Mapping the last frontier
阿拉斯加是美国人口稠密但最大的州。以各种风景和寒冷的天气而闻名，在冬季，旅行可能很困难。在该州的北部，苔原很广泛，冬季克利群岛苛刻，使用冰路很受欢迎，并且对于运输资源是必不可少的。由于该州的规模大于20英亩，因此拥有超过20英亩的湖泊，因此需要对景观有清晰的了解，以最好地确定这些道路可以安全和可持续地建造。德克萨斯大学奥斯汀分校的研究部门的经济地质局（The Bureau）着手使用Leica Chiroptera空中激光雷达（Leica Chiroptera Airmorne Lidar System2014年的阿拉斯加北部斜坡。
A unique landscape
阿拉斯加北坡微观图支持北极苔原环境中各种潜在的鱼类栖息地水体和湿地地区。一般而言，浅水湖泊深度不到2米，是该地区苔原景观的主要组成部分，它们占总面积的约20％。它们在一个日历年中只有几周的时间完全无冰，因此我们安排了相应的实地考察，从7月中旬开始，并于8月初结束。
The lakes’ depth, ice growth, and decay determine whether they are suitable habitat for wildlife and aquatic fauna, as well as for industrial development. Ice accumulation is assumed to be 1.5 to 2 m thick in this area, and liquid water most likely lies below in the central basins of these lakes if the water is deeper than 2 m. Survey findings were particularly important because they would reveal lakes deeper than 2 m, suitable for building ice roads, but with potential fish habitat. Findings were also expected to assist other environmental and hydrological assessments in the area.
“With thousands of lakes – with varying turbidity levels – scattered throughout the survey area and challenging weather conditions that limited the airborne survey activities, this was certainly not an easy task,” said John Andrews, a research scientist, who was responsible for ground truthing and overall logistical support. “With airborne LiDAR surveying, though, we were able to obtain very detailed and precise topographic and bathymetric data in areas where traditional survey methods would not be feasible.”
Flying with double the scanning power
A total of 95 lines were flown to cover the entire survey area, where line numbers increased in the westerly direction. The average flight line was approximately 50 km long. To ensure complete coverage, the flight line spacing was set at 160 to 180 m, where the ground laser swath footprint was calculated to be 280 to 290 m wide. To compensate for the changing ground elevation (30 m in the north, 95 m in the south), atmospheric pressure was monitored during flights to maintain a constant flight altitude and swath above the ground.
The Chiroptera uses two LiDAR scanners to acquire topographic and bathymetric data. Data from the topographic LiDAR (red wavelength) was fired at 300 kHz and used to acquire high-resolution 3-D positional data on vegetation height and earth topography. Data from the bathymetric LiDAR (green wavelength) was emitted at 35 kHz and used to determine water related statistics; such as depth, volume and area size. We also collected colour-infrared and natural-color imagery at 400 m and 1700 m, respectively, for visual reference and ortho-rectification purposes.
“The technological cornerstone of this project was the Chiroptera airborne LiDAR and imaging system,” said John Hupp, a research scientist from the Bureau, who was responsible for field data processing and system calibration. “Simultaneously collecting high resolution imagery with the LiDAR data allowed us to easily discriminate water bodies, vegetation characteristics, wetlands, and uplands, saving us time and costs compared to any other conventional type of surveys.”
For both LiDAR scanners, the average vertical offset was measured at less than 1 cm, while the standard deviation was calculated at approximately 3 cm compared to the ground control points collected at Deadhorse airport runway pavement. Calibra-tion procedures were applied to both scanners individually, where average roll and pitch biases were measured to be less than 2.6 cm.
“我们也检查和纠正任何明显的激光雷达system calibration errors caused mostly by incorrect inertial navigation system (INS) rotation angles of roll, pitch, and yaw. These errors can be detected through analysis of adjacent and op-posing LiDAR strips,” said Hupp. “In theory, if no rotational misalignments are pre-sent, LiDAR points registered from different strips should match each other seam-lessly on an unobstructed surface; although not expected to have perfection, we can achieve very close results in practice.”
Faster, more accurate data analysis
Leica Lidar调查套件LLSS v2.09用于将原始数据文件转换为行业标准LAS1.2以进行输出。由于LAS数据集采用二进制格式，因此它们可以快速轻松地访问信息，以用于分析或可视化目的。来自两个扫描仪的数据集均匀地铺平到1 x 1 km，以简化数据查看和分析的计算要求。结果，我们在整个调查区域生成了829个瓷砖，每个瓷砖在每个方向上都包含一个20 m的缓冲区，以生成一个无缝的1 m数字高程模型（DEM），以实现映射。
The deepest water body was calculated at 3.5 m. Of all 4,697 water bodies analysed, 3,837 (81.7 percent) were classified as shallow or very shallow, with measured depths of less than 1 m. Only 4.6 percent (216 total) of the water bodies had depths that exceeded 2.0 m. The average depth of all water bodies was calculated at 0.67 m.
