Backscatter Coefficient Measurements Research Articles

Calibration of an airborne oceanographic lidar using ocean backscattering measurements from space.

We used satellite measurements of the optical backscattering coefficient to calibrate the signal from an airborne oceanographic lidar. This technique provided the radiometric calibration for the lidar signal and a local estimate of the ratio of the particulate backscattering coefficient, bbp, to the volume scattering function at the scattering angle of 180°, βp(180). Results using an ordinary regression, a reduced major axis regression, and a least squares bisector suggest that either of the latter two provided a better result than an ordinary regression. The statistical errors in the two recommended regressions, the difference in calibrations factors between them, and the difference between these and a laboratory calibration were all less than 5%.

Optimal iodine absorption line applied for spaceborne high spectral resolution lidar.

Spaceborne high spectral resolution lidar (HSRL) provides a wide range of observations, e.g., measurements of aerosol backscattering and extinction coefficients and aerosol depolarization ratio with high accuracy, which are of great significance to the study of air pollution monitoring and climate change. With different cells and finger temperatures, the transmittance of the different absorption lines of the iodine vapor filter at 532nm wavelength was measured. The 1064nm fundamental frequency pulse energy and the 532nm frequency-doubled pulse energy output of different seeder laser wavelengths were measured. Based on the relationship among the laser output power, the absorption line shape of the iodine vapor filter, and the atmospheric model, the echo power was calculated and compared. The 1110 iodine absorption line was selected as the optimized filter for the HSRL, which could increase in 22% and 14% efficiency compared with the traditional 1109 line, and a new proposed 1105 line at the 532nm HSRL channel at 5km altitude with an enhanced aerosol model, respectively.

Inter-sonographer reproducibility of quantitative ultrasound outcomes and shear wave speed measured in the right lobe of the liver in adults with known or suspected non-alcoholic fatty liver disease.

To assess inter-sonographer reproducibility of ultrasound attenuation coefficient (AC), backscatter coefficient (BSC) and shear wave speed (SWS) in adults with known/suspected non-alcoholic fatty liver disease (NAFLD). The institutional review board approved this HIPAA-compliant prospective study; informed consent was obtained. Participants with known/suspected NAFLD were recruited and underwent same-day liver examinations with a clinical scanner. Each participant was scanned by two of the six trained sonographers. Each sonographer performed multiple data acquisitions in the right liver lobe using a lateral intercostal approach. A data acquisition was a single operator button press that recorded a B-mode image, radio-frequency data, and the SWS value. AC and BSC were calculated from the radio-frequency data using the reference phantom method. SWS was calculated automatically using product software. Intraclass correlation coefficient (ICC) and within-subject coefficient of variation (wCV) were calculated for applicable metrics. Sixty-one participants were recruited. Inter-sonographer ICC was 0.86 (95% confidence interval: 0.77-0.92) for AC and 0.87 (0.78-0.92) for log-transformed BSC (logBSC = 10log10BSC) using one acquisition per sonographer. ICC was 0.88 (0.80-0.93) for both AC and logBSC averaging 5 acquisitions. ICC for SWS was 0.57 (0.29-0.74) using one acquisition per sonographer, and 0.84 (0.66-0.93) using 10 acquisitions. The wCV was ~7% for AC, and 19-43% for SWS, depending on number of acquisitions. Hepatic AC, BSC and SWS measures on a clinical scanner have good inter-sonographer reproducibility in adults with known or suspected NAFLD. Multiple acquisitions are required for SWS but not AC or BSC to achieve good inter-sonographer reproducibility. • AC, BSC and SWS measurements are reproducible in adults with NAFLD. • Inter-sonographer reproducibility of SWS measurement improves with more acquisitions being averaged. • Multiple acquisitions are required for SWS but not AC or BSC.

Backscattering coefficient measurement and land use land cover classification using ENVI SAT ASAR data

Backscattering coefficient measurement and land use land cover classification using ENVI SAT ASAR data

Simultaneous polarimeter retrievals of microphysical aerosol and ocean color parameters from the "MAPP" algorithm with comparison to high-spectral-resolution lidar aerosol and ocean products.

