Advanced Data Analysis Techniques for Active Microwave Occultation Experiments

这项拨款促进了基于低地球轨道卫星接收的GPS信号的测量和解释的大气探测方法。由于折射，当无线电信号从GPS发射卫星传播到LEO接收器时，会沿着一条稍微弯曲的路径传播，并且速度会稍微降低。从弯曲量和多余的时间延迟可以推断出大气射电折射率的垂直分布。折射率与电离层中的电子密度以及中性大气的温度、压力和水蒸气含量有关。大气探测利用掩星技术分离折射率的不同贡献，以确定高大气中的电子密度分布和低大气中的温度和湿度分布。该项目分为两个主要部分。第一个是解决利用现有的GPS卫星系统监测温度、湿度和电子密度的某些问题。它包括(1)对电离层对低层大气测量的影响进行校正；(2)研究对流层低层多径传播的影响；(3)将剖面向下延伸至边界层；(4)将射电掩星数据纳入天气预报模式。该项目的第二部分旨在发展一种先进的探测系统，其中将装备多达六颗低地球轨道卫星阵列，以便在选定的水蒸气和臭氧吸收带内发射和接收频率的信号（所谓的交联实验）。通过测量这些信号的振幅和相位，可以确定掩星产生的温度、水蒸气和臭氧的分布。这项研究为新的大气探测方法奠定了基础，这些方法将在数值天气预报模式和通过探测长期趋势在气候研究中有重要的应用。

This grant advances methods of atmospheric sounding based on measurement and interpretation of GPS signals received by low earth orbiting (LEO) satellites. Because of refraction, radio signals follow a slightly bent path and have a slightly reduced speed when they propagate through the earth's atmosphere from a GPS transmitting satellite to a LEO receiver. From the amount of bending and the excess time delay can be inferred the vertical profile of the radio refractivity of the atmosphere. The refractivity is related to the electron density in the ionosphere and to the temperature, pressure, and water vapor content of the neutral atmosphere. Atmospheric sounding using the occultation technique separates the different contributions to the refractive index to determine both the electron density profile in the high atmosphere and the profiles of temperature and humidity in the lower atmosphere.The project is divided into two main parts. The first is concerned with solving certain problems in using the existing system of GPS satellites to monitor profiles of temperature, humidity, and electron density. It includes (1) developing corrections for the effects of the ionosphere on measurements in the lower atmosphere; (2) studying the effects of multipath propagation in the lower troposphere; (3) extending the profiling down to the boundary layer; (4) assimilating radio occultation data into weather forecasting models. The second part of the project is aimed at developing an advanced sounding system in which an array of as many as six LEO satellites will be equipped for both transmitting and receiving signals at frequencies within selected water vapor and ozone absorption bands (so-called crosslink experiments). Measuring the amplitudes and phases of such signals enables the determination of profiles of temperature, water vapor, and ozone from radio occultations. This research lays the groundwork for new methods of atmospheric sounding that will have important application in numerical weather prediction models and, through the detection of long-term trends, in climate studies.