The utilization of digital television and radio signals for atmospheric science

使用计算机模型预测天气的主要困难之一是保持模型不断更新天气的实际情况。近年来，数值天气预报模式取得了巨大的进步，大大提高了数值天气预报模式的能力。模型能够摄取各种天气观测;地面测量，空间测量，气象气球测量等等。然而，计算机模型永远只能与用于表示大气状态的输入数据一样好。随着模型的分辨率和能力的提高（与网格的大小有关），为了获得模型改进的好处，输入数据也必须得到改进。在计算机模拟中特别重要的是大气中水分的输送，因为这是形成可能导致洪水的严重暴雨的关键因素。目前，几乎没有仪器能够对英国面积大小的大气层低几公里处的湿度进行常规远程测量。由于研究中使用的计算机模型的网格长度小至1公里，因此正在寻找能够提供类似规模测量的仪器，以便从模型中获得最佳结果。该项目的目的是开发一种廉价的仪器，可以测量大气中的水分。这项建议的一个主要新奇是它利用了现有的数字无线电和电视信号广播。基本概念很简单：发射器和接收器之间的路径上沿着的水蒸气越多，信号传播的时间就越长。假设接收器的位置保持固定，信号时间的变化可能与水蒸气的变化有关。要实现这一目标，首先需要解决许多技术挑战。无线电信号并没有被设计成以这种方式使用，因此需要相当数量的信号处理。此外，由于信号的飞行时间非常小，因此难以测量并且需要非常稳定的时钟。这种方法的优点是它便宜，消耗相对较少的功率，并且不需要发送额外的信号来进行测量。

One of the major difficulties with using computer models to forecast the weather is keeping the models constantly updated with what the weather is actually doing. There have been enormous advances in recent years that have considerably improved the ability of numerical weather prediction models. The models are able to ingest all manner of weather observations; measurement on the ground, measurements from space, measurements from weather balloons to name a few. However, the computer models will only ever be as good as the input data that is used to represent the state of the atmosphere. As the resolution and ability of the models improve, (related to the size of the grid) to get the benefit of the model improvement, the input data must also be improved. Particularly important in computer modelling is the transportation of moisture in the atmosphere since this is a key factor in the formation of severe rain storms which can lead to flooding. Currently there is almost no instrument capable of making routine remote measurements of moisture in the lower few kilometres of the atmosphere over an area the size of the UK. With the grid-length of computer models used in research as small as 1 km, the search is on to find instruments that can provide measurements on a similar scale in order to get the very best results from the model. The aim of this project is to develop an inexpensive instrument that can measure moisture in the atmosphere. A key novelty of this proposal is that it makes use of existing digital radio and television signals broadcasts. The basic concept is simple: the more water vapour along the path between the transmitter and receiver, the longer it takes for the signal to travel. Assuming the location of the receiver is kept fixed, changes in the signal time can be related to changes in water vapour. To accomplish this there are many technical challenges that first need to be solved. The radio signals were not designed to be used in this way so a consdiderable amount of signal processing is required. In addition because the time of flight of the signal is very small it is difficult to measure and requires a very stable clock. The advantage of this approach is that it is inexpensive, consumes relatively little power and requires no additional signals to be transmitted in order to make the measurements.