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Scientific Report SAC/EPSA/AOSG/SR/22/2014
Sea Ice Advisory using Earth Observation Data
for Ship Routing during Antarctic Expedition
D. Ram Rajak, R.K. Kamaljit Singh, Megha Maheshwari, Jayaprasad P., Sandip R. Oza, Javed M. Beg*,
Rashmi Sharma and Raj Kumar
Atmospheric and Oceanic Sciences Group, EPSA.
Space Applications Centre, Indian Space Research Organization,
Ahmedabad – 380015, India.
December 2014
Current Location & Next Destination of Ship
SIE
SIC
SIT
SID
SIDr
SITr
Ship Entering Sea Ice ?
Next Shorter Route with Lowest SIC & Lowest SIT
SIC=100% & High SIT ?
Polynya Or Deformation?
Refreezing ?
DriftHindrance ?
No Sea Ice Advisory
Likely Safe Route
Yes
No
No
No
No
No
Wait ?
Yes
Yes
YesYes
ii
Scientific Report SAC/EPSA/AOSG/SR/22/2014
Sea Ice Advisory using Earth Observation Data for Ship Routing during Antarctic Expedition
D. Ram Rajak, R.K. Kamaljit Singh, Megha Maheshwari, Jayaprasad P., Sandip R. Oza, Javed M. Beg*,
Rashmi Sharma and Raj Kumar
Atmospheric and Oceanic Sciences Group, EPSA. Space Applications Centre,
Indian Space Research Organization, Ahmedabad – 380015, India.
December 2014
iii
GOVERNMENT OF INDIA
INDIAN SPACE RESEARCH ORGANISATION SPACE APPLICATIONS CENTRE
AHMEDABAD – 380 015 DOCUMENT CONTROL AND DATA SHEET
1 Date December 15, 2014
2 Title Sea Ice Advisory using Earth Observation Data for Ship Routing during Antarctic Expedition
3 Version 1.0
4 Document No. SAC/EPSA/AOSG/SR/22/2014 5 Type of Report Scientific 6 No. of pages 30 7 Authors D. Ram Rajak, R.K. Kamaljit Singh, Megha
Maheshwari, Jayaprasad P., Sandip R. Oza, Javed M. Beg*, Rashmi Sharma and Raj Kumar
8 Originating Unit OSD/AOSG/EPSA, SAC, Ahmedabad, India. 9 Abstract A brief description on the potential of earth observation
data to derive sea ice parameters needed to provide sea ice
advisory for safer shipping has been presented. Extraction
of near real time information needed for ship routeing has
been discussed with respect to a case study of successful
delivery of sea ice condition (derived from satellite data
analysis) during 33rd Indian Scientific Expedition to
Antarctica (33ISEA). The technique of multi-sensor remote
sensing data analysis to derive sea ice characteristics has
been explained. The actual route followed by the 33ISEA
voyage ship has been compared with the route advised
based on satellite derived sea ice conditions.
10 Classification Non Restricted 11 Circulation General
* Javed M. Beg from NCAOR, Goa
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
1
Sea Ice Advisory using Earth Observation Data for Ship Routing during Antarctic Expedition
1. Introduction
Safe shipping depends on a number of factors related to sea state, weather condition,
and ship’s own characteristics. The ship routing for a scientific expedition may differ a
lot than that for a cargo ship and is a little more complicated due to an additional factor
of achieving scientific objectives. Research Vessels or ships on a scientific mission may
not necessarily follow the shortest route or the most economic route with least fuel
consumption because of the scientific objectives / targets that are to be met. Navigation
in polar regions through sea ice is perhaps most tedious task and requires a lot of extra
information on sea ice condition for routing through path of least resistance. Continuous
processes of sea ice melting, freezing and drifting warrants near real time information
on sea ice condition. Traditional ship routing does not provide adequate real time
information on sea ice status. The availability of remote sensing data over ocean offers
an opportunity to derive and use near real time information needed for ship Routing.
–
Attempts have been made to develop algorithm and to numerically model the problem
of ship routing (Tsou and Cheng, 2013; Mannarini et al, 2013; Al-Hamad et al, 2012;
Shigeaki et al, 2010; Kotovirta et al, 2009). A prototype Decision Support System for an
operational ship routing using time‐dependent meteo‐oceanographic fields was
presented by Mannarini et al, 2013. Another prototype system for optimizing routes
through the ice field was presented by Kotovirta et al, 2009. Vlachos, 2004 presented a
method for manipulating the POSEIDON system forecasts for the Greek seas and for
producing optimal routes for small and medium size ships. Shigeaki et al, 2010 studied
a numerical navigation system for a small ship sailing in coastal waters with SWAN,
RIOS and MMG models and concluded that it is possible to achieve an optimum route
by numerical simulation if winds, waves, and tidal currents can be predicted. The basic
isochrone method was attempted to obtain an optimal route on the basis of the
dynamically changing weather, which could be forecasted by the coupled atmosphere-
wave-ocean model (Zhang and Huang, 2007).
