Gregory L. Schuster

AERONET-OC: a Network for the Validation of Ocean Color Primary Products

Abstract The ocean color component of the Aerosol Robotic Network (AERONET-OC) has been implemented to support long-term satellite ocean color investigations through cross-site consistent and accurate measurements collected by autonomous radiometer systems deployed on offshore fixed platforms. The AERONET-OC data products are the normalized water-leaving radiances determined at various center wavelengths in the visible and near-infrared spectral regions. These data complement atmospheric AERONET aerosol products, such as optical thickness, size distribution, single scattering albedo, and phase function. This work describes in detail this new AERONET component and its specific elements including measurement method, instrument calibration, processing scheme, quality assurance, uncertainties, data archive, and products accessibility. Additionally, the atmospheric and bio-optical features of the sites currently included in AERONET-OC are briefly summarized. After illustrating the application of AERONET-OC dat...

A network for standardized ocean color validation measurements

The Aerosol Robotic Network (AERONET), originally developed to evaluate aerosol optical properties and validate satellite retrievals of those properties at various scales with measurements from worldwidedistributed autonomous Sun photometers [Holben et al., 1998],since January 2006 has been extended to support marine remote sensing and monitoring applications. This new network component, called AERONETOcean Color (AERONET-OC), provides the additional capability of measuring the radiance emerging from the sea—the ‘water-leaving radiance’—with modified Sun photometers installed on offshore platforms such as lighthouses, oceanographic towers, and derricks. AERONET-OC is proving to be instrumental in supporting satellite ocean color validation activities through standardized measurements performed at different sites with identical measuring systems and protocols, calibrated using a single reference source and method, and processed with the same code. Recent investigations [Zibordi et al., 2006] suggest that in order to generate accurate climate data records from remote sensing data, time series of in situ measurements from a cadre of AERONET-OC sites could play a major role in the assessment and merging of radiometric products from different ocean color missions.

A multiparameter aerosol classification method and its application to retrievals from spaceborne polarimetry

Classifying observed aerosols into types (e.g., urban-industrial, biomass burning, mineral dust, maritime) helps to understand aerosol sources, transformations, effects, and feedback mechanisms; to improve accuracy of satellite retrievals; and to quantify aerosol radiative impacts on climate. The number of aerosol parameters retrieved from spaceborne sensors has been growing, from the initial aerosol optical depth (AOD) at one or a few wavelengths to a list that now includes AOD, complex refractive index, single scattering albedo (SSA), and depolarization of backscatter, each at several wavelengths, plus several particle size and shape parameters. Making optimal use of these varied data products requires objective, multidimensional analysis methods. We describe such a method, which makes explicit use of uncertainties in input parameters. It treats an N-parameter retrieved data point and its N-dimensional uncertainty as an extended data point, E. It then uses a modified Mahalanobis distance, DEC, to assign an observation to the class (cluster) C that has minimum DEC from the point. We use parameters retrieved from the Aerosol Robotic Network (AERONET) to define seven prespecified clusters (pure dust, polluted dust, urban-industrial/developed economy, urban-industrial/developing economy, dark biomass smoke, light biomass smoke, and pure marine), and we demonstrate application of the method to a 5 year record of retrievals from the spaceborne Polarization and Directionality of the Earths Reflectances 3 (POLDER 3) polarimeter over the island of Crete, Greece. Results show changes of aerosol type at this location in the eastern Mediterranean Sea, which is influenced by a wide variety of aerosol sources.

Coherent beam combining: optical loss effects on power scaling

A model for a coherent array of amplifiers that has multiple stages and uses pairwise beam combining at the final stage has been developed. The model accounts for gain saturation of the individual amplifier elements, optical-coupling losses, and coherent-combining efficiency. The individual amplifier parameters are derived from experimental data. System size, efficiency, and output power are calculated as functions of optical-coupling efficiency and combining efficiency. Because of the exponential losses associated with pairwise beam combining, the coherent-combining losses are the dominant contribution to system efficiency reduction and increased system size.

High-power and high-spatial-coherence broad-area power amplifier

A broad-area AlGaAs amplifier operating cw has delivered 425 mW of total power with 342 mW in a single lobe diverging at 1.02x the diffraction limit (FWHM 0.483 degrees , 87.4-microm actual aperture) for a master oscillator input power of 70 mW. The spatial coherence of the amplifier output is 0.97, and the mutual spatial coherence between the oscillator and amplifier is 0.96.

