基于NOAA/AVHRR数据的北极反照率反演及其变化研究

极地海冰反照率直接影响极区的热收支,反照率的变化对地气系统热量收支平衡及气候变化等的研究具有重要意义。本文采用由美国国家海洋与大气管理局NOAA (National Oceanic and Atmospheric Administration)发射的NOAA卫星携带的先进的甚高分辨率辐射仪AVHRR (Advanced Very High Resolution Radiometer) Level-1B (L1B) 数据,经宽带反射率转换、各向异性校正、大气订正、云检测等处理,得到4 km宽带晴空地表反照率产品。将AVHRR反照率与北冰洋地表热收支SHEBA (Surface Heat Budget of the Arctic Ocean)实验数据进行印证,印证结果显示在冰雪冻结期二者平均偏差为-0.07,标准偏差为0.05。本文处理了2008年—2010年的AVHRR数据,结合第4次北极科学考察现场观测数据研究了北极冰面月平均反照率的变化,从降雪和冰脊两个方面分析了反照率的变化,结果显示反照率在冰雪融化过程中变化约为0.3,变化较大且较为迅速,表面粗糙的多年冰海域和较为平滑的一年冰海域的反照率在雪融化时期变化约为0.2且变化相对缓慢。研究结果表明,由冰雪融化引起的反照率变化较为快速且幅度较大,是引起北极反照率变化的主导因素。

Retrieval and analysis of Arctic albedo from NOAA/AVHRR data

Surface albedo in the Arctic is one of the most important factors influencing the polar heat budget. The impact of variations of the Arctic sea ice albedo on the heat budget of the earth-atmosphere system and on global climate change is significant. In this paper, the surface albedo in the Arctic was derived using the Level-1B (L1B) data from the advanced very high resolution radiometer (AVHRR) onboard the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites. We applied narrow-to-broadband conversion, anisotropic correction, atmospheric correction, and cloud detection to the satellite data, and obtained broadband surface albedo products in clear conditions with a 4 km spatial resolution. Comparisons between the AVHRR albedo products and in situ measurements collected during the Surface Heat Budget of the Arctic Ocean (SHEBA) project showed a bias of -0.07 and a standard deviation of 0.05 during the spring-winter season. Monthly averaged NOAA/AVHRR surface albedo data from 2008 to 2010, combined with in situ measurements from the fourth Chinese Arctic research expedition, were used to study the variation of the Arctic sea ice albedo. The influence of snowfall and ice ridges on the variation of surface albedo was analyzed. The albedo decreased significantly and rapidly by about 0.3 when the snow was melting. Comparing between the albedo variations in the rough multi-year ice area and smooth first-year ice area shows an albedo difference of 0.2 during the melting season. The results indicate that the melting of snow and ice was the dominant factor for the variation of the Arctic albedo.