Earth is a cloudy planet—at every moment, 62–72% of the planet is covered by cloud. Its presence and properties affect the flow of energy between the sun, Earth and the atmosphere. More comprehensive information about cloudiness is important to improve our understanding of the impact of cloud on Earth’s radiation budget. The aim of our work is to assess the accuracy of ground-based high-level cloud detections over Poland compared with satellite data. This project is the very first evaluation of error in visual high-cloud observation. Specifically, we answer a fundamental question: how effective are ground-based observers in detecting high-level cloud? Our unprecedented analysis is based on two datasets: traditional, visual observations from 43 selected synoptic stations and satellite (lidar) data, for the years 2006–2017. Ground-based observations were obtained from the archives of the Polish National Weather Service (IMWM-NRI), while satellite data came from the CALIPSO mission. Our final dataset comprised 7548 ground-based and satellite observations. Accuracy was assessed using the following indicators: probability of detection (Pd), probability of false alarm (Pfa), and overall accuracy (ACC). Overall (day and night observations), in the absence of lower-level cloud, observers correctly detected 80% of high-level cloud. However, when lower-level cloud was present, observers could not detect around 70% of high-level cloud. In sum, ground-based, high-level cloud detection is a function of the presence of lower-level cloud, the time of day, and the size of the area over which cirrus are observed/detected.

地球是一个多云的星球，每时每刻都有62-72％的星球被云覆盖。它的存在和性质影响太阳，地球和大气之间的能量流。关于云度的更全面的信息对于增进我们对云对地球辐射预算的影响的理解至关重要。我们的工作目的是评估与卫星数据相比在波兰进行的地面高空云探测的准确性。该项目是视觉高云观测中误差的第一个评估。具体来说，我们回答一个基本问题：地基观测员在检测高层云层中的效率如何？我们空前的分析基于两个数据集：2006-2017年间来自43个选定天气站的传统视觉观测和卫星（激光）数据。地面观测是从波兰国家气象局（IMWM-NRI）的档案中获得的，而卫星数据来自CALIPSO任务。我们的最终数据集包括7548个地面观测和卫星观测。使用以下指标评估准确性：检测概率（Pd），错误警报概率（Pfa）和总体准确性（ACC）。总体而言（白天和黑夜观察），在没有低层云的情况下，观察者正确地检测到80％的高层云。但是，当存在低层云时，观察者无法检测到约70％的高层云。总而言之，基于地面的高水平云检测取决于低水平云的存在，一天中的时间以及观察/检测到卷云的区域的大小。