Search

Presents a letter to the editor in response to Chou and Lindzen's claim that the long-term Earth Radiation Budget Satellite (ERBS) nonscanner measurements reflect a negative feedback between top of the atmosphere radiation and surface temperature.

An approach is developed to infer the optical thickness of semitransparent ice clouds (when optical thickness is less than 5) from Atmospheric Infrared Sounder (AIRS) high spectral resolution radiances. A fast cloud radiance model is developed and coupled with an AIRS clear-sky radiative transfer model for simulating AIRS radiances when ice clouds are present. Compared with more accurate calculations based on the discrete ordinates radiative transfer model, the accuracy of the fast cloud radiance model is within 0.5 K (root mean square) in terms of brightness temperature (BT) and runs three orders of magnitude faster. We investigate the sensitivity of AIRS spectral BTs and brightness temperature difference (BTD) values between pairs of wavenumbers to the cloud optical thickness. The spectral BTs for the atmospheric window channels within the region 1070-1135 cm-1 are sensitive to the ice cloud optical thickness, as is the BTD between 900.562 cm-1 (located in an atmospheric window) and 1558.692 cm-1 (located in a strong water vapor absorption band). Similarly, the BTD between a moderate absorption channel (1587.495 cm-1) and the strong water absorption channel (1558.692 cm-1) is sensitive to ice cloud optical thickness. Neither of the aforementioned BTDs is sensitive to the effective particle size. Thus, the optical thickness of semitransparent ice clouds can be retrieved reliably. We have developed a spectrum-based approach and a BTD-based method to retrieve the optical thickness of semitransparent ice clouds. The present retrieval methods are applied to a granule of AIRS data. The ice cloud optical thicknesses derived from the AIRS measurements are compared with those retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) 1.38- and 0.645-μm bands. The optical thicknesses inferred from the MODIS measurements are collocated and degraded to the AIRS spatial resolution. Results from the MODIS and AIRS retrievals are in reasonable agreement over a wide range of optical thicknesses. [ABSTRACT FROM AUTHOR]

Recent studies of the Earth Radiation Budget Satellite (ERBS) nonscanner radiation data indicate decadal changes in tropical cloudiness and unexpected radiative anomalies between the 1980s and 1990s. In this study, the ERBS decadal observations are compared with the predictions of the Iris hypothesis using 3.5-box model. To further understand the predictions, the tropical radiative properties observed from recent Clouds and the Earth's Radiant Energy System (CERES) radiation budget experiment [the NASA Langley Research Center (LaRC) parameters] are used to replace the modeled values in the Iris hypothesis. The predicted variations of the radiation fields strongly depend on the relationship (-22% K[sup -1] ) of tropical high cloud and sea surface temperature (SST) assumed by the Iris hypothesis. On the decadal time scale, the predicted tropical mean radiative flux anomalies are generally significantly different from those of the ERBS measurements, suggesting that the decadal ERBS nonscanner radiative energy budget measurements do not support the strong negative feedback of the Iris effect. Poor agreements between the satellite data and model predictions even when the tropical radiative properties from CERES observations (LaRC parameters) are used imply that besides the Iris-modeled tropical radiative properties, the unrealistic variations of tropical high cloud generated from the detrainment of deep convection with SST assumed by the Iris hypothesis are likely to be another major factor for causing the deviation between the predictions and observations. [ABSTRACT FROM AUTHOR]

This study aims to model the effects of multiple laser peening (LP) on the mechanical properties of AA2024-T351 by including the material microstructure and residual stresses using the crystal plasticity finite element method (CPFEM). In this approach, the LP-induced compressive residual stress distribution is modeled through the insertion of the Eigenstrains as a function of depth, which is calibrated by the X-ray measured residual stresses. The simulated enhancement in the tensile properties after LP, caused by the formation of a near-surface work-hardened layer, fits the experimentally obtained tensile curves. The model calculated fatigue indicator parameters (FIPs) under the following cyclic loading application show a decrease in the near-surface driving forces for the crystal slip deformation after the insertion of the Eigenstrains. This leads to a higher high cycle fatigue (HCF) resistance and the possible transformation of sensitive locations for fatigue failure further to the depth after LP. Experimental observations on the enhancement in the HCF life, along with the relocation of fatigue crack nucleation sites further to the depth, reveal the improvement in the HCF properties due to the LP process and validate the numerical approach. [ABSTRACT FROM AUTHOR]

