Laser Echo Research Articles

Comment to: Six-year follow-up of endovenous laser ablation for great saphenous vein incompetence, by Spreafico G, Piccioli A, Bernardi E, Giraldi E, Pavei P, Borgoni R, Ferrini M, Baccaglini U. J Vasc Surg 2013;1:20-5.

A prospective cohort study to assess the efficacy of endovenous laser ablation (EVLA) for treatment of great saphenous vein (GSV) insufficiency over a 6-year follow-up period was conducted at the Multidisciplinary Centre of Outpatient Surgery - University Hospital, Padua (Italy). Patients were recruited between January 2003 and July 2004, and the follow-up phase lasted until July 2010. Two hundred and four patients underwent EVLA procedure at the outpatient surgery unit. A 980-nm diode laser and tumescent echo color doppler (ECD) guided perivenous anesthesia were used. The most prominent varices were treated with stab-vein avulsion immediately after the EVLA procedure. All patients had to wear 35-mm Hg elastic compression stockings for 24 h daily during the first week after EVLA, and then switch to second-class graduated elastic compression stockings for 4 weeks more. Patients were scheduled for clinical and ECD assessments at 3, 7, 30, and 90 days after EVLA; and thereafter once a year, for 6 years. The main outcome of the study was the incidence of clinical (e.g., lack of improvement or worsening of leg symptoms) and ECD-confirmed (e.g., finding of measurable venous reflux in the treated segment) EVLA failures (ECEFs) during the planned 6-year follow-up period. The ECEFs were categorized as type 1 (venous reflux limited to the junction and/or the residual saphenous stump, for a maximum length of 5 cm from the junction, without reflux in its collaterals); type 2 (reflux also in a collateral vein without clinically evident recurrent varices ); or type 3 (same as 2 with clinically evident recurrent varices, either symptomatic or asymptomatic). One hundred and twenty four patients (60.8%) underwent stab-vein avulsion as well; and 65 patients (32.8%) with residual varicose veins received sclerotherapy within 12 weeks from the procedure. Fourteen (6.8%) out of 204 patients were lost for follow up. No deep vein thrombosis was detected during the follow-up period. After 6 years, 168 (88.4%) patients reported a symptomatic improvement; of them, 87 patients had no residual symptoms, and 81 experienced a significant reduction of their leg complaints. Fourteen patients complained of persistent symptoms, six reported unsatisfactory aesthetic results, and two patients had worsened skin alterations. Of these 22 patients, only two had an ECEF as well. Patients with a competent saphenous junction and a persistently occluded saphenous trunk were 70.0% (133/190); therefore, 57 (30.0%) had an ECEF. Of them, 20 patients had a type 1 ECEF, 18 had a type 2 ECEF [three of which were at the anterior accessory saphenous vein (ASSV)], and 19 had a type 3 ECEF (12 of which were at the ASSV). An atypical junction or one with a diameter ≥8 mm and a mean trunk diameter ≥8 mm, were highly significantly associated with ECEF. Expected EVLA results, either from a clinical or technical (ECD) perspective, were obtained in 88.4% and 70.0% patients, respectively, and persisted throughout the 6-year follow-up period. All failures were observed within the first 2 years from EVLA. The unexpectedly high (57/190; 30.0%) rate of ECEF is possibly due to the systematic application of the Valsalva maneuver during ECD; this probably accounts for the high rate of type 1 ECEF. It is likely that most of the technical failures observed will soon be eliminated thanks to the use of adequate linear endovenous energy density (LEED) (at least 70 joules/cm), which was not in use in the period studied, and to the latest implements now available.

