摘要
基于MODIS 500 m分辨率数据,利用MODTRAN 4+模型和可见光波段、近红外波段的波段比方法反演雪粒径,建立1个消融期内的雪粒径变化的时间序列,通过采集七一冰川上设立的观测点对应时间段内雪粒径验证MODIS模拟的雪粒径值,结合位于观测点附近的气象站的气温数据,探讨气温对雪粒径的影响。结果表明,雪粒径的增长存在着明显的日变化趋势;模拟的雪粒径普遍高于实测的雪粒径值,因此反演模型需要约为1.1倍的校正因子;气温对雪粒径的影响显著。
The 500 m resolution Moderate Resolution Imaging Spectroradiometer （MODIS） L1B scenes over Qiyi glacier, Qilian Mountain is used to estimate the snow grain size. The retrieval is based on ratios of near-in-frared albedo to visible albedo which predicts snow reflectance as a function ofsnowpack grain size and ice ab- sorption. ＂Bow-tie＂ effects were removed by the ENVI software. Atmospheric effects are taken into account and corrected through the MODTRAN4＋ model. By this approach snow optical grain size was determined by the volume-to-surface area ratio on account of non-oriented spheroids produce the same scattering results as spheres. The time series analysis of derived grain size shows a good sensitivity to snow melting and snow pre- cipitation events. This inversion technique has been validated using a combination of ground-based grain size measurements derived from the handle lenses which measure the snow grain size over the top 1 cm layer. The retrievals correlate well with measurements when radii is in range of-0.1-1 mm, although retrieved optical snow grain size general is lower than physical measured grain size , the model may be need about a factor of 1.1. As part of validation analysis for the Qiyi glacier, the retrieved snow grain size from MODIS over selected sites in the period of September 7-15 in 2011 was compared to the temperature measurement of the automatic weather station near the selected sites. The relationship between the measured snow grain size, simulated snow grain size and average temperature patterns suggests that rapid destructive metamorphism of the fresh snow oc-curred when temperatures were near 0℃, once temperatures were higher than 0℃ and kept for a long time, the snow particle size change was evident, snow particle size increased significantly, and vice versa. But in this prossess, snow particle size also existed evolution process of deformation; snow particle size and temperature showed significantly positive correlation. The future work is to study the better cloud mask algorithm to re-move the cloud effects and build the long and continuous time series of the snow grain size.
出处
《地理科学》
CSCD
北大核心
2013年第3期378-384,共7页
Scientia Geographica Sinica
基金
全球变化研究重大科学研究计划(2010CB951404)
国家自然科学基金重点项目(40930526)
国家自然科学基金青年科学基金(40901041)资助
