Backscattering Intensity Profiles Research Articles

Determination of mixing layer height from co-located lidar, ceilometer and wind Doppler lidar measurements: Intercomparison and implications for PM2.5 simulations

Mixing layer height (MLH) is retrieved at an urban site in Seoul, Korea, from 2-year collocated remote sensing instrument measurements: elastic aerosol lidar, ceilometer, and wind Doppler lidar (WDL). All three measurements captured clear diurnal patterns of MLH development and break down, but large discrepancies were noted in the nocturnal MLH and the onset time of MLH development. Vertical wind speed standard deviation (σw) from WDL measurements displayed low MLHs during nighttime, compared to MLH retrieved from aerosol backscattering intensity profiles (mean bias = −0.21 km). To this extent, mixing represented by σw showed close correlation with surface heating but significant discrepancies with the vertical distribution of atmospheric constituents, especially at night. Comparison of MLH from elastic aerosol lidar and WDL with WRF-Chem simulation results showed that WRF-Chem MLH closely resembled MLH retrieved from WDL, indicating that WRF-Chem sufficiently simulated turbulence, but displayed lower nocturnal MLH compared to lidar-derived MLH. Furthermore, investigation of the vertical profiles of PM2.5 in the model displayed confined distribution of aerosols within the nocturnal MLH, leading to overestimation of surface PM2.5 concentration. For the case studies of May 12 and 18, 2016, implicating full mixing within the MLH defined by aerosol lidar measurements on WRF-Chem PM2.5 vertical distribution simulations was shown to significantly reduce WRF-Chem PM2.5 simulation errors from mean normalized bias of 52% to 19%.

Optical coherence tomography for differentiation of parathyroid gland tissue

Optical coherence tomography (OCT) is a high-resolution imaging technique that allows the identification of microarchitectural features in real-time. Can OCT be used to differentiate parathyroid tissue from other cervical tissue entities? All investigations were carried out during cervical operations. Initially, ex vivo images were analyzed to define morphological imaging criteria for each tissue entity. These criteria were used to evaluate a first series of ex vivo images. In a second phase the practicability of the technique was investigated in vivo and in the third phase backscattering intensity measurements were analyzed employing linear discriminant analysis (LDA). In the ex vivo series parathyroid tissue could be differentiated from other tissue entities with a sensitivity and specificity of 84 % and 94 %, respectively. Parathyroid tissue was correctly identified in the in vivo series in only 69.2 %. The analysis of backscattering intensity profiles employing LDA reliably distinguished between the different tissue types. The OCT images displayed typical characteristics for each tissue entity. Due to technical problems in handling the probe the in vivo OCT images were of much poorer quality. Backscattering intensity measurements illustrated that OCT images provide an individual profile for each tissue entity independent of the defined morphological assessment criteria. The results show that OCT is fundamentally suitable for intraoperative differentiation of tissues.

Diagnostic efficacy of backscattering intensity measurements in optical coherence tomography of cervical intraepithelial dysplasia

The aim of this study was to determine the diagnostic efficacy of backscattering intensity measurements in optical coherence tomography in identifying different grades of cervical intraepithelial dysplasia. OCT images were taken from 153 unsuspicious and suspicious areas of 30 fresh conisation and hysterectomy specimens, evaluated by two blinded investigators using a six-grade classification (normal, inflammation, CIN1, CIN2, CIN3, squamous carcinoma) and later compared to the corresponding histology. Differences between judgments based on either the histology or the OCT images were investigated employing Correspondence Analysis (CA). Further, we explored the extent as to which backscattering intensity profiles of OCT images contained the essential information required for a reliable and valid diagnosis, using Linear Discriminant Analysis (LDA). The CA of histology- and OCT-based judgments suggests that the diagnostic process may be characterized in terms of two stochastically independent underlying ("latent") variables, the first of them reflecting the definiteness with which CIN classes are identified, the second reflecting a bias towards diagnosing inflammation on the side of the OCT-based judgments. This finding is supported by the results of LDAs, where histology and OCT categorizations differ in particular with respect to the positions of inflammation and CIN1. Possibly, a second canonical variable has to be assumed accounting for the evaluation of carcinoma. The systematic differences between histology-based and OCT-based diagnoses suggest that the use of available information is influenced by perceptual and/or cognitive biases. Apart from this it seems that the profiles appear to provide a remarkably large amount of information determining the main course of the diagnostic process.

