根据气温变化率进行三角高程测量的折光改正

Atmospheric Vertical Refraction Correction for Triangular Altitude Survey according to Atmospheric Temperature Change Rate

不同的气温梯度会产生不同的大气折射，根据测程前后两半段的气温梯度与－ ００３４２ 之差值，可将光线沿测程方向的折射分为４ 种类型，它们对三角高程测量的往返高差均值会产生不同的影响．利用测程两端及１４ Ｓ，１２ Ｓ，３４ Ｓ三点之间的气温变化率，模拟光程前、后两半段气温梯度的二次曲线；经数学推导，提出一种根据测程上不同区间的气温变化率直接对三角高程测量中的高差观测值进行大气折光改正且对４ 种折射类型均适用的方法．实验初步证明，运用该方法，只要同时测定两端点及３ 个以上特征点的气温，求得相应的测程区间气温变化率，据此直接对高差观测值进行折光改正，由此得到的三角高程测量往返高差均值与真值比较的标准差可缩小约５０ ％ ，即可较好地削弱大气折射对三角高程测量产生的影响．

Different atmospheric temperature gradients can bring about different atmospheric vertical refraction. The light refraction along the surveying distance can be divided into four types on the basis of different atmospheric temperature gradients on two half surveying distance minus -0.0342. The four types have different influence on average forward and backward triangular altitude difference. This paper presents a method about atmospheric vertical refraction correction for triangular altitude survey according to atmospheric temperature change rate between two end points and three points from 1/4S, 1/2S, 3/4S ,and simulates curves of the second degree of atmospheric temperature gradients along two half surveying distance by mathematics. The method is applied to all the four types of atmosphere vertical refraction. The experiment bears out that by surveying atmospheric temperatures of two end points and three salient points at the same time it is possible to obtain the atmospheric temperature change rate for different regions of surveying distance,and to make the atmospheric vertical refraction correction for observed value of triangular altitude survey. The standard error of forward and backford altitude difference average value of triangular will reduce about 50%, obviously the method can cut down the influence on triangular altitude survey due to atmospheric vertical refraction.