Signal-induced Noise Research Articles

Study of Signal-Induced Noise in Single-Photon Ranging Lidar Systems

Study of Signal-Induced Noise in Single-Photon Ranging Lidar Systems

Characterisation of signal-induced noise in Hamamatsu R11265 Multianode Photomultiplier Tubes

Signal-induced noise is observed in Hamamatsu R11265 Multianode Photomultiplier Tubes, manifesting up to several microseconds after the single photoelectron response signal and localised in specific anodes. The mean number of noise pulses varies between devices, and shows significant dependence on the applied high-voltage. The characterisation of this noise and the mitigation strategies to perform optimal single-photon counting at 40 MHz, as required by the LHCb Ring-Imaging Cherenkov detectors, are reported.

Analysis of relative error in detection caused by signal-induced noise in Na lidar system

Signal-induced noise (SIN) in a photomultiplier tube (PMT) introduces bias into the Na density results that are retrieved from the backscattered signals of Na resonance fluorescence lidar systems. The response characteristics of a PMT when stimulated by a series of light pulses with a fixed width of 1 μs are therefore used to develop a precise SIN model to estimate the relative error caused by SIN. Unless the strong signals that are returned from the lower atmosphere are excluded, the measured density results are always smaller than the actual values, and the resulting relative error may be 50% or more. Three potential solutions to reduce the SIN were quantified for comparison, including use of a chopper system, use of a gated circuit, and separation of the laser beam and the telescope receiver. When optimized parameters are used for these technologies, the relative error can then be reduced to less than 2%.

Normally off-gated photomultiplier tube module in photon-counting mode for use in light detection and ranging measurements

In order to increase the detected range and reduce the effect of signal-induced noise in light detection and ranging (LIDAR) measurements of the high atmospheric layers, we have developed a normally off-gated photomultiplier tube module for use in the photon-counting mode. The module allows the detection of the weak backscattering signal, while at the same time rejecting the intense backscattering signal from the near range with an adjustable rejection range. The gating of our module is based on the application of positive voltage pulses on all the even dynodes of a photomultiplier head. We describe the electronic circuit design and discuss the implementation of the module. The capability of the module in rejecting intense backscattering signal from the near range was tested on our LIDAR system. The agreement between the range-corrected LIDAR signals and the standard atmospheric molecular number density up to a height of 60 km indicates a good performance by the module. Comparison between Raman and elastic backscattering signals under cloudy sky conditions indicates that the intense backscattering from near range is sufficiently suppressed and has a negligible effect on the performance of our module.

瑞利散射激光雷达强光感生噪声修正的新方法及大气温度探测

瑞利散射激光雷达强光感生噪声修正的新方法及大气温度探测

New methods of data calibration for high power-aperture lidar

For high power-aperture lidar sounding of wide atmospheric dynamic ranges, as in middle-upper atmospheric probing, photomultiplier tubes' (PMT) pulse pile-up effects and signal-induced noise (SIN) complicates the extraction of information from lidar return signal, especially from metal layers' fluorescence signal. Pursuit for sophisticated description of metal layers' characteristics at far range (80~130km) with one PMT of high quantum efficiency (QE) and good SNR, contradicts the requirements for signals of wide linear dynamic range (i.e. from approximate 10(2) to 10(8) counts/s). In this article, Substantial improvements on experimental simulation of Lidar signals affected by PMT are reported to evaluate the PMTs' distortions in our High Power-Aperture Sodium LIDAR system. A new method for pile-up calibration is proposed by taking into account PMT and High Speed Data Acquisition Card as an Integrated Black-Box, as well as a new experimental method for identifying and removing SIN from the raw Lidar signals. Contradiction between the limited linear dynamic range of raw signal (55~80km) and requirements for wider acceptable linearity has been effectively solved, without complicating the current lidar system. Validity of these methods was demonstrated by applying calibrated data to retrieve atmospheric parameters (i.e. atmospheric density, temperature and sodium absolutely number density), in comparison with measurements of TIMED satellite and atmosphere model. Good agreements are obtained between results derived from calibrated signal and reference measurements where differences of atmosphere density, temperature are less than 5% in the stratosphere and less than 10K from 30km to mesosphere, respectively. Additionally, approximate 30% changes are shown in sodium concentration at its peak value. By means of the proposed methods to revert the true signal independent of detectors, authors approach a new balance between maintaining the linearity of adequate signal (20-110km) and guaranteeing good SNR (i.e. 10(4):1 around 90km) without debasing QE, in one single detecting channel. For the first time, PMT in photon-counting mode is independently applied to subtract reliable information of atmospheric parameters with wide acceptable linearity over an altitude range from stratosphere up to lower thermosphere (20-110km).

