Two-channel Methods Research Articles

Detection and Avoidance of Atmospheric Aviation Hazards Using Infrared Spectroscopic Imaging

Atmospheric aviation hazards due to turbulence, poor visibility, high-altitude ice crystals and volcanic ash and gases are known problems for aviation and can cause both economic damage to engines and airframes as well as having the potential to cause the engines to stall in flight with possible loss of the aircraft. Current space- and ground-based assets allow observations of some of these hazards and their detection and movement can be forecast using modern computer weather forecasting and dispersion models. These largely strategic resources have proved very valuable but somewhat limited in the tactical sense, where commercial aviation must make rapid decisions in order to avoid an undetected or un-forecast hazardous cloud or atmospheric condition. Here we investigate the use of multi-spectral (two channels or more) infrared imaging from an aircraft perspective, and show that it is possible to use this information to provide tactical awareness tools for use by aviators and other stakeholders. This study has a strong focus on volcanic ash as an aviation hazard but also includes applications to some forms of clear air turbulence (CAT), to high-altitude ice crystals (HAIC) and windblown desert dust. For volcanic ash detection, the research shows that current two-channel satellite-based infrared techniques provide acceptable discrimination and quantification, but two-channel infrared imaging airborne solutions have significant drawbacks. Because of the limitation of two-channel methods, infrared spectroscopic techniques are investigated and it is shown they can significantly reduce the confusion caused by meteorological hydrometeors and potentially provide information on other atmospheric hazards to aviation, such as HAIC and some forms of turbulence. Not only are these findings important for on-going efforts to incorporate IR imaging onto commercial aircraft, but they also have relevance to the increasing use of drones for hazard detection, research and monitoring. Uncooled infrared bolometric imaging cameras with spectroscopic capabilities are available and we describe one such system for use on airborne platforms.

Retrieval of Aerosol Optical Depth from Optimal Interpolation Approach Applied to SEVIRI Data

This paper presents two algorithms used to derive Aerosol Optical Depth (AOD) from a synergy of satellite and ground-based observations, as well as aerosol transport model output. The Spinning Enhanced Visible Infrared Radiometer (SEVIRI) instrument on board Meteosat Second Generation (MSG) allows us to monitor aerosol loading over land at high temporal and spatial resolution. We present the algorithms which were fed with the data acquired via the SEVIRI channel 1, and also channels 1 and 3 in conjunction. In both cases, the surface reflectance is the most important parameter that should be estimated during the retrieval process. The surface properties are estimated during days with a low AOD (less than 0.1 at 500 nm) based on the radiance measured by the SEVIRI detector and aerosol optical properties modeled with the aerosol transport model or measured by the MODIS sensor. For data from the model and the MODIS, ground-based stations equipped with a sun photometer have been applied to correct the AOD fields using the optimal interpolation method. By assuming that surface reflectance at the SEVIRI resolution changes slowly over time, the AOD has been computed. Comparison of the SEVIRI AOD with the sun photometer observations shows good agreement/correlation. The mean bias is small (an order of 0.01–0.02) and the root mean square (rms) is about 0.05 for both one- and two-channel methods. In addition, the rms for the one-channel method does not change with the AOD.

Experimental study on the effects of physical training on the defibrillation threshold

Background: Chest compression artifacts during cardiopulmonary resuscitation (CPR) deteriorate the rhythm diagnosis of automated external defibrillators (AED). Cardiopulmonary resuscitation must therefore be interrupted for a reliable shock/no-shock decision. However, these hands-off intervals adversely affect the defibrillation success, and, in addition, pauses in chest compressions compromise circulation. An accurate diagnosis of the rhythmwhile performing CPR is therefore needed to minimize these hands-off intervals. Methods: The characteristics of the CPR artifact are very variable, and the artifact presents an important spectral overlap with human cardiac arrest rhythms. Consequently, elaborate adaptive signal processing techniques are needed to filter the CPR artifact and reconstruct the underlying artifact-free ECG. Following an additive noise model, several methods were initially tested by artificially mixing human ventricular fibrillation samples and CPR artifacts recorded from pigs in asystole. The performance of the filters was evaluated for different levels of corruption, that is, signal-to-noise ratio. These studies showed satisfactory results after the filters were applied, both in terms of the improved signal-to-noise ratio and the sensitivity of the AED, which exceeded the 90% performance goal set by the American Heart Association (AHA). A posterior study reported similar results using a mixture of human ventricular fibrillation and human CPR artifacts extracted from real out-of-hospital interventions. Results: The first filtering method tested on shockable and nonshockable cardiac arrest rhythms from of out-of-hospital interventions was published in 2004. The artifact was estimated using up to 4 additional reference channels, acquired using a modified version of a commercial AED. The sensitivity after filtering (96.7%) exceeded AHA goals; the method, however, failed to accurately identify nonshockable rhythms because the specificity (79.9%) fell below the 95% AHA performance goal. Later, efforts focused on simplifying the filtering methods by either analyzing the ECG alone or using only 1 reference channel (2-channel methods). The ECG alone is not sufficient to estimate the artifact; however, comparable results were reported for multichannel and 2-channel methods on out-of-hospital rhythms. The possibility of identifying the rhythm by directly analyzing the corrupted ECG has also been proposed, although the reported specificity is also unsatisfactory. Conclusion: Currently, a reliable rhythm analysis during CPR is not possible because the specificity is too low. Two-channel filtering methods combined with rhythm identification applied to the filtered ECG should be further investigated to improve the detection of nonshockable rhythms.