We present an optimal-estimation-based retrieval framework, the microphysical aerosol properties from polarimetry (MAPP) algorithm, designed for simultaneous retrieval of aerosol microphysical properties and ocean color bio-optical parameters using multi-angular total and polarized radiances. Polarimetric measurements from the airborne NASA Research Scanning Polarimeter (RSP) were inverted by MAPP to produce atmosphere and ocean products. The RSP MAPP results are compared with co-incident lidar measurements made by the NASA High-Spectral-Resolution Lidar HSRL-1 and HSRL-2 instruments. Comparisons are made of the aerosol optical depth (AOD) at 355 and 532 nm, lidar column-averaged measurements of the aerosol lidar ratio and Ångstrøm exponent, and lidar ocean measurements of the particulate hemispherical backscatter coefficient and the diffuse attenuation coefficient. The measurements were collected during the 2012 Two-Column Aerosol Project (TCAP) campaign and the 2014 Ship-Aircraft Bio-Optical Research (SABOR) campaign. For the SABOR campaign, 73% RSP MAPP retrievals fall within ±0.04 AOD at 532 nm as measured by HSRL-1, with an R value of 0.933 and root-mean-square deviation of 0.0372. For the TCAP campaign, 53% of RSP MAPP retrievals are within 0.04 AOD as measured by HSRL-2, with an R value of 0.927 and root-mean-square deviation of 0.0673. Comparisons with HSRL-2 AOD at 355 nm during TCAP result in an R value of 0.959 and a root-mean-square deviation of 0.0694. The RSP retrievals using the MAPP optimal estimation framework represent a key milestone on the path to a combined lidar+polarimeter retrieval using both HSRL and RSP measurements.

Advances in atmospheric temperature profile measurements using high spectral resolution lidar

This paper reports the atmospheric temperature profile measurements using a University of Wisconsin-Madison High Spectral Resolution Lidar (HSRL) and describes improvements in the instrument performance. HSRL discriminates between Mie and Rayleigh backscattering [1]. Thermal motion of molecules broadens the spectrum of the transmitted laser light due to Doppler effect. The HSRL exploits this property to allow the absolute calibration of the lidar and measurements of the aerosol volume backscatter coefficient. Two iodine absorption filters with different line widths are used to resolve temperature sensitive changes in Rayleigh backscattering for atmospheric temperature profile measurements.

Vertically- resolved phytoplankton carbon and net primary production from a high spectral resolution lidar.

Passive ocean observing sensors are unable to detect subsurface structure in ocean properties, resulting in errors in water column integrated phytoplankton biomass and net primary production (NPP) estimates. Active lidar (light detection and ranging) sensors make quantitative measurements of depth-resolved backscatter (bbp) and diffuse light attenuation (Kd) coefficients in the ocean and can provide critical measurements for biogeochemical models. Sub-surface phytoplankton biomass, light, chlorophyll, and NPP fields were characterized using both in situ measurements and coincident airborne high spectral resolution lidar (HSRL-1) measurements collected as part of the SABOR (Ship-Aircraft Bio-Optical Research) field campaign. We found that depth-resolved data are critical for calculating phytoplankton stocks and NPP, with improvements in NPP estimates up to 54%. We observed strong correlations between coincident HSRL-1 and in situ IOP measurements of both bbp (r = 0.94) and Kd (r = 0.90).

