Here we describe the standardised protocol used by the Canadian Airborne Biodiversity Observatory (CABO) to measure leaf spectral reflectance and transmittance, using an integrating sphere fitted to a portable full-range field spectroradiometer. This standard version of our protocol describes the common case where an individual leaf is large enough to entirely cover the reflectance or transmission port of the integrating sphere. Briefly, six mature, healthy-looking and sunlit leaves from a canopy plant are selected for measurements of adaxial reflectance and transmittance. Leaf scans are referenced to a calibrated Spectralon® disk and corrected for stray light. Our leaf spectroscopy protocol builds from that of the Carnegie Airborne Observatory, as well as from integrating sphere user manuals from two companies (ASD Inc., SVC).