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
2
Recently an ice class ship on way to Antarctica got struck in sea ice (Akademic
Shokalskiy, 2013). It was not the only case of ship routing trouble in polar sea ice
regions. Earlier, many polar expedition ships got struck in sea ice (Arctic supply ships,
2012; 1000 ships, 2013; Passenger ferry, 2010; Ships in Baltic Sea ice, 2010; Kapitan
Khlebnikov, 2009; Cold Irony, 2008; Rescue, 2002). To avoid and minimise such
instances, effective ship routing is an important aspect of polar navigation.
2. Factors Affecting Ship Routing
Factors influencing ship routing in polar regions for scientific expeditions may be
categorised in four classes –
–
1. Atmosphere / weather parameters e.g. wind speed, wind direction, atmospheric
pressure, atmospheric temperature, visibility etc.
2. Sea state parameters like significant and maximum wave height, wave direction,
current speed and direction, sea surface temperature etc. Sea ice conditions like
sea ice thickness, sea ice type, sea ice concentration etc.
3. Economics (distance to be travelled, fuel consumption, travel time etc) and Ship
Characteristics (ship type, hull type, speed capability, safety considerations etc).
4. Scientific Objectives to be achieved and expedition time window.
Wind speed affects ship navigation in a complex way. While ships lose speed in light
headwinds (less than 20-knots),) they gain speed slightly in following light winds. In
case of high wind speed, ship speed decreases in both head and following winds. In
such cases, wave action dominates over wind action for determining ship performance.
Additionally, the ship navigation gets influenced by direction, speed and persistence of
wind due to its direct impact on drifting ice, in polar regions. Winds are considered as
either pushing-off or pushing-in factors in such situation. While the pushing-off
contributes in weakening of compression due to concentrated ice, pushing-in does
strengthening of ice. Hence, accurate forecast of wind, which is a critical parameter for
all sailing ships, is vital to a successful voyage.
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
3
Wave height is a major factor that affects ship performance in open waters. The
development of waves in any region of ocean mostly depends on wind speed and
direction, water depth and presence and distribution of ice in that region. Wave action
causes increased drag and ship motions which reduces propeller thrust. The
relationship of wave direction and height with ship performance is also not simple. Head
waves reduce ship speed, while following waves increase ship speed slightly to a
certain point, beyond which they start reducing it. In very high wave seas, prediction of
performance may be difficult because of the adjustments to course and speed for ship
handling. In a study carried out by Haltiner et al, 1962, inspection of the basic
differential equations and the empirical relation between ship's speed and the state of
the sea was carried out which indicated that in cases of moderate wave heights, the
dependence on wave direction may be omitted as a good approximation. Usually, the
effect of sea waves and swells is much greater for large size ships than that of wind
speed and direction. However, it is difficult to separate the effects caused by these two
in ship routing.
Ocean currents don’t change frequently over a region of ocean and may be considered
relatively constant over a short span of voyage duration. Direction and speed of ocean
currents are more predictable than wind and sea waves. Hence they do not present a
significant problem in ship routing; although they can be a determining factor in route
selection and diversion. Ocean currents can get disrupted for short duration by very
intense weather systems such as hurricanes and by global phenomena such as El Nino.
While sailing to Antarctica, ships need to cross Antarctic Circumpolar Current (ACC)
which is considered the strongest ocean current on this planet.
Sea ice has remained a challenge for ship navigation in Polar regions. It causes
retardation in ship speed due to friction. It varies in lateral extent and thickness which
depends mainly on geographical position and host of whether parameters. The greater
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
4
the extent and thickness of sea ice, bigger shall be the duration and force of friction
which adversely affects the ship’s speed and fuel consumption. At times, with the sea
ice thickness being greater than the ship’s capability to break or cut through results in
ships getting stuck and being crushed under the formidable pressure that sea ice can
exert because of the ocean currents or volumetric expansion due to cooling
temperatures. Recent trends on climate change suggests contrasting rather
contradicting effects on sea ice. The Arctic sea ice extent is declining at a rate of 0.53 ×
106 km2 per decade, whereas Antarctica exhibits a positive trend at the rate of 0.167 ×
106 km2 per decade (Teleti and Luis, 2013).
3. Traditional Methods of Data Collection and Ship Routing
The sea state, characterised by statistics, including the wave height, period, and power
spectrum was traditionally assessed by the experienced observers (e.g. trained
mariners) or through instruments like weather buoys. Based on Douglas Sea Scale,
World Meteorological Organization (WMO) has assigned 10 sea codes for describing
sea sate condition. While sea state code 0 corresponds to calm (glassy) sea surface
with almost 0 meter wave height; sea state 9 represents phenomenal rough sea surface
with wave height of more than 14 meters. Ocean currents at local scales may be
measured by arrays of current meter moorings. Radars located at shores can map
coastal currents, Sea-Surface Currents, swell-wave parameters etc (Gurgel et al., 2003;
Bathgate et al., 2006; Braun et al, 2008) up to certain range inside ocean. Circulation
patterns over larger areas may be obtained by tracking ocean drifters, but it takes long
time to accomplish the task. Similarly, forecast of wind condition in any region was
conventionally based on the few available data points which were collected by buy
network and ships sailing in that region. The inaccurate wind condition would represent
inaccurate atmospheric cyclonic features resulting into inaccurate swells during wave
forecast.
