MAPPING SVALBARD GLACIERS WITH THE CRYOWING UAS

The remoteness of most Svalbard glaciers makes it difficult to perform regular in situ monitoring, especially in the melting season. Terminus areas (into the sea) and crevassed areas are in practice only accessible from the air. In this paper, first investigations on the feasibility of UAS based 3D measurements of glacier elevation is performed. The results show that UAS can be a valuable tool for glacier measurements in remote areas like Svalbard, where the only real alternative to measure glacier elevation in the ablation zone during the melt season is by manned aircraft. Imagery from repeated observations within a few days can be used to estimate dynamic mass loss rates when coupled to 3D modeling and feature tracking. Retrieval of these data is valuable, especially for glaciers terminating in the sea and surging glaciers

Unmanned aerial system nadir reflectance and MODIS nadir BRDF-adjusted surface reflectances intercompared over Greenland

Albedo is a fundamental parameter in earth sciences, and many analyses utilize the Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF)/albedo (MCD43) algorithms. While derivative albedo products have been evaluated over Greenland, we present a novel, direct comparison with nadir surface reflectance collected from an unmanned aerial system (UAS). The UAS was flown from Summit, Greenland, on 210 km transects coincident with the MODIS sensor overpass on board the Aqua and Terra satellites on 5 and 6 August 2010. Clear-sky acquisitions were available from the overpasses within 2 h of the UAS flights. The UAS was equipped with upward- and downward-looking spectrometers (300–920 nm) with a spectral resolution of 10 nm, allowing for direct integration into the MODIS bands 1, 3, and 4. The data provide a unique opportunity to directly compare UAS nadir reflectance with the MODIS nadir BRDF-adjusted surface reflectance (NBAR) products. The data show UAS measurements are slightly higher than the MODIS NBARs for all bands but agree within their stated uncertainties. Differences in variability are observed as expected due to different footprints of the platforms. The UAS data demonstrate potentially large sub-pixel variability of MODIS reflectance products and the potential to explore this variability using the UAS as a platform. It is also found that, even at the low elevations flown typically by a UAS, reflectance measurements may be influenced by haze if present at and/or below the flight altitude of the UAS. This impact could explain some differences between data from the two platforms and should be considered in any use of airborne platforms

Structure-From-Motion Photogrammetry to Support the Assessment of Collapse Risk in Alpine Glaciers

The application of Structure-from-Motion (SfM) Photogrammetry with ground-based and UAV camera stations may be exploited for modelling the topographic surface of Alpine glaciers. Multi-temporal repeated surveys lead to geometric models that may be applied to analyze the glacier retreat under global warming conditions. Thanks to the integration of point clouds obtained from ground-based and UAV imaging platforms, a complete 3D reconstruction also including vertical and sub-vertical surfaces may be achieved. These 3D models may be also exploited to understand the precursory signals of local collapse that might represent a risk for tourists and hikers visiting glaciers. In this paper a review on the application of SfM Photogrammetry in the field of glaciological studies is reported. The case of Forni Glacier in the Italian Alps is presented as emblematic study. Photogrammetric data sets obtained from measurement campaigns carried out in 2014, 2016, 2017 and 2018 have been processed using a common workflow. Attention is paid to a few crucial aspects, such as image orientation and calibration, dense surface matching, georeferencing and data fusion. In the end, the use of output point clouds to evaluate the risk of collapse in the Forni Glacier is addressed