High-Resolution Soil Moisture Retrieval With ASCAT

Satelliteborne C-band scatterometer measurements of the radar backscatter coefficient $(\sigma^{0})$ of the Earth can be used to estimate soil moisture levels over land. Such estimates are currently produced at 25- and 50-km resolution using the Advanced Scatterometer (ASCAT) sensor and a change detection algorithm originally developed at the Vienna University of Technology (TU-Wien). Using the ASCAT spatial response function (SRF), high-resolution (approximately 15–20 km per pixel) images of $\sigma^{0}$ can be produced, enabling the creation of a high-resolution soil moisture product using a modified version of the TU-Wien algorithm. The high-resolution soil moisture images are compared to images produced with the Water Retrieval Package 5.5 algorithm, which is also based on the TU-Wien algorithm, and to in situ measurements from the National Oceanic and Atmospheric Administration U.S. Climate Reference Network (NOAA CRN). The WARP 5.5 and high-resolution image products generally show good agreement with each other; the high-resolution estimates appear to resolve soil moisture features at a finer scale and demonstrate a tendency toward greater moisture values in some areas. When compared to volumetric soil moisture measurements from NOAA CRN stations for 2010 and 2011, the WARP 5.5 and high-resolution soil moisture estimates perform similarly, with both having a root-mean-square difference from the in situ data of approximately 0.06 m3/m3 in one study area and 0.09 m3/m3 in another.

Impact of Light Polarization on the Measurement of Water Particulate Backscattering Coefficient

Particulate backscattering coefficient is a main inherent optical properties (IOPs) of water, which is also a determining factor of ocean color and a basic parameter for inversion of satellite ocean color remote sensing. In-situ measurement with optical instruments is currently the main method for obtaining the particulate backscattering coefficient of water. Due to reflection and refraction by the mirrors in the instrument optical path, the emergent light source from the instrument may be partly polarized, thus to impact the measurement accuracy of water backscattering coefficient. At present, the light polarization of measuring instruments and its impact on the measurement accuracy of particulate backscattering coefficient are still poorly known. For this reason, taking a widely used backscattering coefficient measuring instrument HydroScat6 (HS-6) as an example in this paper, the polarization characteristic of the emergent light from the instrument was systematically measured, and further experimental study on the impact of the light polarization on the measurement accuracy of the particulate backscattering coefficient of water was carried out. The results show that the degree of polarization(DOP) of the central wavelength of emergent light ranges from 20% to 30% for all of the six channels of the HS-6, except the 590 nm channel from which the DOP of the emergent light is slightly low (-15%). Therefore, the emergent light from the HS-6 has significant polarization. Light polarization has non-neglectable impact on the measurement of particulate backscattering coefficient, and the impact degree varies with the wave band, linear polarization angle and suspended particulate matter (SPM) concentration. At different SPM concentrations, the mean difference caused by light polarization can reach 15.49%, 11.27%, 12.79%, 14.43%, 13.76%, and 12.46% in six bands, 420, 442, 470, 510, 590, and 670 nm, respectively. Consequently, the impact of light polarization on the measurement of particulate backscattering coefficient with an optical instrument should be taken into account, and the DOP of the emergent light should be reduced as much as possible.

Atmospheric Temperature Profile Measurements Using Mobile High Spectral Resolution Lidar

The High Spectral Resolution Lidar (HSRL) designed at the University of Wisconsin-Madison discriminates between Mie and Rayleigh backscattering [1]. It exploits the Doppler effect caused by thermal motion of molecules, which broadens the spectrum of the transmitted laser light. That allows for absolute calibration of the lidar and measurements of the aerosol volume backscatter coefficient. Two iodine absorption filters with different absorption line widths (a regular iodine vapor filter and Argon buffered iodine filter) allow for atmospheric temperature profile measurements. The sensitivity of the measured signal-to-air temperature ratio is around 0.14%/K. The instrument uses a shared telescope transmitter-receiver design and operates in eyesafe mode (the product of laser average power and telescope aperture equals 0.1 W m 2 at 532 nm).

Aerosol Products from The Future Space Lidar AEOLUS

Ready for launch by the end of 2016, the Doppler lidar mission AEOLUS from the European Space Agency (ESA) will be the first High-Spectral Resolution Lidar (HSRL) in space. Operating in the UV, it implements two detection channels for aerosol and molecular backscatter. The system is primarily designed for the measurement of winds, but the HSRL capability enables the measurement of the particulate backscatter and extinction coefficients without any a priori assumption on the aerosol type. The level-2A (L2A) processor has been developed for these measurements and tested with synthetic data. The results show good aerosol backscatter profiles can be retrieved. Extinction coefficients are reasonable but do not reach the quality of backscatter coefficients. A precise, full, radiometric calibration of the lidar is required. A major limitation of the system is a single polarization component of the light is detected leading to an underestimation of backscatter coefficients when the atmospheric particles are depolarizing. The vertical resolution goes from 250 meters in the lowest part of the atmosphere, to 2 km in the lower stratosphere. The maximum altitude can reach above 20km. The basic horizontal averaging is 90km. Averaging on shorter distances (down to a few km) are possible but require a sufficient signal to noise ratio.

