|A view of laser beam |
emitted from the ground
(National Institute for
LIDAR is a remote sensing equipment that uses laser beam to measure in real-time DSS passing in the sky.
Many things could be identified by analyzing the laser beams reflected back from suspended matter that is originally transmitted from the ground.
The real-time monitoring data is automatically sent from the observation points, and is updated approximately every 20 minutes.
(For example, the data for the time period between 09:00 to 10:00 is updated at 10:20.)
|Electron microscope photograph |
of DSS particles
(fromthe DSS Pamphlet)
Although atmospheric pollutant particles such as exhaust gas are generally spherical, DSS particles are not (see the photograph on the right).
Since LIDAR can distinguish this difference in shape, it is possible to distinguish DSS from other atmospheric particles that cannot be seen with the naked eye.
Polarized laser beam (where the phases of light waves are all in the same direction) is used in LIDAR.
The state of polarized laser beam does not change and is reflected back to the ground when the laser hits spherical matter. However, when a laser beam hits non-spherical matter, scattered light is reflected in a disordered angle, and through such extent of scattered light, the shape of the suspended matter can be determined.
It is possible to estimate the amount (concentration) of suspended matter based on the amount of laser beams that hit fine particles and are reflected back.
■ Figure showing the principle of estimating the amount (concentration) of suspended matter based on the amount of laser beams
The orange cylinders displayed on the screen represent the average concentration of DSS near the ground (up to 1 km above ground).
The figures listed on this page are DSS concentrations calculated based on data (changes in the amount of light) obtained from LIDAR. The DSS concentrations [mg/m3] used on this page represent observed values (amount of light), which are calculated as the (estimated) amount of DSS based on the characteristics of the corresponding region.
Based on the disorder of laser beams that hit fine particles and are reflected back, it is possible to determine the concentration of DSS by altitude (= area above the air and to the extent DSS is occurring in real-time).
When the cylinders on the map are clicked, each cylinder will be magnified and concentration of the DSS, 6km above ground by altitude, will be displayed.
For example, if only the top part of a magnified cylinder is red, it means the DSS is not occurring close to the ground, but rather, it is passing through the air close to 6 km above ground.
■ Principle of comprehending the altitude of suspended matter
When you click on , a window appears and the hourly changes in the DSS concentration at the point are displayed. In addition, by switching the selection button, it is also possible to display daily changes.
When the character appears on the cylinder, it suggests that the DSS concentration near the ground is high.
This character (a panda wearing a mask) is displayed when the provisional data for suspended particulate matter (SPM) concentration (SPM monitoring data from the ambient air pollution monitoring station closest to the LIDAR location) exceeds the environmental standard (hourly figure) of 0.2 mg/m3, and when the concentration of DSS near the ground is determined as being high (exceeding 0.3 mg/m3) by LIDAR as well.
SPM refers to fine particulate matter (with a particle diameter of less than 10 μm) suspended in the atmosphere, and includes, in addition to exhaust gas from automobiles and soot from factories, fine DSS particles. In spring, the concentration of SPM may become high temporarily due to the impact of DSS. As a result, when this character is displayed (= when high concentration is observed both by SPM and LIDAR), DSS is likely to be occurring near the ground.
*This display function is available only for observation points in Japan.
The CFORS image displayed on the bottom left of the screen is a forecast for the distribution of DSS in East Asia based on a simulation model using LIDAR data. This information is provided as part of joint research by the National Institute for Environmental Studies and Kyushu University. On this page, the distribution diagram for the time closest to the displayed time is shown.
■ The CFORS distribution diagram shows the average concentration of DSS up to 1 km in altitude from the ground surface.
■ For seasons other than spring, a slightly higher figure is displayed.
■ Forecast distribution diagrams up to the day after next can be viewed on the CFORS home page.
Questions and Comments
If you have any questions or comments regarding this website, please contact the Air Environment Division, Environmental Management Bureau, Ministry of the Environment at KOUSA01@env.go.jp
Copyrights of materials, data, etc. listed on this website are owned by the respective agencies at which LIDAR systems are installed, as well as the National Institute for Environmental Studies.