Accurate and precise characterization of cirrus cloud geometrical and optical properties is essential for better constraining their radiative footprint. A lidar-based retrieval scheme is proposed here, with its performance assessed on fine spatio-temporal observations over the Arctic site of Ny-Ålesund, Svalbard. Two contributions related to cirrus geometrical (dynamic Wavelet Covariance Transform (WCT)) and optical properties (constrained Klett) are reported. The dynamic WCT rendered cirrus detection more robust, especially for thin cirrus layers that frequently remained undetected by the classical WCT method. Regarding optical characterization, we developed an iterative scheme for determining the cirrus lidar ratio (LR_ci) that is a crucial parameter for aerosol - cloud discrimination. Building upon the Klett-Fernald method, the LR_ci was constrained by an additional reference value. In established methods, such as the double-ended Klett, an aerosol-free reference value is applied. In the proposed constrained Klett, however, the reference value was approximated from cloud-free or low cloud optical depth (COD up to 0.2) profiles and proved to agree with independent Raman estimates. For optically thin cirrus, the constrained Klett inherent uncertainties reached 50% (60-74%) in terms of COD (LR_ci). However, for opaque cirrus COD (LR_ci) uncertainties were lower than 10% (15%). The detection method discrepancies (dynamic versus static WCT) had a higher impact on the optical properties of low COD layers (up to 90%) compared to optically thicker ones (less than 10%). The constrained Klett presented high agreement with two established retrievals. For an exemplary cirrus cloud, the constrained Klett estimated the COD³⁵⁵ ($LR_{ci}^{355}$) at 0.28 ± 0.17 (29 ± 4 sr), the double-ended Klett at 0.27 ± 0.15 (32 ± 4 sr) and the Raman retrievals at 0.22 ± 0.12 (26 ± 11 sr). Our approach to determine the necessary reference value can also be applied in established methods and increase their accuracy. In contrast, the classical aerosol-free assumption led to 44 sr LR_ci overestimation in optically thin layers and 2-8 sr in thicker ones. The multiple scattering effect was corrected using Eloranta (1998) and accounted for 50-60% extinction underestimation near the cloud base and 20-30% within the cirrus layers.

中文翻译：

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基于激光雷达的扩展卷云检索方案：在北极站点上的首次应用

卷云的几何和光学特性的准确和精确表征对于更好地限制其辐射足迹至关重要。本文提出了一种基于激光雷达的检索方案，该方案的性能是根据斯瓦尔巴特群岛Ny-Ålesund北极地区的精细时空观测结果进行评估的。报告了与卷云几何（动态小波协方差变换（WCT））和光学特性（约束Klett）有关的两个贡献。的动态WCT渲染卷云检测更加健壮，尤其是对于经常仍然通过经典方法WCT未被发现薄卷云层。关于光学特性，我们开发了一种用于确定卷云激光雷达比（LR _ci）的迭代方案。）是气溶胶的关键参数-云的辨别力。在Klett-Fernald方法的基础上，LR _ci受一个附加参考值的约束。在已建立的方法中（例如双端Klett），将应用无气溶胶的参考值。但是，在拟议的约束Klett中，参考值是从无云或低云光学深度（COD最高为0.2）剖面中近似得出的，并证明与独立的拉曼估计值一致。对于光学稀薄的卷云，约束的Klett固有不确定性以COD（LR _ci）计达到50％（60-74％）。但是，对于不透明的卷云化学需氧量（LR_ci）的不确定性低于10％（15％）。与光学上较厚的层（小于10％）相比，检测方法的差异（动态WCT与静态WCT）对低COD层（高达90％）的光学特性有更高的影响。受束缚的克莱特（Klett）与两个既定的检索结果高度吻合。对于示例性的卷云，约束的Klett估计的COD ³⁵⁵（ $ LR_ {ci} ^ {355} $）为0.28±0.17（29±4 sr），双端Klett的估计值为0.27±0.15（32±4 sr） ）并在0.22±0.12（26±11 sr）处进行拉曼检索。我们确定必要参考值的方法也可以应用于既定方法并提高其准确性。相比之下，经典的无气雾假设导致光学薄层中的sr LR _ci高估，而较厚层中的2-8 sr。多重散射效应使用Eloranta（1998）进行了校正，并导致云基附近的消光低估了50-60％，卷云层内的消散低估了20-30％。