Articles | Volume 9, issue 1
Research article
09 Feb 2015
Research article |  | 09 Feb 2015

Regional melt-pond fraction and albedo of thin Arctic first-year drift ice in late summer

D. V. Divine, M. A. Granskog, S. R. Hudson, C. A. Pedersen, T. I. Karlsen, S. A. Divina, A. H. H. Renner, and S. Gerland

Abstract. The paper presents a case study of the regional (≈150 km) morphological and optical properties of a relatively thin, 70–90 cm modal thickness, first-year Arctic sea ice pack in an advanced stage of melt. The study combines in situ broadband albedo measurements representative of the four main surface types (bare ice, dark melt ponds, bright melt ponds and open water) and images acquired by a helicopter-borne camera system during ice-survey flights. The data were collected during the 8-day ICE12 drift experiment carried out by the Norwegian Polar Institute in the Arctic, north of Svalbard at 82.3° N, from 26 July to 3 August 2012. A set of > 10 000 classified images covering about 28 km2 revealed a homogeneous melt across the study area with melt-pond coverage of ≈ 0.29 and open-water fraction of ≈ 0.11. A decrease in pond fractions observed in the 30 km marginal ice zone (MIZ) occurred in parallel with an increase in open-water coverage. The moving block bootstrap technique applied to sequences of classified sea-ice images and albedo of the four surface types yielded a regional albedo estimate of 0.37 (0.35; 0.40) and regional sea-ice albedo of 0.44 (0.42; 0.46). Random sampling from the set of classified images allowed assessment of the aggregate scale of at least 0.7 km2 for the study area. For the current setup configuration it implies a minimum set of 300 images to process in order to gain adequate statistics on the state of the ice cover. Variance analysis also emphasized the importance of longer series of in situ albedo measurements conducted for each surface type when performing regional upscaling. The uncertainty in the mean estimates of surface type albedo from in situ measurements contributed up to 95% of the variance of the estimated regional albedo, with the remaining variance resulting from the spatial inhomogeneity of sea-ice cover.

Short summary
Regional melt pond coverage and albedo of thin (70-90cm) first year Arctic sea ice in advanced stage of melt was estimated from a combination of low-altitude imagery and in situ measurements north of Svalbard in summer 2012. The study revealed a homogeneous melt across the study area with a typical pond fraction of 0.29 and sea-ice albedo of 0.44. A decrease in pond fraction was, however, observed in the 30km marginal ice zone, occurring in parallel with an increase in open-water coverage.