A significant fraction of liquid clouds are not captured in existing CloudSat radar-based products because the clouds are masked by surface clutter or have insufficient reflectivities. To account for these missing clouds, we train a random forest regression model to predict cloud optical depth and cloud top effective radius from other CloudSat and CALIPSO observables that do not include the radar reflectivity profile. By assuming a subadiabatic cloud model, we are then able to retrieve a vertical profile of cloud microphysical properties for all liquid-phase oceanic clouds that are detected by CALIPSO's lidar but missed by CloudSat's radar. Daytime estimates of cloud optical depth, cloud top effective radius, and cloud liquid water path are robustly correlated with coincident estimates from the MODIS instrument onboard the Aqua satellite. This new algorithm offers a promising path forward for estimating the water contents of thin liquid clouds observed by CloudSat and CALIPSO at night, when MODIS observations that rely upon reflected sunlight are not available. [ABSTRACT FROM AUTHOR]

The modeling of laser-induced forward transfer process (LIFT) is helpful to understand and optimize its complex transfer process. In this work, a coupling model is developed to investigate the dynamic response of a thin polymer layer used as the release layer in the blister-actuated LIFT. In this model, the vapor pressure generated by nanosecond laser irradiation is computed through coupling with the transient vapor volume obtained from different step durations to simulate the dynamic blister formation. And the model is validated by experiments on polyimide film irradiated with different laser fluences, which is found to be capable of providing a consistent prediction of blister profiles under several laser conditions. The calibrated energy conversion ratios imply that laser pulse energy is mainly allocated for the heating and vaporizing of polymers, but increasing laser fluence can make this expense gradually saturated to allow more pulse energy to increase the vapor pressure. Transient pressure development from the coupling model is observed to increase rapidly within the pulse duration, but then to decrease because of vapor expansion. Forward velocity in axial direction is also observed to increase with laser fluence. The maximum velocity is possible to exceed the sound velocity under a high laser fluence. And the thin polymer layer is more preferred to obtain a high transfer velocity. [ABSTRACT FROM AUTHOR]

In order to investigate the hydrogen permeation behavior of 316L stainless steel during the microstructural evolution induced by laser peening (LP), an electrochemical hydrogen charging system for initial hydrogen charging of LPed and non-LPed specimen was developed. Afterward, the microhardness, residual stress, and microstructures of the samples were determined and analyzed. Finally, electrochemical hydrogen permeation experiments were undertaken to verify LP’s influence on hydrogen permeation parameters of 316L. The results showed that LP reduced the hydrogen-induced hardening rate of the alloy and additionally invoked high magnitude compressive residual stress on its surface. At the layer close to the face of the specimen, the grain refinement rate was as high as 56.18%, which was accompanied by the appearance of high-density dislocations. Compared with the non-LPed sample, the hydrogen permeation time increased significantly, and the saturation current density in steady state hydrogen permeation also decreased gradually. [ABSTRACT FROM AUTHOR]

Multi-angle polarimeters (MAP) are powerful instruments to perform remote sensing of the environment. Joint retrieval algorithms of aerosols and ocean color have been developed to extract the rich information content of MAPs. These are optimization algorithms that fit the sensor measurements with forward models, which include radiative transfer simulations of the coupled atmosphere and ocean systems (CAOS) based on adjustable atmosphere and ocean properties. The forward model consists of sub-models to represent the optics of the atmosphere, ocean water surface, and ocean body. The representativeness of these models for observed scenes is important for retrieval success. In this study, we have evaluated the impact on MAP retrieval accuracy of three different ocean bio-optical models with 1, 3, and 7 optimization parameters that represent the spectral variation of inherent optical properties (IOP(λ)s) of the water body. The Multi-Angular Polarimetric Ocean coLor (MAPOL) joint retrieval algorithm was used to process data from the airborne Research Scanning Polarimeter (RSP) instrument acquired in different field campaigns. We performed ensemble retrievals along three RSP legs to evaluate the applicability of bio-optical models along geographically varying waters. The average differences between the MAPOL aerosol optical depth (AOD) and spectral remote sensing reflectance (Rrs(λ)) retrievals and the MODerate resolution Imaging Spectroradiometer (MODIS) products are also reported. We studied the distribution of retrieval cost function values obtained for the ensemble retrievals using the 3 bio-optical models under clear to highly turbid waters. For the 1-parameter model, retrieval cost function values show narrow distributions over any type of water, regardless of the cost function values, whereas for the 3 and 7- parameter models, the retrieval cost function distribution is water type dependent, showing the widest distribution over clear, open waters. We observed that the 3 and 7-parameter models have similar MAP retrieval performances relative to the 1- parameter model.We also demonstrated that the 3 and 7-parameter bio-optical models can be used to accurately represent both clear, open, and turbid, coastal waters, whereas the 1-parameter model is most successful over extremely clear waters. Given the computational efficiency requirements, we recommend the 3-parameter bio-optical model as the coastal water bio-optical model for future MAPOL studies. This study guides MAP algorithm development for current and future satellite missions such as NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission and ESA's Meteorological Operational-Second Generation (MetOp-SG) mission. [ABSTRACT FROM AUTHOR]