Double-pass propagation of laser pulses reflected by a diffuse whiteboard or a corner-cube retroreflector in turbulent atmosphere

Atmospheric turbulence affects the transmission of laser pulses through the atmosphere. The effects mean that the peak power of the laser pulses is not stable. For laser pulses reflected by a cooperative target, the peak power instability is greater because of the double-pass propagation of the laser pulses through the same atmosphere. The atmospheric turbulence can be monitored by detecting the peak power instability of echo laser pulses. This paper presents a method for monitoring atmospheric turbulence based on a cooperative target. Comparative experiments are carried out based on using a diffuse whiteboard and a corner-cube retroreflector (CCR) as the cooperative target. The distance between the two terminals of the experimental system is 1550m. The size of the diffuse whiteboard is 60×60cm2. The bottom surface of the CCR is a circle with a diameter of 1in. and the three mirrors of the CCR are coated with silver. Experiment results show that the peak power instability of echo laser pulses retroreflected by the CCR is 28.3%. This is much larger than that diffuse reflected by the whiteboard (11.2%). This indicates that the method based on the CCR has higher atmospheric sensitivity. In addition, the peak power of the echo laser pulses retroreflected by the CCR is also much larger. Therefore, the system based on the CCR is more suitable for monitoring of atmospheric turbulence.

Research on the Enhancement and Processing of Faint Laser Signal in Foggy Conditions

For the echo of the laser signal was relatively weak and accompanied by a lot of noise in a foggy condition, a multi-pulse cumulative method for enhancing weak laser signal was proposed. The enhancement principle and method of multi-pulse signal accumulation was studied, and with it the weak signal was processed. The matched filter algorithm was used to extract the characteristics of laser echo signal, the original signal and the accumulated signal was processed by the matched filter, respectively, which greatly improves the signal to noise ratio (SNR). The experimental results show that: four separate laser signals accumulated together enhance SNR by twice; the accumulation of multi-pulse laser signal can effectively improve SNR, and the matched filter can strengthen the signal while suppressing noise.

A correction method for range walk error in photon counting 3D imaging LIDAR

A correction method for the range walk error is presented in this paper, which is based on a priori modeling and suitable for the GmAPD photon counting three-dimensional(3D) imaging LIDAR. The range walk error is mainly brought in by the fluctuation in number of photons in the laser echo pulse. In this paper, the priori model of range walk error was established, and the function relationship between the range walk error and the laser pulse response rate was determined using the numerical fitting. With this function, the range walk error of original 3D range image was forecasted and the corresponding compensated image of range walk error was obtained to correct the original 3D range image. The experimental results showed that the correction method could reduce the range walk error effectively, and it is particularly suitable for the case that there are significant differences of material properties or reflection characteristics in the scene.

Lunar laser topography by LALT on board the KAGUYA lunar explorer – Operational history, new topographic data, peak height analysis of laser echo pulses

In this paper we review the lunar laser ranging conducted by the laser altimeter (LALT) on board the KAGUYA lunar explorer (2007–2009). Five aspects of LALT measurements are described: (1) General operational history, (2) Laser shot and data statistics, (3) Revisions to LALT topographic data, (4) Variations in laser output energy, and (5) Peak height analysis of laser echo pulses. LALT was able to range to the lunar surface despite some troubles with respect to laser output energy in the middle of the KAGUYA mission. The time series topographic data set was revised (Ver. 2) by incorporating new lunar gravity model based on KAGUYA and other historical lunar satellite’s orbit data, along with other improvements, for example by incorporating the accurate position of the laser collimator on board the KAGUYA; however, more than half of the acquired range data could not be converted properly due to problems with orbit accuracy during the extended phase of the mission. The spherical harmonic coefficients and the basic lunar figure parameters derived from LALT_LGT_TS agree very well with LRO-LOLA and the Chang’E-1 LAM model. It is possible that partial failure to the laser diode was responsible for the gradual degradation of laser power (0.835mJ per million shots) and the rapid decrease that occurred over April 9–14, 2008. The laser power also proved to be extremely sensitive to the temperature of the laser oscillator. The peak height ratio – that is peak height telemetry data divided by calculated ratio – is about 19% on average using the mean slope and albedo data from LALT and Spectral Profiler on KAGUYA space craft, respectively, which suggests the performance of peak height measurement is more than 1/5 for more than 70km altitude, if compared with calculated one. The peak height ratio may be better if we take the effect of small scale topography within a footprint into account.