Estimation of global black carbon direct radiative forcing and its uncertainty constrained by observations

Black carbon (BC) contributes to global warming by absorbing sunlight. However, the size of this contribution, namely, the direct radiative forcing (RF), ranges from +0.1 to +1.0 W m A2 , largely due to differences between bottom-up and observation-based estimates. Current global models systematically underestimate BC radiation absorption relative to observations, which is often attributed to the underestimation of BC emissions. Several studies that adjusted emissions to correct biases of global aerosol models resulted in a revised upward estimate of the BC RF. However, the BC RF was never optimized against observations in a rigorous mathematical manner. Here we simulated the absorption of solar radiation by BC from all sources at the 10 km resolution by combining a highly disaggregated emission inventory with a nested aerosol climate model and a downscaling method. As a result, the normalized mean bias in BC radiation absorption was reduced from A56% to A5% in Asia and from A71% to A46% elsewhere. We applied a Bayesian method that makes the best account of all model, representativeness, and observational uncertainties to estimate the BC RF and its uncertainty. Using the new emission inventory and high-resolution model reduces uncertainty in BC RF from A109%/+172% to A77%/+78% over Asia and from A83%/+114% to A64%/+70% over other continental regions. Finally, we derived an observationally constrained BC RF of 0.53 Wm A2 (0.14 to 1.19 as 90% confidence) as our best estimate, less than previous estimates. Our estimate implies that reduction in BC emissions would contribute to slow down global warming, but the contribution could be less than previously thought.

Coherent summation of saturated AlGaAs amplifiers.

Coherent summation of the output of two saturated traveling-wave amplifiers, each injected from a common semiconductor laser and all operated cw, has resulted in a single diffraction-limited beam containing 93% of the power originally contained in the two individual amplified beams. The 372 mW of power in a single diffraction-limited lobe is a 1.5-fold enhancement over the power available from a single amplifier.

OFFSHORE RADIATION OBSERVATIONS FOR CLIMATE RESEARCH AT THE CERES OCEAN VALIDATION EXPERIMENT A New "Laboratory" for Retrieval Algorithm Testing

Abstract When radiometers on satellites point toward Earth with the goal of sensing an important variable quantitatively, rather than just creating a pleasing image, the task at hand is often not simple. The electromagnetic energy detected by the radiometers is a puzzle of various signals; it must be solved to quantify the specific physical variable. This task, called the retrieval or remote-sensing process, is important to most satellite-based observation programs. It would be ideal to test the algorithms for retrieval processes in a sealed laboratory, where all the relevant parameters could be easily measured. The size and complexity of the Earth make this impractical. NASAs Clouds and the Earths Radiant Energy System (CERES) project has done the next-best thing by developing a long-term radiation observation site over the ocean. The relatively low and homogeneous surface albedo of the ocean make this type of site a simpler environment for observing and validating radiation parameters from satellite-b...

Aerosol Absorption: Progress Towards Global and Regional Constraints

Purpose of ReviewSome aerosols absorb solar radiation, altering cloud properties, atmospheric stability and circulation dynamics, and the water cycle. Here we review recent progress towards global and regional constraints on aerosol absorption from observations and modeling, considering physical properties and combined approaches crucial for understanding the total (natural and anthropogenic) influences of aerosols on the climate.Recent FindingsWe emphasize developments in black carbon absorption alteration due to coating and ageing, brown carbon characterization, dust composition, absorbing aerosol above cloud, source modeling and size distributions, and validation of high-resolution modeling against a range of observations.SummaryBoth observations and modeling of total aerosol absorption, absorbing aerosol optical depths and single scattering albedo, as well as the vertical distribution of atmospheric absorption, still suffer from uncertainties and unknowns significant for climate applications. We offer a roadmap of developments needed to bring the field substantially forward.

Spatial Representativeness Error in the Ground‐Level Observation Networks for Black Carbon Radiation Absorption

Abstract There is high uncertainty in the direct radiative forcing of black carbon (BC), an aerosol that strongly absorbs solar radiation. The observation‐constrained estimate, which is several times larger than the bottom‐up estimate, is influenced by the spatial representativeness error due to the mesoscale inhomogeneity of the aerosol fields and the relatively low resolution of global chemistry‐transport models. Here we evaluated the spatial representativeness error for two widely used observational networks (AErosol RObotic NETwork and Global Atmosphere Watch) by downscaling the geospatial grid in a global model of BC aerosol absorption optical depth to 0.1° × 0.1°. Comparing the models at a spatial resolution of 2° × 2° with BC aerosol absorption at AErosol RObotic NETwork sites (which are commonly located near emission hot spots) tends to cause a global spatial representativeness error of 30%, as a positive bias for the current top‐down estimate of global BC direct radiative forcing. By contrast, the global spatial representativeness error will be 7% for the Global Atmosphere Watch network, because the sites are located in such a way that there are almost an equal number of sites with positive or negative representativeness error.