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

人类引起的气候变化的规模和速度预计在高纬度（极地）地区最大。地表与大气之间的辐射相互作用是理解气候变化的关键，在极地地区，在中红外到远红外异常透明的大气下，冰冻圈与开阔海洋之间的相互作用增强了这种相互作用。在整个可见光和近红外范围内，对地球仪的许多地表类型的地表反射/发射率进行了广泛的研究。然而，最近的气候模式模拟强调，迄今尚未认识到的反馈过程可能会显着加快北极地区的变暖速度，通过IR的相互作用。被称为“冰-发射率”反馈，该过程被假定为依赖于来自雪覆盖的和海洋表面的远红外（FIR）辐射（波长在~ 15微米和100微米之间）的差异表面发射（Feldman等人，2014）。在FIR中，对表面发射率的理论估计表明，海洋的发射率低于上覆的冰雪层，因此，随着冰雪融化，更多的热量可以被困在上层海洋中，加速冰融化，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，雪和冰的表面确实有一个发射率光谱，这是显着不同的一个完美的，黑体发射器（在大多数当前的天气和气候预测模型的假设）。帝国理工学院的空间和大气物理小组最近的工作已经提供了有史以来第一次从空中观测中对FIR表面发射率的原位估计（Bellisario等人，2017年）。我们目前还在开发通过专门设计的便携式地面系统测量整个红外线表面发射率的能力。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，但其对较短的“天气”时间尺度的未研究影响以及它给月尺度预测增加的大量不确定性来源不应被估计。在这个项目中，你将：（1）进一步利用北极飞行活动数据来评估我们的初步结果的鲁棒性，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，获得一系列不同表面和条件下的中红外和远红外红外发射率的现场估计，最初侧重于冰雪覆盖的高纬度地区。(3)与共同主管机构合作，评估新的可靠的红外表面反射率/发射率测量对EO校准/瓦尔、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.