Doppler Frequency Shift Measurement Research Articles

Photonic Doppler frequency shift measurement without ambiguity based on cascade modulation

A novel scheme based on the cascade structure of a dual-polarization Mach–Zehnder modulator (DPol-MZM) and a phase modulator (PM) is proposed which can simultaneously identify the value and direction of Doppler frequency shift (DFS). A low frequency reference signal and an echo signal are modulated by the DPol-MZM into orthogonal polarization states. The transmitted signal is modulated onto the reference signal by the PM and then one side band of the modulated signal is suppressed after a filter. The value of DFS is obtained by mixing the echo signal and the transmitted signal and the direction is distinguished by mixing the echo signal and the modulated reference signal. The system has only one channel and DFS measurement only needs a low frequency electrical spectrum analyzer (ESA). The measurement error is less than 0.1 Hz. Because of the cascade modulation structure and the direct frequency mixing of the transmitted signal and the echo signal, the operation frequency range of the system is not limited by the carrier frequency and the scheme has high measurement accuracy.

A PM-based approach for Doppler frequency shift measurement and direction discrimination

A novel photonic approach for wideband Doppler frequency Shift (DFS) measurement and direction discrimination based on phase modulators (PMs) and optical frequency shift module is proposed and experimentally demonstrated. In the proposed scheme, a light emitted from the laser is split into two paths, one of which is modulated by the transmitted signal through the first PM and the other of which passes through the carrier frequency shifter and then is modulated by the echo signal through the second PM. After combining two optical signals and filtering out the negative sidebands, the value and direction of DFS can be obtained by comparing two peak frequencies in the low-frequency electrical signals generated by a low-speed photodetector. Proof-of-concept experiments with DFSs from -1 MHz to 1 MHz at an optical carrier frequency shift of 40 MHz are implemented, where the measurement errors are kept within ±0.7 Hz.

Wideband DFS Measurement Using a Low-Frequency Reference Signal

A novel Doppler frequency shift (DFS) measurement system based on a cascaded modulator topology is presented. It is capable to measure both the object speed and moving direction on an electrical spectrum analyzer with the use of a fixed low-frequency reference signal. It has a simple single-laser and single-photodetector structure, a robust performance and a wide operating frequency range, which is only limited by the optical modulator bandwidth. Experimental results are presented that demonstrate DFS ranging from −100 kHz to +100 kHz with an error of less than ±0.1 Hz at different microwave signal frequencies. Over 35 dB suppression in unwanted frequency components present at the system output is also demonstrated.

6–40 GHz photonic microwave Doppler frequency shift measurement based on polarization multiplexing modulation and I/Q balanced detection

A novel optical approach to implement broadband Doppler frequency shift (DFS) measurement is proposed and demonstrated. Through I/Q balanced detection using a polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) and two balanced photodetectors, the concerned microwave DFS is estimated with clear direction discrimination and a significant improved resolution. In the experiments, the DFSs from -100 to 100 kHz in 20-kHz step are successfully measured and estimated for microwave signals with the operating frequency from 6 to 40 GHz. The error of measuring is calculated to be less than 8 Hz. The approach is uncomplicated and manageable to implement, which provides an alternative solution for future wideband electronic systems such as Doppler radar, satellite communications or electronic countermeasures.

Photonic approach to wideband Doppler frequency shift estimation system based on a DPMZM and a Sagnac loop

A photonic approach to wideband Doppler frequency shift (DFS) measurement and direction discrimination is proposed and demonstrated. In the proposed scheme, a dual-parallel Mach-Zehnder modulator is used to generate carrier suppressed double sidebands signals, which are orthogonally polarized in a Sagnac loop incorporating a fiber Bragg grating. The DFS is transformed into a low-frequency electrical signal. The value of the DFS is obtained by analyzing the spectrum of the output current. The orientation of the DFS is estimated by a 90° hybrid coupler. The entire DFS measuring process is independent of the radar carrier frequency and suitable for wideband spectrum measurement range. Simulations are performed to verify the proposed scheme, the value and the orientation of the DFS can be estimated simultaneously. As the target moves toward the radar or moves away from the radar, there are, respectively, 36.8 dB and 39.1 dB power difference between the two branches of the hybrid coupler. In addition, the performance of the proposed approach in term of the signal-to-noise ratio and stability are discussed.

