Detection of Arctic icebergs on the

basis of satellite SAR

V. Alexandrov, V. Volkov, S. Sandven,

and K. Kloster

NIERSC and NERSC

The main objective of our study is to estimate the possibility of using different satellite images for iceberg detection among open water, fast ice and drifting ice.

Monthly maximum number of icebergs in August (from Abramov, 1996)

Iceberg drift from Argos buoys

Drift of buoys PTT4148 and 4149, deployed on icebergs in 1992: a) from 85 till 212, b) from 84 till 197 Julian days (Data by L.I. Eide).

Icebergs in the Eurasian Arctic

North-eastern Barents Sea, April 16, 2006 North-eastern Barents Sea, April 17, 2006

North-western coast of Novaya Zemlya, April 17, 2006 FJL, Salm island, April 25, 2006

Icebergs in the Eurasian Arctic seas are significantly smaller than those in the Antarctic and Greenland.

The average length and width of icebergs in the Barents Sea amounts to:

•64 m and 46 m according to ship observations, and

•103 m and 16 m, according to air reconnaissance data

Their maximum sizes amounts to:

•180 m and 30 m according to ship observations, and

•700 m and 50 m according to air reconnaissance data

(from Abramov atlas, 1996)

Overview of satellite data types

• Optical data• Landsat ETM+ • Resolution: 15 m panchr., 30 m multich. Pixel size: 12.5 m / 25 m• Swath: 180 x 180 km• Terra ASTER: • Resolution & pixelsize: 15 m panchr/multichan. Swath: 60 x 60 km

• SAR data• ENVISAT ASAR: Wideswath: 75 m pixels, 400 km swath• Alternating Polarisation: 12.5 m pixels, 100 km swath• RADARSAT ScanSAR Narrow: 25 m pixels, 300 km swath

Three situations1. Icebergs in open water: icebergs will show bright

spots against dark background for both optical and SAR, higher wind reduces the contrast between open water and icebergs

2. Icebergs in drifting ice: iceberg will create tracks in the drifting ice if there are larger floes of consolidated ice. Difficult to distinguish icebergs from background both for optical and SAR if only backscatter information is available

3. Icebergs in fast ice near calving areas: optical data shows shadows against background, stationary ice means possible to identify icebergs over longer time periods

Iceberg detection in visible satellite images

Optical Aster images of area west of Novaya Zemlya for March 29, 2006.

Icebergs are evident as bright spots

Iceberg detection in visible satellite images

Landsat image of the area west of Novaya Zemlya for April 23, 2006. Detected icebergs are marked with red triangles

Iceberg analysis: 3 ASTER images 2005south of Franz Josef land

•245 icebergs identified in 3 ASTER images: each 60 x 60 km

•(≈ 10 000 km2)

The sampling problem• Example of ASTER analysis April 2006: 245 icebergs

observed in 10,000 km2

• Results from previous aircraft surveys: maps of maximum iceberg concentration shows much lower occurrence of icebergs (see the map for April)

• Are iceberg observations severely underestimated ?

• Are there dense observations from aircraft in the past which can be compared with new satellite image analysis ?

Iceberg detection in satellite SAR images

ENVISAT ASAR WSM sub-image of FJL (Vilczek Land) for March 31, 2006. Icebergs are detected as bright spots among dark background of fast ice

Iceberg detection in SAR and visible images

“Monitor-E” sub-image for April 7, 2006

ENVISAT ASAR sub-image for April 5, 2006,

Landsat sub-image for April 14, 2006

Iceberg detection in SAR and visible images

•Red circles: from ASTER analysis

•Red triangles: from RSAT (05.04) observations during AARI expedition 2005

Iceberg detection in satellite SAR images

ENVISAT ASAR WS image of the area between FJL and NovayaZemlya for September 15, 2006. Open water prevails

Map of iceberg distribution, composed from this image

Sub-images of ENVISAT ASAR WS for September 15. Icebergs are evident as bright spots among open water background.

Iceberg detection in satellite SAR images

ENVISAT IMM sub-image for October 14,2006, covering area west of Vilkitskiy strait. Icebergs among drifting ice are clearly evident as bright spots

Map of iceberg distribution

Iceberg detection in satellite SAR images

ENVISAT ASAR WS sub-image (March 31, 2006) of the area to the west of Salm Island in FJL. Icebergs are marked with 1, 2, and 3. Their sizes are 100 х 250 m, 80 х 150 m, and 30 х 60 m (visual estimate)

iceberg photo from helicopter

Compare Landsat and RSAT iceberg detection

in drifting ice

•Example from 10 April (RSAT) and 14 April (Landsat) 2006

•The example shows pronounced difference between optical and SAR images to identify ice types, floes, leads and icebergs

Definition of the area under study

Determination of icebergs detection conditionsOpen water Fast ice Drifting ice

Selection of image type (coverage and resolution)and search of available images in archive

Image analysis – estimate of iceberg features and icebergs identification

Validation of identification results using sequentialimages

Combined analysis of identification results fromsatellite images in different spectral bands

Composition of iceberg distribution map

Supplement of iceberg data base

Methodology of iceberg detection in satellite images

Conclusions:• Iceberg detection requires combined use of optical and SAR images of high resolution ( ≈ 10 m pixels or better)

• Detection of icebergs in ENVISAT ASAR WS images among open water, fast ice and drifting ice of size 100 m and more is demonstrated, but if only SAR is used there is ambiguity (false positives) in observations. With ASTER icebergs down to 30-50 m can be detected in fast ice. The smallest icebergs (growlers and bergy bits) cannot be detected by the present images with 10 m pixels• Obtaining robust estimates of iceberg detectability from satellite images needs implementation of sub-satellite experiments in different seasons and analysis of sequential images

•Iceberg monitoring by satellites can be significantly improved by systematic acquisition of SAR and optical images, using resolution of 10 m or better