Feng-Chi Yu

Cycle slips detection algorithm for low cost single frequency GPS RTK positioning

Abstract Conventionally, cycle slips are detected by combining phase observations or phase/code observations. However, this is unsuitable for single frequency receivers in real time kinematic (RTK) positioning. Therefore, this study introduces an algorithm based on outlier detection concept to the detection and repair of cycle slip during GPS RTK positioning. The efficacy of the algorithm was verified on a low cost single frequency GPS receiver. To investigate the ability of the algorithm to detect error within a single cycle, minimum detectable bias (MDB) of less than one cycle was used as the index of success. Experiments verified the availability of the algorithm up to 96·12% (10° mask angle). The algorithm was able to accurately detect the time when cycle slips occur and precisely estimate their size in various simulated scenarios. Finally, tests were performed based on real data, and the results confirm that the proposed algorithm is applicable for single frequency RTK positioning.

The Feasibility of Applying Single-frequency Receivers to Slope Monitoring

Traditional instruments which monitor the slope stability are often installed underground or buried in the ground. Survey of the monitoring points in a slope is normally done using GPS or a level. GPS surveying is efficient, can be used on most of the year except under snow storms and been used worldwide. Comparing with dual-frequency geodetic receivers, the single-frequency receivers are cheaper. If working with single-frequency receivers can maintain reliable readings, the cost will be reduced. In this paper, the ability of single-frequency GPS receivers was checked. First, in the experiments of GPS static surveying, the precision with single-frequency and dual-frequency in a slope survey was compared. It showed that we can achieve reliable reading in a slope area using single-frequency receivers. Finally, the reliability of low-cost receivers with single-frequency was tested in the case of short baseline (less than 5 km). An efficient approach by single-frequency GPS receiver was also suggested in the paper.

Land subsidence monitoring with a network of continuously operating GPS stations in Yunlin County, Middle Taiwan

Land subsidence in western Taiwan has been an issue since 1970s due to over extraction of ground water for aquaculture. This problem became serious in Yunlin County because high-speed rail way transects the center of land subsidence which may cause safety problem. Leveling survey is applied annually. A more efficient method with 6 continuous GPS stations is used in this study to observe the subsidence. The effectiveness and advantages are compared with leveling survey and underground monitoring wells in the period from 2007 to 2012. It is concluded that the trend of the subsidence can be fully observed by the GPS network and the observation frequency of GPS prevails the annual survey of traditional approach which is an important factor for early warning purposes.

The Use of a VRS-Based Pioneer 3-AT Robot in Pavement Inspections

This study proposed a framework of the Pioneer 3-AT (P3-AT) autonomous robot for pavement inspection that was integrated with a highly accurate virtual reference station (VRS) positioning technique. The two test sites were 60 km apart; one was rigid pavement and the other was flexible pavement. Two VRS systems were adopted: (1) A VRS system developed by Taiwan Control Signal Co., Limited and (2) Virtual Base Station Real-Time Kinematic (also called e-GPS system) from Taiwan National Land Surveying and Mapping Center. First, the tire pressure and horizontal movement of the P3-AT were calibrated on the two test sites. Then the accuracy of the positioning data provided by VRS to guide the P3-AT was investigated under both static and dynamic conditions at distances of movement from 0.25 to 20 m, to verify the stability and feasibility of this framework. We observed that standard deviations in positioning were less than 0.03 m and rms values were close to prescribed distances in static tests. The reproducible errors were less than 0.03 m in dynamic tests. The results showed that the two VRS systems were able to provide the P3-AT with accurate positioning data on the two test sites. This study also successfully demonstrated the use of the P3-AT in autonomously surveying surface distresses and manholes and its ability to accurately plot slabs on a rigid pavement. Since the P3-AT possesses the properties of low volume, slow speed, flexible modules, and low price, this study confirms that the P3-AT integrated with the VRS positioning technique has the potential to provide significant assistance in automatic pavement inspections of specific areas, such as airports, and for particular purposes, such as Quality Control/Quality Assurance testing.

Estimating surface temperature and land cover change in Hsinchu City

Changes in land use and land cover (LULC) are the critical driving forces of change in atmospheric, climatic and ecological systems. The purposes of this study are thus aiming to understand the relationship between land cover changes and thermal properties of urban heat island effects using Landsat images spanning from 1991 to 2007. On basis of the images of 17 years, the temperature differences between urban and rural of Hsinchu had been raised from 2–3 degrees to 4–5 degrees. Moreover, local hot spots showed up in downtown, Nan-Liao fishing port, and the traffic arteries surrounding residential area. It shows that urban expansion and heat discharged by traffic vehicles are major reasons for the temperature anomaly in the study area. Further study is required for understanding the sources of these features.

