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首页> 外文会议>CryoSat third user workshop >INLAND WATER SAR ALTIMETRY: NEW TECHNIQUES AND METHODS FOR THE HYDROLOGICAL E XPLOITATION OF CRYOSAT DATA
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INLAND WATER SAR ALTIMETRY: NEW TECHNIQUES AND METHODS FOR THE HYDROLOGICAL E XPLOITATION OF CRYOSAT DATA

机译：内陆水SAR Altimetry：用于冷冻数据的水文E XPLOITIT的新技术和方法

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The concept of SAR Altimetry has found so far its immediate application and interest among the users principally over open ocean and coastal zone domains. But a new applicative territory remains still basically unexplored: the inland water theme. Indeed, the SAR/SARin technology looks very attractive for inland water users thanks to the resolution shrinkage in along-track direction that will allow now to monitor more efficiently small water bodies and to reduce the land contamination from the off-nadir land targets. Further, with respect to the SAR mode, the SARin Mode has the additional advantage of: 1) a more robust on-board tracking lock system and a four time longer receiving window that enables the radar to follow better the very steep topographic reliefs without loss of tracking, 2) the possibility to infer the echo origin’s angle and distinguish between nadir and off-nadir return. The current Delay/Doppler processing, that is actually applied over open ocean, is suitable as well for inland water studies, provided that: 1) a weighting function is applied in azimuth before the beam forming operation is executed, in order to limit the azimuth ambiguities or “ghosting” effect. 2) an oversampling at least by factor 2 is applied during the range compression in order to properly sample the specular echoes. On top of this, clearly a standard open ocean SAR Echo physically-based model (like SAMOSA or CNES/CPP Model) is not always suitable for inland water studies because of the very peaky waveforms from still waters. For this scope, we developed a re-tracking scheme able to change and adapt the model’s waveform to specular water conditions (still water) or diffusive water conditions (rough water). In SAR mode, thanks to the high instrumental Pulse Repetition Frequency and to an accurate Delay/Doppler Processing, the real antenna beam-width (with an alongtrack footprint of 16 km) can be split in a series of Synthetic Doppler Beams, each one with a footprint of 300 meters. Because these Doppler Beams are synthetic, they can be steered to any point of the overflown ground-track and hence virtually a SAR Altimeter has the potential to provide an altitude measurement at any desired surface location along the ground-track. Because rivers and small lakes are very localized targets, it seems sensible, in case of application of SAR Altimetry over inland water domain, to steer all the Doppler Beams exactly in the middle of the river/lake’s water body in order to get a water level measurement the most clean and uncontaminated possible. A secondary option could be to over-sample the river/lake’s crossing, fixing surface locations along the lake/river’s cross at a space distance lesser than 300 meters (the intrinsic CryoSat’s along track resolution) in order to increase the number of available water measurements at the lake/river’s cross. For the first time, this concept will be attempted and implemented for a series of selected rivers/lakes targets. The current work is a feasibility study preparatory for the data exploitation of the Sentinel-3 Topography Mission over inland water.
机译：到目前为止，SAR Altimetry的概念已经发现，其直接应用和兴趣，主要在公开的海洋和沿海区领域。但新的申请领域仍然仍然是未开发的：内陆水主题。事实上，特区/沙林技术长相用水户由于内陆沿航迹方向的分辨率收缩，这将使我们更有效地监控小水体的非常有吸引力，并降低最低偏离用地指标的土地污染。此外，关于SAR模式，Sarin模式具有以下优点：1）更强大的车载跟踪锁系统和四个时间更长的接收窗口，使雷达能够遵循更好的非常陡峭的地形浮雕而不会损失跟踪，2）推断回声起源角度的可能性，区分Nadir和Off-Nadir返回。实际应用于开放海洋的当前延迟/多普勒处理是适用于内陆水研究的，如：1）在执行波束形成操作之前在方位角处施加加权函数，以限制方位角歧义或“重影”效应。 2）在范围压缩期间至少施加至少因子2的过采样，以便适当地样本镜面回波。在此之上，显然，基于标准的开放海洋SAR回声（如Samosa或CNE / CPP模型）并不总是适用于内陆水研究，因为来自静物的峰值波形。对于此范围，我们开发了一种能够改变和调整模型的波形（静水）或扩散水条件（粗糙水）的重新跟踪方案。在SAR模式下，由于高仪器脉冲重复频率和准确的延迟/多普勒处理，真正的天线波束 - 宽度（沿着16公里的距离）可以分成一系列合成多普勒梁，每个都有占地面积300米。因为这些多普勒梁是合成的，所以它们可以转向溢出地面轨道的任何点，因此实际上，SAR高度计具有沿着地面轨道的任何所需表面位置提供高度测量。因为河流和小湖泊是非常局部的目标，所以在内陆水域上的SAR高度乘坐的情况下，似乎很明智，以便在河水/湖泊的水体中间排列所有多普勒梁，以获得水位测量最干净，不可污染的可能。次要选项可以是在河流/湖的过境情况下，在距离湖泊/河流的十字架上固定在距离小于300米的空间距离（沿着轨道分辨率的内在冷冻机）的空间距离，以增加可用水测量的数量在湖/河的十字架上。这是第一次，将尝试并实施一系列选定的河流/湖泊目标。目前的工作是一种可行性研究准备，用于内陆水的哨兵-3地形任务的数据开发。

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