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Glint Removal Assessment to Estimate the Remote Sensing Reflectance in Inland Waters with Widely Differing Optical Properties
摘要： The quality control of remote sensing reflectance (Rrs) is a challenging task in remote sensing applications, mainly in the retrieval of accurate in situ measurements carried out in optically complex aquatic systems. One of the main challenges is related to glint effect into the in situ measurements. Our study evaluates four different methods to reduce the glint effect from the Rrs spectra collected in cascade reservoirs with widely differing optical properties. The first (i) method adopts a constant coefficient for skylight correction (ρ) for any geometry viewing of in situ measurements and wind speed lower than 5 m·s?1; (ii) the second uses a look-up-table with variable ρ values accordingly to viewing geometry acquisition and wind speed; (iii) the third method is based on hyperspectral optimization to produce a spectral glint correction, and (iv) computes ρ as a function of wind speed. The glint effect corrected Rrs spectra were assessed using HydroLight simulations. The results showed that using the glint correction with spectral ρ achieved the lowest errors, however, in a Colored Dissolved Organic Matter (CDOM) dominated environment with no remarkable chlorophyll-a concentrations, the best method was the second. Besides, the results with spectral glint correction reduced almost 30% of errors.
关键词： remote sensing accuracy,inland waters,optically complex systems
更新于2025-09-23 15:23:52
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Complexity mapping of a photonic integrated circuit laser using a correlation-dimension-based approach
摘要： Quantifying complexity from experimental time series generated by nonlinear systems, including laser systems, remains a challenge. Methods that are based on entropy, such as permutation entropy (PE), have proven to be useful tools for the relative measure of time series complexity. However, the numerical value of PE is not readily linked to a specific type of dynamical output. Thus, the quest to calculate quantitatively meaningful fractal dimension values, such as the correlation dimension (CD), from experimental signals, is still important. A protocol for calculating minimum gradient values and their spread, an integral part of CD analysis, is used here. Minimum gradient values with small spread are presented as approximate CD values. Here-in we report mapping these values, derived from analyzing experimental time series, obtained from a 4-section photonic integrated circuit laser (PICL) across a large parameter space. The PICL is an integrated form of a semiconductor laser subject to controllable optical feedback system. The minimum gradient/approximate CD mapping shows it has some qualitatively different map regions in its dynamics as compared to a free-space-based equivalent system. We show that the minimum gradient values give insight into the dynamics even when approximate CD values cannot be determined. The agreement between the qualitative features of permutation entropy mapping and minimum gradient/approximate CD value mapping provides further support for this. Regions of time series with close to periodic and quasi-periodic dynamics are identifiable using minimum gradient value maps.
关键词： semiconductor lasers,integrated optoelectronic devices,nonlinear dynamics,complex systems,Chaos,complexity
更新于2025-09-23 15:19:57
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Energy Transfer Networks Within Upconverting Nanoparticles Are Complex Systems With Collective, Robust, and History-Dependent Dynamics
摘要： Applications of photon upconverting nanoparticles (UCNPs) in biological imaging and solar energy conversion demand that their anti-Stokes luminescence be both tunable and efficient. Rational design of more efficient UCNPs requires an understanding of energy transfer (ET) between their lanthanide dopants – dynamics that are typically characterized by measuring luminescence lifetimes. Existing knowledge, however, cannot explain basic observations in lifetime experiments such as their dependence on excitation power, significantly limiting the generality and reliability of lifetime measurements. Here, we elucidate the origins of the ET dynamics and luminescence lifetimes of Yb3+,Er3+-codoped NaYF4 UCNPs using time-resolved luminescence and novel applications of rate equations and stochastic simulations. Experiments and calculations consistently show that, at high concentrations of Er3+, the luminescence lifetimes of UCNPs decrease as much as 6-fold when excitation power densities are increased over six orders of magnitude. Since power-dependent lifetimes cannot be explained by intrinsic relaxation rates of individual transitions, we analyze lifetime data by treating each UCNP as a complex ET network. We find that UCNP ET networks exhibit four distinguishing characteristics of complex systems: collectivity, nonlinear feedback, robustness, and history dependence. We conclude that power-dependent lifetimes are the consequence of thousands of minor relaxation pathways that act collectively to depopulate and repopulate Er3+ emitting levels. These ET pathways are dependent on past excitation power because they originate from excited donors and excited acceptors; however, each transition has an unexpectedly small impact on lifetimes due to negative feedback in the network. This robustness is determined by systematically 'knocking out,' or disabling, ET transitions in kinetic models. Our classification of UCNP ET networks as complex systems explains why UCNP luminescence lifetimes do not match the intrinsic lifetimes of emitting states. In the future, UCNP networks may be engineered to rival the complexity of biological networks that pattern features with unmatched precision.
关键词： complex systems,energy transfer,upconverting nanoparticles,lanthanide dopants,power dependence,luminescence lifetimes
更新于2025-09-19 17:15:36
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Four-Dimensional Coherent Spectroscopy of Complex Molecular Systems in Solution
摘要： An understanding of microscopic interactions in solution is of fundamental importance in chemistry. However, the structure and dynamics of complex systems in the condensed phase, especially far from thermal equilibrium, are masked by broad and often featureless absorption and emission spectra. Nonlinear optical spectroscopy has proven to be a powerful and general approach to disentangling congested spectra by spreading information across multiple dimensions, revealing features oftentimes hidden in lower-order projections. As the dimensionality of the measurement increases, the better the microscopic interactions are revealed as spectral bands disperse in the large hyper-spectral volume. This capability, however, comes at a steep price as the signal decreases exponentially at higher orders of optical response and added experimental complexity increases noise. Here, we discuss a four-dimensional coherent spectroscopy known as Gradient Assisted Multidimensional Electronic–Raman Spectroscopy (GAMERS) that reveals coupling between electronic and vibrational transitions in complex, condensed phase systems ranging from organic molecules to semiconductor nanocrystals. We reveal that high-resolution spectra may be extracted from these systems even in the presence of severe spectral broadening, both homogeneous and inhomogeneous in origin. The theoretical and experimental underpinnings of this method are discussed. Increasingly, higher-order and higher-dimensionality spectroscopies like GAMERS are needed to understand the microscopic interactions that connect structure to dynamics to function.
关键词： condensed phase,GAMERS,complex systems,electronic and vibrational transitions,Nonlinear optical spectroscopy
更新于2025-09-10 09:29:36