Agricultural and Forest Meteorology 114 (2003) 213–234 Spatial source-area analysis of three-dimensional moisture fields from lidar, eddy covariance, and a footprint model D.I. Cooper a,∗ , W.E. Eichinger b , J. Archuleta a , L. Hipps c , J. Kao a , M.Y. Leclerc d , C.M. Neale c , J. Prueger e a Los Alamos National Laboratory, Los Alamos, NM 87545, USA b University of Iowa, Iowa City, Iowa, IA 52242, USA c Utah State University, Logan, UT 84322, USA d University of Georgia, Griffin, GA 30223, USA e National Soil Tilth Laboratory, Ames, IA 50011, USA Received 1 May 2001; received in revised form 23 August 2002; accepted 4 September 2002 Abstract The Los Alamos National Laboratory scanning Raman lidar was used to measure the three-dimensional moisture field over a salt cedar canopy. A critical question concerning these measurements is; what are the spatial properties of the source region that contributes to the observed three-dimensional moisture field? Traditional methods used to address footprint properties rely on point sensor time-series data and the assumption of Taylor’s hypothesis to transform temporal data into the spatial domain. In this paper, the analysis of horizontal source-area size is addressed from direct lidar-based spatial analysis of the moisture field, eddy covariance co-spectra, and a dedicated footprint model. The results of these analysis techniques converged on the microscale average source region of between 25 and 75 m under ideal conditions. This work supports the concept that the scanning lidar can be used to map small scale boundary layer processes, including riparian zone moisture fields and fluxes. Published by Elsevier Science B.V. Keywords: Spatial source-area analysis; Three-dimensional moisture; Latent energy flux 1. Introduction The Los Alamos National laboratory (LANL) scanning Raman lidar has been used to measure mul- tidimensional water vapor fields for nearly a decade (Cooper et al., 1992). More recently, it has been used to estimate spatially resolved latent energy flux (LE) using a scalar gradient-based similarity ap- proach (Cooper et al., 2000; Eichinger et al., 2000). Three-dimensional fields of water vapor can be trans- ∗ Corresponding author. Tel.: +1-505-665-6501; fax: +1-505-667-7460. E-mail address: dcooper@lanl.gov (D.I. Cooper). lated into spatial estimates of surface fluxes if a known surface emitting region can be connected to the wa- ter vapor concentration at any particular height. This paper addresses the surface water vapor source-area sampling criteria and the extent of the flux footprint for application to remote sensing observations in the boundary layer. The sampling size depends on surface–atmosphere coupling and data acquisition properties, including the time required to scan over an area of interest. This study attempts to charac- terize lidar footprints and compare them with eddy covariance-derived co-spectra and a footprint model. The “footprint issue” has been studied by inves- tigators for the past decade (Leclerc et al., 1997, 0168-1923/02/$ – see front matter. Published by Elsevier Science B.V. PII:S0168-1923(02)00175-2