The European Survey of Arctic Gravity (ESAG-2002) field campaign was
successfully carried out in temperatures of -20 C, close to the North
Pole earlier this month. The purpose of the airborne survey was to
collect gravity data and ice surface height measurements in the Fram
Strait and in an area over the north of Greenland and Canada.

The ESAG campaign and its subsequent analysis are designed to support
activities related to two future ESA Earth Explorer missions — GOCE
and Cryosat. The GOCE mission (Gravity Field and Steady-State Ocean
Circulation), due to launch at the beginning of 2006 will study the
Earth’s gravity field and geoid and the Cryosat mission, to be
launched in 2004 will measure ice sheets and sea-ice.

The National Survey and Cadastre of Denmark organised the field
campaign based upon experience gained in previous years, when data
in a region close to Greenland were collected within the scope of
the Arctic Gravity Project (ArcGP) under the umbrella of the
International Association of Geodesy (IAG). The Canadian military
station Alert at 82.5 N and the Danish military’s Station Nord at
81.5 N were the main airbases for the survey flights.

Following the success of the ESAG field campaign, comes the task of
processing the huge amount of data collected in order to derive
gravity and geoid maps, sea-ice heights and thickness for scientific


Since the GOCE mission will not cover an area of the Arctic north of
Canada and Greenland the main aim of the ESAG campaign is to fill
this ‘gravity data gap’. These data along with the Arctic Gravity
Project results will be used to determine an improved Arctic geoid
model. Secondly, laser measurements taken over different types of
polar pack sea-ice in combination with the geoid, will allow
estimates to be made of the amount of ice above sea level and its
thickness. These data collected off the coast of North Greenland
and in the Fram Strait support the preparations for ESA’s Cryosat
mission. It is thought that sea-ice conditions and thickness are
important parameters that play a role in ocean circulation processes.
However, at present the interplay between the transport of sea-ice
and its melt and how this cools the warm water from the Gulf Stream
as it runs north of Norway and into the Fram Strait, is not completely

The Infrastructure

During the ESAG campaign a Twin-Otter airplane was equipped with an
airborne gravimeter, a laser altimeter and scanning system, GPS, an
inertial navigation system (INS), a video camera, and a data logging
system. Ground reference stations for GPS installed at the bases
completed the scientific infrastructure. This allowed the
determination of the precise location and attitude of the aircraft
during operations. The ice profiles and the gravity data need to
be freed from errors caused by the motion of the aircraft and also
have to be referenced to the correct location. In addition, the
Swedish icebreaker Oden conducting the oceanographic ARTIC2002
campaign was installed with video equipment for ground truth
registration of sea-ice conditions and thickness. Fortunately, the
weather conditions throughout the ESAG campaign were good, around
minus 20 C, light winds, partial cloud and sunny periods with little
fog. Therefore, all planned tracks could be flown and unobscured
laser observations made.

The Surveys

It took 60 hours of flying time over a period of 17 days at the
beginning of May to carry out the airborne surveys. The Twin-Otter
equipped for ice-surface landings, allowed ‘in-situ’ samples to be
taken to investigate for example, the depth of this year’s snowfall
and specific ice conditions. Specific other data for comparison
were obtained during a flight between northern Greenland and
Svalbard; a sea-ice thickness profile was observed both by the
airborne laser system and by a video system on board the Swedish
icebreaker Oden. Some of the other flights were coordinated with the
LaRA campaign, where the aircraft carries both a laser and a radar
altimeter system. This is intended to analyse the difference in snow
penetration between laser and radar in order to optimally combine
future data from ESA’s Cryosat satellite and the American Icesat
mission. For example, very different structures in the surface of
the ice are present in the coastal areas caused by the force of the
pull of glaciers that flow from the side of the icecap into the sea
within a relatively short distance.

A special task during one of the flights was an attempt to confirm
the existence of small islands just south of Tobias Island off the
north east coast of Greenland. In Nature (vol. 416 March 2002),
J. Mohr and R. Forsberg suggested the possible presence of islands
in this area based upon InSAR time series analyses done with data
from ERS-1 and ERS–2. Although the survey was carried out in the
area, it was unfortunately difficult to conclude anything from the
first observation due to uniform snow-covered ice conditions. Video
recordings were made and will need to be analysed carefully in order
to able to draw definite conclusions.

Related news

* Four Future Campaigns further the Earth Explorers programme

Related links

* Campaigns

* GOCE introduction

* CryoSat introduction


[Image 1:]
Danish military airbase ‘Station Nord’ in Greenland (distances in km)

[Image 2:]
Arctic sea-ice with varying thickness and surface conditions

[Image 3:]
Set-up of a GPS reference station at ‘Station Nord’ 81.5° North

[Image 4:]
In-situ samples of this year’s snowfall on the Greenland icecap

[Image 5:]
Glacier flows into the sea in North East Greenland