–
All said such information was available in parts of oceans where high level of marine
activities take place like North West Shelf in Europe is an example wherein, countries
like Norway, Denmark, Netherlands and UK have deployed buoy Such network of buoys
measure both winds and wave heights with the spatial and temporal sampling. These
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
5
dedicated buoy networks have high running costs of over a million pounds per annum
for each 10 buoy network (https://earth.esa.int/web/guest/-/wind-and-wave-forecasts-
for-offshore-operations-and-ship-routing-4024).
On the contrary oceans in polar region especially surrounding Antarctica did not have
such networks of buoys and radars etc because of very little traffic. And the navigation
was mainly depended on experienced eyes of mariners with little support in for from of
historical weather data tables for ship routing. The climatic data available from such
resources include wind speed and direction, wave height, ocean currents, visibility,
barometric pressure, sea surface temperatures and ice limits, for the major ocean
basins of the world for each month of the year. There are a few online service that
provide some information on ship routing based on scanty data available through ships
around the area, (http://www.bocmetocean.com/index.php;
https://www.marinetraffic.com/en/; http://www.meteogroup.com/en/gb/sectors/ marine/
shipping/routeguard.html).
For the Indian Antarctic Expedition vessel the routing decisions are made by the
Captain/ Ice Navigator in consultation with the Leader of the expedition keeping in view
the safety of the ship and the mission objectives based on the limited field of view, aided
by the scanty information available through online services providing weather
information and not necessarily taking fuel economics into account. The experience of
the ship navigators plays an important role in optimum ship routing.
The ship navigators usually take help of Atlas of Pilot Charts
(http://www.offshoreblue.com/navigation/pilot-charts.php), the Sailing Directions both
Planning Guides and En-route (http://www.offshoreblue.com/navigation/ sailings.php)
and other climatological data.
Prior to satellite era, availability of sea ice records was poor. Limited information was
available through the whalers or other ships that visited the polar sea ice regions. Now-
a-days sea ice records prepared based on satellite data include sea ice extent, area,
concentration, thickness and the age of the sea ice. Sea ice in Antarctic region is very
different that in Arctic region as far as its age, thickness, growth/melting patterns, snow
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
6
coverage etc are concerned. Based on analysis of 10 years data, Massom et al, 2001 found large regional and seasonal differences in snow properties and thicknesses and
thicker snow and thinner ice in the Antarctic relative to the Arctic.
4. Earth Observation Data to Support Ship Routing
Traditional methods of data collection over ocean have certain limitations. Insufficient
data and time consumption are two of the major concerns. Moreover, in many cases
incompatibility problems prevent neighbouring countries from sharing the data. The
availability of useful data in Southern Hemisphere is further poor in comparison to
Northern Hemisphere. With the increasing availability of remotely sensed data this
situation is gradually improving. Weather data and other environmental information
obtained from satellites are contributing greatly to an improvement in southern
hemisphere forecasts.
Wind speed and direction, sea surface temperature, and significant wave height are
some of the parameters that are derived from satellite data analysis. Data available
from microwave radiometers as well as scatterometer can be used for estimating wind
speed and wind direction over ocean surface.
Ocean surface wind vector can be modelled using angular sigma-0 measurements by
scatterometer at different azimuth angles. Sigma-0 over the ocean depends on
backscattering from wind-generated capillary-gravity waves, which are generally in
equilibrium with the near-surface wind vector. Viewed from different azimuth angles, the
observed backscatter from these waves varies. Relating wind with backscattering
sigma-0 using a geophysical model function enables estimation of wind vector using
scatterometer data.
–
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
7
Gohil and Pandey, 1985 presented an algorithm for retrieval of oceanic wind vectors
from the simulated SASS (Seasat A satellite scatterometer) normalized radar cross-
section measurements. Wentz, 1992 investigated the retrieval of wind speed and
direction over ocean using microwave radiometer measurements. Bentamy et al, 1999
compared the wind estimates derived from scatterometer (ERS-1), altimeter (ERS-1)
and radiometer (SSM/I) and established the usefulness of merging of these estimates to
generate wind fields. Data available from Advanced Scatterometer (ASCAT) onboard
EUMETSAT MetOp-A and MetOp-B satellites is successfully used for ocean wind
vector generation (http://www.remss.com/missions/ascat). Wind vector has been
generated using polarimetric microwave radiometry from WindSat, a satellite-based
multifrequency polarimetric microwave radiometer (Gaiser et al, 2004). An algorithm
was developed by Gohil et al, 2006, for retrieving wind vector from scatterometer with a
solution ranking criteria of minimum normalized standard deviation of wind speeds
derived using backscatter measurements through a geophysical model function.
