Surface Parameterization Schemes Research Articles

Evaluation of the MODIS Collection 6.1 3 km aerosol optical depth product over China

The Moderate Resolution Imaging Spectroradiometer (MODIS) 3 km aerosol product was released to resolve fine aerosol features and provide regional high-resolution aerosol distributions required by the air quality community. It has been publicly available since the Collection 6 (C6) release. In the Collection 6.1 (C6.1) release, a new surface parameterization scheme has been introduced to improve the accuracy of retrieved aerosol optical depth (AOD) over urban surfaces, whereas few detailed evaluations have been conducted. In the present study, we comprehensively evaluated the MODIS C6.1 3 km (C6.1_3km) AOD product over China for the 2001–2017 period. The C6.1_3km product was validated against Aerosol Robotic Network (AERONET) data and compared with the C6 3 km (C6_3km) and C6.1 10 km (C6.1_10km) products. The spatial averaging technique was used to generate MODIS-AERONET collocations for C6_3km and C6.1_3km, whereas the single pixel collocation technique was used for comparing the C6.1_3km and C6.1_10km retrievals. Different collocation techniques were used because we found that the single pixel collocation technique was more suitable for evaluating aerosol products of different spatial resolutions over urban areas. Results indicated that the C6.1_3km product outperformed the C6_3km product over urban areas because of the new C6.1 surface parameterization scheme, while the upstream changes implemented in C6.1 have minor effects on the improvement. The C6.1_3km product showed a similar performance as compared to the C6.1_10km product, which indicated that the C6.1 surface scheme originally designed on a 10 km scale performed equally well at the 3 km spatial resolution. However, the evaluation statistics also indicated that an overestimation of AOD values over urban areas still existed in the C6.1_3km aerosol product. Therefore, refinement of the DT algorithm is required to further improve the C6.1_3km product for air quality studies over urban areas in China.

Blind Robust 3-D Mesh Watermarking Based on Oblate Spheroidal Harmonics

In this paper, a novel transform-based, blind and robust 3-D mesh watermarking scheme is presented. The 3-D surface of the mesh is firstly divided into a number of discrete continuous regions, each of which is successively sampled and mapped onto oblate spheroids, using a novel surface parameterization scheme. The embedding is performed in the spheroidal harmonic coefficients of the spheroids, using a novel embedding scheme. Changes made to the transform domain are then reversed back to the spatial domain, thus forming the watermarked 3-D mesh. The embedding scheme presented herein resembles, in principal, the ones using the multiplicative embedding rule (inherently providing high imperceptibility). The watermark detection is blind and by far more powerful than the various correlators typically incorporated by multiplicative schemes. Experimental results have shown that the proposed blind watermarking scheme is competitively robust against similarity transformations, connectivity attacks, mesh simplification and refinement, unbalanced resampling, smoothing and noise addition, even when juxtaposed to the informed ones.

Numerical Investigations on the Influence of Subgrid-Scale Surface Heterogeneity on Evapotranspiration and Cloud Processes

Abstract Numerical experiments were performed with a meso-β-scale meteorological model to investigate the influence of subgrid-scale surface heterogeneity on the prediction of evapotranspiration, cloud, and precipitation formation. The results of simulations using different horizontal grid resolutions and assuming the dominant land-use type within a grid box as the representative surface type for the entire grid element am compared with those obtained from model runs considering subgrid-scale heterogeneity by separately determining the fluxes of the respective subgrid-scale land-use types. The same surface parameterization scheme was applied in both cases. All of these numerical experiments show that the surface characteristics and, hence, the subgrid-scale surface processes strongly affect the predicted microclimate close to the ground. Furthermore, the model results also provide evidence that in the case of applying dominant land-use types the grid resolution may strongly affect the calculated water and...