The open-source Video In Situ Snowfall Sensor (VISSS) is introduced as a novel instrument for the characterization of particle shape and size in snowfall. The VISSS consists of two cameras with LED backlights and telecentric lenses that allow accurate sizing and combine a large observation volume with relatively high pixel resolution and a design that limits wind disturbance. VISSS data products include various particle properties such as maximum extent, cross-sectional area, perimeter, complexity, and sedimentation velocity. Initial analysis shows that the VISSS provides robust statistics based on up to 10000 unique particle observations per minute. Comparison of the VISSS with the collocated PIP (Precipitation Imaging Package) and Parsivel instruments at Hyytiälä, Finland, shows excellent agreement with the Parsivel but reveals some differences for the PIP that are likely related to PIP data processing and limitations of the PIP with respect to observing smaller particles. The open-source nature of the VISSS hardware plans, data acquisition software, and data processing libraries invites the community to contribute to the development of the instrument, which has many potential applications in atmospheric science and beyond.@en

During the ERS-1 and ERS-2 missions, the application of synthetic aperture radar interferometry (InSAR) become known as a very important method for topographic mapping and high accuracy surface displacement measurements. Further investigations, however, showed that the expected accuracy could not be achieved in practice. It appeared that radiowave propagation heterogeneities through the atmosphere cause significant distortion to the observed signal and consequently to the derived topography and/or deformation signal. Inversely, it was shown that if topography is known and deformation is absent, the InSAR observations can be used to derive very accurate information on the state of atmosphere at the time of measurements. Due to the co-existence of MERIS (Medium Resolution Imaging Spectrometer) and ASAR (advanced synthetic aperture radar) on board of ENVISAT and the fact that their acquisitions can be collocated both in time and space, there are unique opportunities for complementary analysis. In this work we compare MERIS water vapor products and the integrated precipitable water vapor as observed with ASAR. Three complementary applications of the sensors are discussed. First, this is the correction of the atmospheric phase screen in InSAR products using the MERIS-derived water vapor signal. Second, we discuss the possibility for validating the MERIS water vapor product using InSAR data. Finally, we comment on the joint estimation of water vapor above and below the top of the cloud layers.@en