Validation of quantitative attenuation and backscattering coefficient measurements by optical coherence tomography in the concentration-dependent and multiple scattering regime

Optical coherence tomography (OCT) has the potential to quantitatively measure optical properties of tissue such as the attenuation coefficient and backscattering coefficient. However, to obtain reliable values for strong scattering tissues, accurate consideration of the effects of multiple scattering and the nonlinear relation between the scattering coefficient and scatterer concentration (concentration-dependent scattering) is required. We present a comprehensive model for the OCT signal in which we quantitatively account for both effects, as well as our system parameters (confocal point spread function and sensitivity roll-off). We verify our model with experimental data from controlled phantoms of monodisperse silica beads (scattering coefficients between 1 and 30 mm(−1) and scattering anisotropy between 0.4 and 0.9). The optical properties of the phantoms are calculated using Mie theory combined with the Percus–Yevick structure factor to account for concentration-dependent scattering. We demonstrate excellent agreement between the OCT attenuation and backscattering coefficient predicted by our model and experimentally derived values. We conclude that this model enables us to accurately model OCT-derived parameters (i.e., attenuation and backscattering coefficients) in the concentration-dependent and multiple scattering regime for spherical monodisperse samples.

Structure-factor model for quantifying the ultrasound scattering from concentrated cell pellet biophantoms

Ultrasonic backscatter coefficient (BSC) measurements were performed on K562 cell pellet biophantoms with cell concentrations ranging from 0.6% to 30% using ultrasound in the 10–42 MHz frequency band. The concentrated biophantoms mimic densely packed cells with known concentrations and are thus simplified versions of real tumor. Three scattering models, the fluid-filled-sphere model (FFSM), the Gaussian model (GM), and the structure factor model (SFM), were compared for modeling the scattering of the biophantoms. The GM and FFSM assume sparse, independently, and randomly distributed scatterers and are thus suitable for modeling dilute media; however, the SFM does not contain these assumptions and therefore can model dense media accurately. First, a parameter-estimation procedure was developed to estimate scatterer size and acoustic impedance contrast (assuming that cell concentrations were known a priori) and thereby compare theoretical with measured BSCs for all studied concentrations. The SFM yielded scatterer-radius estimates of 6.4 μm, which were consistent with the cell radius measured by optical microscopy. Second, the ability of the three models to estimate the scatterer size and acoustic concentration was compared. These scatterer properties were predicted well by the SFM, whereas the GM and the FFSM underestimated cell size and overestimated acoustic concentration for the more-concentrated biophantoms.

Spectral attenuation and backscattering as indicators of average particle size.

Measurements of the particulate beam attenuation coefficient at multiple wavelengths in the ocean typically exhibit a power law dependence on wavelength, and the slope of that power law has been related to the slope of the particle size distribution (PSD), when assumed to be a power law function of particle size. Recently, spectral backscattering coefficient measurements have been made using sensors deployed at moored observatories, on autonomous underwater vehicles, and even retrieved from space-based measurements of remote sensing reflectance. It has been suggested that these backscattering measurements may also be used to obtain information about the shape of the PSD. In this work, we directly compared field-measured PSD with multispectral beam attenuation and backscattering coefficients in a coastal bottom boundary later. The results of this comparison demonstrated that (1)the beam attenuation spectral slope correlates with the average particle size as suggested by theory for idealized particles and PSD; and (2)measurements of spectral backscattering also contain information reflective of the average particle size in spite of large deviations of the PSD from a spectral power law shape.