Algorithm improvement and validation of National Institute for Environmental Studies ozone differential absorption lidar at the Tsukuba Network for Detection of Stratospheric Change complementary station

Recently, a data processing and retrieval algorithm (version 2) for ozone, aerosol, and temperature lidar measurements was developed for an ozone lidar system at the National Institute for Environmental Studies (NIES) in Tsukuba (36 degrees N,140 degrees E), Japan. A method for obtaining the aerosol boundary altitude and the aerosol extinction-to-backscatter ratio in the version 2 algorithm enables a more accurate determination of the vertical profiles of aerosols and a more accurate correction of the systematic errors caused by aerosols in the vertical profile of ozone. Improvements in signal processing are incorporated for the correction of systematic errors such as the signal-induced noise and the dead-time effect. The mean vertical ozone profiles of the NIES ozone lidar were compared with those of the Stratospheric Aerosol and Gas Experiment II (SAGE II); they agreed well within a 5% relative difference in the 20-40 km altitude range and within 10% up to 45 km. The long-term variations in the NIES ozone lidar also showed good coincidence with the ozonesonde and SAGE II at 20, 25, 30, and 35 km. The temperatures retrieved from the NIES ozone lidar and those given by the National Center for Environmental Prediction agreed within 7 K in the 35-50 km range.

Signal induced noise in PMT detection of lidar signals

Experiments are reported to evaluate the photomultiplier tube (PMT) used in Rayleigh/aerosol lidar system. The response of PMT to pulsed light signal of different intensity have been investigated. A green light emitting diode driven by a function generator is used as a pulsed light source. In this article we report the response of PMT used in the system to the pulsed source generating light signal comparable to the signal received by the PMT during laser firing in to the atmosphere. The signal induced noise (SIN) is found to be a linear combination of two exponentially decaying functions. Other results of SIN are presented.

Method for the reduction of signal-induced noise in photomultiplier tubes

A new method to reduce photomultiplier tube detector signal-induced noise (SIN) in a lidar system is successfully demonstrated. A metal ring electrode placed external to the photomultiplier tube photocathode is pulsed during the intense near-field lidar return with a potential between 15 and 500 V, resulting in a significant reduction in SIN. The effect of the metal ring voltage on the decay time constant and the magnitude of a simulated lidar signal is presented. Optimal experimental conditions for the use of this device in lidar receivers, such that the lidar decay time constant is not affected, are determined. Mechanisms for this SIN suppression system are discussed in detail, and data were recorded to show that the voltage on the metal ring functions by altering the photomultiplier electron optics.

Correction scheme for experimental biases in differential absorption lidar tropospheric ozone measurements based on the analysis of shot per shot data samples

From lidar signals detected with a shot per shot differential absorption lidar instrument tuned for tropospheric ozone measurements and recording each individual return, we reconstruct histograms of their sampled values for each channel of our digitizers. The analysis of their shape permits the correction of our measurements for experimental biases. In particular, a negative correlation is found between the skew of the histograms and the intensity of the backscattered light. The skew comes from a tail at high sampled values, interpreted as due to a raise of the relative contribution to the signal of a signal-induced noise when this intensity diminishes. By fitting a Gaussian function to the histograms without considering their tails, we calculate average signals unbiased by the corresponding noise. This approach allows us to increase the range of our ozone profiles, up to as much as double it in some cases.

Crustal structure of the southeastern flank of the Kenya rift deduced from wide-angle P-wave data

