Acta Geodaetica et Cartographica Sinica

Calibration of the Satellite Gravity Gradients for GOCE and Analysis on Its Drag Free Control System

ZOU Xiancai

2018, 47(3): 291-297. doi:10.11947/j.AGCS.2018.20170219

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GOCE is the first modern satellite, which carried a gravity gradiometer measuring the earth gravity filed with high accuracy by the differential measurements of the accelerometers. Its along track is in a drag-free status and the accelerometers are off-center mounted. These characteristics make GOCE a significant difference from the standard satellite-satellite tracking (SST) technique. In this paper, the problem of non-strictness in the common mode acceleration calibration of GOCE is pointed out first and, then the schemes to calibrate six accelerometers individually to separate the bias parameters are presented. The precise kinematic orbit of GOCE is used in the accelerometer calibration and drag-free control system evaluation by the dynamics method. Some fundamental results are achieved. Firstly, although the neutral atmosphere density at the altitude of GOCE orbit is higher than that of GRACE satellites with two to three orders of magnitude, the residual non-conservative force of the GOCE satellite along the track is one order of magnitude lower than the corresponding component of the GRACE satellites, which shows the compensation effect of the drag-free control system fully. Secondly, it can be concluded that the drag-free control system has a significant effect on the determination of GOCE's velocity by comparing the orbital velocity interpolated from the position and integrated with the orbit dynamics. Thirdly, the non-conservative force acting on GOCE satellite is analyzed and the accelerometer calibration parameters are estimated and evaluated. The possible developments on the preprocessing of the satellite gravity gradients with the accelerometer calibration results are also discussed in this paper.

High-accuracy Long Arc Almanac Model Design for BDS

CHANG Zhiqiao, HU Xiaogong, CHEN Liucheng, LI Xiaojie, ZU Anran, TANG Chengpan, HUANG Hua

2018, 47(3): 298-307. doi:10.11947/j.AGCS.2018.20170103

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Almanac parameters can be used to assist signal acquisition for both conventional navigation and autonomous navigation. The extended validity of the almanac parameters not only enables the terrestrial receiver to make full use of almanac data when starting up,but also determines the frequency of the almanac uploaded and the satellite storage resources on-board for autonomous navigation with inter-satellite link observation. Based on analysis of the major perturbations of three types of BeiDou satellites and their effects on the long-term and long-period terms of the orbital elements,an almanac model with six orbital elements and five perturbation parameters is designed. The almanac fitting test is carried out based on the 90-day long arc orbit of BeiDou satellites in orbit throughout 2013. The results show that the new almanac model improves accuracy of almanac fitting. For Geostationary Earth Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO) satellites,position fitting error is reduced from 200 km to more than 10 km even to several km and velocity error is reduced from 15 m/s to 0.6 m/s. The accuracy of the new model is about 20 to 30 times higher than that of the conventional model. For Medium Earth Orbit (MEO) satellite,position fitting error is about 5 km and velocity error is about 0.6 m/s regardless of which model,and the accuracy of the new method is improved about 15%. For 10 km position error upper limit of inter-satellite link,the maximum fitting arc length of the conventional model is about 14 days,and the maximum fitting arc length of the new almanac model can be extended to 45 days. The new almanac model extends the validity of almanac parameters,and optimizes almanac model for BeiDou Navigation Satellite System (BDS).

