Urban Ground Surface Research Articles

Monitoring and Prediction of Ground Surface Settlement in Kunming Urban Area by Building GWO-LSTM Model Based on TS-InSAR

Long-term series monitoring of ground surface settlement by remote sensing has become an effective method. Based on TS-InSAR (time series Interferometric Synthetic Aperture Radar) interferometry, this paper proposes a new model based on the Grey Wolf Optimizer (GWO) and Long Short-Term Memory (LSTM) to monitor and predict the ground surface settlement in Kunming City. The results show that the MAPE (mean absolute percentage error), RMSE (root mean square error), and MAE (mean absolute error) of GWO-LSTM are significantly reduced. R2 (goodness of fit) in the six sub-study areas of Kunming City is improved in comparison to the LSTM model. The problem of manual parameter selection in the LSTM model is solved by the GWO algorithm to select parameters automatically. This approach not only significantly reduces the model’s training time but also identifies the most suitable network parameters. This can bring the best performance. Based on TS-InSAR data, the prediction of urban ground surface settlement by the GWO-LSTM model has good accuracy and robustness, which offers a scientific foundation for monitoring and issuing early warnings about urban land disasters.

Evaluating the impacts of three-dimensional building morphology on urban near-surface energy fluxes: A case study in Beijing, China

Large-scale urbanization is associated with three-dimensional (3D) urban morphology variations worldwide. 3D building morphology alters the partitioning of urban near-surface energy fluxes and varies both temporally and spatially. Taking Beijing in China, as a case study, we modeled 64 scenarios to explore the relationships between 3D building morphology and urban ground-surface energy fluxes by adopting the ENVI-met model. We found that (1) the dimension of 3D fractal (3DF) significantly influences all the urban energy balance indicators. (2) Large values of 3DF cause decreases in the incoming shortwave radiation of 85.0 W/m2, 50.0 W/m2, 200.0 W/m2, and 125.0 W/m2 in summer, winter, summer daytime, and winter daytime, respectively. Correspondingly, the energy balance pattern varies with season and daytime/nighttime. (3) The explanatory power of 3DSI for the atmosphere–soil energy processes was weak and did not exceed 15 %. These findings can enhance our understanding of the effects of 3D building morphology on energy exchanges and provide information relevant to the management of 3D building morphology at a fine scale.

Numerical simulation of ground surface settlement of underpass building in tunnel boring machine double-line tunnels

Ground surface settlement under subway tunnel construction is one of the main sources of urban ground surface settlement, which may threaten the safety of existing buildings. Therefore, it is necessary to study the influence of subway tunnel construction on the safety and stability of surface subsidence. In the current study, the ground settlement originating from the operation of a tunnel-boring machine (TBM) while excavating a double-line tunnel that underpasses existing buildings is studied. To this end, numerical simulations were carried out and experimental data were analyzed. The boring parameters for the underpass interval section were derived by simulating the construction process and analyzing the TBM parameters in a real project. Then, the influence of thrust force, grouting pressure, and frictional force was considered on the surface settlement. For spatial locations between the existing buildings and the tunnel in the underpass area, the width of the ground surface settlement caused by different excavation sequences of the TBM two-line tunnel was analyzed. The obtained results demonstrate that the performed calculations are consistent with the monitoring data. It is found that the width and depth of the ground surface settlement trough are affected by the distance between the existing buildings and the TBM construction tunnel. However, the settlement location is independent of the excavated sequence but depends on the location of the TBM tunnel and the existing building.

Development and Evaluation of a New Urban Parameterization in the Weather Research and Forecasting (WRF) Model

AbstractIn mesoscale Weather Research and Forecasting (WRF) model, several urban‐modeling options exist, such as Single‐layer Urban Canopy Model, Building Effect Parameterization, and Building Energy Model. However, these models have limitations in terms of the choice of land surface models (LSMs) and planetary boundary layer (PBL) schemes, the associated computational expenses, and other constraints. Recently, Dy et al. (2019, https://doi.org/10.1029/2018JD029333) included the urban‐momentum drag effect for wind‐speed modeling by developing a new multilayer model based on a modified nonlocal Asymmetric Convective Model version‐2 (ACM2) PBL scheme. This urban‐based ACM2 (UACM) has demonstrated a significantly improved ability over the base‐ACM2 (BACM) to predict wind speed near the urban ground surface and shown an inflection point at roof level in the vertical profile of horizontal wind. In this study, urban thermal and moisture components are introduced into the Pleim‐Xiu (PX) LSM and coupled with UACM. The diurnal variation in street, walls, and roof‐surface temperatures is modeled using the two‐layer force‐restore algorithm. Simple radiation treatment is considered to account for shadowing on streets based on the solar zenith angle and building morphology. Heat and moisture flux evolution are considered explicitly on all urban surfaces. The advantages of this novel UACM are simple formulation, more efficient execution, and its requirement for only a few fundamental urban morphological parameters. The idealized and real urban data case WRF simulations are performed over the Pearl River Delta region in southern China to test the new UACM. The computationally efficient UACM is expected to perform faster for operational forecasting runs.

