Estimation of Attenuation Coefficient Values Using Remote Sensing and Its Relationship With Shallow Water Depth

In marine remote sensing areas, the intensity of the light that enters the water column will decrease exponentially with increasing depth due to scattering and absorption. The process of reducing intensity is called the attenuation process. This process became a limiting factor in detecting objects at the bottom and water column using a remote sensing method that depends on light intensity. Diffuse attenuation coefficient (Kd ) is an important optical property of seawater because it provides information on water clarity and the level of light attenuation. This research analyzed the Kd and its variability from in situ measurement and Sentinel-2 level 2A MSI (Multi Spectral Imagery) data in Karang Lebar, Panggang Island, and Air Island, in Seribu Island, North Jakarta. We determined the Kd (490) value using several algorithms. The result showed that Kd (490) in situ and from the model has a good correlation (r = 0.75 – 0.86).

The diffuse attenuation coefficient (K d) for downwelling irradiance is calculated from solar irradiance data measured in the Arctic Ocean during 3rd and 4th Chinese National Arctic Research Expedition (CHINARE), including 18 stations and nine stations selected for irradiance profiles in sea water respectively. In this study, the variation of attenuation coefficient in the Arctic Ocean was studied, and the following results were obtained. First, the relationship between attenuation coefficient and chlorophyll concentration in the Arctic Ocean has the form of a power function. The best fit is at 443 nm, and its determination coefficient is more than 0.7. With increasing wavelength, the determination coefficient decreases abruptly. At 550 nm, it even reaches a value lower than 0.2. However, the exponent fitted is only half of that adapted in low-latitude ocean because of the lower chlorophyll-specific absorption in the Arctic Ocean. The upshot was that, in the case of the same chlorophyll concentration, the attenuation caused by phytoplankton chlorophyll in the Arctic Ocean is lower than in low-latitude ocean. Second, the spectral model, which exhibits the relationship of attenuation coefficients between 490 nm and other wavelength, was built and provided a new method to estimate the attenuation coefficient at other wavelength, if the attenuation coefficient at 490 nm was known. Third, the impact factors on attenuation coefficient, including sea ice and sea water mass, were discussed. The influence of sea ice on attenuation coefficient is indirect and is determined through the control of entering solar radiation. The linear relationship between averaging sea ice concentration (ASIC, from 158 Julian day to observation day) and the depth of maximum chlorophyll is fitted by a simple linear equation. In addition, the sea water mass, such as the ACW (Alaskan Coastal Water), directly affects the amount of chlorophyll through taking more nutrient, and results in the higher attenuation coefficient in the layer of 30–60 m. Consequently, the spectral model of diffuse attenuation coefficient, the relationship between attenuation coefficient and chlorophyll and the linear relationship between the ASIC and the depth of maximum chlorophyll, together provide probability for simulating the process of diffuse attenuation coefficient during summer in the Arctic Ocean.

Investigation of gamma-ray attenuation coefficients for solid boronized 304L stainless steel

While access to discharge data is key to hydrologic studies, it is a serious obstacle in ungauged basins. Currently, Sentinel-2 imagery at high spatiotemporal resolution offers a unique opportunity to infer the relation between pixel-based discharge rate and surface reflectance. One promising approach in this respect has been to find the complex relationship between river discharge and the spectral ratio between two benchmark pixels, namely the wet and dry pixels, whose dynamics resembles river discharge variation. However, this has been challenging due to the adverse impact of soil moisture and mixed land cover on the spectral behavior of the dry pixel. The selection of the wet pixel must also guarantee sufficient sensitivity of its spectral response to water depth fluctuations. To tackle the above issues, in this study, we developed a novel framework that automatizes the selection of the wet and dry pixels by using Sentinel-2 imagery. We also introduced the Normalized Difference Discharge Index (NDDI), as the best band combination, to predict river discharge. We used linear regression with leave-one-out cross-validation as the prediction model, which leverages limited satellite data due to the cloud cover. By implementing the developed framework at multiple gauged points across the continental United States, the best location of the dry pixel was consistently found in urban pixels whose longwave reflectance fall within a certain range. By analyzing the pixel-wised correlation coefficient between surface reflectance at NIR band and river discharge across the studied river widths, we found that the best wet pixels are located along river banks with shallow water depth. These pixels were characterized by the average reflectance higher than the 98th percentile in the green band. Finally, by testing over 4000 band combinations as input to the river discharge prediction model, we found that the normalized difference between B11 and B4 for the wet pixel, as well as the B11 ratioing between the dry and wet pixels yielded the most accurate predictions with R2 = 0.88 and R2 = 0.73, respectively.