Photonics‐based wideband Doppler frequency shift measurement by in‐phase and quadrature detection

The authors propose and demonstrate a photonics-based wideband Doppler frequency shift (DFS) measurement scheme through in-phase and quadrature detection. The system has a compact structure applying cascaded phase modulation and polarisation modulation. It is easy to implement since both the value and sign of the DFS can be estimated by simple signal processing. More importantly, the proposed scheme is suitable for both DFS measurement and direction discrimination over a very wide frequency range. In the experiment, accurate DFS measurement with a large carrier frequency range from 5 to 40 GHz is demonstrated with the measurement error kept within ±12 Hz.

Use of global ionospheric maps for HF Doppler measurements interpretation

The HF Doppler technique, a method of measurement of Doppler frequency shift of ionospheric signal, is one of the well-known and widely used techniques of ionosphere research. It allows investigation of various disturbances in the ionosphere. There are different sources of disturbances in the ionosphere such as geomagnetic storms, solar flashes, meteorological effects and atmospheric waves. The HF Doppler technique allows us to find out the influence of earthquakes, explosions and other processes on the ionosphere, which occurs near the Earth. HF Doppler technique has high sensitivity to small frequency variations and high time resolution but interpretation of results is difficult. In this paper, we attempt to use GPS data for Doppler measurements interpretation. Modeling of Doppler frequency shift variations with use of TEC allows separation of ionosphere disturbances of medium scale.

Wideband Doppler Frequency Shift Measurement and Direction Discrimination Based on a DPMZM

A wideband microwave Doppler frequency shift (DFS) measurement approach based on a single dual-parallel Mach–Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. The light wave is modulated by the transmitted and echo signals in the DPMZM to generate carrier suppressed double sidebands signals. Based on the phase difference and powers of the upper bands and lower bands of the modulated signal, the DFS value, as well as the sign, can be measured. An experiment is carried out. The DFS from –100 to +100 kHz at the carrier frequencies of 10, 20, 30, and 39 GHz is accurately measured with errors of less than $5 \times {10^{ - 6}}$ Hz.

Photonic Doppler frequency shift measurement based on a dual-polarization modulator.

In this paper, a novel photonic-assisted Doppler frequency shift (DFS) measurement scheme based on an integrated dual-polarization Mach-Zehnder modulator is presented. In the proposed scheme, the DFS to be identified is transformed into a low-frequency electrical signal through an optical frequency-conversion link. The value of the DFS can be acquired by analyzing the spectrum of the low-frequency electrical signal. Meanwhile, the orientation of the DFS can be easily determined utilizing a 90° hybrid coupler. If the receiver is moving toward the transmitter, only the positive port has an output signal, while only the negative port has an output signal if the receiver is moving away from the transmitter. The scheme can simultaneously obtain the value and the orientation of the DFS. In addition, to investigate the frequency tunability of the proposed scheme, the DFS, which varies from -100 to 100 KHz at a step of 10 KHz for different microwave signals at frequencies of 10, 15, and 18 GHz, is demonstrated experimentally, and the errors are within ±5×10-6 Hz.

An Effective and Simple Solution for Stationary Target Localization Using Doppler Frequency Shift Measurements

An Effective and Simple Solution for Stationary Target Localization Using Doppler Frequency Shift Measurements

Wideband Microwave Doppler Frequency Shift Measurement and Direction Discrimination Using Photonic I/Q Detection

An enhanced approach to realizing wideband microwave Doppler frequency shift (DFS) measurement and direction discrimination based on photonic in-phase and quadrature coherent detection is proposed and demonstrated experimentally. In the proposed approach, the DFS between the transmitted microwave signal and the received echo signal is converted into two quadrature low-frequency electrical signals through the coherent detection by using an optical hybrid and two balanced photodetectors. The microwave DFS of interest can be estimated with an unambiguous direction, and in particular with a greatly improved resolution. Meanwhile, photonic coherent and balanced detection effectively eliminates the optical signal to signal beating interferences. In the proof-of-concept experiment, the DFSs from –90 to +90 kHz are successfully estimated for microwave signals at 10, 14, 18, and 38 GHz. The measurement errors are estimated to be less than ±5.8 Hz which are an order of magnitude lower than those (i.e., ±60 Hz) released before. Such results provide a high resolution for radial velocity measurement as well. In addition, the performance of the proposed approach in term of the signal-to-noise ratio and stability is discussed.

Wideband Doppler frequency shift measurement and direction ambiguity resolution using optical frequency shift and optical heterodyning.

