Many targets that remote sensing scientists encounter when conducting their research experiments do not lend themselves to laboratory measurement of their surface optical properties. Removal of these targets from the field can change their biotic condition, disturb the surface composition, and change the moisture content of the sample. These parameters, as well as numerous others, have a marked influence on surface optical properties such as spectral and bi-directional emissivity. This necessitates the collection of emissivity spectra in the field. The propagation of numerous devices for the measurement of midwave and longwave emissivity in the field has occurred in recent years. How good are these devices and how does the accuracy of the spectra they produce compare to the tried and true laboratory devices that have been around for decades? A number of temperature/emissivity separation algorithms will be demonstrated on data collected with a field portable Fourier transform infrared (FTIR) spectrometer and the merits and resulting accuracy compared to laboratory spectra made of these identical samples. A brief look at off-nadir view geometries will also be presented to alert scientists to the possible sources of error in these spectra that may result when using sensing systems that do not look straight down on targets or when their nadir looking sensor is looking at a tilted target.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.