303 research outputs found

    Algorithm to derive inherent optical properties from remote sensing reflectance in turbid and eutrophic lakes

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    Inherent optical properties play an important role in understanding the biogeochemical processes of lakes by providing proxies for a variety of biogeochemical quantities, including phytoplankton pigments. However, to date, it has been difficult to accurately derive the absorption coefficient of phytoplankton [aph(位)] in turbid and eutrophic waters from remote sensing. A large dataset of remote sensing of reflectance [ Rrs (位)] and absorption coefficients was measured for samples collected from lakes in the middle and lower reaches of the Yangtze River and Huai River basin (MLYHR), China. In the process of scattering correction of spectrophotometric measurements, the particulate absorption coefficients [ap(位)] were first assumed to have no absorption in the near-infrared (NIR) wavelength. This assumption was corrected by estimating the particulate absorption coefficients at 750 nm [ap(750)] from the concentrations of chlorophyll-a (Chla) and suspended particulate matter, which was added to the ap(位) as a baseline. The resulting mean spectral mass-specific absorption coefficient of the nonalgal particles (NAPs) was consistent with previous work. A novel iterative IOP inversion model was then designed to retrieve the total nonwater absorption coefficients [anw(位)] and backscattering coefficients of particulates [bbp(位)], aph(位), and adg (位) [absorption coefficients of NAP and colored dissolved organic matter (CDOM)] from Rrs (位) in turbid inland lakes. The proposed algorithm performed better than previously published models in deriving anw(位) and bbp(位) in this region. The proposed algorithm performed well in estimating the aph(位) for wavelengths \u3e 500 nm for the calibration dataset [N = 285, unbiased absolute percentage difference (UAPD) = 55.22%, root mean square error (RMSE) = 0.44 m鈭1] and for the validation dataset (N = 57, UAPD = 56.17%, RMSE = 0.71 m鈭1). This algorithm was then applied to Sentinel-3A Ocean and Land Color Instrument (OLCI) satellite data, and was validated with field data. This study provides an example of how to use local data to devise an algorithm to obtain IOPs, and in particular, a ph (位), using satellite Rr s (位) data in turbid inland waters

    Impact of multichannel river network on the plume dynamics in the Pearl River estuary

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    Author Posting. 漏 American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 5766鈥5789, doi:10.1002/2014JC010490.Impacts of the multichannel river network on plume dynamics in the Pearl River estuary were examined using a high-resolution 3-D circulation model. The results showed that during the dry season the plume was a distinct feature along the western coast of the estuary. The plume was defined as three water masses: (a) riverine water (22 psu), respectively. A significant amount of low-salinity water from Hengmen and Hongqimen was transported through a narrow channel between the QiAo Island and the mainland of the Pearl River delta during the ebb tide and formed a local salinity-gradient feature (hereafter referred to as a discharge plume). This discharge plume was a typical small-scale river plume with a Kelvin number K鈥=鈥0.24 and a strong frontal boundary on its offshore side. With evidence of a significant impact on the distribution and variability of the salinity and flow over the West Shoal, this plume was thought to be a major feature of the Pearl River plume during the dry season. The upstream multichannel river network not only were the freshwater discharge sources but also played a role in establishing an estuarine-scale subtidal pressure gradient. This pressure gradient was one of the key dynamical processes controlling the water exchange between discharge and river plumes in the Pearl River estuary. This study clearly showed the role of the river network and estuary interaction on river plume dynamics.The research work was supported by the National Natural Science Foundation of China (grant 41206005), the Ocean Public Welfare Scientific Research Project, State Oceanic Administration of the People's Republic of China (grant 201305019-3) and the CAS Strategic Pilot Science and Technology (XDA11020205). Changsheng Chen's participation was supported by the International Center for Marine Studies, Shanghai Ocean University.2016-02-2

    Inversion of inherent optical properties in optically complex waters using sentinel-3A/OLCI images: A case study using China\u27s three largest freshwater lakes

