Abstract. An optical model is developed based on the diffuse attenuation coefficient (K d ) to estimate particulate backscattering coefficients b bp (λ) in oceanic waters. A large in situ data set is used to establish robust relationships between b bp (530) and b bp (555) and K d (490) using an efficient nonlinear least-square method which uses the trust region algorithm with Bisquare weights scheme to adjust the coefficients. These relationships are obtained with good correlation coefficients (R 2 = 0.786 and 0.790), low root mean square error (RMSE = 0.00076 and 0.00072) and 95 % confidence bounds. The new model is tested with three independent data sets: the NOMAD SeaWiFS Match ups, OOXIX IOP algorithm workshop evaluation data set (Version 2.0w APLHA), and IOCCG simulated data set. Results show that the new model makes good retrievals of b bp at all key wavelengths (from 412-683 nm), with statistically significant improvements over other inversion models. Thus, the new model has the potential to improve our present knowledge of particulate matter and their optical variability in oceanic waters.
Even though the contribution of the aviation sector to the global economy is very notable, it also has an adverse impact on climate change. Improvements have been made in different areas (i.e., technology, sustainable aviation fuel, and design) to mitigate these adverse effects. However, the rate of improvement is small compared to the increase in the demand for air transportation. Hence, greenhouse gas emissions in the aviation sector are steadily increasing and this trend is expected to continue unless adequately addressed. In this context, this study examined the following: (i) the factors that affect the growth of aviation, (ii) trends in greenhouse gas emissions in the sector, (iii) trends in energy demand, (iv) mitigation pathways of emissions, (v) mitigation challenges for the International Civil Aviation Organization, (vi) achievements in mitigating emissions, (vii) barriers against mitigating emissions, and (viii) approaches of overcoming barriers against emissions mitigation. This study finds that continued research and development efforts targeting aircraft fuel burn efficiency are crucial in reducing greenhouse gas emissions. Although biofuels are promising for the reduction of aviation emissions, techniques to reduce NOx emissions could enhance large-scale deployment. Pragmatic market-based mechanisms, such as the Emissions Trading Scheme (ETS) and/or carbon tax must be enforced on a global scale to capitalize on a collective stakeholder effort to curb CO2 emissions. The findings of this study will help in understanding the emissions and energy consumption scenarios, which will provide a comprehensive package of mitigation pathways to overcome future emissions reduction challenges in the aviation sector.
The absorption coefficient of chromophoric dissolved organic matter (CDOM) is a major variable used in developing robust bio-optical models and understanding biogeochemical processes. Over the last decade, the optical properties of CDOM in the open sea have been intensely studied. However, their variations in clear water are poorly documented, particularly in the Red Sea, owing to the absence of in situ measurements. We performed several cruises in the Red Sea to investigate the spatial distribution of the absorption coefficient of CDOM. The spectral absorption coefficients were determined from 400 nm to 740 nm using a WETLabs ac-s hyper-spectral spectrophotometer. In general, we found a latitudinal gradient in the CDOM absorption coefficient at 443 nm (a CDOM (443)) from south to north that is likely influenced by the exchange of water through the strait of Bab-el-Mandeb and the thermohaline circulation of the Red Sea. However, high a CDOM (443) values were observed in the northern Red Sea due to the existence of a sub-mesoscale feature that may induce an increase in phytoplankton production and lead to CDOM production. The a CDOM (443) covaried with the chlorophyll a concentration ([Chl a],) despite a high scatter. Furthermore, the a CDOM (443) for a given [Chl a] concentration was higher than those predicted by global ocean bio-optical models. This study advances our understanding of CDOM concentration in the Red Sea and may help improve the accuracy of the algorithms used to obtain CDOM absorption from ocean color.
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