总共3,014个水体（64.1％）含有少于1,000平方米的水量，而1,683个湖泊的水量超过1,000平方米（35.9％）。所有分析的所有水体的平均体积均在分析的所有水体中计算出12,771平方米（3,373,741加仑）。
A unique landscape
阿拉斯加北坡微观图支持北极苔原环境中各种潜在的鱼类栖息地水体和湿地地区。一般而言，浅水湖泊深度不到2米，是该地区苔原景观的主要组成部分，它们占总面积的约20％。它们在一个日历年中只有几周的时间完全无冰，因此我们安排了相应的实地考察，从7月中旬开始，并于8月初结束。
The lakes’ depth, ice growth, and decay determine whether they are suitable habitat for wildlife and aquatic fauna, as well as for industrial development. Ice accumulation is assumed to be 1.5 to 2 m thick in this area, and liquid water most likely lies below in the central basins of these lakes if the water is deeper than 2 m. Survey findings were particularly important because they would reveal lakes deeper than 2 m, suitable for building ice roads, but with potential fish habitat. Findings were also expected to assist other environmental and hydrological assessments in the area.
“With thousands of lakes – with varying turbidity levels – scattered throughout the survey area and challenging weather conditions that limited the airborne survey activities, this was certainly not an easy task,” said John Andrews, a research scientist, who was responsible for ground truthing and overall logistical support. “With airborne LiDAR surveying, though, we were able to obtain very detailed and precise topographic and bathymetric data in areas where traditional survey methods would not be feasible.”
Flying with double the scanning power
A total of 95 lines were flown to cover the entire survey area, where line numbers increased in the westerly direction. The average flight line was approximately 50 km long. To ensure complete coverage, the flight line spacing was set at 160 to 180 m, where the ground laser swath footprint was calculated to be 280 to 290 m wide. To compensate for the changing ground elevation (30 m in the north, 95 m in the south), atmospheric pressure was monitored during flights to maintain a constant flight altitude and swath above the ground.
The Chiroptera uses two LiDAR scanners to acquire topographic and bathymetric data. Data from the topographic LiDAR (red wavelength) was fired at 300 kHz and used to acquire high-resolution 3-D positional data on vegetation height and earth topography. Data from the bathymetric LiDAR (green wavelength) was emitted at 35 kHz and used to determine water related statistics; such as depth, volume and area size. We also collected colour-infrared and natural-color imagery at 400 m and 1700 m, respectively, for visual reference and ortho-rectification purposes.
“The technological cornerstone of this project was the Chiroptera airborne LiDAR and imaging system,” said John Hupp, a research scientist from the Bureau, who was responsible for field data processing and system calibration. “Simultaneously collecting high resolution imagery with the LiDAR data allowed us to easily discriminate water bodies, vegetation characteristics, wetlands, and uplands, saving us time and costs compared to any other conventional type of surveys.”
For both LiDAR scanners, the average vertical offset was measured at less than 1 cm, while the standard deviation was calculated at approximately 3 cm compared to the ground control points collected at Deadhorse airport runway pavement. Calibra-tion procedures were applied to both scanners individually, where average roll and pitch biases were measured to be less than 2.6 cm.
“我们也检查和纠正任何明显的激光雷达system calibration errors caused mostly by incorrect inertial navigation system (INS) rotation angles of roll, pitch, and yaw. These errors can be detected through analysis of adjacent and op-posing LiDAR strips,” said Hupp. “In theory, if no rotational misalignments are pre-sent, LiDAR points registered from different strips should match each other seam-lessly on an unobstructed surface; although not expected to have perfection, we can achieve very close results in practice.”
Faster, more accurate data analysis
Leica Lidar调查套件LLSS v2.09用于将原始数据文件转换为行业标准LAS1.2以进行输出。由于LAS数据集采用二进制格式，因此它们可以快速轻松地访问信息，以用于分析或可视化目的。来自两个扫描仪的数据集均匀地铺平到1 x 1 km，以简化数据查看和分析的计算要求。结果，我们在整个调查区域生成了829个瓷砖，每个瓷砖在每个方向上都包含一个20 m的缓冲区，以生成一个无缝的1 m数字高程模型（DEM），以实现映射。
The deepest water body was calculated at 3.5 m. Of all 4,697 water bodies analysed, 3,837 (81.7 percent) were classified as shallow or very shallow, with measured depths of less than 1 m. Only 4.6 percent (216 total) of the water bodies had depths that exceeded 2.0 m. The average depth of all water bodies was calculated at 0.67 m.
总共3,014个水体（64.1％）含有少于1,000平方米的水量，而1,683个湖泊的水量超过1,000平方米（35.9％）。所有分析的所有水体的平均体积均在分析的所有水体中计算出12,771平方米（3,373,741加仑）。
安德鲁斯说：“脊骨翅目的先进技术提供了准确，详细且具有成本效益的结果，可以在世界偏远地区对微观图和测深的FEA进行分析。”“各种形状和尺寸的水体 - 送货环境，湿地和高地，山丘和平坦区域以及所有其他地形特征 - 经过迅速，准确的绘制和分析。”
Written by Kutalmis Saylam
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