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    Inherent optical properties (IOPs) play an important role in underwater light field, and are difficult to estimate accurately using satellite data in optically complex waters. To study water quality in appropriate temporal and spatial scales, it is necessary to develop methods to obtain IOPs form space-based observation with quantified uncertainties. Field-measured IOP data (N = 405) were collected from 17 surveys between 2011 and 2017 in the three major largest freshwater lakes of China (Lake Chaohu, Lake Taihu, and Lake Hongze) in the lower reaches of the Yangtze River and Huai River (LYHR). Here we provide a case-study on how to use in-situ observation of IOPs to devise an improved algorithm for retrieval of IOPs. We then apply this algorithm to observation with Sentinel-3A OLCI (Ocean and Land Colour Instrument, corrected with our improved AC scheme), and use in-situ data to show that the algorithm performs better than the standard OLCI IOP product. We use the satellite derived products to study the spatial and seasonal distributions of IOPs and concentrations of optically active constituents in these three lakes, including chlorophyll-a (Chla) and suspended particulate matter (SPM), using all cloud-free OLCI images (115 scenes) over the lakes in the LYHR basin in 2017. Our study provides a strategy for using local and remote observations to obtain important water quality parameters necessary to manage resources such as reservoirs, lakes and coastal waters

    Fremanezumab for the Preventive Treatment of Chronic Migraine.

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    BACKGROUND: Fremanezumab, a humanized monoclonal antibody targeting calcitonin gene-related peptide (CGRP), is being investigated as a preventive treatment for migraine. We compared two fremanezumab dose regimens with placebo for the prevention of chronic migraine. METHODS: In this phase 3 trial, we randomly assigned patients with chronic migraine (defined as headache of any duration or severity on 鈮15 days per month and migraine on 鈮8 days per month) in a 1:1:1 ratio to receive fremanezumab quarterly (a single dose of 675 mg at baseline and placebo at weeks 4 and 8), fremanezumab monthly (675 mg at baseline and 225 mg at weeks 4 and 8), or matching placebo. Both fremanezumab and placebo were administered by means of subcutaneous injection. The primary end point was the mean change from baseline in the average number of headache days (defined as days in which headache pain lasted 鈮4 consecutive hours and had a peak severity of at least a moderate level or days in which acute migraine-specific medication [triptans or ergots] was used to treat a headache of any severity or duration) per month during the 12 weeks after the first dose. RESULTS: Of 1130 patients enrolled, 376 were randomly assigned to fremanezumab quarterly, 379 to fremanezumab monthly, and 375 to placebo. The mean number of baseline headache days (as defined above) per month was 13.2, 12.8, and 13.3, respectively. The least-squares mean (卤SE) reduction in the average number of headache days per month was 4.3卤0.3 with fremanezumab quarterly, 4.6卤0.3 with fremanezumab monthly, and 2.5卤0.3 with placebo (P CONCLUSIONS: Fremanezumab as a preventive treatment for chronic migraine resulted in a lower frequency of headache than placebo in this 12-week trial. Injection-site reactions to the drug were common. The long-term durability and safety of fremanezumab require further study. (Funded by Teva Pharmaceuticals; ClinicalTrials.gov number, NCT02621931 .)

    Downwelling wind, tides, and estuarine plume dynamics

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    Author Posting. 漏 American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 4245鈥4263, doi:10.1002/2015JC011475.The estuarine plume dynamics under a downwelling-favorable wind condition were examined in the windy dry season of the Pearl River Estuary (PRE) using the PRE primitive-equation Finite-Volume Community Ocean Model (FVCOM). The wind and tide-driven estuarine circulation had a significant influence on the plume dynamics on both local and remote scales. Specifically, the local effect of downwelling-favorable winds on the plume was similar to the theoretical descriptions of coastal plumes, narrowing the plume width, and setting up a vertically uniform downstream current at the plume edge. Tides tended to reduce these plume responses through local turbulent mixing and advection from upstream regions, resulting in an adjustment of the isohalines in the plume and a weakening of the vertically uniform downstream current. The remote effect of downwelling-favorable winds on the plume was due to the wind-induced estuarine sea surface height (SSH), which strengthened the estuarine circulation and enhanced the plume transport accordingly. Associated with these processes, tide-induced mixing tended to weaken the SSH gradient and thus the estuarine circulation over a remote influence scale. Overall, the typical features of downwelling-favorable wind-driven estuarine plumes revealed in this study enhanced our understanding of the estuarine plume dynamics under downwelling-favorable wind conditions.National Natural Science Foundation of China Grant Number: (41206005); Ocean Public Welfare Scientific Research Project, State Oceanic Administration of the People's Republic of China Grant Number: (201305019-3)2016-12-2
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