A Holographic In-Line Imaging System for Meteorological Applications

A digital holographic in-line imaging instrument aimed for meteorological measurements is presented. The system is designed to capture detailed information of macroscopic hydrometeors in a large imaging volume. We suggest the use of holographic imaging to overcome the depth of field limitations of conventional macroimaging systems in meteorological imaging applications. The first low magnification holographic imaging prototype built for measuring free falling hydrometeors in the size range of a few tens of micrometers to several millimeters is described. The design of the imaging setup is discussed in detail, calibration and characterization measurements of magnification, position accuracy, and resolving power are presented. Field measurements during snow falls and rain were made and reconstructed images of snowflakes and raindrops are shown and analyzed. The results of laboratory tests and the field tests show high quality and resolution of reconstructed holograms to enable detailed image analyses on snowflakes, raindrops, and other types of hydrometeors.