Abstract. Snow avalanches can endanger people and infrastructure, especially in densely populated mountainous regions. In Switzerland, the public is informed by an avalanche bulletin issued twice a day during winter which is based on weather information and snow and avalanche reports from a network of observers. During bad weather, however, information about avalanches that have occurred can be scarce or even be missing completely. To assess the potential of weather-independent radar satellites, we compared manual and automatic change detection avalanche mapping results from high-resolution TerraSAR-X (TSX) stripmap images and medium-resolution Sentinel-1 (S1) interferometric wide-swath images for a study site in central Switzerland. The TSX results were also compared to available mapping results from high-resolution SPOT-6 optical satellite images. We found that avalanche outlines from TSX and S1 agree well with each other. Cutoff thresholds of mapped avalanche areas were found with 500 m2 for TSX and 2000 m2 for S1. S1 provides a much higher spatial and temporal coverage and allows for mapping of the entire Alps at least every 6 d with freely available acquisitions. With costly SPOT-6 images the Alps can even be covered in a single day at meter resolution, at least for clear-sky conditions. For the SPOT-6 and TSX mapping results, we found a fair agreement, but the temporal information from radar change detection allows for a better separation of overlapping avalanches. Still, the total mapped avalanche area differed by at least a factor of 3 because with radar mainly the avalanche deposition zone was detected, whereas the release zone was very visible already in SPOT-6 data. With automatic avalanche mapping we detected around 70 % of manually mapped new avalanches, at least when the number of old avalanches is low. To further improve the radar mapping capabilities, we combined S1 images from multiple orbits and polarizations and obtained a notable enhancement of resolution and speckle reduction such that the obtained mapping results are almost comparable to the single-orbit TSX change detection results. In a multiorbital S1 mosaic covering all of Switzerland, we manually counted 7361 new avalanches which occurred during an extreme avalanche period around 4 January 2018.

Abstract-Differential interferometry using groundbased radar systems permits to monitor displacements in natural terrain with high flexibility in location, time of acquisition and revisit time. In combination with polarimetric imaging, discrimination of different scattering mechanisms present in a resolution cell can be obtained simultaneously with the estimation of surface displacement. In this paper we present the pre-processing steps and the calibration procedure required to produce high-quality calibrated polarimetric single-look complex imagery with KAPRI, a new portable Ku-band polarimetric radar interferometer. The processing of KAPRI data into SLC images is addressed, including the correction of beam squint and of azimuthal phase variations. A polarimetric calibration model adapted to the acquisition mode is presented and used to produce calibrated polarimetric covariance matrix data. The methods are validated by means of a scene containing five trihedral corner reflectors. Data pre-processing is assessed by analyzing the oversampled response of a corner reflector and the polarimetric calibration quality is verified by computing polarimetric signatures and residual calibration parameters.

Abstract. Snow avalanches can endanger people and infrastructure, especially in densely populated mountainous regions. In Switzerland, the public is informed by an avalanche bulletin issued twice a day during winter which is based on weather information and snow and avalanches reports from a network of observers. During bad weather, however, information about occurred avalanches can be scarce or even be missing completely. To asses the potential of weather independent radar satellites we compared manual and automatic avalanche mapping results from high resolution TerraSAR-X (TSX) stripmap images and from medium resolution Sentinel-1 (S1) interferometric wide swath images. Within a selected test site in the central Swiss Alps the TSX results were also compared to available mapping results from high-resolution SPOT-6 optical satellite images. We found that avalanche outlines from TSX and S1 agree well with each other but with TSX about 40 % more, mainly smaller avalanches were detected. However, S1 provides a much higher spatial and temporal coverage and allows for mapping of the entire Alps at least every 6 days with freely available acquisitions. With costly SPOT-6 images the Alps can be even covered in a single day at meter-resolution, at least for clear sky conditions. For the SPOT-6 and TSX mapping results we found a fair agreement but the temporal information from radar change detection allows for a better separation of overlapping avalanches. Still, with radar, mainly the avalanche deposition zone was detected, whereas the release zone was well visible already in SPOT-6 data. With automatic avalanche mapping we detected around 70 % of the manually mapped new avalanches in the same image pair, at least when the number of old avalanches is low. To further improve the radar mapping capabilities, we combined S1 images from multiple orbits and polarizations and obtained a notable enhancement of resolution and speckle reduction such that the obtained mapping results are almost comparable to the single orbit TSX change detection results. In a multiorbital S1 moasic covering entire Switzerland, we detected 7361 new avalanches which occurred during an extreme avalanche period around Jan 4th 2018.

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<p>Since July 2022, a high-density CO<sub>2</sub> monitoring network has been operating in and around Zürich City, Switzerland as part of the ICOS Cities project. The network is formed of 80 sites that have been equipped with CO<sub>2</sub> monitors with varying performance and cost points. Three high-precision CO<sub>2</sub> gas analysers, 20 mid-cost sensors (installed with reference gas cylinders), and 114 low-cost sensors are in use with some sites having multiple sensors installed. Combined with several modelling approaches, the observations from the sensor network will allow for the characterisation of the city's emissions and to validate the city's CO<sub>2</sub> emission inventory. The different types of CO<sub>2</sub> monitors are combined with different data processing strategies to ensure their observations are adjusted for sensor drift and changes in responses so they can be used for robust analysis in near-real time. Between July 2022 and early January 2023, the CO<sub>2</sub> network's mean concentration was 446 ppm and the difference between the network's background and urban-traffic sites was 31 ppm suggesting a significant urban enhancement during this period. Distinct daily and seasonal patterns were observed for different types of sensor locations, reflecting diverse emission regimes across the urban area. Despite careful efforts during the site selection process, local contamination has been observed for many rooftop sensors due to their proximity to heating stacks. However, the installation of wind sensors allows for the observations to be flagged for such situations, which will be important for downstream data users. Details on the sensor adjustment strategies, the technologies in use for the data processing pipeline, the results from several months of CO<sub>2</sub> monitoring, and future plans with the other two ICOS Cities sensor network collaborators (Munich and Paris) will be discussed. </p>

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