Keywords: underwater topographic survey ArcGIS
China Library Classification Number: P208 Document Identification Number: Part A Number:1672-3791(2012) 07 (b)-0019-01.
1 overview
With the rapid development of economy and society, the arrival of information society and the rapid improvement of informatization level, people have to face a lot of information every day. Faced with this information, they need to organize and edit it according to their own needs in order to achieve their own goals. The quality requirements for various topographic maps are also constantly improving. New measuring instruments and technologies are widely used in measurement, and more and more data are collected in field work. In the process of processing, it is necessary to check the rationality of the data. In the case of correct data, the generated graphics are required to be neat and beautiful. Especially in underwater topographic survey, due to the influence of wind and waves, velocity, turning and other factors in the construction process, the measured points are often staggered and chaotic, and the underwater topographic map obtained after the points are expanded is also irregular. Therefore, it is necessary to process the measurement data to meet different users.
Introduction to 1. 1 ArcGIS
Geographic Information System (GIS) is a new subject that collects, stores, manages, calculates, analyzes, displays and describes all or part of the space on the earth's surface with the support of computer software and hardware. It 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 map drawing and editing.
1.2 Brief introduction of sound generator
The working principle of the sounder is that the transducer emits sound waves in the water, and when the sound waves reach the bottom of the river, they are reflected. According to the sound wave propagation speed and round-trip time, the distance from the transducer to the river bottom, that is, the water depth, can be obtained.
1.3 RTK technology introduction
RTK survey system is a combined system composed of GPS survey technology and data transmission technology. RTK positioning technology is a real-time dynamic positioning technology based on carrier phase observation. The system is mainly composed of reference station, mobile station and data communication system, which can obtain the three-dimensional coordinates of the measuring station in a specific coordinate system in real time. The measurement accuracy reaches centimeter level. Jiangsu province has established a global navigation satellite system with high spatial and temporal resolution, high precision and full coverage, commonly known as network RTK, which has higher measurement efficiency and longer working distance.
2 Field data collection
2. 1 Basic information
The basin where Houfu River is located belongs to warm temperate semi-humid monsoon climate, and the annual precipitation changes greatly, with the maximum annual precipitation being more than twice the minimum annual precipitation. The distribution of precipitation in a year is uneven. About 70% of precipitation is concentrated in June-September, and the proportion of precipitation in dry season is small. The Yubo River collects floods from Shuyang County, Guanyun County and the urban area, and flows eastward into the Yellow Sea through the Yubo Gate. Manual excavation of houhe river system. Lianyungang River is about 50 kilometers long. This survey is 4 kilometers long and 300 meters wide. The reach is straight, the section is regular, the banks are clay, the water quality of the river is good, the water flow is stable, and there is no diversion phenomenon.
2.2 Hydrological eigenvalue
Through statistical analysis of the water level data measured at 1954 ~ 20 10 station, the hydrological characteristic values of this station are shown in table 1.
2.3 Location of survey area
The survey area is located at east longitude 1 19 15' 25 "and north latitude 34 27' 48", belonging to the Yi River system of Huaihe River Basin, at the intersection of Houfu River and Yanhe River. It is about 1.0km south of Banpu Town, with convenient transportation. It is under the jurisdiction of Haizhou District, Lianyungang City.
2.4 Instruments and equipment
The GPS used in this survey is a set of 5700 produced by Trimble Company in the United States. A set of HD-27T sounder produced by China Haida Company.
2.5 Soundfinder data acquisition
Four C-level outlets in Jiangsu Province were collected around the survey area, and three E-level GPS static points were laid along the river. In order to meet the needs of engineering design, the coordinates of WGS84 measured by CORS are transformed.
Install GPS directly above the sensor, so that the plane position of GPS antenna and sensor is consistent. Then start the GPS receiver, connect CORS, and get the fixed solution before underwater topographic survey. The survey ship sails according to the adjusted planned route, so that the sailing route of the ship is the process of collecting water depth, and the elevation of each point can be obtained to complete the surveying and mapping data collection of underwater terrain. In the process of collection, we should pay attention to the sensor not to be entangled with weeds to avoid data error.
3 in-house data collation
In the field measurement, due to the influence of weeds and other floating objects, the signal sent by the transducer is wrong, and the measured water depth is inconsistent with the actual situation, which should be eliminated. The data processing software carried by the sounder converts the data measured in the field into the river bottom elevation. After being checked and confirmed, ArcGIS9.0 software is used to draw isobath according to the measured underwater topographic elevation points to generate topographic map. In the process of data collection, due to the influence of wind direction and flow direction, the ship can't sail according to the predetermined route when turning, so the collected data is chaotic in the underwater topographic map. Draw contour lines with this software. After the isobath is generated, draw equidistant vertical and horizontal lines on the topographic map (according to the requirements of the specification), and then extract the data of intersection elevation points. This elevation point data is obtained by triangulation interpolation based on the actual data in underwater survey, which can truly reflect the terrain and match the isobath. Close the original survey data layer to make all elevation points on the map neat and make the topographic map look neat and clear.
4 feelings
(1) In the previous topographic survey software, South CASS6.0 software is commonly used by all units and individuals, and contour lines can be drawn according to survey requirements, but the graphics are irregular. The previous methods were manual adjustment, deletion and mirroring. This is usually inconsistent with the isobath. (2) For the underwater topographic map made by CASS6.0 software in South China, graphic processing can also be carried out. The method is to open ArcGIS9.0 software and import topographic map. The underwater topographic map with the same effect can also be edited by the above method. (3) In the map, you can also edit various statistical information such as geographic information, hydrological information, population information, etc., and you can get the needed information and data by making explanations in the needed graphics.
refer to
[1] Guoan Tang, Yang Xin. Experimental Course of Spatial Analysis of ArcGIS Geographic Information System [M]. Science Press.
Gao Bin, Wu Xiangyang, Liu Juan. Application of GPS in underwater topographic survey [J]. Surveying and Mapping Science, 2009(S2).