Effect of Remote Sensing Resolution on Evapotranspiration Estimates for the Jornada and Sevilleta, NM Experimental Rangeland Sites

The effect of remote sensing resolution on estimation of evapotranspiration (ET) is important for determining modeling uncertainties and for planning future remote sensing missions such as the NASA HyspIRI satellite. Higher spatial resolutions, 30 m or better, are often needed to discriminate many land cover classes critical for accurate ET modeling. However, coarser remote sensing resolutions, up to 100-200 m, may still provide valuable observations with small increases in ET modeling uncertainties. To investigate the quantitative effects of resolution upon ET estimation, a remote sensing study was conducted over semi-arid rangeland sites in New Mexico: Jornada and Sevilleta. Using 15-m resolution airborne data collected between 2001 and 2010, multispectral visible, near infrared, and thermal infrared data were progressively degraded to 120 m scales and modeled for ET using a two-source energy balance approach. Results showed that range in observed ET was strongly reduced between 15 and 60 m, but also that little ET bias (<50 Wm2) was introduced. This outcome was due to landscape heterogeneities at very fine scales, 3 m. A way to estimate the loss of ET range will be discussed using 1 m resolution panchromatic image data.