Sharma et al (2007a and 2007b) developed and applied new technique based on
genetic algoritm for predicting wind field in the Bay of Bengal using satellite
scatterometer observations. They found that the predictions made by the proposed
technique up to 5 days in advance were superior to the forecast by persistence method.
Reul et al, 2012 demonstrated that surface wind speeds estimated from SMOS (Soil
Moisture and Ocean Salinity) brightness temperature images agreed well with the
observed and modelled surface wind speed features. Recently, Tang et al, 2014 have
presented and validated a method of reconstructing high-resolution sea surface wind
fields from multi-sensor satellite data.
Satellite remote sensing data can be used to determine currents synoptically over
extensive ocean. It may be used to monitor dynamic ocean conditions, including surface
currents, local wind speed, significant wave height etc (Klemas, 2011). For many years,
active satellite remote sensing data, from Synthetic Aperture Radar (SAR) and
altimeter, have been used to determine ocean wave height. Now these estimation
techniques are imbedded on many meteorological and oceanographic forecasting
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
8
systems. Satellite data has been used for sea surface topography measurement since
the first radar altimeter was tested on NASA's Skylab space station in 1973 (Mourad et
al, 1976). Barrick and Fedor, 1978 presented some of the first wave height plots
prepared using the satellite based radar data. Rufenach, 1978 measured ocean wave
height using altimeter signals transmitted from the low-orbiting satellite Geos 3.
Mognard and Lago, 1979 processed radar altimeter data from more than 100 Geos 3
passes and found that the wave height and wind speed estimates were in favourable
agreement with the meteorological information obtained from weather maps.
Techniques of observing ocean variability using satellite altimetry and the challenges
faced during 1980s have been discussed by Fu et al, 1988. The ocean wave heights
products are prepared from the shape and intensity of the satellite based altimeter radar
echo. Romeiser et al., 2005 presented a study on ocean current retrievals from
interferometric Synthetic Aperture Radar (InSAR) data acquired during the Shuttle
Radar Topography Mission (SRTM) in February 2000.
Sea ice condition derived from earth observation data is becoming available for ship
routing in polar regions. Sea ice detection, classification and extent mapping using
remote sensing data available from different sources have been demonstrated by
various researchers (Riggs et al., 1999; Remund and Long, 1999; Haarpaintner et al.,
2004; Oza et al., 2010; Rivas and Stoffelen, 2011; Belmonte et al., 2012). Sea ice
extent mapping attempt was made by Laxon (1994a, 1994b) using pulse-peakiness
parameter derived from altimeter data. Kim et al., 2001 studied distribution of sea ice in
the Weddell Sea, Antarctic region using radar altimeter data from Topex/Poseidon and
ERS-1. Cavalieri et al., 1984 presented an algorithm to determine sea ice concentration
from SSMR (Scanning Multichannel Microwave Radiometer) data. Long term sea ice
concentration data are available at NSIDC (National Snow and Ice Data Center at
University of Colorado, Boulder) site. These sea ice concentrations products are
generated from brightness temperature data derived from the Nimbus-7 SMMR, the
Defense Meteorological Satellite Program (DMSP) SSM/I i.e. Special Sensor Microwave
Imager sensors, and the DMSP SSMIS i.e. Special Sensor Microwave Imager/Sounder
(Cavalieri et al., 1995; Cavalieri et al., 1996). Near Real Time (NRT) daily gridded sea
ice concentration products available at NSIDC site are based on an algorithm
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
9
developed by Maslanik and Stroeve, 1999. There are a number of studies that discuss
the problem of sea ice freeboard and thickness determination using remotely sensed
data (Kwok and Cunningham, 2008; Zwally et al., 2008; Singh et al., 2011; Kurtz et al.,
2012; Laxon et al., 2012; Kurtz et al., 2013; Kurtz et al., 2014). Kwok and Rothrock,
2009 examined sea ice thickness records from submarines (1958 to 2000) and ICESat
observations (2003 to 2008). They found that mean Arctic sea ice thickness declined
from 3.64 meters in 1980 to 1.89 meters in 2008—a decline of 1.75 meters. Zwally et al,
2008 derived sea ice freeboard heights in the Weddell Sea of Antarctica from ICESat
(Ice, Cloud, and Land Elevation Satellite) laser altimeter measurements. Singh et al.,
2011 presented an algorithm for estimating sea ice thickness using passive microwave
data over thin ice. The overall sea ice thickness is much higher in Arctic than in
Antarctic. Moreover, high inter annual variability of sea ice in Arctic (Laxon et al., 2003)
poses a greater challenge for ship routing experts. Recently, Kern et al., 2014
discussed about uncertainties involved in retrieving sea ice thickness using satellite
based altimeter data.
