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, for the special case where an individual leaf is too small and/or too narrow to entirely cover the reflectance or transmission port of the integrating sphere. Briefly, three arrays of mature, healthy and sunlit leaves from a canopy plant are arranged on a custom sample mount, and are then used for measurements of adaxial reflectance and transmittance. Leaf array scans are referenced to a calibrated Spectralon® disk and corrected for stray light to yield NIST-traceable, leaf spectral reflectance and transmittance measurements. Our leaf spectroscopy protocol builds from that of Noda et al. (2013), as well as Carnegie Airborne Observatory's protocol and integrating sphere user manuals from two companies (SVC, ASD Inc.).