Human ECGs corrupted with real CPR artefacts in an animal model: Generating a database to evaluate and refine algorithms for eliminating CPR artefacts

Aim For the analysis of ECG rhythms during ongoing CPR, single- or two-channel methods have been proposed to eliminate artefacts from the CPR-corrupted ECG. To refine, test and evaluate these algorithms with a realistic data set, we introduce an animal model with which we created an extended database of human ECGs with real CPR artefacts. Material and methods In a pig model real CPR-related artefacts were added to annotated human emergency ECGs. Via a special catheter placed in the oesophagus, ECG sequences (duration > 10 s) were fed in close to the dead pig's heart. The resulting surface potential was recorded on the thorax without and during ongoing chest compressions, which were monitored using a miniature force sensor. Results The animals served as a vehicle for human ECGs, making it possible to create a database in which 918 real human ECG sequences (437 shockable and 481 non-shockable) were corrupted with CPR-induced artefacts. The achieved signal-to-noise ratios (SNR) ranged from −17 to +15 dB, sensitivity was 93.5% and specificity was 50.51%. The fed-in ECG and the uncorrupted surface ECG correlated almost perfectly ( r = 0.926 ± 0.081; n = 918), indicating negligible signal distortion due to the dead pig itself. Conclusion As the generated database includes both the original and the corrupted ECG covering a wide range of SNRs as well as the compression force signal, it provides an extended data set to evaluate the reconstruction performance of CPR artefact-removal algorithms.

Intercomparison of height assignment methods for opaque clouds over the tropics

Several methods of determining the height of opaque clouds over the tropics were compared using geostationary satellite measurements. The possible use of ozone channel measurements around the 9.7-μm ozone absorption band was examined in conjunction with the infrared window (IRW; 10.8 μm), H2O (6.3 μm), and CO2 (13.4 μm) channels, which are generally used for the assignment of cloud heights. Cloud top heights were retrieved from Meteosat-8 measurements with the aid of radiative transfer calculations using reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) as inputs. By using cloud top heights from collocated CloudSat observations as a reference, cloud top heights were determined from the one-channel radiance, two-channel brightness temperature difference (BTD), and two-channel radiance ratio methods, and the respective results were then compared for clouds with geometrical thicknesses of > 4 km. Overall, the retrievals from the CO2-IRW ratio and O3-CO2 ratio methods are in substantial agreement with CloudSat observations, while the other methods either underestimate cloud top heights or demonstrate a lower ratio of successful height assignment. The O3-CO2 ratio method appears to be less practical than the CO2-IRW ratio method because it requires two absorption channels. Our comparison also shows that the BTD between the ozone and IRW channels yields information that is similar to that of the IRW channel alone. It further shows that the O3-IRW combination is not appropriate for the two-channel radiance ratio method. These results suggest that the inclusion of the ozone channel in BTD and ratio methods may not offer any significant improvement in convective cloud height retrieval over the tropics. In conclusion, the CO2-IRW ratio method appears to provide the most accurate retrievals for opaque clouds.

Strong corruption of electrocardiograms caused by cardiopulmonary resuscitation reduces efficiency of two-channel methods for removing motion artefacts in non-shockable rhythms

