Inter-sensor impacts of satellite-derived albedo and emissivity on terrestrial evapotranspiration retrievals

Albedo and broadband emissivity (BBE) derived from MODIS and AVHRR are key inputs for global evapotranspiration (ET) estimation, yet sensor differences introduce significant uncertainties. This study analyzes Global Land Surface Satellite (GLASS) albedo and BBE tempo-spatial discrepancies (2001-2019) between MODIS and AVHRR and evaluates their impacts on global ET retrieval, validated by eddy covariance observations. Temporally, MODIS and AVHRR albedo (BBE) exhibit pronounced discrepancy during November to May (November to April), with maximum discrepancy of 0.045 (0.007). Spatially, the difference occurs in desert and arid regions (arid index <1), high-altitude and mountainous areas ( >5200 m), and high-latitude areas ( >60°). The largest absolute (relative) difference in albedo and BBE reaches -0.25 and 0.11 (-110% and 11%), respectively. Notably, BBE discrepancies exert larger impacts on ET than albedo differences, causing maximum monthly ET variance >9 mm/month and mean absolute error fluctuation $\sim$ 10 mm/month against observations. Specifically, the most significant impacts are found in high-altitude regions (>6500 m; ET difference: 140 mm/yr, 24%) and deserts/arid zones (albedo >0.4; ET difference: -52 mm/yr, -190%). Overall, ET estimates from MODIS products outperform those from AVHRR products with lower relative error (9.04%), higher correlation (0.42), and reduced RMSE (23.88 mm/month). This advantage is particularly pronounced during summer and in arid regions. These findings inform the optimal application of GLASS products for global ET retrieval and highlight the need for careful sensor selection in hydrological and climate studies.