| 1. |
- Gao, Yanhong, et al.
(författare)
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Comparison between past and future extreme precipitations simulated by global and regional climate models over the Tibetan Plateau
- 2018
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 38:3, s. 1285-1297
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Tidskriftsartikel (refereegranskat)abstract
- Past studies on regional climate change over the Tibetan Plateau (TP) have mainly looked at changes in the mean climate. This study focuses on past and future extreme precipitations, simulated by global and regional climate models over the TP. To assess the influence of large-scale forcing on dynamic downscaling using Weather Research and Forecasting (WRF) model, downscaling results for the historical period (1980–2005) with ERA-Interim reanalysis and CCSM4 as forcings are evaluated against a gridded observational data set. These are inter-compared before future projections for the period 2005–2100 under two scenarios (RCP4.5 and RCP8.5). The followings are obtained: (1) the reanalysis greatly overestimates not only the mean, but also extreme precipitation. The overestimation in CCSM4 is even larger than that of the reanalysis. (2) The two downscalings outperform their forcings, reflected by reduced overestimation for extreme precipitation frequency, increased spatial pattern correlations and more accurate linear trends, especially for the downscaling driven by CCSM. This demonstrates the constraining power of the fine-scale modelling and the importance of more realistic representations of surface forcing and related processes in the TP. (3) CCSM4 projects a general wetting across the whole TP with increases of heavy precipitation as well as the wetting intensification with warming. WRF also projects an overall wetting, but the wetting is less sensitive to the warming and there is more of an increase in light precipitation frequency. More importantly, a diverse pattern with wetting in the north and drying in the south is found in the dynamical downscaling in contrast to the uniform wetting in its forcing.
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| 2. |
- Wang, Wei, et al.
(författare)
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Enhanced edge detection for polarimetric SAR images using a directional span-driven adaptive window
- 2018
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Ingår i: International Journal of Remote Sensing. - : TAYLOR & FRANCIS LTD. - 0143-1161 .- 1366-5901. ; 39:19, s. 6340-6357
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Tidskriftsartikel (refereegranskat)abstract
- Automatic edge detection for polarimetric synthetic aperture radar (PolSAR) images plays a fundamental role in various PolSAR applications. The classic methods apply the fixed-shape windows to detect the edges, whereas their performance is limited in heterogeneous areas. This article presents an enhanced edge detection method for PolSAR data based on the directional span-driven adaptive (DSDA) window. The DSDA window has variable sizes and flexible shapes, and is constructed by adaptively selecting samples that follow the same statistical distribution. Therefore, it can overcome the limitation of classic fixed-shape windows. To obtain refined and reliable edge detection results in heterogeneous urban areas, we adopt the spherically invariant random vector (SIRV) product model since the complex Wishart distribution is often not met. In addition, a span ratio is combined with the SIRV distance to highlight the dissimilarity measure and to improve the robustness of the proposed method. The simulated PolSAR data and three real data sets from experimental synthetic aperture radar, electromagnetics institute synthetic aperture radar, and Radarsat-2 systems are used to validate the performance of the enhanced edge detector. Both quantitative evaluation and visual presentation of the results demonstrate the effectiveness of the proposed method and its superiority over the classic edge detectors.
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