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Arctic Icebergs Climatology 1992 to Present from Altimeter Data

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Abstract

Description of the Arctic small icebergs data base from altimeter data analysis (1992-present)
Arctic Icebergs Climatology 1992 to
Present from Altimeter Data
J. Tournadre R. Gourves-Cousin
IFREMER LOPS BREST
Arctic Icebergs Climatology 1992 to
Present from Altimeter Data
J. Tournadre and R. Gourves-Couzin , LOPS, Ifremer Brest
Why study iceberg: scientic interrest
Interest for icebergs and their impact on the ocean circulation and biology has increased
during the recent years.
Southern oceanlarge icebergs (>6km) tracked routinely and monitored using
scatterometer data (BYU, Long et al), In the Northern hemisphere iceberg monitoring for
hazard purposes (International Ice Patrol (IIP) Iceberg Sightings Database, Version 1
limited between 40 and 65°N)
Smaller icebergs (less than some km) were largely unknown as they are difficult to detect
operationally using conventional satellite
Iceberg may account for a signicant part of the freshwater flux in the southern ocean and
most of it in the northern ocean [Silva et al., 2006; Martin and Adcroft , 2010; Gladstone et
al., 2001; Jongma et al., 2009]
They can transport nutriments (in particular labile iron) that could have a signicant impact
on ocean primary productivity [Schodlok et al., 2006; Raiswell et al., 2008; Lancelot et al.,
2009; Schwarz and Schodlok ,2009],
Important to detect the possible climate change impact on the quantity of ice and
freshwater
Iceberg and Freshwater ux
(b) (b) (b)
Impact of iceberg on the
North Atlantic freshwater
from OGCM model
including iceberg
modules ;
Difference of freshwater flux
by including bergy bits.
Proportion of freshwater flux from
iceberg
Iceberg Detection from Altimeter WF
Targets emerging from the sea (iceberg, ships, lighthouse) : detectable signature in the noise
part of Altimeter WF [Tournadre et al , 2008, 2012].
In the waveform space the signature is a parabola determined by the orbital parameters.
Detection algorithm: detection of parabola in the noise part of the WF. Works only in open
water.
EX. signature of single iceberg
(Jason WF)
Peak of
before the mean sea level
Iceberg signature in SAR echoes
RDSAR -PLRM
SAR
The parabolic signature in LRM reduces to
a bright spot in SAR echoes
Several image processing algorithms have
been developed to detect bright spots in
imagery (especially for medical
applications)
range alignment including slant, tracker
and Doppler range corrections , stacking
and incoherent summation of stacks of co-
located Doppler beams are used to
produce L1B echoes.
The ALTIBERG DATA BASE for the Southern Ocean
From 1987 (Geosat) to present
All past and present altimeters except GFO (no Wf easily available).
11 Altimeters
GEOSAT, ERS-1, ERS-2, Topex, Jason-1, Jason-2, Envisat, Cryosat (3
modes, LRM, SAR, SARIn), Altika , HY2A, Jason3 , Sentinel 3.
Available at CERSAT
For each iceberg
Latitude, longitude, time, sigma0, distance from nadir, surface
For each altimeter
Gridded product (100x100km polar and 1x2° lat/lon)
Volume of ice, probability of presence, mean surface
Application of large and small iceberg database
Distribution of iceberg size from 1 to 10000km2
-1.5 power law : fragile fragmentation
Problem for Greenland, a large proportion of the icebergs rift near the coast
where therre are many unchartered rocks and small island.
Construction of a database of fixed targets by analysis of the detected targets
and comparison with Google Earth. ~600 rocks detected.
Icebergs detected by all altimeters 1992-present
Icebergs detected by all altimeters 1992-present
Icebergs detected by altimeters 1992-present
Icebergs detected by month 1992-present
Intercomparison intercalibration vs envisat
Backscatter and slope of size distribution
Intercomparison using monthly total volume estimate
Merged volume : over 26 years linear fit gives 1.5 % per year
Comparison to be done with Petermann Ice Island events 2008
2010 2012
Mean volume of ice 50 km grid
Mean length of iceberg
7 years mean volume
To be further analyzed to confirm the 1.5 %/year increase
of the volume of ice
Problem of continuity of observation (Jason1-Jason2-
Jason3 can’t be used)
Analysis of the distribution of size and freeboard from
Cryosat-2 SARIn mode
Sentinel-3 but problem of noise level in SAR WF (too
high so too many detections)
Will be distributed by CERSAT as part of ALTIBERG data
set
Cryosat SARIn over iceberg A68.
sigma0 elevation MODIS IR
image
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