Millimetre wave remote sensing of the atmosphere

Recent advances in millimetre wave technology has opened up a new region of the spectrum to remote sensing from artificial satellites. The main part of this work involves a millimetre wave proving experiment for a satellite borne millimetre wave active sounder to measure surface pressure over the oceans. The Microwave Pressure Sounder is a6 channel, low power radar operating in the spectral range from 24 to 75 GHz. The strength of the return echoes from the sea surface determines the amount of oxygen in the path which can be directly related to the surface pressure to an accuracy of 1 mb, when corrected for sea surface reflectivity and atmospheric temperature and water content by this multichannel instrument. Measurements of atmospheric attenuation along a horizontal path were related to atmospheric pressure changes by a millimetre wave instrument built at Heriot-Watt University. The transmissometer measured the differential absorption between two frequencies (54 and 58 GHz) over a 650 metre path. The deduced atmospheric pressure was found to compare with the barometric pressure with a standard deviation of two millibars for the best data set. These results demonstrate that atmospheric attenuation can be measured with sufficient precision for a satellite borne instrument to determine the surface atmospheric pressure over the oceans to an accuracy of approximately one millibar. This accuracy would lead to significant improvements in the modelling of the atmosphere and weather forecasting. Various other techniques to remotely sense surface atmospheric pressure are reviewed. Recently, increased awareness of the sensitivity of the environment and evidence of the effects of man-made pollutants has given rise to an increased awareness in the health of the Earth and led to several instruments being developed to monitor our planet. One of these instruments, the Microwave Limb Sounder to be flown on the Upper Atmosphere Research Satellite (launch October 1991) is described. This instrument uses millimetre wave radiometers at 63 GHz, 183 GHz and 205 GHz to measure the amount of chlorine oxide, ozone and water vapour in the upper atmosphere. These gases are important in understanding the photochemistry of the mesosphere. Global distributions of the gases will be produced and changes in concentration will be monitored during the three year mission

Interface Circuits for Microsensor Integrated Systems

ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Recent advances in sensing technologies, especially those for Microsensor Integrated Systems, have led to several new commercial applications. Among these, low voltage and low power circuit architectures have gained growing attention, being suitable for portable long battery life devices. The aim is to improve the performances of actual interface circuits and systems, both in terms of voltage mode and current mode, in order to overcome the potential problems due to technology scaling and different technology integrations. Related problems, especially those concerning parasitics, lead to a severe interface design attention, especially concerning the analog front-end and novel and smart architecture must be explored and tested, both at simulation and prototype level. Moreover, the growing demand for autonomous systems gets even harder the interface design due to the need of energy-aware cost-effective circuit interfaces integrating, where possible, energy harvesting solutions. The objective of this Special Issue is to explore the potential solutions to overcome actual limitations in sensor interface circuits and systems, especially those for low voltage and low power Microsensor Integrated Systems. The present Special Issue aims to present and highlight the advances and the latest novel and emergent results on this topic, showing best practices, implementations and applications. The Guest Editors invite to submit original research contributions dealing with sensor interfacing related to this specific topic. Additionally, application oriented and review papers are encouraged.

