Construction, drilling and navigation can all require dedicated and intensive monitoring of ice conditions to ensure that hazards are first detected and then responded to with sufficient time to implement an appropriate course of action; this is formalised in an ice management plan. Tactical ice support can be defined as near real time and near continuous updates on ice conditions, typically upstream of a fixed structure or along the planned route of a moving vessel. It is only recently that satellite earth observation has become sufficiently frequent in coverage and flexible to provide an effective complement to ground-based observations of ice conditions.

The proliferation of satellite radar imaging missions has meant that it is now possible, in principle, to obtain images of any ice-prone area frequently during a single day, even in the presence of clouds, fog and darkness. There are now also a range of radar image resolutions, coverage, frequency bands, incidence angles and polarisations which enable the observations to be tailored very closely to the types of ice hazard and sampling required. Further improvements in image planning (some missions requiring shorter lead times, some being mostly pre-planned) and in data delivery times (less than an hour becoming more common) are also enhancing the potential use of satellite imagery for tactical operations support.

In a growing number of cases, satellite imagery is being used on vessels for direct support to decision making. Efforts have been made in recent years to provide the technologies to enable these images to be accessed from servers as soon as they have been acquired and processed, and delivered to the vessel or offshore platform. The technologies make use of some advance planning prior to operations and then employ appropriate image compression techniques to support efficient distribution, in some cases to areas where communications bandwidths remain relatively poor. A key requirement for effective use of earth observation in tactical ice support lies in effectively combining the imagery with observations from the ground-based platform or vessel, marine-based radar being the most obvious example.

A key challenge in using earth observation in support of tactical operations lies in dealing with the latency associated with the space-based imagery, with the locations of the ice in the image being correct for the time of acquisition of the image and not for the time of image delivery. A second challenge lies in the interpretation of the imagery. Most tactical ice imagery will be radar imagery because of its reliability in being able to "see" through clouds, fog and darkness. Radar imagery is not simple to interpret and can on occasions be misleading. Therefore, there is a challenge in ensuring that the imagery is used safely and effectively, by personnel who have appropriate training and experience. In some cases, imagery collected for tactical ice support is interpreted before being provided offshore, or may even be replaced by a local ice chart that enables the information to be provided with no danger of ambiguity, although these do add a significant delay. As well as providing more spatial detail on ice conditions than a regional ice chart, local ice charts can also provide information on specific ice hazards such as ridges, rafting and stamukha, or may be tailored to provide information along a planned navigation route.

While there are a range of practices in the use of earth observation for tactical ice support, each with advantages and disadvantages, it is clear that earth observation in playing an increasingly important role in supporting tactical operations in ice.

A special case of tactical ice support is iceberg monitoring.

Tanker mooring in Vitino, Russia (Yay Micro images).

A stamukha. Stamukha represent a potential threat to offshore operations, notably towards the end of the season when they refloat. Identifying these threats in a new area of interest is important (photo courtesy Trine Pedersen, Danish Meteorological Institute, www.dmi.dk).