Measurement of bi-direflectance (BRDF) of sea-ice for Earth Observing Satellites

政府间气候变化专门委员会（IPCC）称，目前对雪和海冰中黑碳的气候影响的认识“非常低”，显然需要对这些过程进行更好的研究。由于人为（和生物）燃烧而增加的黑碳沉积在极地雪和海冰中，显著降低了海冰或雪的反射率。地球表面反射率的降低导致地球变暖的加剧。卫星观测可以对地球的大部分地区进行天气观测。可见光和近红外遥感观测（如Meris、MODIS、AVHHR）在海洋、陆地和冰雪相关气候研究中具有广泛的应用，可作为主要和次要信息来源。然而，尽管分析来自单个传感器的数据具有重要价值，但任何全球观测系统，特别是需要不同空间分辨率和长时间基础的研究，都需要准确了解传感器对传感器的偏差。这就要求在空间中操作的所有光学辐射计的灵敏度可以相互比较，并可追溯到一个共同的参考标准。地球观测卫星委员会（地球观测卫星委员会）制定了若干地球目标作为国际参考标准，每一个目标都有或将有地面现场测量的特点。自然表面的反射率不是各向同性的。反射率随光照和观测几何形状而变化，从而影响卫星观测。因此，自然表面的双向反射率（BRDF）是使用卫星数据的先决条件。海冰是一个潜在的校准目标。博士生将与两位导师密切合作，在新的RHUL海冰模拟器中生成海冰。在2000L的储罐中会产生掺入不同浓度黑碳的海冰。海冰的反射率将在太阳光谱中以不同的天顶角和方位角测量紫外线和可见光部分。BRDF将记录海冰温度为-5至-25℃，黑碳含量为0-100 ng g（-1）。该项目将提供：(1)海冰BRDF，可用于地球观测卫星间校准。这将由CASE的合作伙伴——国家物理实验室的奈杰尔·福克斯博士交付给最终用户。(2) BRDF作为黑碳含量的函数，并评估EO卫星对黑碳负荷的敏感性，即EO卫星是否可以用于测量海冰中的BC。(3)三篇学术论文报道了海洋BRDF与(a)温度、(b)黑碳浓度、(c) BRDF对黑碳大小、形状、折射率的敏感性的函数关系。提议的研究是低风险，高回报和成本效益的，皇家霍洛威和国家物理实验室之间的合作伙伴关系是一个很好的培养博士生的机会。申请人已在初步研究中证明所有实验都是可行的，并在为卫星校准和测量冰雪光学而进行BRDF测量方面具有丰富的经验。这个项目是非常令人兴奋和高度相关的，因为它将提高对冰雪辐射过程中黑碳的理解。所需的财政资源很少，RHUL用CIF的资金建造了海冰模拟器，并提供了一个研究冰生物地球化学的博士奖学金。学生将有两个极好的学习环境，这个跨学科的项目将直接向最终用户提供地球观测卫星对气候研究的重要校准，即有明显的社会效益。这对英国卫星和地球观测行业有工业效益，最终用户是CASE的合作伙伴，因此该项目有一个真正的影响途径。

The current understanding of climatic influences of black carbon in snow and sea-ice has been described by the intergovernmental panel on climate change, IPCC, to be 'very low' and a better examination of these processes is clearly required. Black carbon from increasing anthropogenic (and biogenic) combustion deposits in polar snow and sea-ice to significantly reduce the reflectivity of the sea-ice or snow. The reduced reflectivity of the Earth surface results in increased warming of the planet. Satellite observations allow for the synoptic observation of large areas of the globe. Remote sensing observations performed in the visible and near infrared (e.g. Meris, MODIS, AVHHR) have wide application in marine, land and snow/ice related climate studies serving as both primary and secondary sources of information. However, although there is significant value in the analysis of data from individual sensors, any global observing system and in particular studies requiring different spatial resolutions and long time bases require accurate knowledge of sensor to sensor biases. This requires the responsivities of all optical radiometers operated in space to be intercompared and traceable to a common reference standard. CEOS (Committee on Earth Observing Satellites) has established a number of Earth targets to serve as international reference standards, each being, or to be, well characterized by surface based in-situ measurements. The reflectance of natural surfaces is not isotropic. The reflectance varies with the illumination and viewing geometries, and consequently impacts satellite observations. Thus the bi-directional reflectance (BRDF) of natural surfaces is a pre-requisite for use of satellite data. Sea-ice is a strong potential calibration target. Working closely with both supervisors the PhD student will generate sea ice in the new RHUL sea-ice simulator. Sea-ice doped with different concentrations of black carbon will be generated in 2000L tanks. The reflectivity of the sea-ice will be measured in the UV and visible parts of the solar spectrum with different zenith and azimuthal angles. The BRDF will be recorded for the sea-ice temperatures of -5 to -25C and black carbon loading of 0-100 ng g(-1). The project will deliver:- (1) A BRDF for sea-ice that can be used by Earth observing satellites to inter-calibrate. This will be delivered to the end users by CASE partner - Dr Nigel Fox, NPL. (2) A BRDF as a function of black carbon content with an assessment of sensitivity of EO satellites to Black carbon loading - i.e. can EO satellites be used to measure BC in sea-ice. (3) Three academic papers reporting the BRDF of seaice as a function of (a) temperature, (b) black carbon concentration, and (c) the sensitivity of BRDF to size, shape, refractive index of the black carbon. The proposed research is low risk, highly rewarding and cost effective and the partnership between Royal Holloway and the NPL is an excellent training opportunity for a PhD student. The applicants have demonstrated in preliminary studies that all experiments are feasible, and have complimentary extensive experience in making BRDF measurements for satellite calibration and measuring the optics of snow and ice. The project is very exciting and highly relevant since it will improve the understanding of black carbon in snow and ice radiative processes. The financial resources required are minimal, RHUL has constructed the sea-ice simulator with CIF money and supported it with a PhD studentship to study ice biogeochemistry. The student will have two fantastic learning environments for this very interdisciplinary project that will directly deliver an important calibration for climate studies by earth observing satellites straight to an end user - i.e. there is clear societal benefit. There is industrial benefit to the UK satellite and Earth observing industry, and end-user is the CASE partner so the project has a real pathway to impact.