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.