Retrieval for physical parameters of aerosols in an urban area by ground‐based FTIR measurement

An IR Fourier‐transformed spectrometer for use in field observation, named the tropospheric infrared interferometric sounder (TIIS), was developed by the Central Research Institute of Electric Power Industry (CRIEPI). Downwelling atmospheric infrared emission spectra were measured by ground‐based operation of the TIIS in the Tokyo area. From the measured spectra, the aerosol extinction coefficient spectra in the lowest layer (0–2 km) were retrieved, and then using the retrieved aerosol extinction coefficient spectra we carried out the retrieval of the volume density of each aerosol component, in which aerosols in the lowest layer of the urban area were assumed to consist of three components, namely, water‐soluble, soot, and dust‐like components. The results were evaluated by means of comparisons with backscattering intensity profiles and the size‐selective particle number density, which were measured from synchronized operations of a lidar and a laser particle counter, respectively. The retrieved values of water‐soluble and dust‐like aerosol components were found to correspond with results from the lidar measurement and the laser particle counter. Regarding the soot component, we were unable to make a direct comparison using data measured by the lidar and the laser particle counter. However, the spectrum calculated by FASCODE3 applying the retrieved aerosol parameters corresponded closely to the spectrum measured by TIIS. Therefore, the retrieved soot aerosol parameters were considered to be reliable.

Weak localization of light by cold atoms: The impact of quantum internal structure

Since the work of Anderson on localization, interference effects for the propagation of a wave in the presence of disorder have been extensively studied, as exemplified in coherent backscattering (CBS) of light. In the multiple scattering of light by a disordered sample of thermal atoms, interference effects are usually washed out by the fast atomic motion. This is no longer true for cold atoms where CBS has recently been observed. However, the internal structure of the atoms strongly influences the interference properties. In this paper, we consider light scattering by an atomic dipole transition with arbitrary degeneracy and study its impact on coherent backscattering. We show that the interference contrast is strongly reduced. Assuming a uniform statistical distribution over internal degrees of freedom, we compute analytically the single- and double-scattering contributions to the intensity in the weak-localization regime. The so-called ladder and crossed diagrams are generalized to the case of atoms and permit to calculate enhancement factors and backscattering intensity profiles for polarized light and any closed atomic dipole transition.

Improvements in acoustic sediment concentration profiling using an LMS compensation algorithm

In sediment concentration profiling, sound attenuation becomes important for high-frequency acoustic backscattering systems (ABSS) when sediment concentration is high and/or the range of remote sensing is long. In the present study, a test of a least mean square (LMS) compensation algorithm was performed in order to determine the advantages over the more frequently used iteration algorithm. Numerical simulation and laboratory experiments in a mixing tank as well as an open channel suggest that the new algorithm is much more robust to white Gaussian noise and fixed-echo noise, and errors do not accumulate along the profiling path. Good linearity of this instrument in concentrations up to 20 kg/m/sup -3/ is found by comparison with a suction-sampler. In the mixing tank, backscattering intensity profiles in concentrations up to 120 kg/m/sup -3/ vary little along a propagation path of 40 cm and fit well to the expected homogeneous concentration. Furthermore, by using the oscillation errors in the LMS solution, a procedure has been developed to compensate for the errors in the instrument constants evaluated from the attenuation between the transducer and the first measuring volume. The feasibility of the proposed instrument-constant compensation is verified by experiments. This allows instantaneous correction of the influence of sediment deposition on the transducer surface which is important when the system is applied to coastal investigation.

Multiple scattering of narrow light beams in aerosols

A multiple scattering propagation model of narrow light beams in aerosol media is described. It is based on a paraxial approximation of the radiative transfer equation in which the flux normal to the incident beam direction is modeled by a diffusion process. The model solutions are the forward- and backscattered intensity profiles for the specified geometry and receiver aperture and field of view. The required inputs are the system parameters, and the aerosol single scattering angular phase function and extinction and scattering coefficients which are allowed to vary along the beam axis. Good agreement is shown with measurements performed in the laboratory over scales ranging from a few tens of mm to a few m, and in the atmosphere over a scale of the order of 1 km. The solutions are valid for optical depths smaller than ≈ 10, for phase functions corresponding to average size parameters of order one or greater, and for off-axis positions not exceeding ≈ 25% of the reciprocal of the scattering coefficient.