Significant Topographic Impacts on Moderate-Resolution Satellite Products: Evidence From Both Geostationary and Polar-Orbiting Satellites and Model Simulations

Abstract

<p>It is well known that complex topography can affect satellite observations, leading to substantial uncertainties in surface parameter estimation when topographic effects are ignored. However, most existing studies have focused on high-resolution satellite data (e.g., <100 m resolution), while the impacts of topography on the moderate-resolution satellite data [e.g., moderate resolution imaging spectroradiometer (MODIS)] observation, product generation, and further applications have not been well explored. In this context, we investigated how topography-induced deviations propagate through moderate-resolution satellite observations, product generation, and downstream applications. We examined proxies such as top-of-atmosphere (TOA) reflectance, surface reflectance, land surface temperature (LST), leaf area index (LAI), and gross primary production (GPP), systematically analyzing their topographic effects across representative mountainous regions using multiple satellite datasets and radiative transfer models. Specifically, we conducted the following three tasks: 1) we utilized simultaneous observations from geostationary operational environmental satellite–16 (GOES-16) and GOES-17, which have differing viewing angles, to evaluate the topographic effects on geostationary satellite data; 2) we analyzed MODIS-Terra and MODIS-Aqua data, with varying sun and viewing angles, to assess the impact of topography on polar-orbiting satellite products; and 3) we employed radiative transfer models to gain theoretical insights into how topography influences satellite data across different terrain conditions. Our findings showed that topography induced an average deviation of 7.4% in near-infrared (NIR) band TOA reflectance in concurrent GOES-16 and GOES-17 observations. The surface reflectance and LST had similar deviation patterns as TOA reflectance. For NIR band surface reflectance, topographic effects lead to a maximum error of 0.37 in simulated data and an average of 16.7% deviation in MODIS-based evaluations. Furthermore, topographic impacts on LAI and GPP were found to average 36.0% and 10.4%, respectively, across four 1∘×1∘ mountainous regions globally. Long-term GPP trend analyses revealed uncertainties of 5.2% in the Alps and 3.8% in the Qinghai-Xizang Plateau, attributable to topographic effects. Our study demonstrates that topographic influences not only affect satellite observations but also propagate through to downstream applications for moderate-resolution data. By quantifying these effects, we underscore the importance of integrating topographic considerations into high-level satellite products over mountainous regions.</p>