GPS-based regional ionospheric models and their suitability in Antarctica

There are a number of ionospheric models available for research and application, such as the polynomial model, generalized trigonometric series function model, low degree spherical harmonic function model, adjusted spherical harmonic function model, and spherical cap harmonic function analysis. Using observations from more than 40 continuously operating stations across Antarctica in 2010, five models are compared with regard to their precision and applicability to polar regions. The results show that all the models perform well in Antarctica with 0.1 TECU of residual mean value and 2 TECU of root mean square error

Mass change of the Antarctic ice sheet inferred from ICESat and CryoSat-2

This study examined the mass change of the Antarctic ice sheet (AIS) based on ICESat and CryoSat-2 observations. We estimated the AIS exhibited mass losses of −101±15 Gt·a−1 during the ICESat period (Sept–Nov 2003 to Sept–Oct 2009) and −186±55 Gt·a−1 during the CryoSat-2 period (Jan 2011 to Dec 2015). Mass losses occurred mainly in the sectors of the Amundsen and Bellingshausen seas. Benefitting from the 30-d subcycle of CryoSat-2, we obtained monthly estimates of mass evolution. Considerable annual variations were observed in the mass evolution sequences and the climatological monthly mass evolution. Seasonal mass evolutions in the sectors of the Bellingshausen and Amundsen seas were found most representative of the annual variation. The geographical distribution characteristics of interannual AIS mass evolution were revealed by the annual average mass evolution sequences. During Jan 2011 to Dec 2015, the ice sheets in the sectors of the Bellingshausen and Amundsen seas, and the Totten Glacier, experienced increasingly rapid areal mass loss. An area of mass gain with a moderate rate of increase was found between Dronning Maud Land and Enderby Land. Rapid mass accumulation has occurred in a limited area of the Kamb Ice Stream

Temporal distribution characteristics of GNSS ionospheric occultation data and its effects in earthquake-ionosphere anomaly detection

The temporal distribution characteristics of COSMIC occultation data are analyzed in detail, and the limitations in earthquake-ionosphere anomaly detection caused by the temporal distribution characteristics of COSMIC occultation data are discussed using the example of the Wenchuan earthquake. The results demonstrate that there is no fixed temporal resolution for COSMIC occultation data when compared with other ionospheric observation techniques. Therefore, occultation data cannot currently be independently utilized in research studies but can only be used as a complement to other ionospheric observation techniques for applications with high temporal resolution demands, such as earthquake-ionosphere anomaly detection

effectsofrainfallinfiltrationondeepslopefailure

With the finite element method and the limit equilibrium method, a numerical model has been established for examining the effects of rainfall infiltration on the stability of slopes. This model is able to availably reflect the variations in pore pressure field in slopes, dead weight of soil, and the softening of soil strength caused by rainfall infiltration. As a case study, an actual landslide located at the Nongji Jixiao in Chongqing is studied to analyze the effects of rainfall infiltration on the seepage field and the slope stability. The simulated results show that a deep slope failure is prone to occur when rainfall infiltration will lead to a remarkable variation in the seepage field, in particular, for large range pore water pressure increase in slopes

Snow Depth Detection and Error Analysis Derived from SNR of GPS and BDS

There are several significant advantages in snow depth inversion with GNSS reflected signals,such as all-time,all-weather,large amount of data and low cost.An experiment of GNSS-reflectometry was designed at Arctic Yellow River Station and dual-frequency signal to noise ratio (SNR) observations of GPS and BDS were collected.The effects on snow depth inversion,including satellite elevation,arc length,number of satellites,azimuth,time scale,constellation structure,signal frequency and SNR intensity,were discussed comprehensively.And then the inversion accuracy and reliability were improved by large sample statistics,quality control and error analysis.According to the error analysis,we recommend the following inversion strategy:to use L1 and B1I observations,with 5 to 25 degrees satellite elevation,from multi-satellites and four azimuths.In this way,we can finally achieve the accuracy of 5 cm in one day.In addition,arc length,constellation structure and signal frequency have small effects on the accuracy of the results

Long-term prediction of the Arctic ionospheric TEC based on time-varying periodograms.

Knowledge of the polar ionospheric total electron content (TEC) and its future variations is of scientific and engineering relevance. In this study, a new method is developed to predict Arctic mean TEC on the scale of a solar cycle using previous data covering 14 years. The Arctic TEC is derived from global positioning system measurements using the spherical cap harmonic analysis mapping method. The study indicates that the variability of the Arctic TEC results in highly time-varying periodograms, which are utilized for prediction in the proposed method. The TEC time series is divided into two components of periodic oscillations and the average TEC. The newly developed method of TEC prediction is based on an extrapolation method that requires no input of physical observations of the time interval of prediction, and it is performed in both temporally backward and forward directions by summing the extrapolation of the two components. The backward prediction indicates that the Arctic TEC variability includes a 9 years period for the study duration, in addition to the well-established periods. The long-term prediction has an uncertainty of 4.8-5.6 TECU for different period sets