5. Satellite Based Sea Ice Advisory to Indian Antarctic Expeditions:
Selection of optimum ship route is a problem of multiple criteria decision making
(MCDM). Based on the multiple objectives, multiple criteria decision analysis (MCDA) is
carried out to support decision ship navigator during planning of ship route as well as
during the real time navigation. A number of software tools are available which perform
MCDA and help ship navigators. Such software tools need real time forecast of data for
the transit to be travelled by ship. The current and past status of sea ice features and
other parameters can be derived using remotely sensed data. Combining satellite
derived information with numerical modelling can be a strong base for sea ice advisory
for ship navigation. Following two sections present brief details on the satellite based
sea ice advisory provided to 32nd and 33rd Antarctic expeditions.
–
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
10
a.
Ships travelling to Antarctica need information of sea ice condition before nearing its
coast. The historical data on sea ice extent and sea ice thickness helps in selecting the
general ship route. The actual route to be followed by ship can be determined only
based on near real time sea ice condition. The first satellite based sea ice advisory was
requested by Voyage Leader of 32nd ISEA in December 2013. The expedition ship was
sailing from Bharati to Maitri while it got struck and could not make any headway for the
next two days. The ice-breaker, which was part of the expedition, was supposed to
create a wide track for voyage ship to move out of fast ice. The track created by ice-
breaker was so narrow and zigzag shaped that the voyage ship could not sail properly.
After struggling for two days, the expedition ship could come out of fast ice. But then
there was thick fast ice near Maitri that the expedition ship was going to encounter. That
is the time when first satellite based sea ice advisory prepared at SAC was made
available to 32nd ISEA through NCAOR. The advisory was mainly based on analysis of
SIC data and MODIS LANCE data.
First Satellite Based Sea Ice Advisory to 32nd ISEA
b.
33rd ISEA was the first Indian Antarctic Expedition for which comprehensive satellite
based sea ice advisory was made available. Following sections provide brief summary
of sea ice advisory provided during second leg of 33rd ISEA –
A Comprehensive Sea Ice Advisory to 33rd ISEA
M/V Ivan Papanin, a Russian Ice Class ship hired by India started its journey of second
leg of ISEA from Cape Town (South Africa) toward Bharati (an Indian Research Station
in Antarctica) on February 14, 2014. The ship Master and Voyage Leader had apriori
information from 1st leg of 33rd ISEA that they will encounter thick sea ice south of 66o
latitude and ship will not be able to break pack ice with almost 100% fraction. To
support ship navigation satellite data analysis was carried out at Space Applications
Centre (SAC), Ahmedabad and sea ice fraction, sea ice deformations and sea ice
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
11
thickness were analysed and the advisory regarding most suitable entry locations were
suggested. The advisory was sent to ship navigator on February 20, 2014 through
National centre for Antarctic & Ocean Research (NCAOR), Goa. After completing the
expedition objectives at Bharati the ship had to sail from Bharati toward Maitri (another
Indian Research Station in Antarctica). Again, based on satellite data analysis sea ice
advisory suggesting the most suitable exit locations was sent on February 26, 2014.
While ship nearing India Bay toward Maitri coast, it encountered densely packed drifting
sea ice with very high concentration. Multi-date satellite data analysis was carried out at
SAC and sea ice drifting pattern was monitored and sea ice advisory suggesting
possible ship route was sent on March 7, 2014. When ship reached 69o 35’ S, 10o 25’ E,
it got trapped within thick pack ice. Based on the sea ice concentration and the
deformation patterns visible on satellite imagery another sea ice advisory was sent on
March 14, 2014. Finally on March 29, 2014 a sea ice advisory was sent that suggested
three exit routes from India Bay to sail toward Cape Town.
6. Satellite Data Analysis for Sea Ice Advisory During 33rd ISEA 2013-14
6.1 Study Area –
–
The study area comprises of two sectors in southern ocean. One sector covers Prydz
Bay in southern ocean extending from 65o South latitude to Ingrid Christensen Coast,
Larsemann Hills between 60o to 90o East longitudes. Indian research station, Bharati is
situated in this section. In Prydz Bay, the ocean circulation is characterized by a closed
cyclonic gyre adjacent to the Amery Ice Shelf. Circumpolar Deep Water (0° to 2°C;
34.50 to 34.75 salinity), a large mass of cold, moderately saline water along with colder
and more saline Antarctic Bottom Water (0°C; 34.60 to 34.72 salinity), are the major
bodies of deep water masses carried by the Antarctic Circumpolar Currents (Smith et
al., 1984). Wong, 1998 postulated the possibility of high salinity bottom water formation
episodically on the continental slope of the Prydz Bay. Yabuki et al., 2006 confirmed,
through their observations, the formation of saltier Low Salinity Shelf Water (LSSW) in
the Prydz Bay region which provides evidence for the idea that saltier LSSW originating
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
12
in the Amery Basin mixed with unmodified Circumpolar Deep Water in continental slope
resulted in the formation of the Antarctic Bottom Water.
