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Advanced techniques of multi-temporal InSAR (MT-InSAR) represent a valuable tool in ground subsidence studies allowing remote investigation of the behavior of mass movements in long time intervals by using large datasets of SAR images covering the same area and acquired at different epochs. The settlement in Beijing is very serious, producing adverse environmental impacts. Excessive groundwater withdrawal is the most direct cause of land subsidence.In this paper, a spatial-temporal analysis of the land subsidence in Beijing was performed using one of the MT-InSAR techniques, referred to as Small Baseline Subset (SBAS). This technique allows monitoring the temporal evolution of a deformation phenomenon, via the generation of mean deformation velocity maps and displacement time series from a data set of acquired SAR images. 52 C-band ENVISAT ASAR images acquired from June 2003 to August 2010 were used to produce a linear deformation rate map and to derive time series of ground deformation. The results show that there are three large subsidence funnels within this study area, which separately located in Balizhuang-Dajiaoting in Chaoyang district, Wangjing-Laiguangying Chaoyang district, Gaoliying Shunyi district. The maximum settlement center is Wangsiying-Tongzhou along the Beijing express; the subsidence velocity exceeds 110 mm/y in the LOS direction. In particular, we compared the achieved results with leveling measurements that are assumed as reference. The estimated long-term subsidence results obtained by SBAS approach agree well with the development of the over-exploitation of ground water, indicating that SBAS techniques is adequate for the retrieval of land subsidence in Beijing from multi-temporal SAR data. [ABSTRACT FROM AUTHOR]

Advanced techniques of multi-temporal InSAR (MT-InSAR) represent a valuable tool in ground subsidence studies allowing remote investigation of the behavior of mass movements in long time intervals by using large datasets of SAR images covering the same area and acquired at different epochs. The settlement in Beijing is very serious, producing adverse environmental impacts. Excessive groundwater withdrawal is the most direct cause of land subsidence.In this paper, a spatial-temporal analysis of the land subsidence in Beijing was performed using one of the MT-InSAR techniques, referred to as Small Baseline Subset (SBAS). This technique allows monitoring the temporal evolution of a deformation phenomenon, via the generation of mean deformation velocity maps and displacement time series from a data set of acquired SAR images. 52 C-band ENVISAT ASAR images acquired from June 2003 to August 2010 were used to produce a linear deformation rate map and to derive time series of ground deformation. The results show that there are three large subsidence funnels within this study area, which separately located in Balizhuang-Dajiaoting in Chaoyang district, Wangjing-Laiguangying Chaoyang district, Gaoliying Shunyi district. The maximum settlement center is Wangsiying-Tongzhou along the Beijing express; the subsidence velocity exceeds 110 mm/y in the LOS direction. In particular, we compared the achieved results with leveling measurements that are assumed as reference. The estimated long-term subsidence results obtained by SBAS approach agree well with the development of the over-exploitation of ground water, indicating that SBAS techniques is adequate for the retrieval of land subsidence in Beijing from multi-temporal SAR data. [ABSTRACT FROM AUTHOR]

The variation characteristics of Ultraviolet-B (UVB; 280-315 nm) radiation over Beijing were explored using measured data that were collected in Beijing from November 2010 to October 2011. Seasonal variations in UVB radiation and influence of ozone and clearness index on the ratio of UVB to broadband solar radiation ( G) were investigated. The annual value of UVB radiation in Beijing is 6.37 MJ m−2, and monthly average value ranges from 4.96 to 28.37 kJ m−2 d−1. The maximum daily total UVB radiation ranges from 6.55 kJ m−2 d−1 in November to 54.22 kJ m−2 d−1 in July. The monthly minimum of daily total UVB radiation varies from 0.5 kJ m−2 d−1 in February to 11.52 kJ m−2 d−1 in July. The monthly average of the ratio of UVB radiation to G ranges from 0.007 to 0.017%, with an annual average value of 0.012%. The variation in slant ozone column causes annual cycle of the ratio UVB radiation to G, with maximum value in summer. In addition, clouds have a greater effect on G than UVB radiation. Thus, the ratio increases by more than 17% when the atmospheric conditions change from clear to cloudy. [ABSTRACT FROM AUTHOR]

Four years measurements of broadband global solar radiation ( RS) and total ultraviolet (UV) radiation (the sum of UV-A and UV-B) were conducted from 2005 to 2008 in Beijing. These data were used to determine the temporal variability of UV/ RS and its dependence on water vapour content and clearness index. A simple, efficient and empirically derived all-weather model is proposed to estimate UV from RS. The estimated data were used to analyse the characteristics of long-term variations in UV radiation. Results revealed that annual mean UV was 0.37 ± 0.17 MJ m−2 d−1. The highest daily value of UV radiation was measured in May, while the lowest value occurred in December. The monthly mean value of UV / Rs gradually increased from 2.7% in November to 3.7% in August. The annual mean value of UV / Rs was 3.1%. The annual mean daily UV radiation during 1958–2005 was 0.46 MJ m−2 d−1. The interannual variations and long-term patterns of UV radiation derived from reconstructed daily UV values are compatible with changes in measured RS. Annual mean UV radiation levels decreased from the early 1960s to the late 1990s but began to increase in the late 1990s. Over the latter half of the 20th century, decrease in UV radiation was 0.018 MJ m−2 d−1 per decade. The decrease trends in long-term annual mean UV radiation of −0.026 MJ m−2 d−1 per year for 1958–1997 and −0.0024 MJ m−2 d−1 per year for 1958–2005. The decreasing trend in UV radiation was sharpest in spring and summer but more gradual in autumn and winter. [ABSTRACT FROM AUTHOR]