High Precision Mesh-Based Drone Image Stitching Based on Salient Structure Preservation and Regular Boundaries

Addressing problems such as obvious ghost, dislocation, and distortion resulting from the traditional stitching method, a novel drone image-stitching method is proposed using mesh-based local double-feature bundle adjustment and salient structure preservation which aims to obtain more natural panoramas.The proposed method is divided into the following steps. First, reducing parallax error is considered from both global and local aspects. Global bundle adjustment is introduced to minimize global transfer error, and then the local mesh-based feature-alignment model is incorporated into the optimization framework to achieve more accurate alignment. Considering the sensitivity of human eyes to linear structure, the global linear structure that runs through the images obtained by segment fusion is introduced to prevent distortions and align matching line segments better. Rectangular panoramas usually have better visual effects. Therefore, regular boundary constraint combined with mesh-based shape-preserving transform can make the results more natural while preserving mesh geometry. Two new evaluation metrics are also developed to quantify the performance of linear structure preservation and the alignment difference of matching line segments. Extensive experiments show that our proposed method can eliminate parallax and preserve global linear structures better than other state-of-the-art stitching methods and obtain more natural-looking stitching results

Influence of spatial gradients on ionospheric mapping using thin layer models

This study provides information about the influence of various ionospheric spatial gradients on the thin layer ionospheric model (TLIM). Particular attention is paid to the errors caused by the slant total electron content (sTEC) when converted to the vertical total electron content (vTEC) by an elevation-dependent mapping function (MF), ignoring the satellite azimuth. We quantify the influence of the spatial gradient on ionospheric mapping using globally distributed GNSS measurements and the NeQuick2 ionospheric electron density model. The ionospheric mapping errors (IME) were confirmed using GNSS measurements that were observed for different solar activity conditions. It was found that the IME in the low latitudes were significantly higher than those at other latitudes, and the high-latitude region IME were more pronounced than those of the mid-latitude regions. A comprehensive simulation analysis based on the NeQuick2 model was conducted for different azimuth angles and geographical locations. It was found that the vTEC converted by the MF is smaller than the real value of vTEC in different spatial directions. The IME in the north-to-south direction were much higher than those in the east-to-west direction and were symmetrical north–south about the geomagnetic equator. The values of the IME had obviously seasonal variation characteristics: The IME in the spring and autumn were significantly higher than those in the winter and summer; however, in the low latitudes, the IME were abnormal and had larger values. There is an interesting phenomenon wherein the IME were symmetrical about the azimuth of 180°, and the value of the IME was less than 1 TECu when the satellite elevation was up to 50°. From the global perspective, when the thin layer height is at 400 km, the IME were relatively minimal. In addition, the modified single-layer model (MSLM) and Ou (Ou J) segmented mapping functions outperformed other mapping functions at low satellite elevations; however, when the elevation angle was increased to approximately 40°, the differences of the different MFs were small

Natural- and Human-Induced Influences on Terrestrial Water Storage Change in Sichuan, Southwest China from 2003 to 2020

A quantitative understanding of changes in water resources is crucial for local governments to enable timely decision-making to maintain water security. Here, we quantified natural-and human-induced influences on the terrestrial water storage change (TWSC) in Sichuan, Southwest China, with intensive water consumption and climate variability, based on the data from the Gravity Recovery and Climate Experiment (GRACE) and its Follow-on (GRACE-FO) during 2003–2020. We combined the TWSC estimates derived from six GRACE/GRACE-FO solutions based on the uncertainties of each solution estimated from the generalized three-cornered hat method. Metrics of correlation coefficient and contribution rate (CR) were used to evaluate the influence of precipitation, evapotranspiration, runoff, reservoir storage, and total water consumption on TWSC in the entire region and its five economic regions. The results showed that a significant improvement in the fused TWSC was found compared to those derived from a single model. The increase in regional water storage with a rate of 3.83 ± 0.54 mm/a was more influenced by natural factors (CR was 53.17%) compared to human influence (CR was 46.83%). Among the factors, the contribution of reservoir storage was the largest (CR was 42.32%) due to the rapid increase in hydropower stations, followed by precipitation (CR was 35.16%), evapotranspiration (CR was 15.86%), total water consumption (CR was 4.51%), and runoff (CR was 2.15%). Among the five economic regions, natural influence on Chengdu Plain was the highest (CR was 48.21%), while human influence in Northwest Sichuan was the largest (CR was 61.37%). The highest CR of reservoir storage to TWSC was in Northwest Sichuan (61.11%), while the highest CRs of precipitation (35.16%) and evapotranspiration (15.86%) were both in PanXi region. The results suggest that TWSC in Sichuan is affected by natural factors and intense human activities, in particular, the effect of reservoir storage on TWSC is very significant. Our study results can provide beneficial help for the management and assessment of regional water resources