Masahiko Sasano

Development of a Regional Coral Observation Method by a Fluorescence Imaging LIDAR Installed in a Towable Buoy

Coral bleaching and mortality is predicted to increase under global climate change. A new observation technique is required to monitor regional coral conditions. To this end, we developed a light detection and ranging (LIDAR) system installed in a towable buoy for boat observations, which acquires continuous fluorescent images of the seabed during day-time. Most corals have innate fluorescent proteins in their tissue, and they emit fluorescence by ultraviolet excitation. This fluorescence distinguishes living coral from dead coral skeleton, crustose coralline algae, and sea algae. This paper provides a proof of concept for using the LIDAR system and fluorescence to map coral distribution within 1 km scale and coral cover within 100 m scale for a single reef in Japan.

Development of coherent Doppler lidar for wind profiling

Space-borne Doppler lidar is expected to make wind profile observations on a global scale with an accuracy of 1 to 2 m/s. It may solve the problem of the shortage of the accuracy and distribution in the current wind data. We have studied an eye-safe coherent Doppler lidar (CDL) model that could be deployed on the exposed facilities of Japanese Experiment Module (JEM) and that would meet the science requirements. We have good prospects of 500mJ output at 10Hz in a conduction cooling sub-scale laser, which could be a small model of space-borne laser for JEM/CDL. We are making studies on improving the system’s efficiency, reducing its weight, and establishing the fundamental technologies involved. Research on another possibility, e.g. a free flyer, for a demonstration mission besides of JEM/CDL is also valuable to be considered. Development of algorithm for application of coherent lidar system is also in progress through air-borne experiments and ground-based observations.

Development of coherent Doppler lidar at CRL

Global wind profiling with a space-borne Doppler lidar is expected to bring big progress in the studies on global climate change and Numerical Weather Prediction. A feasibility study has been done for an eye-safe 2micron coherent Doppler lidar aiming at demonstration of the technology onboard the Japanese Experiment module of the International Space Station. We are now developing an airborne coherent Doppler lidar system to measure wind profile under a jet plane for simulation of the Doppler lidar measurement in space. This system is also operated in the ground to develop algorithm of the wind measurements and the results of the wind profiles are compared with those derived from other instruments.

Coherent Doppler lidar system for airborne measurement: a ground-based experiment of atmospheric wind profiling

An eyes-safe, airborne, coherent Doppler lidar (CDL) system has been developed at the Communications Research Laboratory (CRL). It consists of a 2-mm laser transmitter, a receiver, a heterodyne detector, a scanning device, and signal processing equipments. The main objective of the development of this CDL system is to demonstrate the feasibility of CDL from a moving platform. The second objective is to develop a computational algorithm for calculating wind velocity and wind direction. The performance of the CDL was evaluated by a ground-based experiment on wind profiling. That is, zonal, meridional, and vertical wind profiles were obtained by the CDL and by the velocity-azimuth display (VAD) technique with a height resolution of 150 m for every 20 minutes. These profiles were compared with the wind profiles measured by the WindProfiler (WP) installed at CRL. Although the temporal and vertical resolution measured by the CDL differed slightly from that by the WP, the calculated horizontal wind velocity measured by the CDL corresponded well with the WP calculations. It is thus concluded that the developed computational algorithm provides valid calculations of wind velocity.

Coral Observation by the Boat-Based Fluorescence Imaging Lidar

A boat-based coral observation system was developed using lidar (light detection and ranging) technique for large-area coral monitoring. The system comprises an ultraviolet (UV) pulsed laser and a gated image-intensified CCD (ICCD) camera to obtain fluorescent images of the seafloor. Coral observations were conducted using a glass-bottom boat at Taketomi Island, Okinawa, Japan, and the distributions of live corals along the boat tracks were obtained.