The Weight Matrix Determination of Ionospheric Delay Constraintfor Multi-GNSS Precise Point Positioning Using Raw Observations

ZHANG Hui, HAO Jinming, XIE Jiantao, LIU Weiping, ZHOU Yanglin

2018, 47(3): 308-315. doi:10.11947/j.AGCS.2018.20170151

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The ionospheric delay parameters in the precise point positioning (PPP) using raw observations must be considered.The estimation of the ionospheric delay parameters is strengthened by priori ionospheric correction models. But it is difficult to determine the relative weight ratios between the priori ionospheric corrections and the observations. A weight factor searching algorithm based on ionospheric delay constraint for multi-GNSS PPP using raw observations is proposed in which weight factors are utilized to adjust the variances of priori ionospheric corrections. According to the principle thatthe sum of the quadratic forms of weighted residuals be the minimum, the optimal weight factors are searched for and the variances of priori ionospheric corrections are adjusted dynamically in order to promote the positioning results. Data sets collected from 8 stations of the multi-GNSS experiment (MGEX) tracking network are processed to validate the proposed algorithm. The results of PPP in static mode show that the RMS values of the positioning errors are improved from 3.96 cm to 3.40 cm andthe convergence time is reduced from 76.3 min to 59.9 min whenthe searching algorithm is used, in comparison with the traditional priori ionospheric constraint.

The Characteristics of Gravity and Regional Ocean Tides at Zhongshan Station in Antarctic

LIU Qingchao, SUN Heping, WANG Zemin, CHEN Xiaodong, ZHANG Shengkai, XU Jianqiao

2018, 47(3): 316-323. doi:10.11947/j.AGCS.2018.20170123

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This study investigates the characteristics of gravity and ocean tides using time series recorded with the spring gravimeter and tide gauge at Zhongshan station, CATS2008 regional ocean tide model, and Eot11a global ocean tide model. The results show that the ocean tidal amplitude of O1 wave reaches 28 cm in the diurnal tidal bands. The sum of four tidals (Q1, O1, P1 and K1) difference between the global model and the tide gauge station is 4.2 cm, and that between the regional model and the tide gauge station is 4.4 cm. In contrast, the tidal amplitude of M2 wave reaches 20 cm in the semi-diurnal bands, and the sum of four tidals (N2, M2, S2 and K2) difference are 7.7 cm and 5.1 cm, respectively. This shows that correcting global ocean tide model using regional models is important. Subsequent to the correction of global oceanic loading using the regional model, the amplitudes of final residuals for the main gravity waves K1, M2, and S2 decreased by 9.84%, 56.14%, and 37.08%, respectively, which indicates that the regional ocean tide model can better reflect the true characteristics of ocean tides. Moreover, the validity of correcting global ocean tide model using the regional model is verified.

Assessment of BDS Ambiguity Resolution with GEO/IGSO/MEO Satellites

LI Xin, YUAN Yongqiang, ZHANG Keke, ZENG Qi, ZHANG Xiaohong, LI Xingxing

2018, 47(3): 324-331. doi:10.11947/j.AGCS.2018.20170341

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Since the precision of GEO satellite orbit is low and the observations of GEO are affected seriously by the multipath and code bias, now no analysis center in the world provide the uncalibrated phase delay (UPD) products of BeiDou Satellite Navigation System (BDS) GEO satellites. At present, the BDS precise point positioning (PPP) ambiguity resolution (AR) for global users still limits on the IGSO and MEO satellites. In our study, we eliminated the code bias of IGSOMEO satellite by using the elevation-dependent model proposed by the Wanninger and Beer and the code bias of GEO satellite was corrected by the wavelet transform. We also improve the method of NL UPD estimation by applying accurate UPDs estimated in last epoch to select the correct ambiguities at current epoch. Once we obtain the high-quality UPD products, the BDS PPP ambiguity resolution with GEOIGSOMEO satellites is achieved and then the performance of the PPP AR results is evaluated. Results show that:The convergence time and the time to first fix are both less than 30 min for BDS PPP ambiguity resolution with GEOIGSOMEO satellites. The positioning error based on six-hour observations for East, North and UP direction are reduced by 20%, 27% and 18% (from 1.35, 0.35 and 2.75 cm to 1.07, 0.26, and 2.24 cm).

