Implementation of CILCO (Compact Instrument for Longwave Cirrus Observations)

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The purpose of this project is to build a novel instrument capable of making accurate measurements of cirrus clouds. Cirrus are high altitude (8-12km) ice particle clouds that have a significant effect on the Earth's energy balance. Measurements from this new type of instrument have been shown that they will improve our understanding of climate change and weather predictions. In order to make accurate global predictions of long and short term climate, current knowledge of cirrus properties need to be improved by using new technology and techniques. Light at far infrared and submillimeter wavelengths is ideally suited to measuring cirrus since this wavelength is similar to diameters of ice particle found. These measurements provide information about ice particle size, particle density and particle shape. Cirrus parameters are measured by flying the instrument above the cirrus and facing it towards the Earth. Some of the far-infrared light emitted from the lower atmosphere is scattered by ice particles within the cloud. Relative to clear sky conditions, this scattering is observed by the instrument as a reduced signal. The amount by which this signal is reduced is measured at a number of wavelengths which can then be compared to a model to determine cloud properties. The proposed instrument differs from current instruments at different wavelengths, as this technique directly measures some of the important cirrus properties, which is not possible using the other methods. The new technique has been proven using models and data from a similar instrument called FIRSC (Far InfraRed Sensor for Cirrus). The new instrument will not measure a continual spectrum like FIRSC, but instead discrete parts of the spectrum that are determined by 'windows' between spectral areas that heavily absorb light due to ever present atmospheric water vapour. It will therefore be unique in that it will accurately measure cirrus properties using no moving parts, using fixed frequency channels as apposed to a mechanically driven spectrometer. This makes the instrument low cost, light, small, simple to operate and extremely reliable which results in a package that is easily mountable on a range of aircraft. In the future, this kind of instrument could be satellite mounted using this airborne radiometer as a prototype.