Monitoring the viability of coral reefs

Reef-building corals are important marine organisms. They form tropical coastal topography, have a symbiotic relationship with zooxanthellae, and are the primary producers in tropical oligotrophic (having few nutrients) seas. Coral reefs are typically monitored using the ‘coral cover’ indicator. This is defined as the ratio of the area covered by coral to that of the seafloor. Higher coral cover indicates a better conservation status. To measure coral cover accurately, however, the viability of coral tissue must also be measured. The impact of global climate change has recently become apparent as the warming of oceans. Corals are fragile ecosystems with high sensitivity to water temperature. Coral communities are frequently killed due to high water temperatures, typhoons, and attacks by Acanthaster planci (crown-of-thorns starfish). It is therefore becoming increasingly important to monitor regional coral distributions. We use the fluorescent characteristics of corals to monitor their viability. Peaks in the UV-excited fluorescence spectrum of a coral colony are typical of green fluorescent proteins (see Figure 1).1 UV-excited fluorescence diving investigations, conducted at night, provide more accurate coral viability checks than ordinary coral monitoring, but the size of the areas that can be studied is limited. We have developed a coral observation system that uses fluorescence imaging lidar (light detection and ranging) on a glass-bottom boat.2 Our system enables us to obtain images sequentially along a single boat track. The boat platform for our system allows a long and stable survey line to be maintained, which suppresses most wave and tide disturbances. Coral fluorescence lidar is an active observation technique that uses a pulsed laser, and is not significantly affected by solar altitude or cloud cover. As a result, observations made with our system have a good range, i.e., more than 10m of water depth when water transparency is good. Continuous coral Figure 1. Photographs taken at night of a branch type coral colony in Okinawa, Japan, using white light (top left) and UV light (top right) illumination. The UV-excited fluorescence spectrum of the same coral colony is also shown (bottom). Fluorescence typical of green fluorescent proteins (GFPs) occurs at wavelengths of 490 and 510nm. Fluorescence of chlorophyll-a (Ch-a) occurs at 680nm. a.u.: Arbitrary units.

Coral monitoring with fluorescence imaging lidar

It has been pointed out that globally hermatypic corals in coral reefs have been seriously damaged in recent years, and it is predicted that such damages will expand in area in the future. It is important to monitor corals globally, in detail, and over long-term periods, for preservation of the marine environment and biodiversity. The spot-check method, one of the major coral monitoring methods, is operated by snorkelers or divers, and therefore, its operation is limited by the seastate, and its monitoring areas are often for specific observation points. On the other hand, the satellite remote sensing, another major coral monitoring methods, can cover composite coral reef areas, but the image resolution is a few meters, and it is not possible to monitor small size coral colonies and deep sea areas. The boat-based fluorescence imaging lidar system has been developed to complement these coral monitoring methods. This system obtains linear coral observation data along the boat track, and makes it possible to build a cooperative coral monitoring network. Since most hermatypic corals have fluorescent proteins, living tissues can be monitored using the blue-to-green fluorescence from UV excitation. It is possible to observe the UV-excited fluorescence images from live coral even in the daytime, by the UV excited fluorescence imaging lidar. Additionally, laser bathymetry is also possible by time-of-flight measurement. We have succeeded in observing the pseudo-coral fluorescent images and depths down to 30 m depth at the testing basin. Secondly, we have succeeded in observing the live coral fluorescent images and their depths by the lidar system using a glass-bottom-boat at Taketomi island, Okinawa, Japan. The system summary and observed data are reported in this paper.

Real time measurements of air bubble and oil leakage in water using the 3D acoustic imaging instrument

On the seabed all over the world, the ships which sank during the war and marine disaster exist in great number. The cargo and fuel oil remain inside many wrecks. The wrecks become attenuated for long years. Then the oil is gradually discharged from the ship hull and rarely spouts resulting in a serious marine pollution. This paper describes the possibility of applying the Echoscope to the oil leakage monitoring and measurement method of the quantity of remained oil inside the tank using ultrasonic wave.

Remote Sensing of Oil Spill by Fluorescence Lidar

A tanker accident has a possibility for enormous pollution of coastal environment arising from substantial volume of oil spill. It is desirable to clean up oil spill on the ocean by the oil recovery vessel, or spray oil dispersant immediately after the accident. For these processes, the airborne lidar system is a powerful tool to collect oil spill information in real time.We have developed a helicopter-based fluorescence lidar system for oil spill detection, which also be used as a passive sensor for detection of oil spill in daytime. This system basically consists of a 355nm UV pulse laser. and a four wavelength simultaneous detect ICCD camera to visualize laser induced fluorescence light from oil spill.In this paper, the system specifications and its preliminary results are shown.

The Doppler Lidar for Atmospheric Wind Observation

The multi-channel incoherent doppler lidar is currently developed under Communications Research Laboratory (CRL). This system is designed for the visualization of the stratospheric winds in clear nights. It consists of a stabilized Nd:YAG(SHG) laser, a 75cm collection mirror, Fabry-Perot interferometer and multi-ring photon detector. The preliminary observation was held at Koganei, Tokyo, and the result was compatible with the radiosonde data at Tateno/Hamamatsu between altitude 12km and 24km.