Factors influencing contrail observability in satellite images

Oral Presentation 

Contrails (clouds formed by aircraft) have been identified as the largest component of aviation-induced radiative forcing, contributing a net warming effect estimated to be over half of the industry’s total. Satellites can provide observational data to support model validation, monitoring, and trialling of changes to aircraft operations. It is well-established that not every contrail is observable in satellite imagery due to either sub-pixel structure or low optical depth. The conditions under which a specific contrail can be detected are not well understood but are critically important for designing observations that meet our needs. In this study, the contrail observability has been assessed as a function of the contrail’s properties, the atmospheric background, and the imager used. Artificial satellite images were created using radiative transfer simulations. These synthetic images were analysed using different contrail detection algorithms to determine the conditions and properties controlling contrail observability. The analysis was combined with output from the Contrail Cirrus Prediction (CoCiP) model to determine the fraction of contrails, and of contrail radiative forcing, that is observable with current instrumentation. It was shown that the most strongly warming contrails are also more easily detectable than other contrails, but that significant fractions of climate-relevant contrails are not detected using current techniques. The biases and potential optimisations of imager and algorithm developments were also explored, demonstrating how these systems could be improved in the future.