New methods of generation of ultrashort laser pulses for ranging

To reach the millimeter satellite laser ranging accuracy, the goal for nineties, new laser ranging techniques have to be applied. To increase the laser ranging precision, the application of the ultrashort laser pulses in connection with the new signal detection and processing techniques, is inevitable. The two wavelength laser ranging is one of the ways to measure the atmospheric dispersion to improve the existing atmospheric correction models and hence, to increase the overall system ranging accuracy to the desired value. We are presenting a review of several nonstandard techniques of ultrashort laser pulses generation, which may be utilized for laser ranging: compression of the nanosecond pulses using stimulated Brillouin and Raman backscattering; compression of the mode-locked pulses using Raman backscattering; passive mode-locking technique with nonlinear mirror; and passive mode-locking technique with the negative feedback

Two wavelength satellite laser ranging using SPAD

When ranging to satellites with lasers, there are several principal contributions to the error budget: from the laser ranging system on the ground, from the satellite retroarray geometry, and from the atmosphere. Using a single wavelength, we have routinely achieved a ranging precision of 8 millimeters when ranging to the ERS-1 and Starlette satellites. The systematic error of the atmosphere, assuming the existing dispersion models, is expected to be of the order of 1 cm. Multiple wavelengths ranging might contribute to the refinement of the existing models. Taking into account the energy balance, the existing picosecond lasers and the existing receiver and detection technology, several pairs or multiple wavelengths may be considered. To be able to improve the atmospheric models to the subcentimeter accuracy level, the differential time interval (DTI) has to be determined within a few picoseconds depending on the selected wavelength pair. There exist several projects based on picosecond lasers as transmitters and on two types of detection techniques: one is based on photodetectors, like photomultipliers or photodiodes connected to the time interval meters. Another technique is based on the use of a streak camera as an echo signal detector, temporal analyzer, and time interval vernier. The temporal analysis at a single wavelength using the streak camera showed the complexity of the problem

A daily time-step hydrological-energy-biomass model to estimate green roof performances across Europe to support planning and policies

Nature-based solutions (NBSs) and urban greening are well-established strategies used in various planning and policy instruments to promote the sustainability of cities and mitigate the effects of climate changes. Within this context, green roofs are emerging as an effective NBS in urban areas where space is often limited. The estimation of green roofs' benefits is essential for their effective implementation and engineering design. In this contribution, we present a daily time-step model to estimate the surface temperature, the growth of vegetation cover and the hydrological behaviour of a green roof. The model is tested using twenty time series of real and independent European green roofs. Results show that, in the absence of calibration, the model can reproduce the daily surface temperature with high accuracy. The vegetation growing period is also reproduced. The hydrological variables can be estimated with moderate accuracy, and higher accuracy can be achieved when the model is calibrated. Therefore, the model proves a useful tool to support the appraisal of green roofs and the planning of green infrastructures in European cities.info:eu-repo/semantics/publishedVersio

Self-mode locked operation of a CW Nd:YAG laser using second-harmonic nonlinear mirror

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