Mapping the last frontier
Alaska is the least densely populated yet largest state in the United States. Well-known for its diverse landscape and cold weather, travelling can be difficult during winter months. In the northern parts of the state, where tundra is vast and winter cli-mate is harsh, use of ice roads are popular and necessary for transporting resources. Because the state has more than 3 million lakes that are larger than 20 acres in size, a clear understanding of the landscape is required to best determine where these roads could safely and sustainably be built. The Bureau of Economic Geology (the Bureau), a research unit at the University of Texas at Austin, set out to map a portion of this wild frontier and provide a better understanding of the local habitat, using the Leica Chiroptera airborne LiDAR system to survey the Alaskan Northern Slope in 2014.
独特的风景
The Alaskan North Slope micro-topography supports various potential fish habitat water bodies and wetland areas within the arctic tundra environment. Shallow thaw lakes, less than 2 metres deep, in general, are a major component of the tundra landscape of the area, where they compose approximately 20 percent of the total area. They are completely ice-free only a few weeks in a calendar year, so we scheduled our field trip accordingly, beginning in mid-July and ending in early August.
湖泊的深度，冰的生长和衰减决定了它们是否适合野生动植物和水生动物群以及工业发展。假设在该区域中，假定冰的积聚为1.5至2 m，如果水的深度大于2 m，则液态水很可能位于这些湖泊的中部盆地下方。调查结果尤其重要，因为它们会发现湖泊深度超过2 m，适合于建造冰路，但具有潜在的鱼类栖息地。还期望发现该地区的其他环境和水文评估。
“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.”
用扫描能力加倍飞行
总共飞行了95条线以覆盖整个调查区域，在西风方向上，线数增加。平均飞行线约为50公里。为了确保完全覆盖范围，将飞行线间距设置为160至180 m，在那里，地面激光板块的占地面积为280至290 m宽。为了弥补地面高度变化（北部30 m，南部95 m），在飞行过程中监视大气压力，以保持恒定的飞行高度并在地面上方。
Chiroptera使用两个LiDAR扫描仪获取地形和测深数据。从地形激光雷达（红色波长）的数据以300 kHz的速度发射，并用于获取有关植被高度和地球地形的高分辨率3-D位置数据。从测深痛（绿色波长）的数据以35 kHz发射，并用于确定与水相关的统计数据。例如深度，体积和面积大小。我们还分别在400 m和1700 m处收集了彩色和天然彩色图像，以目视参考和正截止性目的。
“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 Survey Suite LLSS v2.09 was used to convert raw data files into indus-try-standard LAS1.2 for output. Because LAS datasets are in binary format, they pro-vide quick and easy access to information, either for analysis or visualization purposes. Datasets from both scanners were tiled to 1 x 1 km to simplify the computational requirements for data viewing and analysis. As a result, we generated 829 tiles across the survey area, and each tile included a 20 m buffer zone in each direction to generate a seamless 1 m digital elevation model (DEM) for mapping purposes.
最深的水体计算为3.5 m。在分析的所有4,697个水体中，有3,837（81.7％）被分类为浅或非常浅的，深度小于1 m。只有4.6％（总计216个）水体的深度超过2.0 m。所有水体的平均深度计算为0.67 m。
A total of 3,014 water bodies (64.1 percent) contained less than 1,000 m3 of water volume whereas 1,683 lakes were calculated to have more than 1,000 m3 of water volume (35.9 percent). The average volume of all water bodies analysed was calcu-lated at 12,771 m3 (3,373,741 gal) of all water bodies analysed.
独特的风景
The Alaskan North Slope micro-topography supports various potential fish habitat water bodies and wetland areas within the arctic tundra environment. Shallow thaw lakes, less than 2 metres deep, in general, are a major component of the tundra landscape of the area, where they compose approximately 20 percent of the total area. They are completely ice-free only a few weeks in a calendar year, so we scheduled our field trip accordingly, beginning in mid-July and ending in early August.
湖泊的深度，冰的生长和衰减决定了它们是否适合野生动植物和水生动物群以及工业发展。假设在该区域中，假定冰的积聚为1.5至2 m，如果水的深度大于2 m，则液态水很可能位于这些湖泊的中部盆地下方。调查结果尤其重要，因为它们会发现湖泊深度超过2 m，适合于建造冰路，但具有潜在的鱼类栖息地。还期望发现该地区的其他环境和水文评估。
“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.”
用扫描能力加倍飞行
总共飞行了95条线以覆盖整个调查区域，在西风方向上，线数增加。平均飞行线约为50公里。为了确保完全覆盖范围，将飞行线间距设置为160至180 m，在那里，地面激光板块的占地面积为280至290 m宽。为了弥补地面高度变化（北部30 m，南部95 m），在飞行过程中监视大气压力，以保持恒定的飞行高度并在地面上方。
Chiroptera使用两个LiDAR扫描仪获取地形和测深数据。从地形激光雷达（红色波长）的数据以300 kHz的速度发射，并用于获取有关植被高度和地球地形的高分辨率3-D位置数据。从测深痛（绿色波长）的数据以35 kHz发射，并用于确定与水相关的统计数据。例如深度，体积和面积大小。我们还分别在400 m和1700 m处收集了彩色和天然彩色图像，以目视参考和正截止性目的。
“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 Survey Suite LLSS v2.09 was used to convert raw data files into indus-try-standard LAS1.2 for output. Because LAS datasets are in binary format, they pro-vide quick and easy access to information, either for analysis or visualization purposes. Datasets from both scanners were tiled to 1 x 1 km to simplify the computational requirements for data viewing and analysis. As a result, we generated 829 tiles across the survey area, and each tile included a 20 m buffer zone in each direction to generate a seamless 1 m digital elevation model (DEM) for mapping purposes.
最深的水体计算为3.5 m。在分析的所有4,697个水体中，有3,837（81.7％）被分类为浅或非常浅的，深度小于1 m。只有4.6％（总计216个）水体的深度超过2.0 m。所有水体的平均深度计算为0.67 m。
A total of 3,014 water bodies (64.1 percent) contained less than 1,000 m3 of water volume whereas 1,683 lakes were calculated to have more than 1,000 m3 of water volume (35.9 percent). The average volume of all water bodies analysed was calcu-lated at 12,771 m3 (3,373,741 gal) of all water bodies analysed.
“The advanced technology of the Chiroptera provided accurate, detailed, and cost-effective results that permitted analysis of micro-topographic and bathymetric fea-tures in a remote location of the world,” said Andrews. “Water bodies of all shapes and sizes—riverine environments, wetlands and uplands, hills and flat areas, and all other terrain features—were mapped and analyzed rapidly and accurately.”
由库塔米斯·塞拉姆（Kutalmis Saylam）撰写
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