Multitemporal change analysis of the relationship of water ponds and urban change - Taoyuan, Taiwan

Taoyuan County locates approximately 30 km from the capital city of Taipei. It comprises an area of 2,898 Ha of farm ponds on the northwestern portion of Taiwan. Recently, the urban development caused many ponds abandoned and irrigation along rivers destroyed, it seriously affect the local ecological environment. To study the change on Taoyuan, multi-temporal satellite images since 1986 until 2011 are utilized in the paper. The image classification and GIS tool are used to recognize the water ponds and building area. We trace the population with the change trend of farm ponds. And the change in the centrality of city was discussed. It showed that farm ponds have reduced 902 Ha, and the area of building increased 8,499 Ha. The centrality of building moves 1,425 m since 1986 till 2011.

The multitemporal change analysis of deep-seated landslide - Hsiaolin Slide

Due to the active collision between Eurasian and Philippine Sea tectonic plates, the rocks of Taiwan are highly fractured and vulnerable to slope failures. In addition, Taiwan lies in the track of severe tropical cyclones known in East Asia as typhoons. Deep-seated landslides caused by heavy rainfall are usually catastrophic. One of the most catastrophic disaster is Hsiaolin Slide triggered by typhoon Morakot occurred on 9th August 2009 at Shiaolin Village in Kiaosiung City of Southern Taiwan. It was reported that 450 people died in this landslide, of which the volume was about 26 million cubic meters. Airborne LiDAR was conducted to acquire digital elevation models for landform change study after the event on 18 and 23 June 2010 and on 16 and 27 October 2010. The same area was surveyed with airborne LiDAR in 2006. Thus, three times of airborne LiDAR surveys were carried out. With the change from 2006 to June 2010, accurate landslide volume can be estimated. With the change from June to October, local slope of instability was readily identifiable on the difference image. It is concluded that multi-temporal airborne LiDAR can be an effective approach for quantifying the time-series change of deep-seated landslides in the physiographic settings of Taiwan.

The Use of a VRS-Based Pioneer 3-AT Robot in Assisting Pavement Inspections

This study proposes the idea of using robots in pavement inspections and develops a framework for the application of a Pioneer 3-AT (P3-AT) autonomous robot integrated with two types of highly accurate Virtual Reference Station (VRS) technology. The two testing sites constituted in the study were 60 km apart, one of which was a rigid pavement and the other, a flexible pavement. The tire pressure and the horizontal movement of the P3-AT were calibrated. The accuracy of positioning data provided by VRS to the P3-AT was investigated under both static and dynamic conditions at 25 cm to 20 m distances of movement. We saw a standard deviation in the static test of less than 0.03 m, and the root mean square (RMS) to be very close to the specified distance of movement. The results show that VRS can provide the P3-AT with accurate positioning data regardless of pavement types and VRS systems. This study also demonstrated the use of P3-AT in positioning distresses on the pavement, the P3-ATs autonomous monitoring, and its ability to plot slabs on a rigid pavement.

The Applicability Study for Landslide Monitoring with GPS Satellite Survey

Early detection of areas prone to landslides is a necessary safeguard in order to ensure the safety of people, business and facilities within these regions. This paper focuses on the feasibility of using a Global Positioning System Global (GPS) with a system for Mobile Communication (GSM) to relay land movement to remotely located monitoring modules. The system utilized Simple Messaging Services (SMS protocols) in concordance with post- processing software to gather and evaluated land movement. Several tests were conducted in Taiwans Wu Fong Chi district of Ilan. This area is known for landslides. The tests included static and localized simulations along with landslide simulating experiments. Two different distances from the monitoring area to the reference site were assessed. These distances, also known as baselines were evaluated and the differences of accuracy were recorded. Through the usage of Global Systems for Mobile Communication (GSM), the data was successfully conveyed through wireless communication. According to the experiments, the usage of short baseline length promoted both the precision surveying and calculation of the information. Additionally, a Global Positioning Monitoring Systems (GPS) was able to render results for both short and long distance baselines that were within centimeters of

Virtual Reference Station (VRS)-Based Intelligent Robot (Pioneer 3-AT) to Assist in Pavement Inspections

This study develops a framework for the application of a Pioneer 3-AT (P3-AT) autonomous robot integrated with two types of highly accurate Virtual Reference Station (VRS) technology. The tire pressure and the horizontal movement of the P3-AT were calibrated. The positioning accuracy of P3-AT was measured by VRS under both static and dynamic conditions at 25 cm to 20 m distances of movement. We saw a standard deviation in the static test of less than 0.03 m, and the root mean square (RMS) to be very close to the specified distance of movement. This research also conducted the use of P3-AT in positioning distresses on the pavement, the P3-AT’s autonomous monitoring, and its ability to plot slabs on a rigid pavement in order to prove that VRS can indeed provide P3-AT with highaccuracy positioning data that is required when moving on the broad pavement, thus meeting the positioning requirements of pavement inspection.