Theoretical distribution of range data obtained by laser radar and its applications

This paper addresses the distribution of range data obtained by laser radar. An analytical solution of the range distribution was obtained for direct detection laser radar using constant threshold discriminator based on the time-of-flight principle. The analytical solution was verified by experiments and simulations. The results show that the derived analytical function can describe the probability density distribution of the range data obtained by laser radar with a constant threshold discriminator. The probability density distribution of the range data is proportional to the probability density function of the noise and to the slope of the rising edge of the laser echo pulse. The probability density distributions of the range data obtained by laser radar with different pulse shapes, amplitudes, widths and thresholds are also presented. These factors are important for improvements in the design of laser radar systems.

Non-rigid registration of mural images and laser scanning data based on the optimization of the edges of interest

The orientation and correction of mural images by registering them with laser scanning data is critical for the digital protection of ancient murals. This paper proposes a method for the non-rigid registration of mural images and laser scanning data based on the optimization of the edge of interest by using laser echo intensity information as an intermediary. First, the intensity image was generated from the laser echo intensity information, and registered with the mural image using a rigid transformation model. Second, the edges of interest in the mural image and the gradient field of the intensity images were processed as registration primitives. Third, every edge of interest was registered with the optimization base used in the rigid registration of the mural image and intensity image. Finally, the registration was completed after a non-rigid transformation model between these two images was constructed using the control points on the optimized edges. Our experimental results show that the proposed method can obtain high registration accuracy for different data sets.

Polarization-independent optical circulator for high accuracy Faraday depolarization lidar

A high precision, polarization-independent optical circulator was developed for high accuracy Faraday depolarization lidar. Glan laser prisms and other novel optics were utilized in the circulator optics, resulting in a high extinction ratio of polarization of >30 dB. High accuracy is needed to detect a small rotation angle in the polarization plane of the propagating beam. It is generated by the Faraday effect due to the lightning discharge. The developed circulator delivered high performance of insertion loss and isolation as laser transmitter and echo receiver in the inline lidar optics.

激光回波在主动探测中的运用研究

激光回波在主动探测中的运用研究

激光回波在主动探测中的运用研究

激光回波在主动探测中的运用研究

脉冲宽度对云雾回波的影响研究

Scattering effects of clouds and fogs produce the backscattering signal which results in false alarm for laser fuse.Based on the Monte-Carlo technology,cloud-and-fog scattering effects are simulated,and rules of wave shape and peak power of cloud-and-fog scattering echo variable with baseline distance are qualitively given.Results show that peak power and pulse broadening extent of the laser echo goes up with pulse width increasing.However,when pulse width increases to 50 ns,peak power is saturated.Simulated results may provide target discrimination and optimized design of detecting threshold and transmitting pulse width for laser fuse with reference.

Comparing individual tree detection and the area-based statistical approach for the retrieval of forest stand characteristics using airborne laser scanning in Scots pine stands

Airborne laser scanning based forest inventories employ two major methods: individual tree detection (ITD) and the area-based statistical approach (ABSA). ITD is based on the assumption that trees are of a certain form and can be delineated using airborne laser scanning techniques, whereas ABSA is an empirical method based on the relations between area-level forest attributes and laser echo height distributions. These two methods are compared here within the same test area in terms of their usefulness for estimating mean forest stand characteristics and tree size distributions. All evaluations were performed using leave-one-out cross validation. The average errors in volume and basal area did not differ significantly between the methods. ABSA resulted in overall better accuracies when estimating the diameter and height of the basal area median tree and the number of stems, whereas ITD produced significantly biased estimates for the number of stems and the mean tree size. Tree size distributions were estimated with slightly better accuracy using ABSA. More comprehensive investigations revealed that both methods were not able to estimate forest structure (tree size distribution and spatial distribution of tree locations), which in turn, affected the estimation accuracies.