Aim Cardiopulmonary resuscitation (CPR) artefact removal methods provide satisfactory results when the rhythm is shockable but fail on non-shockable rhythms. We investigated the influence of the corruption level on the performance of four different two-channel methods for CPR artefact removal. Materials and methods 395 artefact-free ECGs and 13 pure CPR artefacts with corresponding blood pressure readings as a reference channel were selected. Using a simplified additive data model we generated CPR-corrupted signals at different signal-to-noise ratio (SNR) levels from −10 to +10 dB. The algorithms were optimized on learning data with respect to SNR improvement and then applied to testing data. Sensitivity and specificity were derived from the shock/no-shock advice of an automated external defibrillator before CPR corruption and after artefact removal. Results Sensitivity for the filtered data (>95%) was significantly superior to that for the unfiltered data (76%), p < 0.001. However, specificity was similar for the filtered and unfiltered data (<90% vs 89.3%). For large artefacts (−10 dB) specificity decreased below 70%. No important difference in the performance of the four algorithms was found. Conclusion Using a simplified data model we showed that, when the ECG rhythm is non-shockable, two-channel methods could not reduce CPR artefacts without affecting the rhythm analysis for shock recommendation. The reason could be poor reconstruction when the artefacts are large. However, poor reconstruction was not a hindrance to re-identifying shockable rhythms. Future investigations should both include the refinement of filter methods and also focus on reducing motion artefacts already at the recording stage.

Research on Water-vapor Retrieving Algorithm Based on MODIS Data

Water-vapor in the atmosphere is one of the major factors which affect the weather changing and the application of remote sensing.This paper introduces theories of two-channel and three-channel ratio methods for retrieving water-vapor.Detailed analysis and results are given in this paper.Two retrieving ideas are mixed and a better solution to the weighted average problem is given using the NASA document.Good results are achieved and may have some guidance on precipitation production practically.

Single-channel and two-channel methods for land surface temperature retrieval from DAIS data and its application to the Barrax site

In this paper, a methodology using a single-channel and a two-channel method is presented to estimate the land surface temperature from the DAIS (Digital Airborne Imaging Spectrometer) thermal channels 74 (8.747 µm), 75 (9.648 µm), 76 (10.482 µm), 77 (11.266 µm), 78 (11.997 µm) and 79 (12.668 µm). The land surface temperature retrieved with both methods has been validated over the Barrax site (Albacete, Spain) in the framework of the DAISEX (Digital Airborne Imaging Spectrometer Experiment) field campaigns. Prior to the validation an analysis of the DAIS data quality has been performed in order to check the agreement between in situ data and the values extracted from the DAIS images supplied by the DLR (German Optoelectronic Institute). Suitable differences between in situ and DAIS data have been found. To solve this problem a linear re-calibration of the DAIS thermal channels has been applied using two ground calibration points (bare soil and water). For the land surface temperature retrieved, rms deviations of 0.96 K using a single-channel method and 1.46 K using a two-channel method with the DAIS thermal channels 77 and 78 have been obtained considering re-calibrated data.

Simulation analysis of the ability to estimate motor unit propagation velocity non-invasively by different two-channel methods and types of multi-electrodes

Ability to estimate motor unit propagation velocity correctly using different two-channel methods for delay estimation and different non-invasive spatial filters was analysed by simulation. It was established that longitudinal double difference electrodes could be not a better choice than simple bipolar parallel electrodes. Spatial filtration with a new multi-electrode (performing difference between signals detected by two transversal double difference electrodes positioned along the muscle fibres) promises to give the best estimate. Delay estimation between reference points is more preferable than that based on the cross-correlation technique, which is considerably sensitive to the fundamental properties of the muscle fibre extracellular fields. Preliminary averaging and approximation of the appropriate parts of the signals around chosen reference points could reduce the larger noise sensitivity and the effects of local tissue inhomogeneities as well as eliminate the sampling problem. A correct estimate of the propagation velocity could be impossible, even in the case of not very deep motor units (15 or 10 mm, depending on the spatial filter used) with relatively long (about 120 mm) muscle fibres. In the case of fibres with asymmetrical location of the end-plates in respect to the fibre ends, the propagation velocity estimates could be additionally biased above the longer semilength of the motor unit fibres.

Close-coupling methods applied to the calculation of bound-free bidimensional nonseparable Franck-Condon factors

Various procedures to calculate the bound-free bidimensional Franck-Condon factors (FCF) of linear triatomics are formulated and tested. These include (1) the solution of multichannel coupled equations leading directly to an estimate of the FCF'S; (2) an analytical expansion containing a one-dimensional overlap integral which can be evaluated from either a two-channel calculation, or from a linearization of the potential, or from a uniform Airy approximation. In the multichannel or two-channel methods an iterative procedure using the phase shift in an open channel leads to the position and width of a resonance. All methods are in essential agreement in the examples we have considered (two nuclear coordinates, harmonic potentials). However, with regard to possible extensions. the direct (multichannel) procedure should be useful when introducing anharmonic potentials with a small number of nuclear coordinates, while the algebraic procedure should be more advantageous if there is a larger number of coordinates in the hypothesis of harmonic potentials.

Twin-Channel Receiver for RF voltage Comparison Measurements

The paper surveys single and two-channel methods of comparing phase and amplitude of sinusoidal RF voltages. A highly selective twin-channel system for the HF band is described.