Abstract
Abstract. We present a comparison of Ice, Cloud and land Elevation Satellite-2 (ICESat-2) geolocated photon heights and operational ice charts from the Finnish Ice Service in the Bay of Bothnia in spring 2019. We show that ICESat-2 (IS2) retrievals from ice areas with different ridging characteristics, more precisely the degree of ice ridging (DIR), differ significantly. DIR is a particularly useful parameter for ice navigators, as it provides information on how difficult it is to navigate through an area based on e.g. sail heights and distribution of sea ice ridges. DIR estimates are included in ice charts of the Baltic Sea and are based primarily on in situ observations from an active icebreaker fleet. We show that DIR may potentially be estimated from IS2. We also present a comparison of IS2 measurements and Sentinel-1 synthetic aperture radar frames, discussing several individual cases of IS2 photon elevation behaviour over Baltic sea ice. We suggest that IS2 data can be of benefit to international ice services, especially if a time-critical photon height product were to be made available. Furthermore, we show that the difference between highest and mean photon elevations (elevation anomalies) of IS2 correspond to expected ridge sail heights in our study area. Our study is one of the first steps in creating sea ice applications beyond the traditional goal of freeboard and thickness retrieval for IS2.
Highlights
Rapid changes in the sea ice conditions cause challenges to ship navigation (Duncan et al, 2018)
This is only based on an amplitude parameter representing the ridge sail heights and one track; the surrounding behaviour and conditions of the ice are not known, and it is expected that DIR2 will be present in both the DIR3 and the DIR4 zones
We have presented the correspondence between Finnish Ice Service (FIS) degree of ice ridging (DIR), satellite synthetic aperture radar (SAR) data, and elevation anomalies using geolocated photons heights (ATL03) measured by IS2 during spring 2019 in the Bay of Bothnia
Summary
Rapid changes in the sea ice conditions cause challenges to ship navigation (Duncan et al, 2018). The ability to provide users with reliable and timely information on the ice conditions is time-critical and of high priority (Gegiuc et al, 2018). Wintertime shipping through the ice-covered sea into northern harbours requires timely and accurate ice information provided by the Finnish and Swedish ice services. This information is provided in the form of daily operational ice charts. The sea ice in the Baltic Sea is divided into fast and drift ice. Fast ice occurs in coastal regions and archipelagos and grows thermodynamically as it is attached to the coast where it remains stationary (Ronkainen et al, 2018). Divergent motion forms cracks and leads in the ice cover, and convergent motion results in formation of rafted ice and ice ridges (Gegiuc et al, 2018)
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