Modelling from land to water

Author:Monica Miller Rodgers

气候变化正在影响全球淡水供应的机构。科罗拉多河经过美国的七个州到达墨西哥，在墨西哥倒入科尔特斯海，就是这样的例子。

水流被归类为2015年美国最濒危河流的水。reduce by 10 to 30 per cent到2050年。天气温暖，降雪量较小，河流中内置的数百多个水坝对其生态系统施加了重大压力。这不利地影响了鱼类和野生动植物的栖息地：

• $26 billion recreational economy,
• 40 million people who depend on the river for daily water use,
• 2million hectares of farmland irrigation.

美国填海局（BOR）对科罗​​拉多河的健康有如此多的骑行，负责监督水资源管理和水的水，以便更好地了解盆地地貌学。

“我们正在努力了解科罗拉多河正在发生的事情，”said Carrie Scott, chief of BOR’s Yuma Area Office technical support office.“我们对河流进行建模，以了解整个浅水中的沉积物沉积物，进而帮助我们确定诸如河岸降解或流动中的'choper点'之类的水。”

As with any river’s nature, Colorado River’s meandering is to change its natural course. This poses a threat to nearby structures, such as roads, agricultural and residential communities. BOR strives to keep the river on its course through dredging and armouring bank lines.

“As the water masters of the River, we need to ensure continuous water delivery. We have an ongoing program to contract for a study to map the river by reach to understand how the riverbed is changing,”said Scott.“我们收到的数据有助于我们更好地建模河流的表面和地下。我们拥有的质量越好，我们就越能建模和了解各种水流的影响，并为沿河的项目产生了工程设计。”

Turning to Allied GIS, a mapping firm specialising in GIS, imagery and database applications, the firm was tasked to build a digital orthophotography and a topographical map that met the U.S. national mapping accuracystandard of 30 cm。然后，Allied GIS与德克萨斯大学奥斯汀分校杰克逊地球科学学院（局）的杰克逊地球科学学院合作，以获取机载的浴综合激光雷达数据和另一家调查公司，以提供地形激光雷达和地面支撑。

从测深到地形

A long-time user of Leica Geosystems airborne sensors, researchers at the Bureau used theirLeica Chiropteraairborne system to collect data of the lower Colorado River basin in California and Arizona.

Chiroptera has two independent LiDAR scanners:

1. A near-infrared (red-wavelength) for topographic LiDAR
2. A visible (green-wavelength) for bathymetric LiDAR

Chiroptera旨在与两个扫描仪同时获取数据，从而在具有浅水体的复杂景观中进行调查。河流调查是在400 m above the ground level, which is the optimum altitudefor collecting bathymetric LiDAR data. The topographic scanner acquired data simultaneously with a repetition rate of 300 kHz to distinguish the water-surface, and to map the immediate shoreline.

“Chiroptera allowed us to capture bathymetric aspects of the river and features of the immediate terrain,”said Kutalmis Saylam, the lead research scientist for the Bureau.“We’ve been using our Chiroptera for more than four years now, and we can rely on this robust and intuitive system in the field. That’s very important for us as reliable sensors are a must for our work.”

调查地点的天气状况主要是理想的，总共完成了9个任务。调整了飞行计划，以维护安全飞机操纵，尤其是在调查区的北端，高山峰。整个调查133 flight lines覆盖area of 265 km²was completed with21小时的空降时间。

Seeing clearly through

Part of the mission included collecting bathymetric data from an area of thedeepest dam in the world。亚利桑那州和加利福尼亚州之间的帕克大坝的挡土墙高度为98 m，根据季节的不同，将水排出不同。在与大坝管理局的协调下，该局安排了较低的出院期间的空降任务（146对252 m³/秒)可能降低浊度水平的water-column. Because turbidity absorbs light beams and prevents them from penetrating into deeper water column, it is an essential part of quality assurance procedures for conducting a successful ALB survey. The average reading was 0.41 nephelometric turbidity unit (NTU) in the northern sections of the river, which indicated overall low levels of turbidity in the water-column. In the south, the river was shallower, running through a desert-like environment and losing much of its water to irrigation. These conditions contributed to higher turbidity levels of up to 6.25 NTU and created difficulties for LiDAR beams.

“The strong light beams of Chiroptera easily penetrated the clear waters of the northern sections of the river. We created a seamless water-bottom representation where depths exceeded 10 m,”said Saylam.“In the south, where turbidity levels were higher, we used available returns and interpolation methods to estimate and create a water-bottom representation.

Leica LiDAR Survey Suite LSS v2.3 software contains an updated turbid-water algorithm that filters the backscatter noise created by low or moderate levels of turbidity and selects the most distinctive peak as the water-bottom representation.

“This algorithm enabled the discovery of more returns from deeper waters of the river, and we measured an overall improvement of 81 cm compared to normal returns - a significant achievement in LiDAR bathymetry,”said Saylam.

Facilitating the study of the lower Colorado River basin geomorphology and further understanding of the effects of climate change, the Bureau was able to provide an accurate and detailed map.

“We were able to quantify the water-column depth, map the bottom of the river, the shoreline, and the overall topography of the river as requested by the U.S. Bureau of Reclamation”said Saylam.“This valuable knowledge enables us to undertake similar projects in the future, and the reliability of Chiroptera allows us to continue focusing on similar scientific studies.”

BOR will further use the digital orthophotography and the topographical map to match its in-house survey team’s measurements from boat and ground means. The LiDAR study conclusions will continue to help BOR to keep Colorado River flowing in the right direction and supporting those who depend on it.

“The data we received from the LiDAR was calibrated to our in-house team’s surveys,”said Scott.“This information is important to our ongoing operation to continue to improve our models so we can correctly identify what’s changing what could hap-pen and to develop our projects according to conditions.”