Friday, January 7, 2011

Polar Glacier Motion Monitoring

Glaciers in Polar Regions are accelerating to melt due to complicated global climate change. It is of great importance to monitor glacier motion since glaciers play an important role in the global climate system and sea level rise, interacting in a complex fashion with atmosphere and ocean. The atrocious geographical and natural conditions, however, make it quite difficult and often dangerous to carry out field expeditions to in situ velocity measurement in the remote Polar Regions.

Satellite imagery is suitable for studying Polar Regions. Cross-correlation of sequential optical images can be used to measure the ice flow velocity. Two methods that are widely used and proved to be of good accuracy are Normalized Cross-Correlation (NCC) and Orientation Correlation (OC). Scientists around the world have done such work using remote sensing data such as MODIS, Landsat MSS/TM/ETM+, ASTER, SPOT and EO-1 ALI etc. Optical data are main data sources at the beginning of polar research. Unfortunately, optical data coverage is “spotty”, being severely limited by long polar night, frequent cloud cover, failures of data transmission links, and featureless ice surface. In our team’s Antarctic Mapping Project we collected over 1100 ETM+ images between 1999 and 2003 from thousands against the odds to map the mosaic image of Antarctica in 15m resolution with 6 bands. It is a quite tough job. Nevertheless, optical data are essential and important to glacier motion monitoring since there are large amount of archived data which are valuable for research on earth’s long-term surface change.

Compared with optical data, imaging radars are more suitable for research on glaciers because of their all-weather, day-night imaging capacity. Spaceborne Synthetic Aperture Radar (SAR) is a powerful research tool by virtue of its ability to penetrate the shroud of darkness and cloud cover and acquire high-resolution images in different microwave band frequency and polarizations. SAR interferometry (InSAR) has now become a well-established means of measuring ice velocity in high accuracies. InSAR is of great advantage in monitoring glacier motion since it can detect subtle changes of glacier surface. Additionally, methods based on speckle and fringe tracking are developed. For loss of coherence, i.e., in the case of rapid and incoherent flow and of large acquisition time intervals between the two SAR images, methods of processing optical data are also adopted to process SAR intensity images, which could serve as an alternative to differential InSAR for the measurement of glacier motion.

The main problems of research on glacier motion are data acquisition and accuracy verification. With more and more multi-source data becoming available, the emerging Light Detection and Ranging (LiDAR) data included, the first problem will be gradually solved. Multi-spectral data of high qualities, however, are still difficult to obtain. As for the second problem, historical observational data and field work are essential to verify research results. NASA’s Operation IceBridge aircraft missions are really worthy looking forward to.

[1] Robert Massom. Dan Lubin, Polar Remote Sensing [ M ]. Vol II. UK. 2006
[2] W. Gareth Rees. Remote Sensing of Snow and Ice [ M ]. 2006
[3] Tazio Strozzi, et al. Glacier Motion Estimation Using SAR Offset-Tracking Procedures [ J ]. Geosci & Rem Sens, 2002, 40 (11): 2384~2391.

Saturday, January 1, 2011




节目赢得一片叫好声,不过最后彪哥有点不高兴,因为先前承诺的只要上台表演就每人发一百块钱的奖品,组里报了10个人,正好1K,最后却只发了300的校内超市购物券。高兴的是组里共有五人通过抽奖或参与现场互动活动拿奖了(可惜没有彪哥),小叶童鞋还拿了两个奖品,酸奶机和苏泊尔三件套,我和王K通过领导摇号抽奖获了个三等奖——台灯,京东上竟然卖148。ZZ 和老外John 组成的组合参与现场的活动勇夺第一也拿到了奖品。联欢会结束后每人都领一份围观奖,要么是洗发露套装,要么是吹风机,总体来说收获颇丰。最为关键的是展现了我们组的活力和特色,最后的拼图很给力,展示了组里的成果,让老板感觉很有面子。PS: 老板真是前途无量,在联欢会上大家才知道他已经从副院长提为书记了,去年升的博导,才刚三十来岁,能力和机遇兼得就不得了啊!