Laser rangefinder performance (i.e., maximum range) is strongly affected by environment due to visibility-dependent laser attenuation in the atmosphere and target reflectivity variations induced by surface condition changes (dry vs. wet). Both factors have their unique spectral features which means that rangefinders operating at different wavelengths are affected by specific environmental changes in a different way. Current state of the art TOF (time of flight) semiconductor laser rangefinders are based mainly on two wavelengths: 905 nm and 1550 nm, which results from atmospheric transmission windows and availability of high power pulsed sources. The paper discusses the scope of maximum range degradation of hypothetical 0.9 μm and 1.5 μm rangefinders due to selected water-related environmental effects. Atmospheric extinction spectra were adapted from Standard Atmosphere Model and reflectance fingerprints of various materials have been measured. It is not the aim of the paper to determine in general which wavelength is superior for laser range finding, since a number of criteria could be considered, but to verify their susceptibility to adverse environmental conditions.
The article presents methods of long range distance measurements using pulsed lasers and the Time of Flight principle. Various algorithms of laser distance measurements with digital acquisition of echo pulses (acquisition of a signal’s full waveform) are presented. The main focus of work is concentrated on the method of distance measurements developed by the authors. With this method, during laboratory trials, a total measurement error of one centimeter was achieved using a 905 nm pulsed laser diode and pulse width of 39 ns. The maximum range of measurements with such high precision is limited only by a signal to noise ratio, duration of measurements and atmospheric conditions. All algorithms were implemented in a laser rangefinder module developed by the authors. Simulations and laboratory experiments were conducted and algorithm’s accuracy and precision were tested for various SNR conditions and changing distances.
The paper describes practical application of pulsed microchip laser generating at 1535-nm wavelength to a laser rangefinder. The complete prototype of a laser rangefinder was built and investigated in real environmental conditions. The measured performance of the device is discussed. To build the prototype of a laser rangefinder at a reasonable price and shape a number of basic considerations had to be done. These include the mechanical and optical design of a microchip laser and the opto-mechanical construction of the rangefinder.
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