Multi-angle polarimetric (MAP) measurements can enable detailed characterization of aerosol microphysical and optical properties and improve atmospheric correction in ocean color remote sensing. Advanced retrieval algorithms have been developed to obtain multiple geophysical parameters in the atmosphere-ocean system. Theoretical pixel-wise retrieval uncertainties based on error propagation have been used to quantify retrieval performance and determine the quality of data products. However, standard error propagation techniques in high-dimensional retrievals may not always represent true retrieval errors well due to issues such as local minima and nonlinearity of radiative transfer near the solution. In this work, we analyze these theoretical uncertainty estimates and validate them using a flexible Monte Carlo approach. The Fast Multi-Angular Polarimetric Ocean coLor (FastMAPOL) retrieval algorithm, based on several neural network forward models, is used to conduct the retrievals and uncertainty quantification on both synthetic HARP2 (Hyper-Angular Rainbow Polarimeter 2) and AirHARP (airborne version of HARP2) datasets. In addition, for practical application of the technique to uncertainty evaluation in operational data processing, we use the automatic differentiation method to calculate derivatives analytically based on the neural network models. Both the speed and accuracy associated with uncertainty quantification for MAP retrievals are addressed in this study. Pixel-wise retrieval uncertainties are further evaluated for the real AirHARP field campaign data. The uncertainty quantification methods and results can be used to evaluate the quality of data products, and guide MAP algorithm development for current and future satellite systems such as NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission. [ABSTRACT FROM AUTHOR]

NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, scheduled for launch in the timeframe of 2023, will carry a hyperspectral scanning radiometer named the Ocean Color Instrument (OCI) and two Multi-Angle Polarimeters (MAP): the UMBC Hyper-Angular Rainbow Polarimeter (HARP2) and the SRON Spectro-Polarimeter for Planetary EXploration one (SPEXone). The MAP measurements contain rich information on the microphysical properties of aerosols and hydrosols, and therefore can be used to retrieve accurate aerosol properties for complex atmosphere and ocean systems. Most polarimetric aerosol retrieval algorithms utilize vector radiative transfer models iteratively in an optimization approach, which leads to high computational costs that limit their usage in the operational processing of large data volumes acquired by the MAP imagers. In this work, we propose a deep neural network (NN) model to represent the radiative transfer simulation of coupled atmosphere and ocean systems, for applications to the HARP2 instrument and its predecessors. Through the evaluation of synthetic datasets for AirHARP (airborne version of HARP2), the NN model achieves a numerical accuracy smaller than the instrument uncertainties, with a running time of 0.01s in a single CPU core or 1 ms in GPU. Using the NN as a forward model, we built an efficient joint aerosol and ocean color retrieval algorithm called FastMAPOL, evolved from the well-validated Multi-Angular Polarimetric Ocean coLor (MAPOL) algorithm. Retrievals of aerosol properties and water leaving signals were conducted on both the synthetic data and the AirHARP field measurements from the Aerosol Characterization from Polarimeter and Lidar (ACEPOL) campaign in 2017. From the validation with the synthetic data and the collocated High Spectral Resolution Lidar (HSRL) aerosol products, we demonstrated that the aerosol microphysical properties and water leaving signals can be retrieved efficiently and within acceptable error. The FastMAPOL algorithm can be used to operationally process the large volume of polarimetric data acquired by PACE and other future Earth observing satellite missions with similar capabilities. [ABSTRACT FROM AUTHOR]