Seasonal Variation of Terrestrial Water Storage in Yunnan Province Inferred from GPS Vertical Observations

HE Siyuan, GU Yanchao, FAN Dongming, ZHAO Hongbin, ZHENG Rong

2018, 47(3): 332-340. doi:10.11947/j.AGCS.2018.20170255

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In response to the mass redistribution on the surface of the earth,crustal vertical displacements are deformed in solid elastic earth,which can be recorded by continuous GPS.With GPS vertical observations at 47 stations from crustal movement observation network of China (CMONOC) in and around Yunnan province,we explore the feasibility analysis of using the data to infer the variation of water storage.Simulation experiments are conducted by using GLDAS (global land data assimilation system) Noah hydrological model,whose annual amplitude is referred as real signals.We used the GLDAS annual amplitude to calculate the vertical displacements,and combined the displacements with random errors to constitute simulated vertical displacements.The simulated vertical displacements are then converted to variation of water storage,which is compared with the original GLDAS water storage.We performed 1000 simulated experiments to evaluate robustness of the method,and it is evident that the variation of water storage could be effectively obtained by means of the vertical observations at the 47 CMONOC stations.Therefore,we investigated the variation of water storage over a period from 2010 to 2014.Results inferred from GPS data show obvious spatial and temporal distribution:the seasonal water in the southwestern mountain is much larger than that in eastern plain;the water storage reaches the maximum in October (after summer) and the minimum in April (after winter);a rate of 20 mm/a in total water storage in Yunnan province is presented during 2010-2014.The comparison between GPS-inferred water storage and GRACE,GLDAS and TRMM results showed good consistency in spatial and temporal distribution,indicating that CMONNOC GPS stations could be used as independent measurement to estimate terrestrial water storage changes during the gap between GRACE and future GRACE Follow-on missions.

BeiDou Satellites Multi-GNSS Precise Orbit Determination with Ambiguity Fixed

FANG Yanan, XIN Jingmin, ZENG Guang, WANG Jiasong, LI Jie

2018, 47(3): 341-347. doi:10.11947/j.AGCS.2018.20170378

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Using the global distributed IGS and Multi-GNSS experiment(MGEX) data, a method of multi-GNSS integrated double-difference precise orbit determination(POD) of BeiDou navigation satellites is studied. Then a specific double-difference ambiguity fixing strategy for BDS is proposed. The orbit determination precision of using single system and multi-GNSS, as well as ambiguity-fixed solution and ambiguity-free solution, are compared based on real observation data. The results show that, compared with single system processing, the multi-GNSS integrated method can effectively improve the orbit precision of IGSO and MEO, but except for GEO. The result of IGSO and MEO ambiguity fixing by the proposed strategy is well. The ambiguity fixing success rate has been improved significantly, especially for long baselines. The ambiguity fixed success rateimproves form 40% to 60% or more on the whole. Ambiguity fixing shows a positive contribution to orbit accuracy of IGSO and MEO from the overlapping RMS with that of the free solution for comparison. The 3D-RMS of IGSO could reach 0.048 m, and that of MEO could reach 0.066 m.

Information Recovery Algorithm for Ground Objects in Thin Cloud Images by Fusing Guide Filter and Transfer Learning

HU Gensheng, ZHOU Wenli, LIANG Dong, BAO Wenxia

2018, 47(3): 348-358. doi:10.11947/j.AGCS.2018.20170258

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Ground object information of remote sensing images covered with thin clouds is obscure. An information recovery algorithm for ground objects in thin cloud images is proposed by fusing guide filter and transfer learning. Firstly, multi-resolution decomposition of thin cloud target images and cloud-free guidance images is performed by using multi-directional nonsubsampled dual-tree complex wavelet transform. Then the decomposed low frequency subbands are processed by using support vector guided filter and transfer learning respectively. The decomposed high frequency subbands are enhanced by using modified Laine enhancement function. The low frequency subbands output by guided filter and those predicted by transfer learning model are fused by the method of selection and weighting based on regional energy. Finally, the enhanced high frequency subbands and the fused low frequency subbands are reconstructed by using inverse multi-directional nonsubsampled dual-tree complex wavelet transform to obtain the ground object information recovery images. Experimental results of Landsat-8 OLI multispectral images show that, support vector guided filter can effectively preserve the detail information of the target images, domain adaptive transfer learning can effectively extend the range of available multi-source and multi-temporal remote sensing images, and good effects for ground object information recover are obtained by fusing guide filter and transfer learning to remove thin cloud on the remote sensing images.

