Thermal infrared measurements on a projection screen at Hintereisferner

In this study, an InfraTec VarioCAM HD thermal infrared (TIR) camera (1024 × 768 pixels) was used to monitor air temperature dynamics near a glacier surface. The camera targeted two vertically mounted polyester screens (with emissivity 0.94), which rapidly equilibrate with ambient air temperature and thus serve as reliable proxies for air temperature. Screen 1 (1.9 m × 3 m) was used for along-flow measurements, while Screen 2 (3.8 m × 1.9 m) captured vertical temperature profiles. This analysis focuses on Screen 2 to examine vertical air temperature dynamics in relation to katabatic winds. The screens were aligned with the glacier wind to measure temperature patterns along and across the katabatic jet, typically located 1.7–2.3 m above the ice surface (based on prior HEFEX I data). The TIR camera, positioned at a distance yielding a resolution of ~6 mm/pixel, recorded at 30 Hz. To ensure data accuracy, TIR values were averaged across pixels to account for material variability and contamination. Due to possible solar heating, absolute temperature readings may be positively biased, so the study emphasizes relative temperature changes. TIR measurements were conducted during the Intensive Observation Period (IOP) of the HEFEX II campaign (August 22–24, 2023). Five representative data sequences from August 22–23 2023 were selected, each lasting from one to several hours. These sequences demonstrate the method’s effectiveness in capturing high-resolution spatial and temporal temperature variations during both stable katabatic and disturbed flow conditions. Combining TIR and turbulence data enables estimation of jet height.本研究采用InfraTec VarioCAM HD型热红外（TIR）相机（分辨率1024×768像素），对冰川表面附近的空气温度动态变化进行监测。该相机以两块垂直安装的聚酯屏（发射率0.94）为观测目标，这类屏体可快速与环境空气温度达到热平衡，因此可作为空气温度的可靠替代观测指标。屏体1（尺寸1.9 m × 3 m）用于沿流向的温度测量，屏体2（尺寸3.8 m × 1.9 m）则用于获取垂直温度廓线。本分析聚焦屏体2，以探究与下降风相关的垂直空气温度动态变化。 屏体与冰川风对齐，以测量下降风流沿流向及横流向的温度分布特征，该下降风流通常位于冰面上方1.7–2.3 m处（基于此前HEFEX I项目的观测数据）。本次实验中，热红外相机的布设距离使得其成像分辨率约为6 mm/像素，采样帧率为30 Hz。为保障数据准确性，研究对各像素的TIR值进行平均处理，以抵消屏体材质不均及污染带来的影响。由于存在太阳辐射加热的可能性，绝对温度读数可能存在正偏差，因此本研究重点关注相对温度变化。 本次TIR观测于HEFEX II科考项目的加密观测期（IOP）内开展，时段为2023年8月22日至24日。研究选取了2023年8月22日至23日的5组典型数据序列，单组序列时长为1小时至数小时不等。这些数据序列验证了该方法可有效捕捉稳定下降风及扰动流场条件下的高时空分辨率温度变化。结合TIR观测数据与湍流数据，可实现下降风流高度的估算。