A 2-layer non-hydrostatic model with improved dispersive behaviour is presented. Due to the assumption of a constant non-hydrostatic pressure distribution in the lower layer, the dispersive behaviour is improved without much additional computational time. A comparison with linear wave theory showed that this 2-layer model gives a better result for the dispersion relation and shoaling of waves in intermediate water. This means that the 2-layer model is applicable in shallow and intermediate water depths (up to relative depths kh equals 4), whereas the 1-layer model is only applicable in shallow water depths (kh smaller than 1). Three laboratory experiments, including a fringing reef and a barred beach, were used to validate the presented mode for different hydrodynamic conditions. Based on these results, it can be concluded that the 2-layer model can be applied to accurately simulate the bulk wave height and spectral properties. The low frequency wave height, the setup and in particular the second order statistics contain more scatter, but the model accurately captured the general trend. Furthermore, the model showed good results for complex bathymetries in shallow to intermediate water.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 144:109-118 (1996) - doi:10.3354/meps144109 Penetration of solar UVB radiation in shallow tropical waters and its potential biological effects on coral reefs; results from the central Indian Ocean and Andaman Sea Dunne RP, Brown BE This paper presents the first complete data of global downwelling irradiance (Ed) and the diffuse attenuation coefficient (Kd) for solar ultraviolet-B (UVB; 280 to 320 nm) in tropical waters. The penetration of solar UVB into shallow (0 to 5 m) seawater at 3 sites in the central Indian Ocean and Andaman Sea, adjacent to areas of coral reefs, was studied using a semi-submersible scanning spectroradiometer. Downwelling global spectral irradiance (Ed) was measured at 2 nm intervals over the wavebands 280-320 nm (UVB), 320-400 nm (UVA) and 400-700 nm (PAR) above the sea surface (0+ m) and at each of 5 depths (1, 2, 3, 4, and 5 m). The 3 sites consisted of an ocean atoll in the Maldives (central Indian Ocean), a small (8 km2) high island 11 km off the continental coastline at Phuket, Thailand (Andaman Sea), and an inshore reef at Phuket. Ed at each of the depths was integrated over the wavebands as a percentage of the above-water irradiance. Ed(UVB) at 5 m depth was found to decrease to 12% of incident irradiance at the mid-ocean atoll, to 2% for the high island site, and to 0.4% in the turbid waters of the inshore reef. A 1% Ed(UVB) depth was computed for each site and found to be 11, 6, and 3 m respectively. The diffuse attenuation for downwelling irradiance (Kd) for the depth range 0- m (just below the surface) to 5 m showed a very rapid attenuation with decreasing wavelength in the UVB at all sites. Biological damage potential, as weighted by the DNA-damage action spectrum, showed a more rapid attenuation with depth than Ed(UVB), with a 1% EDNA depth of 9 m for the ocean atoll, 4.7 m for the coastal island, and 2.6 m for the inshore reef. Coral reefs · Diffuse attenuation coefficient · Solar ultraviolet radiation · UVB Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 144. Publication date: December 05, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