A photonic approach for both wideband Doppler frequency shift (DFS) measurement and direction ambiguity resolution is proposed and experimentally demonstrated. In the proposed approach, a light wave from a laser diode is split into two paths. In one path, the DFS information is converted into an optical sideband close to the optical carrier by using two cascaded electro-optic modulators, while in the other path, the optical carrier is up-shifted by a specific value (e.g., from several MHz to hundreds of MHz) using an optical-frequency shift module. Then the optical signals from the two paths are combined and detected by a low-speed photodetector (PD), generating a low-frequency electronic signal. Through a subtraction between the specific optical frequency shift and the measured frequency of the low-frequency signal, the value of DFS is estimated from the derived absolute value, and the direction ambiguity is resolved from the derived sign (i.e., + or -). In the proof-of-concept experiments, DFSs from -90 to 90 kHz are successfully estimated for microwave signals at 10, 15, and 20 GHz, where the estimation errors are lower than ±60 Hz. The estimation errors can be further reduced via the use of a more stable optical frequency shift module.

Estimating both direction and magnitude of flow velocity using photoacoustic microscopy

This report studies absolute estimation of both the direction and magnitude of flow velocity, at microscopic scale, with acoustic resolution photoacoustic microscopy. Fundamentally, it is based on the quantitative measurement of Doppler frequency shift in the short laser pulse induced photoacoustic (ultrasound) signals. Experiments were carried out in a transparent plastic tube through which light absorbing liquid solution (as imaging target) flows. We investigated various cases of flow velocity: (i) variation in direction (0°–90°) and (ii) variation in magnitude (0.5–5 mm/s). This study demonstrates simultaneous recovery of both direction and magnitude from a set of data noninvasively and nondestructively.

Observations of wave activity in the ionosphere over South Africa in geomagnetically quiet and disturbed periods

The present paper deals with observations of wave activity in the period range 1–60min at ionospheric heights over the Western Cape, South Africa from May 2010 to July 2010. The study is based on the Doppler type sounding of the ionosphere. The Doppler frequency shift measurements are supplemented with measurements of collocated Digisonde DPS-4D at SANSA Space Sciences, Hermanus. Nine geomagnetically quiet days and nine geomagnetically active days were included in the study. Waves of periods 4–30min were observed during the daytime independent of the level of geomagnetic activity. Amplitudes of 10–30min waves always increased between 14:00 and 16:15 UT (16:00–18:15 LT). Secondary maxima were observed between 06:00 and 07:00 UT (08:00–09:00 LT). The maximum wave amplitudes occurred close to the time of passage of the solar terminator in the studied region which is known to act as a source of gravity waves.Waves of periods 30–50min were observed in the F2 layer during the daytime on five out of the eighteen days analysed, on four geomagnetically active days and on one quiet day. On the geomagnetically active day of 27 July 2010, waves of periods 1–2.5min occurred in the evening and night hours. These waves appeared simultaneously with 1–2.5min fluctuations of horizontal components of the local geomagnetic field. We suppose that the 1–2.5min ionospheric oscillations are a response to the geomagnetic micropulsations.

Dual-wavelength laser heterodyne interferometer for absolute displacement measurement

In order to meet absolute metrology of displacement in several axes simultaneously; the induced errors due to the fluctuation of atmospheric parameters and Doppler effect should be investigated. Measurements of phase dispersion and Doppler frequency shift over two different axes using dual-wavelength laser heterodyne interferometer (ZMI-1000A) are reported. The principle of this work is to study the induced parameters influences of an absolute measurement of a displacement over two different axes in a free atmosphere using laser heterodyne interferometer.

Automatic full field analysis of perfusion images gained by scanning laser Doppler flowmetry

BACKGROUNDScanning laser Doppler flowmetry (SLDF) enables the measurement of the laser Doppler frequency shift in retinal tissue. This process allows the quantification of retinal and optic nerve head perfusion in...

