11:00 AM - 1:00 PM
[HTT21-P02] Visualization of ALB measurable areas and their seasonal changes
~Utilization of information on optical characteristics of the seawater obtained from satellite images~
Keywords:Kd, ALB, Visualization
ALB is generally known for land surveying using near-infrared light, but it is also used for water surveying using green laser light. The term "Airborne Lidar Bathymetry (ALB) " in this presentation refers to a technology that uses green laser light to seamlessly survey the topography of coastal areas in hydrographic surveys from land to the sea floor using nautical chart standards as the height reference. In general, most hydrographic surveys are conducted using multibeam echo-sounder, which is less efficient in shallow water due to the narrow swath width and the risk of the survey vessel running aground. On the other hand, ALB can quickly survey a wide area of shallow water by surveying from above. Therefore, ALB is widely used for bathymetric mapping and coastal conservation information collection. The maximum measurable depth of ALB can be expressed in terms of transparency and diffused attenuation coefficient (Kd), which represent the optical characteristics of seawater.
Hydrographic and Oceanographic department, Japan Coast Guard has introduced and operated ALB as one of the hydrographic surveying techniques since 2003. While this allows us to survey a wide area safely and efficiently in a short time even in extremely shallow waters, there are many factors to be taken into consideration such as water quality, meteorological and oceanographic conditions as well as air traffic constraints such as air obstructions and restricted airspace. Therefore, compared to multibeam surveying, it takes more time for preliminary coordination and planning.
In order to reduce the burden of operational planning for ALB, this presentation will present the method and results of visualization of the measurable area by ALB around Japan and the seasonal variation of the area using Kd of seawater obtained from satellite images.
First, Kd in the 490 nm wavelength band (Kd490), which can be obtained from satellite images, was converted to Kd in the 532 nm wavelength band of green laser light (Kd532). Next, the maximum measurable depth (Dmax(1)) was calculated using the formula for determining the maximum measurable depth using Kd532 and the system eigenvalues listed in the specification sheet of the ALB system. Then, the 500 m bathymetry data around Japan (J-EGG500: JODC-Expert Grid data for Geography) was regarded as the seafloor topography, and when Dmax(1) was larger than the mesh bathymetry value of J-EGG500, it was judged that the ALB was feasible. In this case, the depth was set as Dmax(2). These tasks were carried out for five patterns of statistical and seasonal averages of Kd (spring, summer, fall, and winter).
The results show that not only does the season suitable for ALB vary depend on area, but also the measurable depth that can be acquired vary depend on season even in the same sea area or point. Although further verification is necessary, the obtained the maximum measurable depths were found to be useful as an index for the consideration of operational planning. The details of the results will be explained in the presentation.
Hydrographic and Oceanographic department, Japan Coast Guard has introduced and operated ALB as one of the hydrographic surveying techniques since 2003. While this allows us to survey a wide area safely and efficiently in a short time even in extremely shallow waters, there are many factors to be taken into consideration such as water quality, meteorological and oceanographic conditions as well as air traffic constraints such as air obstructions and restricted airspace. Therefore, compared to multibeam surveying, it takes more time for preliminary coordination and planning.
In order to reduce the burden of operational planning for ALB, this presentation will present the method and results of visualization of the measurable area by ALB around Japan and the seasonal variation of the area using Kd of seawater obtained from satellite images.
First, Kd in the 490 nm wavelength band (Kd490), which can be obtained from satellite images, was converted to Kd in the 532 nm wavelength band of green laser light (Kd532). Next, the maximum measurable depth (Dmax(1)) was calculated using the formula for determining the maximum measurable depth using Kd532 and the system eigenvalues listed in the specification sheet of the ALB system. Then, the 500 m bathymetry data around Japan (J-EGG500: JODC-Expert Grid data for Geography) was regarded as the seafloor topography, and when Dmax(1) was larger than the mesh bathymetry value of J-EGG500, it was judged that the ALB was feasible. In this case, the depth was set as Dmax(2). These tasks were carried out for five patterns of statistical and seasonal averages of Kd (spring, summer, fall, and winter).
The results show that not only does the season suitable for ALB vary depend on area, but also the measurable depth that can be acquired vary depend on season even in the same sea area or point. Although further verification is necessary, the obtained the maximum measurable depths were found to be useful as an index for the consideration of operational planning. The details of the results will be explained in the presentation.