A Dense Medium Microwave Backscattering Model for the Remote Sensing of Oil Palm

Very little work has been carried out to examine the potential of synthetic aperture radar (SAR) imaging data for growth monitoring, disease monitoring, and yield prediction of oil palm plantations. In this paper, we present a scattering model for oil palm based on the radiative transfer equations, solved iteratively up to the second order, to better understand the backscattering behavior of oil palm canopies for SAR image interpretation. The oil palm canopy is modeled as a multilayer background host medium embedded with discrete scatterers of different shapes, with elliptic disks representing the leaves and cylinders representing the fronds and trunks. We consider the effects of coherent scattering through the dense medium phase and amplitude correction theory, as well as the near-field interactions between closely spaced scatterers through the Fresnel phase and amplitude corrections. Ground-truth data are used as input parameters for the model. The model is used to calculate the backscattering coefficients of oil palm canopies at different stages of growth and for different polarizations, frequencies, and incident angles. Comparisons between model calculations and C-band scatterometer measurements of multipolarization backscattering coefficients of 4-year-old oil palm canopies in Bangi, Malaysia show good agreement. Our model also predicts that SAR images at L-band are more sensitive to changes in the structure of the canopies, particularly that of the fronds, so will be the best frequency for oil palm growth monitoring and disease detection.

Laboratory measurements of acoustic backscattering from polystyrene pseudo-ice particles as a basis for quantitative characterization of frazil ice

Measurements of volume backscattering coefficients in brine suspensions of neutrally buoyant, uniformly-sized, polystyrene spheres and disks were used to quantify size, shape and concentration dependences expected in equivalent measurements on freshwater suspensions of frazil ice. The results confirmed expectations of qualified compatibility with existing scattering theory. Specifically, the measured logarithmic backscattering coefficients were expressible, to within 1–2dB, as products of particle concentration and individual cross sections as calculated from the modal expansion of Faran (1951) applied to spheres with radii equal to either their actual values or (for hexagonal disks) to “effective” spherical radii. The limitations on the applicability of the theory were closely linked to: acoustic frequency, target-volume-determined effective radii; the linear dimensions of the faces of the individual target disks; and to particle concentrations. For combinations of particle dimensions, acoustic frequencies and concentrations outside of a well-defined Rayleigh Linear (RL) concentration dependence range, the relationships between measured volume backscattering coefficients and particle properties were complex and not amenable to a simple interpretation: reflecting, it is believed, polystyrene-specific scattering features. The features of the observed extensive Anomalous Linear (AL) and Non-Linear (NL) concentration dependence regimes were documented in terms of both their parameter dependences and the forms and parameters associated with their deviations from RL regime dependences. Analyses focused on identifying the boundaries of the latter regimes which currently provide the only measurement environments compatible with accurate extraction of particle concentration and size parameters. These identifications, made on the basis of polystyrene in brine data, were used, after insertion of frazil and freshwater material parameters, to identify equivalent RL boundaries for ABS (Acoustic Backscattering Sonar) frazil measurements. In practical terms, this framework led to estimates of upper and lower limits for usable ABS acoustic frequencies and established upper limits on the concentrations of larger frazil particles contributing significantly to backscattering signal returns. These results formed the basis for a measurement framework for obtaining validated frazil characterizations. This framework was tested on mixtures of differently-sized pseudo-frazil species to show compatibility between mixture data and equivalent backscattering coefficients calculated for each mixture on the basis of its composition and measured single species coefficients. Applications of this framework to actual frazil field data are essential for both further testing of effectiveness and to allow refinements of imposed, intentionally conservative, restrictions. Results of such applications are described and interpreted in a second publication.

