How a Laser Can Help Distinguish Water and Ice in Clouds ⚡ экспресс
For determining the thermodynamic phase of clouds (water/ice) using space lidars pointed near-nadir, specular reflection causes serious interference. It is proposed to use a lidar system with quantum parametric mode separation (QPMS), which biases sensitivity towards the specular component of backscattering. Thanks to nonlinear interaction and selectivity in time-frequency modes, the QPMS lidar achieves in-band noise suppression unattainable by linear filtering methods. This allows the signal power to be minimized, thus isolating the specular contribution from other reflections. In this work, a theoretical model of the QPMS lidar is constructed for this task, and its practical feasibility is assessed for calibrating measurements needed to determine the phase composition of clouds.
When a satellite laser beams downward at clouds, it often gets blinded by specular glare—especially if ice crystals form a smooth surface. This glare masks details, making it impossible to tell what's below: water or ice. Instead of fighting the blinding, scientists decided to use it. The quantum filter in the new lidar works like polarized sunglasses: it dampens scattered light, leaving only the direct mirror-like reflection. By comparing images taken with and without the filter, you can confidently distinguish droplets from crystals. Theoretical calculations confirm the method works even with a weak signal. Paradoxically, it's precisely that mirror-like quality that made lasers useless that became the key to solving the puzzle. In the future, this will allow satellites to peer into clouds without errors, improving weather forecasts and climate models.
🎯 The mirror reflection from icy clouds can be so strong that it completely 'blinds' satellite lasers, rendering them useless for analyzing cloud composition.