Abstract: In modern construction surveying work, advanced equipment has greatly improved the accuracy and speed of measurement. Especially in underwater topographic survey, the amount of data obtained is very large, and the work of in-house processing is The volume is also very large. Using ArcGIS software can complete in-house processing relatively quickly and achieve better results.
Keywords: Underwater topographic survey ArcGIS
CLC number: P208 Document identification code: A Article number: 1672-3791(2012)07(b)-0019-01
1 Overview
With the rapid development of the economy and society, the arrival of the information society, and the rapid improvement of the level of informatization, people have to face a large amount of information every day. , all need to be organized and edited according to their own needs to achieve their own goals. The quality requirements for the results of various topographic maps are also constantly improving. New measuring instruments and technologies are widely used in surveying. The data collected during field operations There are more and more data, and in the face of more and more data information, it is necessary to check the rationality of the data during the processing process. When the data is correct, the generated graphics must be neat and beautiful, especially in underwater terrain. During the survey, because the sailing survey ship is affected by wind, waves, flow speed, and turns during the construction operation, it often cannot follow the preset route, causing the measured points to be staggered and messy. After displaying the points, the underwater terrain obtained The graph is also not neat, so necessary processing of the measurement data is required to meet the needs of different users.
1.1 Introduction to ArcGIS
Geographic Information System (GIS) is a system that, with the support of computer software and hardware, analyzes relevant geographical distribution data in all or part of the earth's surface space. The new discipline of collection, storage, management, calculation, analysis, display and description consists of three modules: ArcMap, ArcCatalog, and Geoprocessing. It enhances the tools provided to cartographers and can read and edit various map elements to realize mapping. Map drawing and editing.
1.2 Introduction to the depth sounder
The working principle of the depth sounder is to use a transducer to emit sound waves in the water. When the sound waves reach the bottom of the river, they are reflected. According to the propagation speed of the sound waves and the round-trip time, time, you can find the distance between the transducer and the river bottom, that is, the water depth.
1.3 Introduction to RTK technology
RTK measurement system is a combined system composed of GPS measurement technology and data transmission technology. RTK positioning technology is a real-time dynamic positioning technology based on carrier phase observation. The system mainly It consists of three parts: a base station, a rover, and a data communication system. It can obtain the three-dimensional coordinates of the measuring point in a specific coordinate system in real time. The measurement accuracy reaches centimeter level. A high spatial and temporal resolution, high precision, and full coverage global navigation satellite system, commonly known as network RTK, has been established in Jiangsu Province, making measurement more efficient and operating distance larger.
2 Field data collection
2.1 Basic situation
The basin where Shanhou River is located has a warm temperate semi-humid monsoon climate, with large interannual changes in precipitation, and the maximum annual precipitation The amount is more than twice the minimum annual precipitation. Precipitation is unevenly distributed throughout the year, with about 70% of the precipitation concentrated from June to September, and precipitation in the dry season accounting for a smaller proportion. The Shanhou River collects floods from Shuyang County, Guanyun County and urban areas, and flows eastward into the Yellow Sea through the Shanhou New Gate. After the aftermath, the river system was manually excavated. The length of the river in Lianyungang is about 50km. The length measured this time is 4km and the width is about 300m. The river section is straight, with a regular cross-section, and both sides are clay. The water quality of the river is good, the flow is steady, and there is no diversion.
2.2 Hydrological characteristic values
Through statistical analysis of the measured water level data of the station from 1954 to 2010, the hydrological characteristic values ??of the station are shown in Table 1.
2.3 Location of the survey area
The survey area is located at 119°15′25″ east longitude and 34°27′48″ north latitude. It belongs to the Yihe River system in the Huaihe River Basin and is the intersection of Shanhou River and Yanhe River. at. It is about 1.0km south of Banpu Town, with convenient transportation. It is administratively subordinate to Haizhou District, Lianyungang City.
2.4 Instruments and Equipment
The GPS used in this measurement is a 5700 set produced by the American Trimble Company. A set of HD-27T depth sounder produced by Hi-Tech Company.
2.5 Depth sounder data collection
Four Jiangsu Province C-level outlets were collected around the survey area, and three E-level GPS static points were deployed along the left and right sides of the river. Use CORS to measure the WGS84 coordinates on the E-level point, and convert the coordinates of the measurement area to meet the needs of engineering design.
Install the GPS directly above the transducer so that the plane positions of the GPS antenna and the transducer are consistent. Then start the GPS receiver and connect to CORS. After obtaining the fixed solution, you can conduct underwater terrain measurement. The survey ship sails according to the planned line that has been transferred. In this way, the route the ship travels is the process of collecting water depth. The elevation of each point can be obtained. The collection of underwater terrain mapping data is completed. During the collection process, attention should be paid to changing the The energizer must not be entangled in weeds to avoid data errors.
3 Compilation of internal data
During outdoor measurements, due to the influence of weeds and other floating objects, the signal sent by the transducer is wrong, and the measured water depth is different from the actual situation. If it does not match, it should be eliminated. Use the data processing software that comes with the depth sounder to convert the data measured in the field into the river bottom elevation. After checking and confirming that it is correct, use ArcGIS9.0 software to draw contours based on the measured underwater terrain elevation points. Generate a topographic map. Since during the data collection process, the ship is affected by the wind direction and current direction during navigation and cannot sail according to the predetermined route when turning, the collected data is messy in the underwater topographic map. Use this software to draw After the isobath lines are generated, equidistant vertical and horizontal lines are drawn on the topographic map (according to the specification requirements), and then the elevation point data of the intersection is extracted. This elevation point data is based on the underwater survey. The actual data is obtained by using triangulation network interpolation, which can truly reflect the terrain conditions and match the isobaths. Close the original measurement data layer, so that all you see on the map are neat elevation points, making the topographic map look neat and clear.
4 Feelings
(1) In the past, among the topographic survey software, the software commonly used by various units and individuals was the Southern CASS6.0 software, which could draw contours according to the survey requirements. , but the graphics are not neat, and the previous methods are manual adjustment, deletion, and mirroring. This is often inconsistent with the depth contours. (2) For the underwater topographic maps previously made using the Southern CASS6.0 software, the graphics can also be processed. The method is to open the ArcGIS9.0 software and load the topographic map. The same effect can be obtained by using the above method to edit the graphics. Underwater terrain map. (3) In the map, you can also edit various geographical information, hydrological information, population information and other information that need statistics. You can get the information data you need by making instructions in the graphics you need.
References
[1] Tang Guoan, Yang Xin. ArcGIS geographic information system spatial analysis experimental tutorial [M]. Science Press.
[2 ] Gao Bin, Wu Xiangyang, Liu Juan. Application of GPS in underwater topographic survey engineering [J]. Surveying and Mapping Science, 2009(S2).