UNB3m is a neutral atmosphere delay model, developed at UNB. The neutral atmosphere delay (or tropospheric delay) is suffered by a GPS signal when it travels through the neutral atmosphere, on its way between satellite and receiver. Because of the nature of the neutral atmosphere, which is composed mainly of gases including water vapor, the signal gets refracted, which means its speed changes (the signal travels more slowly than the vacuum speed of light) as does its path (the signal doesn’t travel in a straight line between satellite and receiver antennas). Due to these changes in speed and direction, it takes longer for the signal to reach the receiver’s antenna than if it was traveling through a vacuum. This difference in time, which can also be represented in metric units, is the neutral atmosphere delay. The magnitude of this delay depends on several things, and can be quantified based on the profiles of total atmospheric pressure, temperature, and the partial pressure of water vapor. The variation of these quantities at a particular location drives the variation of the delay from one day to another, over the different climate seasons.

UNB3m is a neutral atmosphere delay model, developed at UNB, whose algorithm is based on the prediction of meteorological parameter values for a particular location (latitude and height) and day of year, which are used to compute hydrostatic and non-hydrostatic zenith delays using the Saastamoinen models. The slant delays (and/or delay rates) are determined using the Niell mapping functions (or mapping function rates in the case of delay rates).

UNB3m is an improved version of UNB3. The improvement comes from the use of more realistic estimates of water vapour pressure. Based on comparisons with radiosonde data from 1990 to 1996 for stations across North America and surrounding territory, UNB3m has a consistent year-to-year bias in non-hydrostatic delay predictions of around -0.5 cm, which is better than the +2 cm provided by UNB3.

UNB3m is available for download as a package (UNB3m_pack) containing its several subroutines in both Fortran and MatLab versions along with test programs. The package can be use to compute slant total neutral atmosphere delays, zenith delays (hydrostatic, non-hydrostatic and total), Niell mapping function values (hydrostatic and non-hydrostatic), delay rates, mapping function rates, barometric pressure, temperature, relative humidity, and mean temperature of water vapour. These values are a function of day of year, latitude, and height and (for some parameters) elevation angle. The subroutines are self contained; i.e., they don’t need any auxiliary files. The user has simply to add to his/her software one or more of the available files and call them in the appropriate way.

#UNB3m中性大气延迟模型（中文） 当 GPS 信号在卫星和接收器之间穿过中性大气时，会受到 GPS 信号的影响。由于主要由包括水蒸气在内的气体组成的中性大气的性质，信号会发生折射，这意味着它的速度会发生变化（信号的传播速度比光的真空速度慢），它的路径也会发生变化（信号不会在卫星和接收器天线之间沿直线传播）。由于速度和方向的这些变化，信号到达接收器的天线比在真空中传播所需的时间更长。这种时间差也可以用公制单位表示，就是中性大气延迟。这种延迟的幅度取决于几个因素，并且可以根据总大气压、温度和水蒸气分压的剖面进行量化。这些数量在特定地点的变化导致了不同气候季节的延迟从一天到另一天的变化。

UNB3m 是一种中性大气延迟模型，由UNB开发，其算法基于气象参数的预测 特定位置（纬度和高度）和一年中的某一天的值，其中 用于计算静压和非静压天顶延迟，使用Saastamoinen模型。倾斜延迟（和/或延迟率）是使用 Niell 映射函数（或延迟率情况下的映射函数速率）。

UNB3m 是 UNB3 的改进版本。这种改进来自于使用更现实的水蒸气压估计。 根据与 1990 年至 1996 年北美及周边地区电台的无线电探空仪数据的比较，UNB3m 的年复一年保持一致 非静水延迟预测的偏差约为 -0.5 cm，优于提供的 +2 cm 由 UNB3 提供。使用 UNB3m 和 UNB3 预测的静水延迟是相同的。

UNB3m 可用于下载为包 （UNB3m_pack），其中包含 Fortran 和 MatLab 版本中的多个子例程以及测试程序。这 包可用于计算倾斜总中性大气延迟，天顶延迟（静压、非静压）、Niell 映射函数值 （静压和非静压）、延迟率、映射函数率、气压 压力、温度、相对湿度和水蒸气的平均温度。 这些值是一年中的某一天、纬度和高度的函数，并且（对于某些参数）仰角。子例程是独立的;即，他们 不需要任何辅助文件。用户只需添加到他/她的软件中一个或多个可用文件，并以适当的方式调用它们。