Monitoring Mountain Rivers From Space: A Pilot Study of Bedrock River Flow Measurement Using Ultra-High Resolution Optical Satellite Imagery

山区河流洪水位流量的测量是一个巨大的后勤挑战，特别是在大的空间和时间尺度上，这种数据的不可避免的缺乏阻碍了我们对山区景观过程的理解。我们提出了一种新的解决方案，它利用新的高分辨率卫星图像(2M，FORMOSAT-2)，在地球科学界(台湾)非常广泛的感兴趣的地区以异常高的重访频率(每天)。我们提出的方法需要对选定的山河河道的正射、地理参考图像的时间序列(2004-2005)进行整理，同时对下游最近的加水站的流量进行同期阶段测量。沿选定航道河段的淹没模式将在每幅图像中绘制出来。借助于低阶段野外绘制的跨航道剖面图，我们将估计低宽度、低深度、平均河床切应力和平均低速。一旦处理了大范围的放电，我们预计将能够根据直接观察到的站内阶段数据构建这些低措施的额定曲线。将评级模型与台湾数十年的台站数据档案相结合，将能够评估沿选定基岩渠道和跨所选基岩渠道的低宽度、深度和剪应力的长期概率分布。这类测量，尽管是间接的，将会引起地貌界的极大兴趣。然而，这种方法并不是有保证的，因为偏远的河流测量从未在山区集水区进行过尝试；预期的水位曲线的精度是否足以满足类似台湾中线的河流的精度还有待观察。试点项目的主要任务将是解决这一问题，并为更全面、更长期地评估台湾大山河流的流量奠定基础。广泛成果：虽然对基岩河道过程感兴趣的人特别关注陡峭山区河流的低水位，但它们也引起了其他方面的极大兴趣：从景观演变模型和气候与构造之间的相互作用，到专注于人口稠密山区环境中洪水风险评估的水文学家。此外，如果试验项目被证明是成功的，它将为台湾航天局提供一个极好的例子，说明FORMOSAT-2在自然灾害评估中的价值，这是它的主要任务之一。因此，将更加重视定期获取热带山区的FORMOSAT-2图像，如果要实现高分辨率、多时相图像存档这一难以实现的目标，这是至关重要的一步--目前，高原地区的图像相对较低(对于FORMOSAT-2和其他同等卫星)，而且仅在紧急时期(如台风)每天获取。这样的档案将在地球科学、水文学、生态学等学科中得到广泛的赞赏，更不用说遥感研发本身了。

The measurement of flood-stage discharge in mountain rivers is an enormous logistical challenge, particularly on large space and time scales, and the inevitable paucity of such data has impeded progressin our understanding of mountain landscape processes. We propose a novel solution that exploits newhigh resolution satellite imagery (2m, FORMOSAT-2) with unusually high revisit frequency (daily) overa region of very broad interest to the earth science community (Taiwan). Our proposed method entailsthe collation of a time series (2004-2005) of orthorecti*ed, georeferenced images of selected mountainriver channels, in tandem with contemporaneous stage measurements of discharge at the nearest gaugingstation downstream. Patterns of inundation along selected channel reaches will be mapped in eachimage. With the aid of cross-channel profiles mapped in the field at low stage, we will make estimatesof low width, depth, mean bed shear stress and mean low velocity. Once a broad range of dischargeshas been processed, we expect to be able to construct rating curves for these low measures as a functionof the directly observed, at-station stage data. Combination of the rating models with the multi-decadalarchive of station data in Taiwan will permit an assessment of the long-term probability distributions oflow widths, depths and shear stresses along and across the selected bedrock channels. Measurements ofthis kind, albeit indirect, will be of enormous interest to the geomorphology community. However, themethod is by no means guaranteed, because remote river gauging has never been attempted in mountaincatchments; it remains to be seen whether the precision of the anticipated rating curves will suffice forrivers akin to those of the Taiwan Central Range. The main task of the pilot project will be to addressthis issue and to lay the foundation for a more comprehensive, longer-term assessment of Taiwanesemountain river discharge.Broader outcomes: While low measurements in steep mountain rivers are particularly sought after bythose interested in bedrock channel processes, they are also of great interest beyond: from modelersof landscape evolution and the interaction between climate and tectonics, to hydrologists preoccupiedwith the assessment of flood hazard in populated mountain environments. Moreover, if the pilot projectproves successful it will provide the Taiwanese space agency with an excellent example of the value ofFORMOSAT-2 in natural hazard assessment, one of its principal missions. As a result, more attentionwill be paid to the regular acquisition of FORMOSAT-2 imagery in tropical mountain areas, an essentialstep if the elusive goal of a high-resolution, multitemporal image archive is to be achieved - at present,images of highland areas are a relatively low prioity (for FORMOSAT-2 and other equivalent satellites)and are only acquired daily during emergency periods (e.g. typhoons). Such an archive would be widelyappreciated across the discplines of earth sciences, hydrology, ecology, not to mention in remote-sensingR&D itself.A-1