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By Vinca Rosmorduc1 and Val Byfield2

1. Collecte Localisation Satellites (CLS), Ramonville St-Agne, France
2. National Oceanography Centre, Southampton, U.K.

 

Map of Arctic sea ice
Arctic sea ice
Click for larger image and explanation

The Arctic is one of the areas where the impacts of global climate change are strongest. It is also an area which is quite difficult to measure in situ and thus one where satellite observations show their full strength. Several different sensors are used to monitor sea ice in the Arctic. Some allow us to see the global picture; others give a closer, more detailed view. This lesson introduces examples of both types. Monthly radiometer data is supplemented with a zoom in on one area with SAR data. The lesson also mentions freeboard measurements from CryoSat altimetry, which will become available as an ESA product towards the end of 2013.

Arctic Ocean circulation
Arctic Ocean circulation
Click for larger image and explanation

This lesson introduces examples of both types. Monthly radiometer data is supplemented with a zoom in on one area with SAR data. The lessons also mentions freeboard measurements from CryoSat altimetry, which will become available as an ESA product towards the end of 2013.

Introduction

The Earth's polar regions with their ice sheets (land ice), ice shelves and sea ice (frozen sea water) are in the front lines of global climate change. Observations show that sea ice around the North Pole has been continuously diminishing since 1979, while the ice shelves and sea ice of Antarctica have remained largely stable, diminishing slightly in some areas and have increasing slightly in others. The climatic, economic and geopolitical stakes are high. Today polar sea ice is an essential parameter to measure, monitor and forecast.

The two poles are quite different: the North Pole is an ocean surrounded by land, whereas the South Pole is a vast continent surrounded by the ocean. At the North Pole, the transpolar current, flowing from Siberia to East Greenland (Fram Strait), allows the ice to leave southwards and melt, while the closed Arctic basin traps it. In some places such as the Canadian Arctic Archipelago or the Beaufort Gyre, ice can remain blocked and accumulate for several years without melting. In this case, we talk about multi-annual ice of the second, third, ... seventh, as much as ninth year. Its average thickness is 3 metres.

Sea ice is characterised by means of several parameters:

Note that icebergs are not properly "sea ice", since they are bits of ice shelves or glaciers (from the polar ice sheets), which have broken off and now float in the sea.

Several types of satellite sensors allow measurement of sea ice:

Lesson Overview

Aim and objectives

The lesson will show you the different sea ice parameters that may be retrieved from different sensors. This will include a brief look at data from ESA's dedicated ice mission, Cryosat.

At the end of the lesson you should be able to:

Lesson Overview

Lesson content

The lesson is divided into 3 sections dealing with different types of data:

  1. Multi-sensors datasets.
  2. Synthetic Aperture Radar.
  3. CryoSat: an ice-dedicated mission.

Data and tools for this lesson

All data used in the lessons are in the original format available from the sources indicated below. The data sets have been compressed, but do not require that you uncompress them before opening these in Bilko.

Data needed to complete the lesson activities

Monthly sea ice concentration from SSM/I sensor for three different months: September 2007, September 2011 and April 2012; data produced and distributed by Cersat/Ifremer (projets.ifremer.fr/cersat/)

Multi-sensor monthly sea ice concentration climatology for the months of April and September; data produced and distributed by Cersat/Ifremer:

Daily sea ice data distributed by MyOcean ( www.myocean.eu) of 3 parameters (ice concentration, ice edge and ice type) each for April 5, 2012 and September 20, 2012:

ASA_WSM_1PNPDE20120405_092253_000004713113_00223_52823_9848.N1.bz2: SAR file HH polarisation on April 5, 2012 (ESA: eopi.esa.int).

CS_OFFL_SIR_SAR_2A_20120404T044246_20120404T045246_B001.zip: CryoSat along-track SAR Level 2 mode data (version A: no freeboard), on April 4, 2012 (ESA: eopi.esa.int).

Coastline data for use with the ASAR and CryoSat data; downloaded from NOAA National Geophysical Data Centre (www.ngdc.noaa.gov/mgg/shorelines/):

Bilko tools used in the lesson

seaice_anomaly_calc.frm: formula to subtract file 2 from file 1 keeping the continents different.

coastline_16bit_unsigned.frm, coastline_32bit_signed.frm: formulas to apply coastlines to different numerical data formats.

anomaly_minblack_maxgrey.pal, rainbow_minblack_maxwhite.pal, ice_conc.pal, palette_s13.pal, ice_conc_3.pal, ice_edge.pal, ice_type.pal: colour palettes.

Downloading the lesson

The lesson downloads contain everything you need to complete the lesson. This includes the data and tools listed above, and three PDF documents:

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