-pipe rectangular waveguides and free-space quasi-optical components, this paper brings the two media together at G-band (140 to 220 GHz), by demonstrating a compact multi-channel front-end subsystem. Here, the proof-of-concept demonstrator integrates eight different types of 3-D printed components (30 individual components in total). In addition, the housing for two test platforms and the subsystem are all 3-D printed as single pieces, to support plug and play development; offering effortless component assembly and alignment. We introduce bespoke free-space TRM calibration and measurement schemes with our quasi-optical test platforms. Equal power splitting plays a critical role in our multi-channel application. Here, we introduce a broadband 3-D printed quasi-optical beamsplitter for upper-millimeter-wave applications. Our quantitative and/or qualitative performance evaluations for individual components and the complete integrated subsystem, demonstrate the potential for using consumer-level desktop 3-D printing technologies at such high frequencies. This work opens-up new opportunities for low-cost, rapid prototyping and small-batch production of complete millimeter-wave front-end subsystems

    Atmospheric remote sensing and radiopropagation: from numerical modeling to spaceborne and terrestrial applications

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    The remote sensing of electromagnetic wave properties is probably the most viable and fascinating way to observe and study physical media, comprising our planet and its atmosphere, at the same time ensuring a proper continuity in the observations. Applications are manifold and the scientific community has been importantly studying and investing on new technologies, which would let us widen our knowledge of what surrounds us. This thesis aims at showing some novel techniques and corresponding applications in the field of the atmospheric remote sensing and radio-propagation, at both microwave and optical wavelengths. The novel Sun-tracking microwave radiometry technique is shown. The antenna noise temperature of a ground-based microwave radiometer is measured by alternately pointing toward-the-Sun and off-the-Sun while tracking it along its diurnal ecliptic. During clear sky the brightness temperature of the Sun disk emission at K and Ka frequency bands and in the under-explored millimeter-wave V and W bands can be estimated by adopting different techniques. Parametric prediction models for retrieving all-weather atmospheric extinction from ground-based microwave radiometers are tested and their accuracy evaluated. Moreover, a characterization of suspended clouds in terms of atmospheric path attenuation is presented, by exploiting a stochastic approach used to model the time evolution of the cloud contribution. A model chain for the prediction of the tropospheric channel for the downlink of interplanetary missions operating above Ku band is proposed. On top of a detailed description of the approach, the chapter presents the validation results and examples of the model-chain online operation. Online operation has already been tested within a feasibility study applied to the BepiColombo mission to Mercury operated by the European Space Agency (ESA) and by exploiting the Hayabusa-2 mission Ka-band data by the Japan Aerospace Exploration Agency (JAXA), thanks to the ESA cross-support service. A preliminary (and successful) validation of the model-chain has been carried out by comparing the simulated signal-to-noise ratio with the one received from Hayabusa-2. At the next ITU World Radiocommunication Conference 2019, Agenda Item 1.13 will address the identification and the possible additional allocation of radio-frequency spectrum to serve the future development of systems supporting the fifth generation of cellular mobile communications (5G). The potential impact of International Mobile Telecommunications (IMT) deployments is shown in terms of received radio frequency interference by ESA’s telecommunication links. Received interference can derive from several radio-propagation mechanisms, which strongly depend on atmospheric conditions, radio frequency, link availability, distance and path topography; at any time a single mechanism, or more than one may be present. Results are shown in terms of required separation distances, i.e. the minimum distance between the earth station and the IMT station ensuring that the protection criteria for the earth station are met

    Radiometric Imaging for Monitoring and Surveillance Issues

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    This paper deals with the recent advances performed by State Research Center “Iceberg” (SRC) in the field of the passive imaging at millimeter wavelengths. In particular, first the paper describes the design and the realization of two systems working in 3 mm and 8 mm wave bands, respectively. Second, the measurements collected by the two systems are enhanced by means of simple data processing strategies developed by the Institute for Electromagnetic Sensing of the Environment (IREA-CNR)
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