Large And Medium-sized Lakes, Like The Influence Of The Geoid, Local Refinement

Nowadays the datumn of elevation measure includes two parts:the first part is the leveling network (points),the second one is the (quasi) geoid. The technology with gps and (quasi)geoid can save a large numbers of time,money and a lot of people, simultaneity the accuracy of elevation points distribute uniformly and haven't the cumulative error from every link of levels. Especially we can get elevation value by this technology in the areas(such as island, mountainous area) where we can't pass the elevation or pass the elevation very hard. The result is uniform to the national elevation datumn and height system.Considering the application of surveying and mapping production, China Quasi Geoid 2000(CQG2000) that State Buareau of Surveying and Mapping offered can basically meet the demand of the middle and small scale(less than 1:10000) plotting in western area. But when we take the demand of big scale( 1:5000 to 1:500) plotting and updating the maps in the middle and eastern developed area into account, the (quasi)geoid resolution and accuracy of relevant areas must be respectively reached to 2.5km and 1.5cm.The CQG2000 have a great way to it. The local (quasi) geoid with hight resolution and centimeter level emerges as the times require.China has a lof of lakes. Due to the low accuracy and lack of underwater topography data, When we determinate local (quasi)geoid we rarely consider the effect of water. Along with the increasing demand on the accuracy of local (quasi)geoid, especially with the emerging of local (quasi) geoid with hight resolution and centimeter level, we can't ignore the effect of water any more when we calculate local (quasi)geoid.Because of these, this article will conclude the method computing quasi-geoid with water effect by analyzing the way computing centimeter level geoid with high resolution;and then through practical computing, the related relationship charts that is between the computing area center and water center ,and the values of water influence to gravitational (quasi) geoid will be protracted.Based on the above ideas, we do the following:1. Researching the implement of two-dimension Fast Fourier Transform and its application to the determination of geoid; compiling GQGP program for computing quasi-geoid with Visual Basic.Net.2. Having concluded local terrain correction formula including water influence with underwater DEM and water surface DEM, by analyzing local terrain correction formula.3. Having analyzed water effect to topographic isostatic correction according to Airy-Heiskannen topographic isostatic commuting model.4. Through practical computing, the related relationship charts that is between the computing area center and water center ,and the values of water influence to gravitational (quasi) geoid will be protracted by practicality computing.