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2.2 Shipboard Ice Observations
Photo 2.8: A shipboard perspective.
Shipboard ISS are a very important part of the ice-observation network. They provide very detailed ice observations, as well as report characteristics of the ice not collected by aerial reconnaissance methods such as snow depth, ice thickness and ice behaviour.
These detailed observations of the ice are used to make more accurate interpretations of aerial charts as well as for climatological studies. Therefore shipboard ISS should always record ice conditions to the maximum possible detail.
Ice information to be collected should include, but not be limited to:
- ridges per linear mile;
- depth and surface coverage of snow;
- melt state;
- behaviour of the ice (i.e. movement, developing or releasing pressure);
- ridge heights;
- iceberg counts; and
- water temperature
Whenever possible, the ISS should disembark from the ship to the ice surface in order to measure its thickness and snow depth and estimate or measure ridge heights.
The shipboard perspective is similar to the far-range of the aerial perspective as the ice cover is viewed from an extreme angle; this, along with its slow speed, limits the geographic extent of a ship-based ice observation. The low angle perspective of a ship's deck requires special attention to maintain ice observation accuracy. Whereas an aerial observation depends primarily on surface features to determine ice types, a shipboard ISS should normally use ice thickness.
2.2.1 Use of Electronic Aids
Photo 2.9: Ship moving through very close pack grey-white ice and patches of nilas.
The ISS on board the icebreaker has several electronic aids which can provide useful information and be combined with visual observations. The ISS can use the onboard marine surveillance radar to indicate the range and bearing of surface targets such as icebergs or ice edges.
As well, airborne imaging radar data (either SAR or SLAR) can be downloaded to most Coast Guard ships through the use of a downlink receiver and Ice-Vu display software. This will provide the ISS with a source of mapped ice information identical to that available to the ISS on board the ice reconnaissance aircraft. This data is mainly used for navigating the vessel through the ice, but can also help in assessing the general ice conditions in the area. In some cases accurate boundaries and features can be extracted from the imagery for the ice chart.
2.2.2 Ice Type Identification
Accurate estimates of ice thickness can be made by observing ice being turned up along the ship's hull. To help improve accuracy, any known reference point can be used such as the ship's deck rail, the sea bucket or pieces of wood tossed over the side.
To record conditions further away from the vessel, surface topography becomes more important for ice type recognition.
Photo 2.10: Airborne view of close pack concentration of vast floes of old ice.
The identification of old ice floes from the ship perspective requires special attention to the surface topography ahead of the vessel. Old ice floes in a mixed field of ice types are often detected by observing a significant difference in freeboard between these floes and other first-year ice floes around them. In many cases there is significant rubble and ridging around these floes; this is caused by the pressure of thinner ice types against the much thicker old ice floe.
The local ice climatology should also be known in order to know what ice types are normal for the area, as well as determining the normal behaviour of the ice.
The ISS should also refer to previous ice charts and imagery (if available) collected and/or generated in the days prior to the ship entering the area. This will help to maintain consistency in the observations and help in ice recognition. For example, if the presence of an ice type has been previously reported in the area, the ISS should be looking for that ice type.
2.2.3 Estimating Ice Concentration:
The low observing position from the ship causes separate ice floes to lose their distinction. This can result in over-estimation of the concentration and/or floe size.
In good light conditions, the ISS shall record ice conditions to a distance of no more than 5 nm from the vessel. Experience has indicated that observations beyond 3 nm are very subjective, but this is left at the discretion of the ISS. Attempts should be made to locate an iceberg or another vessel in the 3-5 nm range from the vessel using the ship's marine radar which will help to estimate distances.
Consideration should be given to the fact that ice conditions in the immediate vicinity of the ship are not always representative of those within the accepted observation limits of 3-5 nm. However, the initial assessment of conditions in the near range serves as a good starting point or baseline and can be modified if required as the ship moves through the ice.
Photo 2.11: Large pans of grey-white ice devoid of snow cover.
Whenever an ice-reconnaissance aircraft is in the area, efforts should be made to speak to the ISS on board. The ISS should try to convey as much information as possible to the aircraft, to help improve the accuracy of the aerial ice charts as they are being generated. Also, an attempt should be made to receive any charts or radar imagery that might be available. The charts or imagery will provide a better overall picture of the ice conditions and will aid in estimating the concentration from the the ship perspective.
It is worth noting that aerial ice charts typically display much larger areas due to their perspective. For this reason, the vessel may find itself in a high-concentration area recorded as a low-concentration area on the aerial chart. It is likely that the ship is in a very localized area of high ice concentration, the limits of which cannot be seen by a shipboard ISS because of the visibility or extent of the ice coverage. When this happens, the ISS should look for signs in the distance to verify the differing concentration, but shall not alter the shipboard chart to comply with the aerial one. Nevertheless, this matter should be discussed with the airborne ISS, if possible.
2.2.4 Chart Production
A daily chart of observed ice conditions shall be produced for the entire area the vessel has travelled while the ISS was on duty. The only exception is when a vessel is in ice-free waters that are not normally subject to sea-ice cover or iceberg intrusion. Data obtained from helicopter reconnaissance flights can either be merged with the daily ice-track chart or plotted as a separate observation. The shipboard charts shall be numbered consecutively from the start of the voyage.
2.2.5 Synoptic Observations
Individual ice observations from ships are an important part of the ice information required to prepare the current ice analysis chart produced daily at the Canadian Ice Service. These observations are used to confirm interpretations of remotely sensed imagery. They also serve as a check on observed charts generated from visual aerial ice reconnaissance.
Marine weather synoptic observations are normally made every 3 hours while a vessel is in transit. The ISS will usually take 3 or 4 observations during the course of their duty day. Synoptic ice observations are taken and recorded using the WMO ice code described in MANMAR (cf. 2). It is important that these observations reach the Canadian Ice Service in a timely manner, so they can be incorporated into the daily ice analysis.
At times when the ISS is engaged in other duties or is off duty, the ship's officers should be encouraged to take, record and transmit marine weather and ice observations in accordance with the codes contained in MANMAR (cf. 2).
- Date Modified: