Portable apparatus for high spatial and temporal resolution of in situ real-time surface albedo measurement in agricultural fields

Abstract

Climate models and global warming mitigation requires finer spatial data for albedo than satellites typically provide. To develop field-ready techniques for assessing albedo changes at the management unit scale, an affordable, highly portable albedometer is needed. This paper describes an apparatus to obtain real-time in situ measurements at sensor heights of 0.3 to 3 m providing direct albedo measurements for 8–1000 m² sensing area. This method allows sampling of multiple locations during a single near-solar-noon. The incoming and reflected solar radiation in an Ohio, USA cover-cropped agricultural field in winter showed a strong linear relationship that was not affected by time of day during 4 days of snowmelt. The portable apparatus is sufficiently sensitive to record changes in albedo resulting from hourly snowmelt. The influence of sensor height and thus footprint was analyzed by measuring albedo at a reduced tillage corn field and perennial forage field. Mean albedo ranged from 0.175 to 0.203. There were small but statistically significant differences between mean albedo within each site at different sensing footprints. These results suggest that heterogeneity in soil surface cover (vegetation and/or residue) within a single sensing footprint influences in situ surface albedo. It is important to examine similarly sized sensing footprints when comparing albedo across sites or monitoring a single site at multiple times especially in areas with heterogeneous surface cover. The method and equipment presented here will facilitate future research to better understood how albedo may be controlled through agricultural land management techniques for increased sustainability.