Investigating the impact of IR surface emissivity knowledge & uncertainties on climate & weather-forecasting timescales

预计人类引起的气候变化的幅度和速度在高纬度（极地）地区最大。地表和大气之间的辐射相互作用是了解气候变化的关键，在极地地区，在异常透明的中远红外大气下，冰冻圈和开放海洋之间的相互作用增强了这种相互作用。地表反射/发射率在全球范围内的可见光和近红外波段进行了广泛的研究。然而，最近的气候模式模拟强调，迄今为止尚未认识到的反馈过程可能通过红外相互作用显著加速北极地区的变暖速度。该过程被称为“冰发射率”反馈，假设依赖于积雪和海洋表面远红外（FIR）辐射（波长在~ 15至100微米之间）的差异表面发射（Feldman等人，2014）。在FIR中，对表面辐射率的理论估计表明，海洋的辐射低于其上的冰雪层，因此，随着冰雪融化，额外的热量可能被困在海洋上层，加速冰融化并导致近地表和地表进一步变暖。现有的研究表明，需要改进目前对整个红外光谱表面发射率的估计。这些研究还表明，冰雪表面的发射光谱确实与一个完美的黑体发射器（这是目前大多数天气和气候预测模型所做的假设）有很大的不同。帝国理工学院空间和大气物理小组最近的工作首次通过航空观测对FIR表面发射率进行了原位估计（Bellisario等人，2017）。我们目前还在开发通过专门设计的便携式地面系统测量红外波段表面发射率的能力。目前的建模工作集中在极地地区对红外表面发射率的长期响应上，但其对较短“天气”时间尺度的未研究影响，以及它给月尺度预测增加的巨大不确定性来源，不应加以估计。因此，在本项目中，您将：(1)进一步利用北极飞行活动数据来评估我们初始结果的稳健性，并对理论雪/冰表面发射率估计进行额外的评估。(2)利用我们新的地面干涉仪系统，在一系列不同表面和条件下获得跨越中、远红外的红外发射率的原位估计，首先关注冰雪覆盖的高纬度地区。(3)与共同主管机构合作，评估新的强大的红外表面反射率/发射率测量对EO cal/val，气候研究和数值天气预报应用领域的影响。

The magnitude and pace of human-induced climate change is projected to be at its largest in high-latitude (polar) regions. The radiative interaction between the surface & atmosphere is key to understanding climate change, enhanced in Polar Regions by the interplay between the cryosphere & open ocean under an exceptionally transparent atmosphere in the mid- to far-IR. Surface reflection/emissivity has been studied extensively throughout the visible and NIR for many surface types across the globe. However, recent climate model simulations have highlighted that a hitherto unrecognised feedback process may significantly accelerate the rate of warming in arctic areas through IR interactions. Termed the 'ice-emissivity' feedback, the process is postulated to rely on differential surface emission of far infrared (FIR) radiation (wavelengths between ~ 15 and 100 microns) from snow covered and ocean surfaces (Feldman et al., 2014). In the FIR, theoretical estimates of surface emissivity suggest that the ocean is less emissive than overlying ice and snow layers, hence as snow/ice melts additional heat can be trapped within the upper ocean, accelerating ice melt and leading to further near surface and surface warming. Existing studies evidence a need for improvements in current estimates of the surface emissivity across the full infrared spectrum. These studies also indicate that snow and ice surfaces do indeed have an emissivity spectrum that is significantly different from that of a perfect, blackbody emitter (an assumption made in most current weather and climate prediction models). Very recent work within Imperial College's Space and Atmospheric Physics group has delivered the first ever in-situ estimates of FIR surface emissivity from airborne observations (Bellisario et al., 2017). We are also currently developing the capability to make measurements of surface emissivity extending across the infrared via a purpose designed portable ground-based system. Current modelling efforts have focused on the long-term response of the polar regions to infrared surface emissivity, but its unstudied impact on shorter 'weather' time-scales and the large source of uncertainty it adds to monthly-scale predictions should not be estimated. In this project you will thus: (1) Further exploit arctic flight campaign data to assess the robustness of our initial results and perform additional evaluation of theoretical snow/ice surface emissivity estimates.(2) Utilise our new ground-based interferometer system to obtain in-situ estimates of infrared emissivity spanning the mid- and far infrared for a range of different surfaces and conditions, focusing initially on snow/ice covered high latitudes.(3) Work with the co-supervisor institutions to assess the impact of new robust IR surface reflectance/emissivity measurements on EO cal/val, climate studies & numerical weather prediction application areas.