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May 30

COS Reviews: All-fiber multifunction continuous-wave coherent laser radar at 1.55μmm for range, speed, vibration, and windmeasurements

Review of 'All-fiber multifunction continuous-wave coherent laser radar at 1.55μmm for range, speed, vibration, and windmeasurements, Christer J. Karlsson, Fredrik Å. A. Olsson, Dietmar Letalick, and Michael Harris, Applied Optics, vol. 39 (21), (2000)'

Reviewed by John Davenport and the Cranfield Optics Society.

This paper describes the function of newly developed coherent laser radar (CLR) system and its application to wind measurements, hard target measurements and vibrometry. Along with basic scientific and photonics terminology, the paper assumes the reader is familiar with LIDARoperation. Readers not already familiar with these areas would be advised to check them in advance.

The structure of the paper was good, with well laid out and clear sections. This is particularly valuable as it is relatively long and quite involved. Where equations are used, they are quoted clearly in the text with a table of terms used given part way though. A reader wishing to locate part of the work within the paper would not have difficulty doing so.

Technical details given in this paper is probably its main strength. Full details of how the system was put together are included and a qualified reader is provided with enough information to repeat the work. The results section is broken down into noise analysis, hard target measurements, wind measurements and vibrometry measurements (more on this later). Each is analysed rigorously and concisely. The potential and limitations of the system are clearly stated.

Hard target measurements are taken using a sandblasted aluminium plates, as stationary or moving targets. Over distances or several kilometres, range measurements can be taken with accuracies of a few metres and the line-of-sight component of velocity can be measured to within around 0.1ms-1. Results conform reasonably well to theoretical expectations although there is some uncertainty as to the contribution of turbulence.

Two methods of wind measurements are discussed, using back scattering from a region of air, and focusing onto a single aerosol particle. The former allows measurements to be taken even under clear atmospheric conditions, showing improvements on earlier systems. The second is novel to this study and presents the opportunity for increased sensitivity.

The system is described as ‘multi function’, being about to perform position and velocity measurements of wind, similar measurements on of hard targets, and long range vibrometry measurements. While the first two are clearly different functions, it was our opinion that the vibrometrymeasurements were not fundamentally different from hard target measurements and did not really warrant a separate mention.

To summarise, the paper describes the CLR system, concentrating on technical detail. Details of both construction and testing are presented, describing use for wind measurements and hard target measurements. Layout is clear and easy to follow. This paper is recommended for readers wishing to work with CLR or LIDAR systems or wishing to understand what they are capable of.