The influence of tree traits on urban ground surface shade cooling

The physical nature of the built urban environment gives rise to urban heat islands (UHI), making many cities frequently thermally uncomfortable in the summer, with potentially serious effects on human health. When climate change effects of higher summer temperatures and prolonged heatwaves are factored in, it is clear that adaptive measures are needed to ensure the liveability of cities. The shade provided by planting trees is one such adaptation measure. This study, in Bolzano, Italy, used a thermal camera to record the surface temperatures of three common urban surfaces – asphalt, porphyry, and grass – in the shade of 332 single tree crowns, of 85 different species, during the peak temperature period of summer days. By comparing with the temperature of adjacent unshaded ground, estimates of the degree of surface cooling were made. Measurements at three locations within the shadow revealed higher cooling in the centre and at the western edge. The cooling was related to a multitude of tree traits, of which Leaf Area Index estimate (LAIcept) and crown width were the most important. Median average cooling of 16.4, 12.9 and 8.5 °C was seen in the western edge of the tree shade for asphalt, porphyry and grass, respectively. Maximum temperatures were reduced by roughly 19 °C for all surface types. Coniferous trees were capable of providing high cooling, however, crown dimensions may limit the receiving surface area. Descriptive and predictive multiple linear regression models were able to predict cooling with some success from several of the predictor variables (LAIcept and gap fraction). Strategic planting of single trees in cities can have significant impacts on the absorption of solar radiation by ground surface materials thus reducing the heat storage that contributes to UHIs.

Urban Ground Surface Subsidence Monitoring Based on Time Series InSAR Technology

D-InSAR technology can measure the settlement of the surface millimeter level. Due to the influence of time and space loss coherence and atmospheric delay, its application in surface settlement monitoring is limited. As a D-InSAR technology innovation, SBAS can overcome the influence of related errors and make the results of interference processing more accurate. In the paper, Jiangjin District of Chongqing City was used as the experimental area. Using the radar image data of 23 scenes sentinel1, the short baseline set (SBAS) technology was used to obtain the range of surface subsidence and cumulative accumulation of time series in Jiangjin City. Provide reference for land and resources utilization and large-scale project construction.

Robust algorithm for detecting floodwater in urban areas using synthetic aperture radar images

Flooding is a major hazard in both rural and urban areas worldwide, but it is in urban areas that the impacts are most severe. High resolution Synthetic Aperture Radar (SAR) sensors are able to detect flood extents in urban areas during both day- and night-time. If obtained in near real-time, these flood extents can be used for emergency flood relief management or as observations for assimilation into flood forecasting models. In this paper a method for detecting flooding in urban areas using near real-time SAR data is developed and extensively tested under a variety of scenarios involving different flood events and different images. The method uses a SAR simulator in conjunction with LiDAR data of the urban area to predict areas of radar shadow and layover in the image caused by buildings and taller vegetation. Of the urban water pixels visible to the SAR, the flood detection accuracy averaged over the test examples was 83%, with a false alarm rate of 9%. The results indicate that flooding can be detected in the urban area to reasonable accuracy, but that this accuracy is limited partly by the SAR’s poor visibility of the urban ground surface due to shadow and layover.

Detection of flooded urban areas in high resolution Synthetic Aperture Radar images using double scattering

Flooding is a particular hazard in urban areas worldwide due to the increased risks to life and property in these regions. Synthetic Aperture Radar (SAR) sensors are often used to image flooding because of their all-weather day–night capability, and now possess sufficient resolution to image urban flooding. The flood extents extracted from the images may be used for flood relief management and improved urban flood inundation modelling.A difficulty with using SAR for urban flood detection is that, due to its side-looking nature, substantial areas of urban ground surface may not be visible to the SAR due to radar layover and shadow caused by buildings and taller vegetation. This paper investigates whether urban flooding can be detected in layover regions (where flooding may not normally be apparent) using double scattering between the (possibly flooded) ground surface and the walls of adjacent buildings. The method estimates double scattering strengths using a SAR image in conjunction with a high resolution LiDAR (Light Detection and Ranging) height map of the urban area. A SAR simulator is applied to the LiDAR data to generate maps of layover and shadow, and estimate the positions of double scattering curves in the SAR image.Observations of double scattering strengths were compared to the predictions from an electromagnetic scattering model, for both the case of a single image containing flooding, and a change detection case in which the flooded image was compared to an un-flooded image of the same area acquired with the same radar parameters. The method proved successful in detecting double scattering due to flooding in the single-image case, for which flooded double scattering curves were detected with 100% classification accuracy (albeit using a small sample set) and un-flooded curves with 91% classification accuracy. The same measures of success were achieved using change detection between flooded and un-flooded images. Depending on the particular flooding situation, the method could lead to improved detection of flooding in urban areas.

