It is fundamental to obtain accurate land surface temperature (LST) to study surface energy process. Infrared thermal imagers are commonly used for deriving LST on the basis of radiance measurements. However, when deriving LST from brightness temperature of a blackbody in thermal imagers, thermal imagers only allow setting a fixed land surface emissivity (LSE). This causes uncertainty in retrieving thermal infrared (TIR) temperature from heterogeneous surfaces with varied LSE, such as those covered in vegetation. Corrections can be made using the Normalized Vegetation Index (NDVI). However, commercial thermal imagers provide only red (R), green (G), and blue (B) bands without a near infrared band so NDVI cannot be calculated on the same instrument and is commonly not available. We propose an alternative method to estimate LSE using RGB-based vegetation index. Thereafter the estimated LSE was used to correct the TIR temperature derived from the fixed LSE. An experiment was conducted to validate the proposed correcting method. The results show that 1) the corrected LST values were closer to the ground truth, with a mean absolute error (MAE) of 0.41 ± 0.34 °C, whereas the MAE was 0.75 ± 0.56 °C for the uncorrected LST; 2) the more heterogeneous the surface, the greater the difference between the corrected and uncorrected LST values, indicating the necessity of LST correction when applying thermal imagers over heterogeneous surface.

中文翻译：

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通过考虑异质发射率来校正热成像仪的地表温度

准确获取地表温度（LST）是研究地表能量过程的基础。红外热像仪通常用于根据辐射测量得出地表温度。然而，当热像仪中从黑体的亮温导出 LST 时，热像仪仅允许设置固定的地表发射率 (LSE)。这会导致从具有不同 LSE 的异质表面（例如被植被覆盖的表面）检索热红外 (TIR) 温度的不确定性。可以使用归一化植被指数 (NDVI) 进行修正。然而，商用热像仪仅提供红色 (R)、绿色 (G) 和蓝色 (B) 波段，而没有近红外波段，因此无法在同一仪器上计算 NDVI，并且通常不可用。我们提出了一种使用基于 RGB 的植被指数来估计 LSE 的替代方法。此后，估计的 LSE 用于校正从固定 LSE 导出的 TIR 温度。进行了实验来验证所提出的校正方法。结果表明：1）校正后的LST值更接近地面真实值，平均绝对误差（MAE）为0.41±0.34℃，而未校正的LST的MAE为0.75±0.56℃； 2）表面越不均匀，校正后和未校正的LST值之间的差异越大，表明在不均匀表面上应用热像仪时需要进行LST校正。