Intersatellite range monitoring using optical interferometry

We report on an interferometer designed to provide 1-10 nm/square root(Hz) displacement measurement resolution, in the range 0.01 Hz to 1 Hz, while in low Earth orbit. The interferometer comprises two units, each with its own laser and in separate satellites, which would be in the same orbit separated by approximately 50 km. We discuss the requirements on the interferometer subsystem and describe the optical transponder distance measurement, including a phase locking method to generate a heterodyne beat signal between the two lasers. Design, fabrication, and testing of a "flightlike" engineering model interferometer is outlined, and results from environmental and performance tests are reported.     

Experimental monitoring of the Earth's ionosphere using satellite navigation systems

A technique for determining the high-altitude profiles of the electron concentration in the ionosphere using the Glonass (Russia) and Navstar (USA) dual-frequency receivers incorporated into satellite navigation systems is developed. The technique is relatively simple and makes it possible to obtain measurements rapidly. It has been used in conducting experimental studies with the IMTS calibration stand produced by the All-Russia Scientific Research Institute for Physical and Radio Engineering Measurements. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 8–10, October, 1997.     

Matching radar and satellite images for ship trajectory estimation using the Hausdorff distance

A novel technique to obtain position, velocity and radar biases estimates of a ship is described by matching ship-borne radar images to geo-referenced satellite images. The matching is performed through the minimisation of the averaged partial Hausdorff distances between data points in each image. The minimisation rapidly yields robust geographical latitude and longitude position measurements, as well as ship heading and radar biases. The accuracy of the measurements is improved by feeding them into a Kalman filter that also allows estimates of the ship's velocity to be obtained. The method provides an alternative effective position sensor for GPS denied environments, which may also be employed for automatic radar calibration of bearing and range biases or for indoor autonomous mobile robot navigation     

Measurement of crack closure after the application of an overload cycle, using moiré interferometry

The crack closure behaviour on the application of a single overload cycle was studied in a Ti-6Al-4V specimen. Moiré interferometry with photoresist gratings was used to measure crack displacements. During the overload cycle a large crack opening displacement was observed at the maximum load. This was similar to predictions from a Dugdale-type crack closure model. When the load was taken back to zero, the crack was open at the crack tip due to the high levels of plastic deformation during the overload cycle. As the crack was grown there was some evidence of the deformed material on the crack faces.Moiré interferometry provided displacement data close to the crack faces, even when the crack had grown to over two-and-a-half times the overload crack length. When the overload was applied the crack bifurcated, and the Dugdale-type model under-predicted the crack opening.     

Estimation of the error in determining pseudorange in satellite radar

The results of an experiment to estimate the systematic error in determining the pseudorange in a satellite radar are considered in cases where the satellite approaches and recedes from a terrestrial object. It is concluded that the hypothesis regarding the medium of propagation of electromagnetic waves corresponds most to Newton’s hypothesis.     

Mine surface subsidence monitoring due to impacts of underground mining using persistent scatterer interferometry

The Singhbhum shear zone in India is well known for its historical underground copper mining activity. As a consequence, today some abandoned underground mines pose a serious risk to the local people and property. Thus it is essential for a long-term wide-range monitoring technique to map the surface subsidence over the mining areas. In this study, it has been tried to establish occurrence of ground subsidence with an advanced differential interferometric synthetic aperture radar technology called persistent scatterer interferometry, which is known for its capability of high-precision monitoring. The results clearly indicate trends of surface subsidence over abandoned mining regions.     

On the importance of path for phase unwrapping in synthetic aperture radar interferometry

Phase unwrapping is a key procedure in interferometric synthetic aperture radar studies, translating ambiguous phase observations to topography, and surface deformation estimates. Some unwrapping algorithms are conducted along specific paths based on different selection criteria. In this study, we analyze six unwrapping paths: line scan, maximum coherence, phase derivative variance, phase derivative variance with branch-cut, second-derivative reliability, and the Fisher distance. The latter is a new path algorithm based on Fisher information theory, which combines the phase derivative with the expected variance to get a more robust path, potentially performing better than others in the case of low image quality. In order to compare only the performance of the paths, the same unwrapping function (phase derivative integral) is used. Results indicate that the Fisher distance algorithm gives better results in most cases.     

Mathematical formulation for estimation of baseline in synthetic aperture radar interferometry

Terrain height estimation through spaceborne interferometric synthetic aperture radar (INSAR) requires accurate knowledge of the orbital shift between repeat passes. Mathematical models are available for the estimation of horizontal orbital shift. However, in reality, the orbital shift between repeat passes is modelled as two-dimensional for the same azimuth scanline. In this paper, a new mathematical formulation has been developed for the estimation of the two-dimensional orbital shift of INSAR based on the fringe line pattern in the interferogram of flat earth.     