The second sector of study area covers India Bay in Southern Ocean. It covers parts of
King Haakon VII Sea from 65o South latitude to Princess Astrid Coast, Antarctica.
Princess Astrid Coast is a portion of the coast of Queen Maud Land lying between 5°
and 20° E longitudes. Indian research station, Maitri is situated at Schirmacher Oasis on
central Queen Maud Land. Its aerial distance from India Bay coast is around 80 km. The
Indian voyage ships arrive in India Bay, unloads cargo, and decant fuel on an ice shelf.
Expedition members disembark from ship on ice shelf and reach Maitri by helicopter.
The study area in shown in Figure 1.
Fig 1: Sea Ice Advisory Study area: Ocean regions near Bharati & Maitri Stations
.
.
Maitri
Bharati
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
13
6.2 Satellite Data, Products and Analysis –
Following are the major remotely sensed data used to derive sea ice condition
parameters –
1. SAR data from RISAT-1 (Obtained from NRSC/ISRO)
2. AltiKa data from SARAL (From MOSDAC/ISRO local database site)
3. Scatterometer data from Oceansat-2 (OSCAT-2 from MOSDAC/ISRO local
database site)
4. MODIS LANCE mosaic (From lance-modis.eosdis.nasa site)
5. Sea Ice Concentration products at 3.125 km resolution (From ftp://ftp-
projects.zmaw.de/seaice/AMSR2 site)
6. Initial Sea Ice Extent (Rajak et al., 2014)
Further details on datasets used in this study are provided in a table given below -
Data Name Satellite Sensor Reso-
lution Derived Information Data Source
A-priori SIE
Multiple Multiple 25 km Sea Ice presence Rajak et al., 2014
RISAT-1 SAR
RISAT-1 SAR 36 m Ice features NRSC
OSCAT Oceansat-2 Scatterometer
12.5 km
Sea Ice Concentration (overall)
MOSDAC Local database (SAC)
SARAL AltiKa
SARAL Altimeter 175 m Sea Ice Thickness MOSDAC Local database (SAC)
Sea Ice Concen-tration
GCOM-W AMSR2 3.125 km
Sea Ice Concentration & Sea ice Trend Analysis
ftp://ftp-projects.zmaw.de/ seaice/AMSR2
MODIS LANCE Mosaic
EOS AM/ EOS PM
MODIS (Terra/ Aqua)
250 m Sea Ice Deformation and Sea Ice drift Analysis
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?mosaic=Antarctica
Satellite data acquired over two segments of study area during the expedition period
were used to derive the information needed for sea ice advisory. Coarse Resolution
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
14
scanSAR (CRS) and Moderate Resolution ScanSAR (MRS) SAR data at C-band (5.35
GHz) available from Radar Satellite-1 (RISAT-1) for two dates were used for polar ice
feature identification. CRS data with 50 m spatial resolution (pixel size of 36 m) over
India Bay was acquired on March 08, 2014 and MRS data with 25 m spatial resolution
(pixel size of 18m) was acquired on March 26, 2014. Oceansat-2 Scatterometer data
[OSCAT-2, enhanced resolution, 10-day running composite prepared at MOSDAC,
SAC, Ahmedabad0 was used to derive sea ice extent and sea ice concentration over
Antarctic region for ship voyage duration. SARAL AltiKa was used for sea ice thickness.
Cloud free mosaic MODIS (Moderate Resolution Imaging Spectro-radiometer) LANCE
(Land Atmosphere Near real-time Capability for EOS) data available from “http://lance-
modis.eosdis.nasa.gov/imagery/subsets/?mosaic=Antarctica” for voyage duration were
used for sea ice deformation analysis and sea ice drift analysis. The 3.125 km sea ice
concentration data available from ftp://ftp-projects.zmaw.de/ seaice/AMSR2 site was
used at selected locations for finer details.
The satellite data and products available from different sources were analysed to derive
polar ice and sea ice parameters like sea ice extent, sea ice concentration, sea ice
thickness, wind speed and direction, sea ice deformations, sea ice growth trend, sea ice
drift analysis etc. A schematic diagram showing major elements of RS data analysis for
arriving at a safer ship route are shown in Figure 2.
6.2.1 Polar Ice Features Identification using RISAT-1 SAR Data –
Synthetic Aperture Radar (SAR) data acquired by Indian satellite RISAT-1 were used
for identification of various polar ice features like ice shelf region near Maitri coast, fast
ice, ice rise, ice bergs, sea ice floe etc. This is a high resolution data with relatively
narrow swath, hence spatial coverage is limited. Accurate geo-graphic locations
(longitude and latitude) of the ship birthing site and finer details around it are derived
from these data. An example of a RISAT-1 SAR scene (36m) acquired on March 8,
2014 near Maitri coast is shown in Figure 3.