The 420-km-long northwest-southeast KRISP (Kenya Rift International Seismic Project) flank line F, part of the KRISP 94 experiment, extends from Athi River (30 km southeast of Nairobi) to the Indian Ocean near Mombasa, Kenya. Line F crosses the Chyulu Hills area, a young Quaternary volcanic field, surrounded by the basement of the Mozambique belt. The basement is at the surface almost along the entire profile with two exceptions, one in the Chyulu Hills area due to the presence of volcanic pyroclastics, the other next to the Indian Ocean where sediments reach a thickness of about 8 km. Below the basement the crust can be divided into three layers. The upper layer extends to about 10 km depth with P-wave velocities of roughly 6.25-6.4 km/s. The mid-crustal layer reaches a depth of about 20 km where P-wave velocities range from 6.55 km/s to 6.7 km/s. The lower crust in the area of the Chyulu Hills is unexpectedly thick (>20 km) and generates strong refracted phases with velocities of about 7.0 km/s. Crustal thickness is about 40 km but thickens in the area of the Chyulu Hills and thins towards the Indian Ocean to 22 km. P n-phases, refracted waves travelling through the uppermost mantle, are identified on four record sections and give good control over the upper mantle velocities which are slightly reduced from 8.1–8.2 km/s to 7.9 km/s underneath the Chyulu Hills area. The upper and lower crust in the region of the Chyulu Hills are significantly heterogeneous, producing strong signal-induced noise which masks secondary arrivals in the corresponding distance range. Underneath the Chyulu Hills P MP-reflections are hard to identify indicating that the crust-mantle boundary is a transition zone, rather than a first-order discontinuity.

A survey of the signal-induced noise in photomultiplier detection of wide dynamics luminous signals

In the LIDAR sounding of wide atmospheric ranges, as in middle atmospheric probing, signal-induced noise (SIN) from the photomultiplier (PMT) has been known since long time as a challenging problem for scientists. In this article the results of investigations on SIN are reported and strategies to minimize its amount proposed. Three different types of PMTs have been tested and their response to pulsed light signals of various duration and amplitude, comparable with close range LIDAR return, have been studied. An analysis of the time properties and spectral characteristics of SIN has been performed, and a method to reduce SIN effects in photon counting acquisition has been proposed. The method is based on a careful choice of discriminator threshold level settings, and exploits differences observed between SIN and signal cumulative pulse height distributions. The method shows dependency on single PMT behavior.

Signal-induced noise in fiber-optic links using directly modulated Fabry-Perot and distributed-feedback laser diodes

A quantitative comparison has been made, both theoretically and experimentally, of signal-induced noise in high-frequency, single-mode fiber-optic links using directly modulated multimode (Fabry-Perot) and single-frequency (distributed-feedback, DFB) lasers. It is shown that the common procedure of evaluating the signal-to-noise (S/N) performance in a typical fiber-optic link by treating the various sources of noise as additive quantities that are independent of the modulation signal is inadequate. This is due to the presence of signal-induced noise, which concentrates at low frequencies, so that a casual observation might lead to the erroneous conclusion that it is of no relevance to high-frequency transmission systems. It is shown that, for Fabry-Perot lasers, signal-induced noise arising from translation of low-frequency noise to high frequencies causes significant degradation in S/N performance in transmission of 6-GHz signals over only 1 km of single-mode fiber. With DFB lasers, signal-induced noise due to interferometric phase arrow intensity conversion is present, but does not become significant even for transmission at 10 GHz up to 20 km.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improvement on lidar data processing for stratospheric aerosol measurements

For lidar measurements of stratospheric aerosols; signal-induced noise (SIN) from a photomultiplier (PMT) has been a problem of particular interest. In this paper, we succeed in simulating lidar signals affected by the PMT, after finding a long tail with a decay time of ~200 micros in the PMT's response to an impulselike light exposure. The PMT studied was an RCA 8852. Computer simulation quantitatively revealed that the SIN caused by the delayed response became greater than the real signal at high altitudes. Based on the results of simulation, a proposal was made to find a practical method for identifying and removing the SIN from the actual lidar signals. In addition, an improved method for the lidar signal calibration was proposed by taking into account the systematic noise component, including background light as well as SIN, in formulating the clean air calibration (the matching method). Validity of the proposed methods was demonstrated by using them both with an actual lidar signal and a simulated lidar signal with SIN.

Time Resolved Photoelectric Spectrography by Electron-Optical Image Detection of Etalon Interferograms

The application of a Fabry–Perot etalon combined with an electron-optical image detector to obtain simultaneously time, spatial, and spectral resolution of plasma and laser sources is discussed, and comparison is made with oscillating Fabry–Perot interferometers. Matching of the interferometer to the image tube is considered, and optimum conditions are determined. Four types of image tubes were tested and the effects of signal-induced background and noise are described. Finally, the interpretation of time-resolved interferograms of wavetrains of very short duration, such as obtained from laser giant pulses, is dealt with, and extension of the interferometer spectral range in the vacuum uv reported.