Properly interpreting lidar (light detection and ranging) signal for characterizing particle distribution relies on a key parameter,
We derived the angular response function (
- NSF-PAR ID:
- 10308252
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Applied Optics
- Volume:
- 60
- Issue:
- 28
- ISSN:
- 1559-128X; APOPAI
- Page Range / eLocation ID:
- Article No. 8676
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
, which relates the particulate volume scattering function (VSF) at 180° ( ) that a lidar measures to the particulate backscattering coefficient ( ). However, has been seldom studied due to challenges in accurately measuring and concurrently in the field. In this study, , as well as its spectral dependence, was re-examined using the VSFs measured in situ at high angular resolution in a wide range of waters., while not measured directly, was inferred using a physically sound, well-validated VSF-inversion method. The effects of particle shape and internal structure on the inversion were tested using three inversion kernels consisting of phase functions computed for particles that are assumed as homogenous sphere, homogenous asymmetric hexahedra, or coated sphere. The reconstructed VSFs using any of the three kernels agreed well with the measured VSFs with a mean percentage difference at scattering angles . At angles immediately near or equal to 180°, the reconstructed depends strongly on the inversion kernel. derived with the sphere kernels was smaller than those derived with the hexahedra kernel but consistent with estimated directly from high-spectral-resolution lidar and in situ backscattering sensor. The possible explanation was that the sphere kernels are able to capture the backscattering enhancement feature near 180° that has been observed for marine particles.derived using the coated sphere kernel was generally lower than those derived with the homogenous sphere kernel. Our result suggests that is sensitive to the shape and internal structure of particles and significant error could be induced if a fixed value of is to be used to interpret lidar signal collected in different waters. On the other hand, showed little spectral dependence. -
Volume scattering functions were measured using two instruments in waters near the Ocean Station Papa (50°N 145°W) and show consistency in estimating the
factor attributable to particles ( ). While in the study area exhibits a limited variability, it could vary significantly when compared with data obtained in various parts of the global oceans. The global comparison also confirms that the minimal variation of is at scattering angles near 120°. With an uncertainty of , can be assumed as spectrally independent. For backscatter sensors with wide field of view (FOV), the averaging of scattering within the FOV reduces the values of needed to compute the backscattering coefficient by up to 20% at angles . -
Cross-platform observing systems are requisite to capturing the temporal and spatial dynamics of particles in the ocean. We present simultaneous observations of bulk optical properties, including the particulate beam attenuation (
) and backscattering ( ) coefficients, and particle size distributions collected in the North Pacific Subtropical Gyre. Clear and coherent diel cycles are observed in all bulk and size-fractionated optical proxies for particle biomass. We show evidence linking diurnal increases in and to daytime particle growth and division of cells, with particles driving the daily cycle of particle production and loss within the mixed layer. Flow cytometry data reveal the nitrogen-fixing cyanobacterium Crocosphaera () to be an important driver of at the time of sampling, whereas Prochlorococcus dynamics () were essential to reproducing temporal variability in . This study is a step towards improved characterization of the particle size range represented by in situ bulk optical properties and a better understanding of the mechanisms that drive variability in particle production in the oligotrophic open ocean. -
Light carries both spin angular momentum (SAM) and orbital angular momentum (OAM), which can be used as potential degrees of freedom for quantum information processing. Quantum emitters are ideal candidates towards on-chip control and manipulation of the full SAM–OAM state space. Here, we show coupling of a spin-polarized quantum emitter in a monolayer
with the whispering gallery mode of a ring resonator. The cavity mode carries a transverse SAM of in the evanescent regions, with the sign depending on the orbital power flow direction of the light. By tailoring the cavity–emitter interaction, we couple the intrinsic spin state of the quantum emitter to the SAM and propagation direction of the cavity mode, which leads to spin–orbit locking and subsequent chiral single-photon emission. Furthermore, by engineering how light is scattered from the WGM, we create a high-order Bessel beam which opens up the possibility to generate optical vortex carrying OAM states. -
The use of multispectral geostationary satellites to study aquatic ecosystems improves the temporal frequency of observations and mitigates cloud obstruction, but no operational capability presently exists for the coastal and inland waters of the United States. The Advanced Baseline Imager (ABI) on the current iteration of the Geostationary Operational Environmental Satellites, termed the
Series (GOES-R), however, provides sub-hourly imagery and the opportunity to overcome this deficit and to leverage a large repository of existing GOES-R aquatic observations. The fulfillment of this opportunity is assessed herein using a spectrally simplified, two-channel aquatic algorithm consistent with ABI wave bands to estimate the diffuse attenuation coefficient for photosynthetically available radiation, . First, an in situ ABI dataset was synthesized using a globally representative dataset of above- and in-water radiometric data products. Values ofwere estimated by fitting the ratio of the shortest and longest visible wave bands from the in situ ABI dataset to coincident,in situ data products. The algorithm was evaluated based on an iterative cross-validation analysis in which 80% of the dataset was randomly partitioned for fitting and the remaining 20% was used for validation. The iteration producing the median coefficient of determination ( ) value (0.88) resulted in a root mean square difference of , or 8.5% of the range in the validation dataset. Second, coincident mid-day images of central and southern California from ABI and from the Moderate Resolution Imaging Spectroradiometer (MODIS) were compared using Google Earth Engine (GEE). GEE default ABI reflectance values were adjusted based on a near infrared signal. Matchups between the ABI and MODIS imagery indicated similar spatial variability ( ) between ABI adjusted blue-to-red reflectance ratio values and MODIS default diffuse attenuation coefficient for spectral downward irradiance at 490 nm, , values. This work demonstrates that if an operational capability to provide ABI aquatic data products was realized, the spectral configuration of ABI would potentially support a sub-hourly, visible aquatic data product that is applicable to water-mass tracing and physical oceanography research.