Abstract
Reliable and fine resolution estimates of surface net-radiation are required for estimating latent and sensible heat fluxes between the land surface and the atmosphere. However, currently, fine resolution estimates of net-radiation are not available and consequently it is challenging to develop multi-year estimates of evapotranspiration at scales that can capture land surface heterogeneity and are relevant for policy and decision-making. We developed and evaluated a global net-radiation product at 5 km and 8-day resolution by combining mutually consistent atmosphere and land data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra. Comparison with net-radiation measurements from 154 globally distributed sites (414 site-years) from the FLUXNET and Surface Radiation budget network (SURFRAD) showed that the net-radiation product agreed well with measurements across seasons and climate types in the extratropics (Wilmott’s index ranged from 0.74 for boreal to 0.63 for Mediterranean sites). Mean absolute deviation between the MODIS and measured net-radiation ranged from 38.0 ± 1.8 W∙m−2 in boreal to 72.0 ± 4.1 W∙m−2 in the tropical climates. The mean bias was small and constituted only 11%, 0.7%, 8.4%, 4.2%, 13.3%, and 5.4% of the mean absolute error in daytime net-radiation in boreal, Mediterranean, temperate-continental, temperate, semi-arid, and tropical climate, respectively. To assess the accuracy of the broader spatiotemporal patterns, we upscaled error-quantified MODIS net-radiation and compared it with the net-radiation estimates from the coarse spatial (1° × 1°) but high temporal resolution gridded net-radiation product from the Clouds and Earth’s Radiant Energy System (CERES). Our estimates agreed closely with the net-radiation estimates from the CERES. Difference between the two was less than 10 W·m−2 in 94% of the total land area. MODIS net-radiation product will be a valuable resource for the science community studying turbulent fluxes and energy budget at the Earth’s surface.
Highlights
Surface net-radiation is a critical component of the global water and energy cycle [1]
We provide details of the field measurements of surface net-radiation obtained from the FLUXNET and Surface Radiation budget network (SURFRAD) networks, share the characteristics of the CERES product, and describe the statistical methods and metrics used in evaluating the accuracy and reliability of our net-radiation product while taking uncertainty into account
We searched for good quality data in the neighborhood of pixels with missing values and progressively enlarged the search window until we found sufficient good-quality similar pixels within the same Moderate Resolution Imaging Spectroradiometer (MODIS) tile
Summary
Surface net-radiation is a critical component of the global water and energy cycle [1]. Remote sensing-based surface net-radiation estimates are available at moderate spatial resolution [6,7,8]. We develop and evaluate a global daily net-radiation product at 5 km, derived from mutually consistent land and atmosphere data from the Moderate Resolution Imaging Spectroradiometer (MODIS) following an approach based on physical principles. We build on previous efforts and derive net-radiation as an independent seamless product at 5 km spatial resolution and eight-day time step for the entire global land area by combining an atmospheric radiative transfer model [17] with land and atmosphere data from MODIS for 2001 to 2009. We rigorously evaluate our product using high-quality, field measurements from 154 field sites (414 site-years) spread all across the globe
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