W. Englisch’s research while affiliated with Battelle Memorial Institute and other places

The benefits of optical carriers in data transmission and the availability of powerful laser sources have turned first development efforts into a practical technology for communications. The combination of high bandwidth capability with the possibility of obtaining tremendous gain with small size antennae has made optical communication also very attractive for space applications.

This paper describes the baseline design of an optical intersatellite communication system using CO2 laser technology, and reports the present status of the relevant technologies and the various hardware development activities. These activities are primarily aimed towards laboratory breadboarding and full operational testing of the system, with the potential for space-qualifying all hardware components for experimental inflight testing in the early 1990s.

Instrument layout and subunit and component specifications of a satellite-borne meteorological lidar are described. Performance analyses indicate that cloud-top height and haze profiles can be measured with a spatial resolution of 150 m vertical and an average grid size 20 km. The distribution of tropospheric aerosols can be determined with good spatial resolution if background radiation is low. Only in the most unfavorable conditions, i.e., looking into the Sun glint at the ocean, very thin aerosol layers may not be detected with the desired spatial resolution. Differential absorption measurements require a much better SN ratio and thus have reduced spatial resolution. Even with a conservative SN (100) spatial resolution is still equal or better than specified for scattering off low tropospheric aerosol layers. At high altitudes, useful measurements can be performed for low levels of background radiation.

The design of CO2 laser transceiver system to establish and maintain a two way 1 Gbit/sec data link between two independently orbiting satellites is presented. The overall package has envelope dimensions of 70x35x90 cm, weighs 37 kg, and consumes 250 W of prime power. It comprises an externally modulated CO2 laser transmitter, an optical homodyne receiver, diffraction limited transceiving optics, a high performance pointing acquisition and tracking subsystem, and a stable light weight mechanical structure. Operational procedures are discussed and calculated performance data are given.

This study presents the detailed design of a CO2 laser transceiver package capable of establishing a two way data link between two geostationary satellites (GEO-GEO) or between an Earth observational satellite in low orbit and a geostationary relay satellite (LEO-GEO) with data rates or = 1 Gbit/s at a bit error rate 10 to the minus 6th power. The transceiver package comprises five major subsystems: transmitter, receiver, PAT (point, acquisition, tracking), optics, and mechanical structure. The technical definition of the various subsystems is at the level of components or parts. In addition mathematical models have been developed which are used to evaluate the functional relationships of the various subassemblies, to optimize the design parameters, and to investigate the implications of nonideal performance.

The Airborne DIALEX instrument /1/ is an active single-ended dual-wavelength sensor. At present it is equipped with two line-tunable cw CO 2 lasers and employs heterodyne detection. The return signal is provided by scattering and reflection at the earth's surface. The processed signal takes the form Filtering the differential albedo effect provides a new exciting possibility for active remote sensing of earth surface spectral signatures. Instruments of the DIALEX-type are well suited for this purpose because the coherent detection scheme provides the required sensitivity even at high flight altitudes.