I tested the hypothesis that the quantity and quality of suspended and sediment organic matter in shallow coastal waters is affected by wind-induced resuspension at a smaller depth scale (<1 m) than usually assumed. Water and sediment surface (0 to 1 cm) samples were collected on a seasonal basis and analyzed for total suspended matter, organic fraction, and phytopigments at 12 shallow sites representing a depth gradient from 0.2 to 2.0 m along the western shore of Sicily. Water column concentrations of all measured variables decreased rapidly with increasing water column depth, and concentrations levelled off at about 1 m water column depth. The likelihood of sediment resuspension by wind for various combinations of water column depth and fetch length was modelled using the CERC (U.S. Army Corps of Engineers, Coastal Engineering Centre, Washington D.C. US) model for 10 years of local wind data. The simulations indicated that even light winds (2 m s−1) increased the likelihood of resuspension in the shallowest basin (0.2 m depth) with an effective fetch of 250 m. This study provides evidence that shallow water systems should not be investigated by considering the entire water column as a single homogenous layer. Investigations of shallow water ecosystems should consider 2 main layers with different ecological conditions and functions: a shallow surface turbulent layer from the surface to a depth of 1 m that is strongly affected by wind-driven physical forces and a deeper, below 1 m to the sediment surface, layer where wind-driven turbulence has less impact.

Hydroelastic analysis of floating elastic thick plate in shallow water depth

To evaluate the diagnostic value of ultrasound-guided attenuation parameter (UGAP) in metabolic fatty liver disease (MAFLD) and to explore the correlation between the attenuation coefficient (AC) value of UGAP and commonly used clinical obesity indicators. A total of 121 subjects who had physical examinations from November 2021 to March 2022 were prospectively selected; the height, weight, and waist circumference (WC) of all subjects were collected, and conventional ultrasound and UGAP examinations for all subjects. Under the standard of conventional ultrasound, among the 121 subjects, 53 had normal liver, 42 had mild fatty liver, 21 had moderate fatty liver, and 5 had severe fatty liver. The mean AC value of 121 patients was 0.66 ± 0.13 dB/cm/MHz. The best cut-off values for diagnosing mild, moderate, and severe fatty liver were 0.65dB/cm/MHz, 0.72dB/cm/MHz, and 0.83dB/cm/MHz, respectively. The area under the curve (AUC) values were 0.891, 0.929, and 0.914, respectively. When grouped by WC, there was a statistically significant difference in AC value between the normal group and the obese group (t=-4.675, P<0.001). Overall WC and within group WC were moderately correlated with the AC value of UGAP (P<0.001). UGAP has a good diagnostic value in the quantitative evaluation of liver steatosis in MAFLD, and the change of WC can reflect the occurrence of liver steatosis to a certain extent.

Measurement of attenuation coefficient, effective atomic number and electron density of oxides of lanthanides by using simplified ATM-method

Correlation of tissue constituents with the acoustic properties of skin and wound

Purpose: To compare and correlate localization and registration of calcified, fibrous and lipid regions within heterogeneous plaque using histology and ultrasound quantitative imaging, and to better characterize carotid plaque. Methods: Atherosclerotic plaque excised after carotid endarterectomy, was imaged ex vivo using a VisualSonics Vevo 770 ultrasound system. Attenuation coefficient images were obtained from the three‐dimensional radiofrequency data collected and rendered into a 3D volume. Fixed plaque tissue was then longitudinally sectioned in increments of 5 um, and sections separated by 100 um were acquired. The thickness of each section of the sample was 5 um. Histopathology images were digitized using a PathScan Enabler IV. The two‐dimensional histology information obtained were registered using Matlab and reconstructed into a 3D volume. Different regions such as the lumen, calcified, fibrous and lipid region were segmented by a pathologist and digitally color‐coded into the 3D histology data. We then compared similar tissue types from the 3D histology volume to the estimated 3D attenuation coefficient using quantitative ultrasound methods. Results: Our results indicate that calcified, fibrous and lipid regions in the two volumes showed a good correlation. Calcified regions delineated on the histology volume correspond to the high attenuation coefficient region (2.48 dB/cm/MHz) in the 3D attenuation coefficient volume, while lipid regions tend to have lower attenuation coefficient values (1.47 dB/cm/MHz). Fibrous regions in histology, correlate to the lowest attenuation coefficient value (0.86 dB/cm/MHz). Conclusion: Most plaques are heterogeneous and difficult to characterize precisely. This work demonstrates a direct correlation between pathology and ultrasound quantitative imaging characterization of plaque. It provides a promising way for direct localization of plaque regions and structures, and for improved determination of plaque composition. This work was supported in part by NIH grants R21 EB010098‐02, R01 NS064034‐04, and 2R01 CA112192‐06.