Impact of Gobi desert dust on aerosol chemistry of Xi'an, inland China during spring 2009: differences in composition and size distribution between the urban ground surface and the mountain atmosphere

Abstract. Composition and size distribution of atmospheric aerosols from Xi'an city (~400 m, altitude) in inland China during the spring of 2009 including a massive dust event on 24 April were measured and compared with a parallel measurement at the summit (2060 m, altitude) of Mt. Hua, an alpine site nearby Xi'an. EC (elemental carbon), OC (organic carbon) and major ions in the city were 2–22 times higher than those on the mountaintop during the whole sampling period. Compared to that in the non-dust period a sharp increase in OC was observed at both sites during the dust period, which was mainly caused by an input of biogenic organics from the Gobi desert. However, adsorption/heterogeneous reaction of gaseous organics with dust was another important source of OC in the urban, contributing 22% of OC in the dust event. In contrast to the mountain atmosphere where fine particles were less acidic when dust was present, the urban fine particles became more acidic in the dust event than in the non-dust event, mainly due to enhanced heterogeneous formation of nitrate and diluted NH3. Cl− and NO3− in the urban air during the dust event significantly shifted toward coarse particles. Such redistributions were further pronounced on the mountaintop when dust was present, resulting in both ions almost entirely staying in coarse particles. On the contrary, no significant spatial difference in size distribution of SO42− was found between the urban ground surface and the mountain atmosphere, which dominated in the fine mode (<2.1 μm) during the nonevent and comparably distributed in the fine (<2.1 μm) and coarse (>2.1 μm) modes during the dust event.

Some insight into the influence of urban ground surface properties on the air-surface exchange of total gaseous mercury

Abstract Experiments utilizing meteorologically normalized sampling conditions were used to illustrate the role and function of urban pavement, bare soil and turf grass surface properties with respect to the air-surface exchange of total gaseous Hg (TGM). After ensuring uniform meteorological effects to each surface, resultant TGM fluxes from turf grass, bare soil and pavement were specifically representative of their diverse physical and biogeochemical properties. Results spanning the entire sampling year show distinct TGM flux signatures for each surface (5.69 ± 5.79 (ng/m 2 h) for bare soil, 0.53 ± 1.25 for turf grass, 0.26 ± 0.41 for pavement). Based on medians, the surface limitations of pavement decreased TGM flux by a factor of 22 compared to bare soil and by a factor of 2 compared to turf grass. Turf surface limitations decreased TGM flux by a factor of 11 compared to bare soil. By comparing these results to a parallel study, meteorological effects were found to develop 24% of the TGM flux signature for pavement, 53% for turf and 60% for bare soil. The remaining percentage contributions to each TGM flux signature were from the cumulative surface property effects of each surface. These results suggest that the greater the TGM flux magnitude for a particular surface, the more measurements are needed under a wide variety of meteorological conditions to develop a broad understanding of its TGM flux characteristics. Seasonal observation allowed closer investigation of a large shift to TGM deposition for the turf surface during the fall season. The large shift toward deposition was suspected to be linked to the formation of a thatch layer on the unexposed soil surface just beneath the turf layer.

