The Chernobyl nuclear accident showed that the scale of impact and risk from radioactive contamination released into the atmosphere could be very wide in the former Soviet Union and in parts of Western Europe. External radiation dose-rate evaluation using UV-DIAL (differential absorption lidar) and PDS (phoswich detector system) is the only book on the market devoted to a new technique to obtain the geographic distribution and spatially resolve measurements of the nuclear risk based on external dose rate. The DIAL measures the density of the radionuclide and its distance simultaneously, whereas the phoswich detection system is quite capable of accurately measuring the type and energy of radiation present in combined radiation fields of X- and/or gamma-rays. In this textbook, after a brief description of DIAL, PDS, and PSD (pulse shape discriminator)the objective of hybrid system to evaluate external-radiation dose-rate is discussed. In addition, the systematic errors in measurements with hybrid system in the lower atmosphere for several visibilities at UV range by taking into account the dependence of refracting on air temperature and pressure are thoroughly investigated.