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
15
6.2.2 Sea Ice Extent & Concentration Analysis –
Sea ice occurrence probability data generated by Rajak et al., 2014 is primarily used for
arriving at first guess of voyage ship encountering sea ice. Current season sea ice
concentration images prepared from OSCAT and ASCAT data were used for overall
assessment of sea ice condition in the Antarctic regions. For assessing the sea ice
status at finer level sea ice concentration products available at ftp://ftp-
projects.zmaw.de/ seaice/AMSR2 site were used. The shortest path of ship from its
current location to next destination is plotted and overlaid on SIC image. SIC values
throughout the transect are plotted and analysed alongwith sea ice thickness values.
Fig 2: A schematic diagram showing major elements of RS data analysis. SIE, SIC,
SID, SIT are Sea Ice Extent, Concentration, Deformation and Thickness, respectively;
SITr and SIDr are Sea Ice Trend and Drift analysis, respectively.
Current Location & Next Destination of Ship
SIE
SIC
SIT
SID
SIDr
SITr
Ship Entering Sea Ice ?
Next Shorter Route with Lowest SIC & Lowest SIT
SIC=100% & High SIT ?
Polynya Or Deformation?
Refreezing ?
DriftHindrance ?
No Sea Ice Advisory
Likely Safe Route
Yes
No
No
No
No
No
Wait ?
Yes
Yes
YesYes
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
16
6.2.3 Sea Ice Thickness Estimation –
Deriving sea ice thickness information using remotely sensed data is a challenging task.
Sea ice freeboard/thickness images were prepared using SARAL/AltiKa IGDR (Interim-
Geophysical Data Records) data. These images with scattered points with estimated
SIT were used for determining the possibility of ship encountering thick sea ice on its
route. A-priori knowledge of sea ice thickness along with relative thickness/thinness
derived from current season altimeter data were taken into consideration. An example
of SARAL/AltiKa data and estimated sea ice thickness over Antarctic region is shown in
Figure 4.
Fig 3: A RISAT-1 SAR scene (March 8, 2014) showing different polar ice features.
6.2.4 Sea Ice Deformation Analysis –
Detection and analysis of Sea ice deformation using remotely sensed data in an important component of sea ice advisory. In case of pack ice, the regions with high sea ice deformation density are usually preferred over the regions with lover deformation density. MODIS data obtained from LANCE-MODIS site were used for sea ice deformation analysis. An example of MODIS data (250m) showing sea ice deformations is shown in Figure 5.
Ice-Shelf
Polynya
Sea-Ice
Indicates Maitri CoastFor Fuel Decanting
Indicates the Location whereShip is expected to reach
Indicates locations of some Of the ice-bergs in India Bay
Ice-RiseIce-Sheet
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
17
Fig 4: An example of SARAL/AltiKa Data and estimated SIT
Fig 5: Sea Ice Deformation Patterns visible on MODIS scene (Near Maitri coast)
Sea Ice Thickness
Estimated using SARAL
Altika Data
Red: Thick Sea Ice
Green: Medium Thick Sea Ice
Blue: Thin Sea Ice
Sea Ice Deformation Pattern as seen from 250 m MODIS Data
OCEAN
The Sea Ice: RED
Open Water / Polynya: BLACK
A N T A R C T I C AMaitri
A
B
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
18
6.2.5 Sea Ice Drift Analysis –
The knowledge of sea ice drift rate and direction are vital parameters before suggesting
the ship route though sea ice ocean region. In this study cloud free MODIS LANCE
mosaics over study area at 250 m were used for tracking big sea ice floe and then to
determine the direction and speed of sea ice. Figure 6 shows 5 images (MODIS
LANCE) from February 23 to March 15, 2014. The track followed by a sea ice floe from
February 23 to March 15, 2014 is depicted by yellow coloured line. The location of the
floe under study at different dates is marked by magenta coloured circles on different
images. Sea ice drift of 284.4 km in 20 days (February 23 to March 15, 2014) was
monitored using 12 dates MODIS cloud free mosaic images.
Fig 6: Sea Ice Drift monitored using MODIS data (Feb 23 to March 15, 2014)
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
19
15- 40
40-70
>70
< 15
Ice Concentration (%)
India Bay
Ship Position on Dec 26
6.2.6 Sea Ice Advisory Workout –
The information needed for sea ice advisory was extracted from different sources as
mentioned above. While the sea ice advisory made available to 32nd ISEA was based
on basic analysis of SIC data (See Figures 7 and 8), during 33rd ISEA comprehensive
data analysis was taken up to provide near real time advisory. The last known location
of 33rd ISEA voyage ship was plotted on current sea ice concentration, sea ice
deformation, RISAT-1 SAR (whenever available) data.
Fig 7: Image showing sea ice concentration near Bharati and Maitri research stations: Part of sea ice advisory sent to 32nd ISEA in December 2013.
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
20
Fig 8: Image showing sea ice concentration trend analysis (RED: Increasing trend; GREEN: Decreasing trend) near Maitri research stations: Part of sea ice advisory sent to 32nd ISEA in December 2013.