ICESat Laser Points Assisted Block Adjustment for Mapping Satellite-1 Stereo Imagery

WANG Jin, ZHANG Yong, ZHANG Zuxun, LI Xiao, TAO Pengjie, SONG Mengxiao

2018, 47(3): 359-369. doi:10.11947/j.AGCS.2018.20170425

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Block adjustment without ground control points (GCPs) is an important technique for satellite images surveying and mapping without GCPs. It has great significance for mapping the areas which are in overseas and difficult to get GCPs. However, the positional accuracy of block adjustment without GCPs is generally hard to meet the requirements of the corresponding scale mapping specification. Making use of readily available, public geographic data as the reference, is an effective way to improve the accuracy of block adjustment without GCPs. ICESat/GLAS data is one of the good vertical control data. To improve the positional accuracy of mapping Satellite-1 imagery without GCPs, an ICESat laser points assisted block adjustment method for stereo satellite images is proposed in this study. First, high quality ICESat laser points are extracted automatically based on multi-criteria constraints. Then, free net adjustment is performed by using tie points obtained from automatic matching to realize the internal consistency in block areas. Finally, the ICESat laser points are used as control points after measured on the satellite images automatically, the horizontal coordinates of ICESat control points are calculated by intersection based on free net adjustment results, while the vertical coordinates of ICESat control points are got from the elevations of ICESat laser points themselves, then the orientation parameters are refined again based on free net adjustment to improve the vertical accuracy of satellite images. Experiments on the Mapping Satellite-1 images of Shandong province proved the effectiveness and feasibility of the presented method.

Traffic Flow Detection Using GNSS-R Signals

YANG Lei, YANG Dongkai, ZHU Yunlong, GAO Chaoqun

2018, 47(3): 370-375. doi:10.11947/j.AGCS.2018.20160496

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In order to detect traffic conditions effectively, a new method of traffic flow detection using GNSS-R (Global Navigation Satellite System-Reflected) signals is proposed. In this method, the direct signals and reflected signals of GNSS are received by two types of antennas respectively and collected by an universal receiver.After signal processing in a SDR(Software Defined Receiver), the correlated power of direct channel and reflected channel, and also the satellites' elevation angles can be obtained. Then vehicles can be detected by the method of dielectric constant retrieving.Test results show that vehicles in the area can be detected effectively using this method, and prove the feasibility of traffic flow detection using GNSS-R signals.

The Double Grid Calculation Principle of Map Algebra

HU Hai, HAO Dalei, YANG Chuanyong, HU Peng

2018, 47(3): 376-384. doi:10.11947/j.AGCS.2018.20170260

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Large data amount and high precision requirements become new characteristics of scientific computing. With the development of cloud computing, spatial calculation with the requirement for precision at the meter and even sub-meter level becomes more and more common. Because small particle size means that the amount of calculation and the space complexity soar, it is difficult to meet the requirements of the calculation accuracy and efficiency through the mechanical reduction of grid size. This paper first discussed the principle and the key of double grid calculation in the practical calculation. This method made full use of the high accuracy of long distance calculation of map algebra and it is based on the differential formula in the metric calculation, which has a rigorous theoretical foundation. Its implementation, computational complexity and experiment results were analyzed and discussed through the theoretical analysis and experimental research. Then the implementation scheme of double grid computation in practical application was elaborated and discussed in detail. The results showed that this method realized the distance calculation at the high resolution measurement scale and broke through the problem of the applicability of grid methods in the large area calculation in theory and practice.

