The Importance of Hyperspectral Soil Albedo Information for Improving Earth System Model Projections

Earth system models (ESMs) typically simplify the representation of land surface spectral albedo to two values, which correspond to the photosynthetically active radiation (PAR, 400–700 nm) and the near infrared (NIR, 700–2500 nm) spectral bands. However, the availability of hyperspectral observations now allows for a more direct retrieval of ecological parameters and reduction of uncertainty in surface reflectance. To investigate sensitivity and quantify biases of incorporating hyperspectral albedo information into ESMs, we examine how shortwave soil albedo affects surface radiative forcing and simulations of the carbon and water cycles. Results reveal that the use of two broadband values to represent soil albedo can introduce systematic radiative-forcing differences compared to a hyperspectral representation. Specifically, we estimate soil albedo biases of  0.2 over desert areas, which can result in spectrally integrated radiative forcing divergences of up to 30 W m−2, primarily due to discrepancies in the blue (404–504 nm) and far-red (702–747 nm) regions. Furthermore, coupled land-atmosphere simulations indicate a significant difference in net solar flux at the top of the atmosphere (> 3.3 W m−2), which can impact global energy fluxes, rainfall, temperature, and photosynthesis. Finally, simulations show that considering the hyperspectrally resolved soil reflectance leads to increased maximum daily temperatures under current and future CO2 concentrations.

地球系统模式（Earth System Models, ESMs）通常将地表光谱反照率简化为两个数值，分别对应光合有效辐射（PAR，400–700 nm）与近红外波段（NIR，700–2500 nm）两个光谱区间。然而，当前高光谱观测技术的发展使得直接反演生态参数、降低地表反射率不确定性成为可能。为探究将高光谱反照率信息纳入地球系统模式的敏感性并量化其偏差，本研究分析了短波土壤反照率对地表辐射强迫及碳、水循环模拟的影响。研究结果显示，相较于高光谱表征方式，采用两个宽带数值表征土壤反照率会引入系统性辐射强迫差异。具体而言，我们估算得到沙漠区域的土壤反照率偏差约为±0.2，由此导致的光谱积分辐射强迫偏差最高可达30 W·m⁻²，该偏差主要源于蓝光波段（404–504 nm）与远红光波段（702–747 nm）的光谱差异。进一步的陆气耦合模拟结果表明，大气顶净太阳通量存在显著差异（>3.3 W·m⁻²），该差异可对全球能量通量、降水、气温及光合作用产生影响。模拟结果还显示，在当前及未来二氧化碳浓度情景下，考虑高光谱分辨率土壤反射率会使日最高气温升高。