Image degradation during single photon emission computed tomography (SPECT) due to attenuation and Compton scatter of photons can cause clinical image artifacts and will also result in inaccurate quantitative data. Therefore attenuation correction methods recently received wide interest. Transmission imaging can be performed to obtain the attenuation coefficients of a nonhomogeneous attenuating medium accurately. The aim of this study was firstly to evaluate the imaging characteristics of the scanning line source assembly. The results obtained with Tc-99m and Ce-139 were compared. Secondly the calculated attenuation coefficients were compared with known values from literature, using Tc-99m and Ce-139 as transmission sources. Lastly the method of acquiring simultaneous transmission and emission data was investigated. This study shows that an attenuation coefficient map can be obtained using a scanning line source for transmission imaging with a dual opposing detector camera. The imaging characteristics of Tc-99m and Ce-139 as transmission sources are similar. The resolution obtained with the Ce-139 line source was poorer than that obtained with the Tc-99m line source. A linear relationship was found between CT numbers and attenuation coefficients for transmission images using both Tc-99m and Ce-139 line sources. The attenuation coefficient value for water was underestimated by 1% using the Tc-99m transmission source and underestimated by 10% using Ce-139 as transmission source. This underestimation of attenuation coefficient values was also obtained in the human study. A myocardial perfusion study processed without and with attenuation correction clearly demonstrated the effect of the attenuation correction in the inferior myocardial region. The potential of using a scanning line source as transmission source with a dual opposing detector camera has been demonstrated in this study. The transmission source, Ce-139 was successfully introduced in this investigation for simultaneous acquisition of transmission and emission data.

In the present work, we carried out a comparative study of the attenuation coefficient of the white matter of the rat brain during the growth of glial tumors characterized by different degrees of malignancy (glioblastoma 101/8, astrocytoma 10-17-2, glioma C6) and during irradiation. We demonstrated that some tumor models cause a pronounced decrease in white matter attenuation coefficient values due to infiltration of tumor cells, myelinated fiber destruction, and edema. In contrast, other tumors cause compression of the myelinated fibers of the corpus callosum without their ruptures and prominent invasion of tumor cells, which preserved the attenuation coefficient values changeless. In addition, for the first time, the possibility of using the attenuation coefficient to detect late radiation-induced changes in white matter characterized by focal development of edema, disruption of the integrity of myelinated fibers, and a decrease in the amount of oligodendrocytes and differentiation of these areas from tumor tissue and healthy white matter has been demonstrated. The results indicate the promise of using the attenuation coefficient estimated from OCT data for in vivo assessment of the degree of destruction of peritumoral white matter or its compression, which makes this method useful not only in primary resections but also in repeated surgical interventions for recurrent tumors.

To assess the feasibility of a novel method of measuring the attenuation coefficient in the thyroid, which offers less variability of results than the conventional method. In our new method, the attenuation coefficient was evaluated on the basis of the following equation with sound field correction: alpha = -1/4[Fc(z)-epsilon(z)] x d/dz[log(M0(z))-tau(z)]. In our system, the attenuation coefficient was also evaluated by the spectral shift central frequency method at the same time. In this study, we used 32 cases of normal thyroid, 26 cases of Graves disease, and 11 cases of Hashimoto thyroiditis in the system. With this novel method, attenuation coefficient values of the thyroid (mean +/- SD) were 1.50 +/- 0.26 dB x cm(-1) x MHz(-1) in the normal group, 0.91 +/- 0.23 dB x cm(-1) x MHz(-1) in the Graves disease group, and 1.10 +/- 0.27 dB x cm(-1) x MHz(-1) in the Hashimoto thyroiditis group. The novel method recorded a statistically significant difference between normal and diseased thyroids (P < .0001) and between Graves disease and Hashimoto thyroiditis groups (P = .0035). Statistical variation of the attenuation coefficient values obtained using the novel method was much smaller than that of those obtained by the spectral shift central frequency method in every group. This new method is considered usable for evaluating the attenuation coefficient of the thyroid in vivo.