A transect between the current location of ship to next scheduled location of ship
destination was drawn. The status of sea ice condition was assessed considering
various sea ice parameters. The technique presented in Figure 2 was adopted to arrive
at a likely safe shipping route for voyage. Predicted atmospheric air temperature, wind
vectors, air pressure values available from different web-sites were analysed along with
satellite based sea ice growth/melt trend and sea ice drift analysis.The advisory was
provided to NCAOR in the form of text and images. NCAOR used to send it to 33rd ISEA
voyage leader and Ship Captain. The feedback from voyage used to reach SAC via
NCAOR. Suggested Entry/Exit likely safe ship routes to/from Bharati and Maitri coasts
are shown in Figure 9 to Figure 12.
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
21
The sea ice advisory was found to be very useful for ship navigation and the voyage
was completed successfully.
Fig 9: Likely safe ship entry points to reach Bharati (Part of sea ice advisory sent to NCAOR on February 20, 2014.
7. Conclusion
–
Advance information about the sea ice within ship transit is very important for
planning of optimum ship routing during Antarctic Expeditions. The information on
sea ice condition has become available after the advent of satellite data. However,
this information is not readily available for ship routing. The information on sea ice
concentration, deformation of pack ice, sea ice drift, sea ice thickness etc were
derived from satellite data analysis. This knowledge along with the other a-priori
information was used to provide sea ice advisory for ship routing durin 33rd ISEA.
The routes suggested during these advisories were followed by the voyage ship and
the expedition could be completed successfully.
SIC: > 99%
SIC: 90-99%
SIC: < 90%
White
Arrow
Heads:
Likely
Safer
Ship
Entry
Points.
Bharati
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
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Fig 10: Likely safe ship points points to leave Bharati (Part of sea ice advisory sent to NCAOR).
Fig 11: Likely safe ship entry points to reach Maitri coast (Part of sea ice advisory sent to NCAOR on March 7, 2014.
OCEAN
A N T A R C T I C AMaitri
A
B
L E G E N DSIC > 95%SIC: 90 to 95%SIC < 90%
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
23
Fig 12: Likely safe ship exit points to leave Maitri coast (Part of sea ice advisory sent to NCAOR on March 29, 2014.
The ship routes actual followed by the ship were compared with those suggested in the advisory. It was found that the ship fairly followed the advisory routes.
8. Future Plan and Scope
The sea ice advisory made available to 32nd and 33rd ISEA was based on satellite data
analysis with extensive involvement of image analysts. It warrants a lot of time and
efforts from subject experts. Also, there are more chances of subjectivity creeping into
the advisory. Efforts are being made toward automation of different modules of data
analysis for sea ice advisory. Hence, the sea ice advisory in future should be more
objective and should be available to Voyage Leader and Ship Master in near real time
through NCAOR.
–
Colour Legend
SIC > 95%
SIC: 90 to 95%
SIC < 90%
BA
Maitri
EW1 & EW2
Are Likely
Safe ship
Exit
Ways.
A & B are
On Indian
Bay.
EW1
EW2
Satellite Based Sea Ice Advisory for Antarctic Expedition Rajak et al, 2014
24
India’s satellite Resorcesat-2 frequently visits Antarctica and Arctic regions. It has got a
very good combination of sensors onboard. It can acquire data at 56 m resolution
(Advanced Wide Field Sensor i.e. AWiFS) with very high revisit capability along with
collecting data at 24 m (Linear Imagine Scanning Sensor 3 i.e. LISS-III) and 6 m (LISS-
IV) resolutions with relatively lower revisit capability. It is planned to acquire wide swath
data over sea ice regions during study period through NRSC along with LISS-III and
LISS-IV data over selected locations. The AWiFS data mosaics will be prepared and
used for sea ice deformation, sea ice drift and other polar feature identification.
Also, there are many polar ice / ocean parameters (wind direction, wind speed, wave
characteristics, currents speed and direction etc) that are useful for safer shipping
navigation, may be derived using remotely sensed data. Inclusion of such parameters
will improve the quality of sea ice advisory. The safe ship routing warrants predictive
data related to various polar parameters. The predicted parameters based on sea ice
modelling may be used to expand the scope of advisory and to make it more
comprehensive.
Acknowlegments –
The authors sincerely acknowledge the encouragement provided by Director SAC. We
thank Deputy Director EPSA for his guidance and support at various stages of the
study. The keen interest taken by Director – NCAOR in this study is also dully
acknowledged. We herewith acknowledge that the sea ice concentration (3.125 km)
data and MODIS LANCE mosaic (250 m) used in this study were downloaded from
ftp://ftp-projects.zmaw.de/seaice/AMSR2 and http://lance-
modis.eosdis.nasa.gov/imagery/subsets/?mosaic=Antarctica sites and OSCAT and
SARAL/AltiKa data were downloaded from MOSDAC/ISRO site.
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