INFLUENCE OF URBANIZED ATMOSPHERE ON LONG-WAVE RADIATION FIELD AT NIGHT

In recent years, numerous climatological studies have been made on the basic parameters of urban heat island. However, these parameters of the actual energy exchange in urban environments are not sufficiently understood so far. Very few observations are, in particular, available for the long-wave radiation balance components in urban environments. Considering a long-wave radiation field as a model, it should be noted that radiatioe energy is basically redistributed on the ground-surface in the rural area, and in the urban area it is redistributed on the roof-level and the ground-surface. The urban roof-level is exposed to the additional long-wave radiation from the aerosol layer and the warm vertical temperature structure of urban atmosphere besides the background longwave radiation. The urban ground-surface is, moreover, under the influence of the screen effects due to buildings. This suggests that the restraint of radiatioe cooling resulting from the double screen effects on the urban ground-surface is one of the main causes of the urban heat island. The existence of the screen effects due to buildings on the urban ground-surface can be confirmed in the previous paper (Kobayashi, 1979). The purposes of this paper are to clarify the urban-rural differences for the long-wave radiation balance components on the roof-level, and to discuss the influence of urbanized atmosphere on the long-wave radiation field on the clear night. Observations were carried out on the roof-level in and around Tokyo on the clear nights of the winter from 1969 to 1970, when the heat island phenomena were developing well. The radiation sensors used in this experiment were polyethylene-shielded net radiometers (C. S. I. R. O., Net Radiometer Model CN-1 and CN-2). Downward long-wave radiation flux (Ri) was computed by R↓RN/e+σTg4 (1) where RN, Tg, σ and are net long-wave radiation flux, the measured surface temperature, the Stefan-Boltzman constant and the infrared emissivity respectively. Since all the observation points have the concrete surfaces, a uniform value of e=0.92 is used in calculating R↓ in and around the city. Observations are restricted to nights, and so the radiation balance equation is expressed in a simple form; RN=R↓-R↑ (2) Upward long-wave radiation flux (R↑) was computed by the equation (2). The results are as follows: 1. The intensity of urban heat island under the condition of the warm-moist polluted atmosphere so called the urbanized atmosphere, in the urban area is about double as much as that under the condition of the clean atmosphere in and around the urban area. 2. The urban-rural difference for the net long-wave radiation (RN) presents a striking con trast according as whether the urbanized atmosphere exists or not. That is to say, when it does not exist, RN of the urban area is more than that of the rural area; when it exists the urban area apparently receives a decrease in RN. This is one of the causes of the intensity of urban heat island. 3. When the urbanized atmosphere does not exist, R↑ is a little larger in the urban areaa than in the rural area, but RI is approximately equal in and around the urban area. 4. When the urbanized atmosphere exists, the urban increases of R↑ and R↓ are distinct. The urban increase of RI is especially larger and its average increase amounts to no less than 22. 3 mly/min (6.9%). 5. The causes for the urban increase of R↓ were analysed by using theoretically calculated values and so on.

COMPARATIVE OBSERVATION OF LONG-WAVE RADIATION BALANCE ON GROUND-SURFACE AND ON ROOF-LEVEL IN THE URBAN AREA

Considering a long-wave radiation field as a model, it should be noted that radiative energy is basically redistributed on the ground-surface in the rural area, but in the urban area it is redistributed on the roof-level and the ground-surface. The urban roof-level is exposed to long-wave radiation additionally caused by the aerosol layer and the warm vertical temperature structure of urban atmosphere besides background long-wave radiation. The urban ground-surface is, moreover, under influence of screen effects due to buildings. This suggests that the restraint of radiative cooling resulting from the double screen effects on the urban ground-surface is one of the main causes of the urban heat island. The objectives of this paper are to obtain the difference between long-wave radiation balance components on the roof-level and on the ground-surface in the urban area, and to discuss the screen effects (the effects of buildings) upon the long-wave radiation field on the ground-surface in the urban area. Measurements of long-wave radiation balances on the ground-surface and on the roof-level were achieved in the urban area of Tokyo on clear nights. The radiation sensors were polyethylene-shielded net radiometers (C. S. I. R. O. Net Radiometer Model CN-l and CN-2). The measurement accuracy of the sensors was ≤±4%. Upward long-wave radiation (R↑) was computed from measured surface temperatures and Stefan-Bolzmann's Law (assuming a concrete emissivity of 0.92 by Falckenberg (1928)). As observations are restricted to nights, the radiation balance equation is expressed by a simple form: RNet=R↓+R↑(1) where RNet is net long-wave radiation; R↓, downward long-wave radiation. Downward long-wave radiation (R↓) was computed by equation (1). The results were as follows: 1) Net long-wave radiation (RNet) on the urban ground-surface is consistently half as much as that on the urban roof-level. This is largely because downward longwave radiation (R↓) on the urban ground-surface is greater than on the urban roof-level. 2) The increased downward long-wave radiation (R↓) on the urban ground-surface is explained by taking the screen effects due to buildings into consideration. 3) It is clear that long-wave radiation components are extremely influenced by clouds. The increase of cloudiness, in particular, causes the increase of downward long-wave radiation (R↓), and then the decrease of net long-wave radiation (RNet). On a closer examination, cloudiness is also of greater influence upon long-wave radiation components on the roof level than on the ground-surface. From this analysis the existence of the screen effects due to buildings on the urban ground-surface can be confirmed.