Interchange Recognition Method Based on CNN

HE Haiwei, QIAN Haizhong, XIE Limin, DUAN Peixiang

2018, 47(3): 385-395. doi:10.11947/j.AGCS.2018.20170265

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The identification and classification of interchange structures in OSM data can provide important information for the construction of multi-scale model, navigation and location services, congestion analysis, etc. The traditional method of interchange identification relies on the low-level characteristics of artificial design, and cannot distinguish the complex interchange structure with interference section effectively. In this paper, a new method based on convolutional neural network for identification of the interchange is proposed. The method combines vector data with raster image, and uses neural network to learn the fuzzy characteristics of the interchange, and classifies the complex interchange structure in OSM. Experiments show that this method has strong anti-interference, and has achieved good results in the classification of complex interchange shape, and there is room for further improvement with the expansion of the case base and the optimization of neural network model.

Backtracking Method of Coloring Administrative Maps Considering Visual Perception Rules

WEI Zhiwei, GUO Qingsheng, YAN Fen, WANG Yong

2018, 47(3): 396-402. doi:10.11947/j.AGCS.2018.20170148

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Color design in administrative maps should incorporate and balance area configuration, color harmony, and users' purposes. Based on visual perceptual rules, this paper quantifies color harmony, color contrast and perceptual balance in coloring administrative maps, and a model is suggested to evaluate the coloring quality after color template is selected. Then a backtracking method based on area balance is proposed to compute colored areas. Experiments show that this method can well meet visual perceptual rules while coloring administrative maps, and can be used for later map design.

Change Analysis and Decision Tree Based Detection Model for Residential Objects across Multiple Scales

CHEN Liyan, ZHANG Xinchang, LIN Hong, YANG Min

2018, 47(3): 403-412. doi:10.11947/j.AGCS.2018.20170373

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Change analysis and detection plays important role in the updating of multi-scale databases.When overlap an updated larger-scale dataset and a to-be-updated smaller-scale dataset,people usually focus on temporal changes caused by the evolution of spatial entities.Little attention is paid to the representation changes influenced by map generalization.Using polygonal building data as an example,this study examines the changes from different perspectives,such as the reasons for their occurrence,their performance format.Based on this knowledge,we employ decision tree in field of machine learning to establish a change detection model.The aim of the proposed model is to distinguish temporal changes that need to be applied as updates to the smaller-scale dataset from representation changes.The proposed method is validated through tests using real-world building data from Guangzhou city.The experimental results show the overall precision of change detection is more than 90%,which indicates our method is effective to identify changed objects.

Determination of Absolute Coordinate of Underwater Control Point Taking Waves and Depth's Constraint into Account

ZHAO Jianhu, CHEN Xinhua, WU Yongting, FENG Jie

2018, 47(3): 413-421. doi:10.11947/j.AGCS.2018.20170246

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To solve the problem that traditional underwater control point absolute positioning is time-consuming and laborious with low vertical precision, itis put forward that an accurate method with constraints of depth while taking waves into account to get absolute coordinate of underwater control point. Firstly, studiesarecarried outon the wave impact.And methods are put forward to determine the elevation difference between underwater points and the absolute elevation with GPS vertical values and the elevation difference. On this basis, methods are put forward, such asthe circle navigationwith depth's constraint to get single point's absolute coordinate, 2D free net adjustment with depth's constraint, integrated constraint adjustment,with accurate elevation difference, and 3D combined adjustment with accurate elevation difference. Finally, the experimental results show that the proposed methods can double the efficiency of traditional methods and improveprecision by one order of magnitude.

Integration of New Generation SAR Data for Extracting the Earth's Surface Topography and Displacement: Methodology and Modelling

DAI Keren

2018, 47(3): 422-422. doi:10.11947/j.AGCS.2018.20170422

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