On the aerosols monitoring by satellite observations

Particulate matter is the general term used to identify a complex mixture of organic and inorganic particles (aerosols) that can be found suspended in the atmosphere in solid, liquid or both physical states. The presence of particulate of non-natural origin is linked to important climatic and environmental effects. The interactions of these particles with the solar radiation, the Earth and the atmospheric gases, can modify the atmosphere physical and chemical characteristics, the temperature vertical profile and other thermodynamic variables, as well as the Earth surface characteristics and its temperature. Studies on the particles have furthermore demonstrated the existence of a link between the presence of fine and ultra-fine particulate of non-natural origin and some effects on the health of human and other living being. The aerosols can contaminate a wide area of the region surrounding the source of particulate. Based upon all these reasons it is considered the utmost importance to develop a satellite-based system capable of monitoring the presence of particulate on very large areas. This paper provides methodologies to identify atmospheric particles by means of satellite-based sensors operating both in the reflective and in the thermal infrared part of the electromagnetic spectrum.     

Application of holographic interferometry to optical monitoring of solid surfaces

A new optical method is proposed for probing transition layers on solid surfaces, which combines the high precision inherent in holographic interferometry and the high sensitivity characteristic of optical microscopy using surface electromagnetic waves. The proposed technique has been numerically modeled for monochromatic radiation in the visible spectral range.     

Comparison of unitary transforms using Franson interferometry

Unknown unitary transforms may be compared to each other in a way which makes it possible to obtain an unambiguous answer, indicating that the transforms are different, already after a single application of each transform. Quantum comparison strategies may be useful for example if we want to test the performance of individual gates in a quantum information or quantum computing network. It is then possible to check for errors by comparing the elements to a master copy of the gate, instead of performing a complete tomography of the gate. In this paper we propose a versatile linear optical implementation based on the Franson interferometer with short and long arms. A click in the wrong output port unambiguously determines that the tested gate is faulty. This set-up can also be used for a variety of other tasks, such as confirming that the two transforms do not commute or do not anticommute.     

Measurement of temperature using speckle shearing interferometry

A laser speckle shearing interferometric technique is used for measuring the temperature profile inside a gaseous flame. The experimental results are compared with the values obtained by a thermocouple and also by speckle photography. Good agreement is seen among the temperatures measured by speckle shearing interferometry, speckle photography, and the thermocouple. Speckle shearing interferometry is easier to implement than speckle photography. This is because in speckle shearing interferometry the accurate positions of the fringes can be known without point-by-point analysis and correction for the halo effect.     

雷达状态监测系统设计

为降低雷达维修成本、提高雷达保障效率,针对雷达的不同信号分别设计不同的采集方式,完成雷达实时状态监测系统,确保采集监测信息的准确性。该设计增加了数据实时处理终端系统,能够实时处理雷达状态信息,对雷达出现的故障能够做到早发现、早报警、早维修,满足保障需求。     

Experimental study of laser-generated shear waves using interferometry

The shear displacements generated by short laser pulses have been measured in aluminum semicylindrical samples, both in the thermoelastic and ablation regimes. We measured the waveforms at different angles and obtained the angular distribution pattern of the amplitudes. For the thermoelastic regime good agreement has been found between the measured and the theoretically predicted shear waveforms. In the ablation regime, the absolute values of the amplitudes are comparable to the ones of compressional waves. The shear waveforms are difficult to interpret, particularly in the case where both thermoelastic and ablative effects play a role, because the phases of the shear pulses are opposite to one another in these two regimes. To measure the in-plane displacements, and hence the shear displacement field generated by the pulsed laser, a speckle heterodyne interferometer was used.This article is dedicated to Professor Dr. Paul Höller on the occasion of his 65th birthday.     

Primary calibration of ultrasonic hydrophone using optical interferometry

A primary calibration method for ultrasonic hydrophones which uses a Michelson interferometer to determine the particle displacement in an ultrasonic field is discussed. The acoustic pressure is derived from this measurement and used to determine the free-field sensitivity of a hydrophone in the frequency range 0.5-15 MHz. The random uncertainty of the method is typically 1%, whereas the systematic uncertainty varies from 2.3 to 6.6% over the frequency range. To obtain this accuracy, the performance of the system has been carefully examined and appropriate correction factors derived. The greatest difficulty in the method lies in determining the frequency response of the optical detection system, and two different approaches have been used to measure this response. Several acoustical effects have also been studied and the calibration procedure modified to take account of them. The calibration results are in agreement with those of other methods and with the theoretically predicted frequency response of a hydrophone. The method has been used to determine the temporal stability of a hydrophone over a period of two years.     

Determination of the coherent scattering length of carbon using neutron interferometry

Highly oriented pyrolytic graphite samples were used for determining the coherent scattering length of the bound carbon atom by means of neutron interferometry. The value of 6.647±0.005 fm agrees well with results obtained by various other techniques.