Coincident Measurement of Arctic Sea Ice using Envisat ASAR and Submarine
Nicholas Hughes(1), Peter Wadhams(2) and João Rodrigues(2)
(1) Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban PA37 1QA, United Kingdom
(2) University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
Achieving wide scale sea ice thickness measurements coincident with modern satellite measurements has proved a difficult undertaking. Whilst ESA satellites have been available, subject to scheduling, there have been limited opportunities to collect surface measurements from ship- or air- supported field experiments. These can only cover limited areas and so are not ideal for regional studies. Fortunately since the launch of Envisat in 2002 there have been two missions by U.K. Royal Navy submarines under-ice in the Arctic Ocean which have been able to provide wide scale sea ice thickness measurement coincident with Envisat overpasses. This paper presents some of the data collected on these expeditions and uses it to validate observations of sea ice from Envisat ASAR.
In 2004 and 2007 the submarine HMS Tireless was able to collect sea ice thickness data in Fram Strait and north of Greenland. A full environmental monitoring programme in which U.K. civilian scientists were allowed to participate was integrated into the mission. On both occasions the track took the submarine from the Marginal Ice Zone (MIZ) in Fram Strait around the north of Greenland at 85°N to the Lincoln Sea around 65°W. This transect encompasses a wide range of differing sea ice conditions, from the highly mobile mixture of first year and multi year ice being transported on the trans-polar drift through to the highly deformed ice north of Greenland and Ellesmere Island. The only previous study utilising remote sensed and submarine data was also along this transect line in May 1987.
We present here a study of how well Envisat ASAR data correlates to upward-looking sidescan sonar imagery and to ice draft measurements from the submarine echosounder. Previous studies have found a reasonable level of correlation between sea ice thickness and SAR image intensity levels. Here both high resolution PRI and medium resolution WSM Envisat ASAR images are evaluated, the previous study in 1987 only had access to airborne X-band SLAR. The combination of submarine measurements of ice thickness and satellite/aircraft top-side measurements allows the potential development of multi-sensor data fusion algorithms for improved sea ice classification and estimation of thickness.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,