Noninvasive Diagnosis of Nonalcoholic Fatty Liver Disease and Quantification of Liver Fat Using a New Quantitative Ultrasound Technique

Liver biopsy analysis is the standard method used to diagnose nonalcoholic fatty liver disease (NAFLD). Advanced magnetic resonance imaging is a noninvasive procedure that can accurately diagnose and quantify steatosis, but is expensive. Conventional ultrasound is more accessible but identifies steatosis with low levels of sensitivity, specificity, and quantitative accuracy, and results vary among technicians. A new quantitative ultrasound (QUS) technique can identify steatosis in animal models. We assessed the accuracy of QUS in the diagnosis and quantification of hepatic steatosis, comparing findings with those from magnetic resonance imaging proton density fat fraction (MRI-PDFF) analysis as a reference. We performed a prospective, cross-sectional analysis of a cohort of adults (N = 204) with NAFLD (MRI-PDFF, ≥5%) and without NAFLD (controls). Subjects underwent MRI-PDFF and QUS analyses of the liver on the same day at the University of California, San Diego, from February 2012 through March 2014. QUS parameters and backscatter coefficient (BSC) values were calculated. Patients were assigned randomly to training (n = 102; mean age, 51 ± 17 y; mean body mass index, 31 ± 7 kg/m(2)) and validation (n = 102; mean age, 49 ± 17 y; body mass index, 30 ± 6 kg/m(2)) groups; 69% of patients in each group had NAFLD. BSC (range, 0.00005-0.25 1/cm-sr) correlated with MRI-PDFF (Spearman ρ = 0.80; P < .0001). In the training group, the BSC analysis identified patients with NAFLD with an area under the curve value of 0.98 (95% confidence interval, 0.95-1.00; P < .0001). The optimal BSC cut-off value identified patients with NAFLD in the training and validation groups with 93% and 87% sensitivity, 97% and 91% specificity, 86% and 76% negative predictive values, and 99% and 95% positive predictive values, respectively. QUS measurements of BSC can accurately diagnose and quantify hepatic steatosis, based on a cross-sectional analysis that used MRI-PDFF as the reference. With further validation, QUS could be an inexpensive, widely available method to screen the general or at-risk population for NAFLD.

Structure factor model for understanding the measured backscatter coefficients from concentrated cell pellet biophantoms

Ultrasonic backscatter coefficient (BSC) measurements were performed on K562 cell pellet biophantoms with cell concentrations ranging from 0.006 to 0.30 in the 10-42 MHz frequency bandwidth. Three scattering models, namely, the fluid-filled sphere model (FFSM), the particle model (PM), and the structure factor model (SFM), were compared for modeling the scattering from an ensemble of concentrated cells. A parameter estimation procedure was developed in order to estimate the scatterer size and relative impedance contrast that could explain the measured BSCs from all the studied cell concentrations. This procedure was applied to the BSC data from K562 cell pellet biophantoms in the 10-42 MHz frequency bandwidth and to the BSC data from Chinese hamster ovary cell pellet biophantoms in the 26-105 MHz frequency bandwidth given in Han, Abuhabsah, Blue, Sarwate, and O'Brien [J. Acoust. Soc. Am. 130, 4139-4147 (2011)]. The data fitting quality and the scatterer size estimates show that the SFM was more suitable than the PM and the FFSM for modeling the responses from concentrated cell pellet biophantoms.

Measurements of aerosol phase function and vertical backscattering coefficient using a charge-coupled device side-scatter lidar

By using a charge-coupled device (CCD) as the detector, side-scatter lidar has great potential applications in the near range atmospheric detection. A new inversion method is proposed for CCD side-scatter lidar (Clidar) to retrieve aerosol phase function and vertical backscattering coefficient. Case studies show the retrieved results from Clidar are in good agreements with those obtained from other instruments. It indicates that the new proposed inversion method is reliable and feasible and that the Clidar is practicable.

Research on backscattering coefficient based on nano-MOSFET noise

In the study of the backscattering coefficient by traditional noise theory, many parameters and quantum mechanical calculations are used, or deviations appear in conclusions due to a lot of assumptions. In the present work, based on the Navid model, the expressions of backscattering coefficient in nano-MOSFET are deduced, and the backscattering coefficient in the linear region and the saturation region are obtained, and gives the back-scattering coefficient measurement method. On this basis, the variations of backscattering coefficient with Channel length, temperature and voltage are analyzed. Furthermore, the variations of backscattering coefficient with voltage in the linear region and the saturation region are verified by experiments and Monte Carlo simulations. Our results are in accordance with other works.