We’re very happy to welcome Mary Langsdale, from King’s College London to give a seminar on Tuesday, 13th February.

Laboratory measurements of spectral emissivity: can we trust the ‘truth’

Spectral emissivity is a key input for remotely sensed retrievals of land surface temperature (LST), an Essential Climate Variable (ECV). However emissivity is non-trivial to estimate from a longwave infrared sensor as there is an undetermined problem such that for N bands, there are N+1 unknowns. Instead emissivity measurements often come from either spectral libraries based upon laboratory spectroscopic measurements or spectroscopic measurements of samples from the field. In each case, known dynamical drivers of emissivity such as soil moisture and canopy structure may be neglected, which can introduce errors into the derived emissivity and consequently LST. Furthermore, due to lack of research into characterization of such setups, uncertainties on these measurements are either typically either derived from repeated measurements or not presented at all. In this talk, I first present results from two published inter-comparison exercises using different laboratory measurements. The results from these exercises suggest that differences between measurements of emissivity derived via laboratory setups may be larger than anticipated and highlight the need for the infrared spectroscopy community to work towards standardized and interlaboratory comparable results. In addition to this, I present a recent study comparing different methods of sample preparation to demonstrate the impact that this can have on emissivity and highlight the potential differences between field and laboratory measurements. In each case, the potential impact on retrieved LST is considered.