The Product Surface Remote Detection Method Based on the Single Laser Pulse Echo

Laser detecting technology can be utilized to the product surface detection for finding the surface deficiency. However, the improving resolving power of laser detecting system is limited by the laser footprint size on the product surface. Employing only echo delay and intensity information, the information of the surface inside the footprint is difficult to be obtained for the echo signal of the objects maybe is submerged by each other. Under the remote laser detecting, the serious loss of image quality may occur because of the large footprint. The product surface detection method based on the single laser return waveform was studied and the provided to get the objects information inside the laser footprint. Firstly, the basis laser echo signal model of the objects inside the footprint was built. On the basis, the decomposition algorithm was provided which can decompose a laser return waveform into a series of components assuming that each component corresponding to a sub-object inside the laser footprint. After the primary sub-target return waveforms was obtained, however, there still exists some small sub-objects inside the laser footprint whose return signal is hardly to be extracted because they are submerged by the neighborhood sub-objects return signal. The subtracting algorithm between the whole return waveform and the components waveform provides the way to get the submerged return waveforms of sub-target. So, the information of sub-objects inside the laser footprint would be obtained. In the end, the actual laser return data of the product surface was analyzed employing the method to get the range position information of the sub-objects inside the laser footprint, which verifies the method validity.

In vivo1H NMR spectroscopy of the human brain at 9.4 T: Initial results

In vivo proton NMR spectroscopy allows non-invasive detection and quantification of a wide range of biochemical compounds in the brain. Higher field strength is generally considered advantageous for spectroscopy due to increased signal-to-noise and increased spectral dispersion. So far 1H NMR spectra have been reported in the human brain up to 7 T. In this study we show that excellent quality short echo time STEAM and LASER 1H NMR spectra can be measured in the human brain at 9.4 T. The information content of the human brain spectra appears very similar to that measured in the past decade in rodent brains at the same field strength, in spite of broader linewidth in human brain. Compared to lower fields, the T 1 relaxation times of metabolites were slightly longer while T 2 relaxation values of metabolites were shorter (<100 ms) at 9.4 T. The linewidth of the total creatine (tCr) resonance at 3.03 ppm increased linearly with magnetic field (1.35 Hz/T from 1.5 T to 9.4 T), with a minimum achievable tCr linewidth of around 12.5 Hz at 9.4 T. At very high field, B 0 microsusceptibility effects are the main contributor to the minimum achievable linewidth.

Real-time target recognition system simulation based on laser near-field detection

This paper constructs a simulation system of near-field laser imaging for 3D grid model of target, provides some methods for the key problems, such as the modeling of target and laser transceiver, the calculation of laser echo power, the imaging algorithms and so on. A target image library is established by a new imaging method in any rendezvous conditions. The four real-time recognition algorithms which are efficient and suitable for hardware implementation are presented at the conditions of the image incompleteness, intensive noise and arbitrary attitude of target. The experimental results show that all the four algorithms can independently recognize the target effectively and a better recognition effect is obtained by the integration of four algorithms.

Ultrasonic echo sounding by thermal optical sources of longitudal waves

Experimental device for ultrasonic laser echo sounding of geomaterials is described. The examples of its application to estimate acoustic characteristics, inhomogeneities, and damaged state intrinsic to structure sample of various-age volcanics are considered.

Mars Orbiter Laser Altimeter: receiver model and performance analysis

The design, calibration, and performance of the Mars Orbiter Laser Altimeter (MOLA) receiver are described. The MOLA measurements include the range to the surface, which is determined by the laser-pulse time of flight; the height variability within the footprint determined by the laser echo pulse width; and the apparent surface reflectivity determined by the ratio of the echo to transmitted pulse energies.

Calculating the laser echo signal from a cloud taking multiple scattering into account

In laser probing of clouds the received signal differs significantly f rom the probe pulse in form and other pa ramete rs . A knowledge of the received signal charac te r i s t i c s is necessa ry in construct ion of probe sys tems and solution of the converse problem of cloud optical pa ramete rs . Signal deformation during propagation in clouds has been studied both experimentally [1] and theoret ical ly [2]. In the latter case the problem consis ts of solving a nonstat ionary t rans fe r equation. The solution by the Monte-Carlo method demonstrated in [2] requi res new voluminous calculations for each set of probe pulse and cloud paramete rs .