This project belongs to the field of laser technology. Ocean vertical profiling and cross-media communication are cutting-edge technologies in the field of ocean observation. Airborne blue-green lidar is currently the only means to realize ocean and aerospace stereo remote sensing. Airborne cross-media blue-green laser communication is the only way to realize air-sea stereo communication. Technical approach. After more than ten years of continuous research, the project team has invented core technologies such as improving blue-green laser ocean penetration depth, suppressing background interference and sea surface disturbance, and solved the problem of airborne blue-green laser ocean profile remote sensing and cross-media high-speed optical communication technology in real sea conditions. Application bottleneck problem, developed my country's only airborne blue-green laser high-resolution ocean detection system and airborne blue-green laser cross-media high-speed communication system, breaking the foreign technical blockade and filling domestic gaps. It has obtained important applications in the fields of surveying and mapping of islands and reefs in the South China Sea, marine environmental monitoring and cross-media information transmission in my country, and has played an irreplaceable role. The main technical inventions and core key technologies of this project are as follows: Invention point 1: Invention of a nonlinear compression technology for the dynamic range of instantaneous optical signals. A special optical spatial frequency filter has been designed to compress the signal dynamic range by more than 20dB, ensuring distortion-free detection of the signal under a dynamic range of 50dB. It has been applied to an airborne laser detection system. After multi-sea area flight verification, the value is 0.2~The accuracy of water depth measurement in the 50-meter depth range is better than plusmn;0.22 meters. Invention point 2: Invention of a weak signal detection technology with a photon number that can be resolved. Through multi-level photon discrimination of the echo signal, photon counting detection with photon number can be realized. Combined with laser encoding modulation and photon counting related technologies, the system can adapt to intensity and time-resolved detection in the range of single photon to multi-photon signals. After a large number of flight verifications in different sea areas, the airborne cross-medium blue-green laser communication system has achieved reliable communication from shallow waters to depths of 120 meters. Invention point 3: Invented the adaptive array receiving technology of multi-aperture field of view splicing and maximum score set. Multi-aperture splicing with narrow field of view is used to increase the total receiving field of view under the equivalent aperture to 60 degrees; the maximum fraction set array and optimal signal weight allocation algorithm are used to realize multi-aperture signal synthesis and adaptive setting of receiving parameters, solving the problem. The alignment problem of blue-green laser communication under dynamic changes in the sea-air interface has expanded its application occasions. After verification under different sea conditions, the airborne cross-medium blue-green laser communication system can achieve high signal stability and low bit error rate communication below level 5 sea conditions. Invention point 4: Invented blue-green pulsed laser source technology that matches the optimal transmittance of seawater and dark solar lines. Using efficient nonlinear frequency conversion technology, a blue-green pulsed laser source with an output wavelength matching the solar Fraunhofer Mg and H-beta; dark line has been invented. The solar background radiation of this wavelength is low and is in the best transmission band of the ocean. It is conducive to the expansion of ocean applications of the airborne blue-green laser ocean detection and transmission system, improving the measurement performance of the system in clean sea areas, and extending the effective working period. Based on the above inventions, the project team has developed multiple sets of airborne blue-green laser ocean detection and transmission systems. The overall technology has reached the international advanced level, some indicators are internationally leading, and relevant achievements have been highly recognized by domestic and foreign counterparts. The system has found important applications in many fields such as surveying and mapping of islands and reefs in the South China Sea, coastal zone monitoring, underwater target detection, profile measurement of marine water quality and environmental parameters, and air-sea cross-medium communications integrated with military and civilian technologies. At the same time, this project has laid an important theoretical and technical foundation for the establishment and application of my country's satellite-borne ocean laser detection and transmission project, supported the strategic development of my country's smart ocean and transparent ocean, and achieved significant social benefits. The project was authorized for 20 invention patents, 4 software copyrights, 62 papers were published, and 12 invited reports were made. Through technology transfer and secondary development and promotion, the project results have been successfully industrialized, with a total direct economic benefits of 130 million yuan in the past three years.