Opt Express. 2023 May 8;31(10):15256-15288. doi: 10.1364/OE.482762.
Rapid radiative transfer models are crucial to remote sensing and data assimilation. An integrated efficient radiative transfer model named Dayu, which is an updated version of the Efficient Radiative Transfer Model (ERTM) is developed to simulate the imager measurements in cloudy atmospheres. In Dayu model, the Optimized alternate Mapping Correlated K-Distribution model (OMCKD) which is predominant in dealing with the overlap of multiple gaseous lines is employed to efficiently calculate the gaseous absorption. The cloud and aerosol optical properties are pre-calculated and parameterized by the particle effective radius or length. Specifically, the ice crystal model is assumed as a solid hexagonal column, of which the parameters are determined based on massive aircraft observations. For the radiative transfer solver, the original 4-stream Discrete ordinate aDding Approximation (4-DDA) is extended to 2N-DDA (2N is the number of streams) which can calculate not only the azimuthally dependent radiance in the solar spectrum (including solar and infrared spectra overlap) but also the azimuthally averaged radiance in the thermal infrared spectrum through a unified adding method. Then the accuracy and efficiency of Dayu model are evaluated by comparing it with the benchmark model, i.e., Line-By-Line Radiative Transfer Model (LBLRTM) and DIScrete Ordinate Radiative Transfer (DISORT). Under the standard atmospheric profile, the maximum relative biases between Dayu model with 8-DDA / 16-DDA and the benchmark model (OMCKD with 64-stream DISORT) are 7.63% / 2.62% at solar channels but decreased to 2.66% / 1.39% at spectra-overlapping channel (3.7 μm). The computational efficiency of Dayu model with 8-DDA / 16-DDA is approximately three / two orders of magnitude higher than that of the benchmark model. At thermal infrared channels, the brightness temperature (BT) differences between Dayu model with 4-DDA and the benchmark model (LBLRTM with 64-stream DISORT) are bounded by 0.65K. Compared to the benchmark model, Dayu model with 4-DDA improves the computational efficiency by five orders of magnitude. In the application to the practical Typhoon Lekima case, the simulated reflectances and BTs by Dayu model have a high consistency with the imager measurements, demonstrating the superior performance of Dayu model in satellite simulation.
快速辐射传输模型对于遥感和数据同化至关重要。为了模拟云大气中的成像仪测量，开发了一种名为大禹的集成高效辐射传输模型，这是高效辐射传输模型（ERTM）的更新版本。在大禹模型中，采用了主要用于处理多个气体线重叠的优化交替映射相关 K 分布模型（OMCKD），以有效地计算气体吸收。云和气溶胶光学特性通过颗粒有效半径或长度预先计算和参数化。具体来说，冰晶模型被假设为固体六方柱，其参数根据大量飞机观测确定。对于辐射传输求解器，原始的 4 流离散坐标加近似（4-DDA）扩展到 2N-DDA（2N 是流数），通过统一的加和方法不仅可以计算太阳光谱中与方位有关的辐射（包括太阳和红外光谱重叠），还可以计算热红外光谱中的方位平均辐射。然后，通过与基准模型（即线通过线辐射传输模型（LBLRTM）和离散坐标辐射传输（DISORT））进行比较，评估大禹模型的精度和效率。在标准大气廓线下，大禹模型 8-DDA/16-DDA 与基准模型（64 流 DISORT 的 OMCKD）之间的最大相对偏差分别为太阳通道的 7.63%/2.62%，但在光谱重叠通道（3.7 μm）下降低到 2.66%/1.39%。大禹模型 8-DDA/16-DDA 的计算效率大约比基准模型高三个/两个数量级。在热红外通道，4-DDA 大禹模型与基准模型（64 流 DISORT 的 LBLRTM）之间的亮度温度（BT）差异被限制在 0.65K 以内。与基准模型相比，4-DDA 大禹模型的计算效率提高了五个数量级。在实际台风利奇马案例中的应用中，大禹模型模拟的反射率和 BT 与成像仪测量值具有很高的一致性，表明大禹模型在卫星模拟中具有优越的性能。