Soda Pop for Vascular La1oratory Quality Control

Quality control of duplex imaging involves consistency in performance of grey scale and Doppler frequency shift or velocity measurements. Phantoms are used to measure the accuracy of Duplex scanners, and many phantoms used for grey scale imaging quality control are available commercially. However, simplistic and inexpensive phantoms for velocity measurements are not available. The authors designed and tested one such phantom—an in-house pump that recirculates fluid in a bottle with inlet and outlet tubes. Different pump settings control the speed of circulating fluid. Initially, the authors used discarded blood from the blood bank. However, because of the associated risks with blood, they searched for a substitute with good reflective properties for ultrasound. Small air bubbles in soda pop worked very effectively, because air is the strongest reflector for ultrasound. To the author's knowledge, use of soda pop for this purpose has not been described previously. Three scanners, an HP 2000, Quantum 2000, and ATL 3000, were evaluated for accuracy of velocity measurements. A similar MHz transducer, 45-degree Doppler angle, and same segment of tube with flowing soda pop were used each time. The Quantum scanner consistently measured velocities as lower than the other two scaners by approximately 10-20% at all velocity ranges (50-350 cm/sec). At the higher end of the spectrum, the Quantum scanner consistently displayed aliasing. Therefore, velocities could not be measured.

In vivo correlation of doppler waveform analysis with arterial input impedance parameters

Previous studies have confirmed that Doppler waveform analysis (DWA) offers a valid reflection of changes in peripheral vascular resistance. However, the ability of the pulsatility index (PI), a parameter of DWA, to reflect the dynamic components of the circulation, as assessed by arterial input parameters, remains uncertain. In addition, the state of the central circulation is considered an important factor influencing the accuracy of this technique. This study evaluated the ability of the aortic PI to reflect alterations of input impedance in a chronically instrumented lamb model that was subjected to pharmacologic alteration of the circulation. Pressure, volumetric flow and continuous-wave Doppler frequency shift measurements were recorded from the infrarenal abdominal aorta. The parameters of input impedance, peripheral vascular resistance ( Zpr), characteristic impedance ( Zo) and reflection coefficient ( Rc), were determined and then correlated with changes in the aortic P1. Initially, perturbations of the circulatory state were created with a vasodilator, hydralazine (HY) and a vasoconstrictor, phenylephrine (PE). During a second set of experiments, the effect of the reflex heart rate (HR) responses on the PI was evaluated. This was accomplished by inhibiting reflex HR responses to these vasoactive agents with either trimethophan (TM) or atropine methyl bromide (AMB). In response to HY and HY with TM, significant decreases in the PI and impedance parameters occurred. Administration of PE and PE with AMB resulted in significant increases in PI and each of the impedance parameters. HY and PE induced changes in PI correlated significantly with changes in volumetric flow ( r = 0.82, 0.80; p < 0.001), mean arterial blood pressure ( r = 0.64, 0.70; p < 0.001) and Zpr ( r = 0.77, 0.80; p < 0.001), but not with Zo ( r = 0.34, 0.36) and Rc ( r = 0.26, 0.31). However, when reflex HR responses were inhibited during the administration of the vasoactive agents, HY with TM and PE with AMB, induced changes in PI correlated significantly with Zo ( r = 0.93, 0.89; p < 0.001) and Rc ( r = 0.84, 0.83; p < 0.001), and the correlation with mean arterial pressure ( r = 0.78, 0.87; p < 0.05) and Zpr ( r = 0.92, 0.91; p < 0.05) was significantly greater. These findings indicate that the PI accurately assesses pharmacologically induced changes in the downstream arterial input impedance. The accuracy of this assessment is enhanced further when central circulatory factors such as changes in HR are considered.

Satellite Doppler-Data Processing Using a Microcomputer

This paper describes a microcomputer which was developed to compute ground radio beacon-position locations using satellite measurements of Doppler frequency shift. Both the computational algorithms and the microcomputer hardware incorporating these algorithms are discussed. Results are presented wherein this microcomputer in conjunction with the Nimbus-6 random-access measurement system (RAMS) provides real-time calculation of beacon latitude and longitude.

Recording Radio Signals from Earth Satellites

SYSTEMATIC recordings of radio transmissions from an Earth satellite for examination of the ionosphere can be used for providing also, for that particular observing site, the orbit data necessary for the prediction of transit times and the computation of ionospheric influences. For this purpose Doppler frequency shift measurements are particularly useful, and a system has been developed in this Laboratory whereby, with relatively simple equipment, the necessary information from 1958 δ 2 (Sputnik III) can be recorded simultaneously with the intensity variations which were previously reported1. The intensity variations and frequency samplings are displayed on adjacent cathode-ray tubes and photographed on 35-mm. film moving vertically at a speed of 6 in. per min. A beat-frequency oscillator is used in the receiver and the audio output applied to the horizontal deflexion plates of a cathode-ray tube without a time-base to give a record of the intensity variations as shown at A in Fig. 1. The pulse modulation of the transmission is clearly denned, but the ‘fading pattern’ is also well delineated.