Laser power stabilization via radiation pressure

This thesis reports a new active power stabilization scheme which can be implemented in high precision experiments, such as gravitational wave detectors. The novel aspect of the scheme is sensing laser power fluctuations via the radiation pressure driven motion they induce on a movable mirror. The mirror position and its fluctuations are determined by means of a weak auxiliary beam and a Michelson interferometer, which form an in-loop sensor for the proposed stabilization scheme. This sensing technique exploits the concept of a nondemolition measurement, since the power fluctuations are inferred by measuring the fluctuations in the phase observable of the auxiliary beam. This process results in higher in-loop signals for power fluctuations than what would be achieved by a direct detection, e.g. via the traditional scheme where a fraction of the laser power is picked off and sensed directly by a photodetector. Other advantages of this scheme are that the full beam power is preserved and available for further use, and that it enables the generation of a strong bright squeezed out-of-loop beam. An extensive theoretical investigation on the concept of the new sensing scheme is presented. In this investigation, different schemes in which power fluctuations are transferred to another observable of the light field, e.g. phase or polarization, are compared to each other, and the advantages of the radiation pressure scheme are highlighted. Furthermore, a complete calculation of the fundamental limit of the proposed radiation pressure scheme, set by the quantum noise in the interferometer and the thermal noise of the movable mirror, is performed. The calculations show that a bright squeezed beam with a power of 4W and up to 11 dB of squeezing might be achievable in the near future. Based on the results of the theoretical investigation, a proof-of-principle experiment was realized with microoscillator mirrors with masses ranging from 25 to 250 ng, and fundamental resonance frequencies from 150 to 210 Hz. Power stabilization in the frequency range from 1 Hz to 10 kHz was demonstrated. The results for the out-of-loop power stability are presented for different beam powers, and a relative power noise of 3.7 * 10^−7 Hz^−1/2 was achieved at 250 Hz for 267 mW. The stability performance was limited by the structural thermal noise of the micro-oscillators, which was particularly high due to operation at room temperature. The results from the investigations conducted in this thesis are a promising step towards generation of a strong bright squeezed beam, and towards an improved stabilization scheme to be used in the future generation of gravitational wave detectors

Laser power stabilization via radiation pressure

This Letter reports the experimental realization of a novel, to the best of our knowledge, active power stabilization scheme in which laser power fluctuations are sensed via the radiation pressure driven motion they induce on a movable mirror. The mirror position and its fluctuations were determined by means of a weak auxiliary laser beam and a Michelson interferometer, which formed the in-loop sensor of the power stabilization feedback control system. This sensing technique exploits a nondemolition measurement, which can result in higher sensitivity for power fluctuations than direct, and hence destructive, detection. Here we used this new scheme in a proof-of-concept experiment to demonstrate power stabilization in the frequency range from 1 Hz to 10 kHz, limited at low frequencies by the thermal noise of the movable mirror at room temperature

Space programs summary no. 37-63, volume 1 for the period 1 March - 30 April 1970. Flight projects

Mariner Mars 1971, Mariner Venus-Mercury 1973 and Viking Orbiter 1975 status report

Comparison of direct and heterodyne detection optical intersatellite communication links

The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity

The 30/20 GHz flight experiment system, phase 2. Volume 2: Experiment system description

A detailed technical description of the 30/20 GHz flight experiment system is presented. The overall communication system is described with performance analyses, communication operations, and experiment plans. Hardware descriptions of the payload are given with the tradeoff studies that led to the final design. The spacecraft bus which carries the payload is discussed and its interface with the launch vehicle system is described. Finally, the hardwares and the operations of the terrestrial segment are presented

Parametric analysis of microwave and laser systems for communication and tracking. Volume 3 - Reference data for advanced space communication and tracking systems

Reference data for advanced microwave and laser communication and tracking systems - Vol.

High data rate optical transceiver terminal

The objectives of this study were: (1) to design a 400 Mbps optical transceiver terminal to operate from a high-altitude balloon-borne platform in order to permit the quantitative evaluation of a space-qualifiable optical communications system design, (2) to design an atmospheric propagation experiment to operate in conjunction with the terminal to measure the degrading effects of the atmosphere on the links, and (3) to design typical optical communications experiments for space-borne laboratories in the 1980-1990 time frame. As a result of the study, a transceiver package has been configured for demonstration flights during late 1974. The transceiver contains a 400 Mbps transmitter, a 400 Mbps receiver, and acquisition and tracking receivers. The transmitter is a Nd:YAG, 200 Mhz, mode-locked, CW, diode-pumped laser operating at 1.06 um requiring 50 mW for 6 db margin. It will be designed to implement Pulse Quaternary Modulation (PQM). The 400 Mbps receiver utilizes a Dynamic Crossed-Field Photomultiplier (DCFP) detector. The acquisition receiver is a Quadrant Photomultiplier Tube (QPMT) and receives a 400 Mbps signal chopped at 0.1 Mhz

Parametric analysis of microwave and laser systems for communication and tracking Quarterly report, 6 Mar. - 6 Jun. 1966

Parametric analysis of microwave and laser systems for communication and tracking - updated reference data for advanced space communication and tracking system