MANICE Chapter 5: Ice Analysis Charts

This chapter deals with basic procedures for preparing and transmitting various chart products from the Canadian Ice Service (CIS), operations division. These charts are of importance to a variety of users for many purposes such as strategic planning, climate studies and or tactical vessel management. These products use different variations of the egg code described in Chapter 3. In some cases, scale and map area restrict and limit the use of the complete code.

5.1 Daily Ice Analysis Charts

5.1.1 Description

These charts are of importance to icebreaker captains, commercial shipping interests and fishing vessels, to assist them in finding the easiest passage through the ice or to avoid the ice when feasible to do so. The charts are meant to provide ice information for strategic planning for their activities during the next 24 hours.

Please note that there are significant differences between daily ice analysis charts and observed/image analysis charts:

  • Frequency

Daily ice analysis charts are done on a daily basis during the season, whereas image analysis charts are done when images arrive for a particular operational area. Observed charts are generated whenever ice conditions are encountered either from ships, helicopters or aircraft.

  • Detail

The other significant difference resides in the amount of detail on each chart. Observed and image analysis charts have more latitude regarding the amount of detail and information that can be placed on the product. Daily ice analysis charts will have less detail pertaining to ice areas and egg definitions. Consequently, daily ice analysis charts have a more generalized look compared to observed/ image analysis charts.

5.1.2 Method of Production

Daily ice analysis charts are computer-generated with the use of mapping and image analysis software. The system allows the forecaster to draw lines and place eggs, symbols, drift arrows, and ship positions.

The forecaster will use a variety of data sources such as National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer, Geostationary Operational Environmental Satellite, Special Sensor Microwave/Imager, QUICKSCAT, ENVISAT and particularly RADARSAT, as well as the image analysis charts from these data. The field observation charts from ships, helicopter and aircraft provide ground truthing. However on days when no data is available, or when the image analysis does not coincide with the valid time of the daily ice analysis chart (1800 UTC), the ice model from the Canadian Ice Service can be used to advance ice to the valid time.

The Egg Code

There are some limitations on the use of the Egg Code for daily analysis charts. Later in this chapter, we will specifically outline the significant differences. For a complete version of the Egg Code, please see Chapter 3.

Diagram of the components of the egg code: total and partial concentration, stage of development and forms of ice. See description below for details.

Note: The symbols CaCbCc and FaFbFc correspond to SaSbSc respectively.

Concentration (C)

Total concentration (Ct ) of ice in the area indicated in tenths and partial concentrations of thickest (Ca ), second thickest (Cb ) and third thickest (Cc ). Note that Cd which appears on observation/Synthetic Aperture Radar image analysis charts, will not be indicated on daily ice analysis charts from the Canadian Ice Service.

Diagram of the egg code indicating the location of concentration of ice.  See description below for details.

Notes:
  1. When only one ice type is present, the partial concentration shall not be indicated (see Example 1).
  2. When only a trace of thinner ice is present with thicker ice, only the concentration of the thicker ice is indicated inside the egg; the thinner ice type will show as Sd (see Example 2).
  3. When 2 or 3 ice types are present with more than 1/10 concentration, the partial concentration for each type will show inside the egg (see Example 3).
Stage of Development (S)

Stage of development of thickest (So), second thickest (Sa), third thickest (Sb) and fourth thickest (Sc) ice and the thinner ice type Sd, of which the concentrations are reported by CaCbCc respectively.

Diagram of the egg code indicating the location of stage of development. See description below for details.

Notes:
  1. Reference to thicker ice should be understood to mean older ice and conversely, thinner ice to mean younger ice types.
  2. Ice is designated Sea, Lake or River depending on where it forms. In Canada, the practice is to use the Lake Ice code to report ice in the Great Lakes and the St. Lawrence Seaway. Elsewhere, including the St. Lawrence River east of Montreal, sea ice coding is used for stages of development.
  3. Reporting of SaSband Sc should generally be restricted to a maximum of three significant classes. In exceptional cases further classes may be reported as follows:
  • So- stage of ice development thicker than Sa , but having a concentration less than 1/10 (see Example 4).
  • Sd- stage of development of the thickest remaining ice types. It is the fourth stage present after Sa, Sb and Sc . Partial concentration must be at least 1/10 (see Example 4), except during the freeze-up period when a trace of new ice may be present (see Example 2).
  • Se- this stage of development will not appear on a daily ice analysis chart.

Table 5.1: Coding for Sea-Ice Stages of Development (So SaSbScSd)

DescriptionThicknessCode
New ice< 10 centimetres1
Grey ice10 - 15 centimetres4
Grey-white ice15 - 30 centimetres5
First Year ice> 30 centimetres6
Thin first-year ice30 - 70 centimetres7
Medium first-year ice70 - 120 centimetres
Thick first-year ice> 120 centimetres
Old ice 
Second-year ice 
Multi-year ice 
Ice of land origin  Symbol for Ice of land origin - triangle
Brash -

Table 5.2: Coding for Lake Ice Stages of Development (SoSaSbScSd)

DescriptionThicknessCode
New lake ice< 5 centimetres1
Thin lake ice5 - 15 centimetres4
Medium lake ice15 - 30 centimetres5
Thick lake ice30 - 70 centimetres7
Very thick lake ice30 - 70 centimetres1·
Notes:
  1. On the horizontal line giving SoSaSbScSd only one dot (·) shall be placed to indicate the distinction between classes of ice. Every coded figure to the left of the (·) is understood to have the (·) as part of its code (see Examples 4 and 5).
  2. The symbol Symbol for Ice of land origin - triangle shall only be used within the egg when the concentration of ice of land origin is 1/10 or more (see Example 12).
  3. Code 8·and 9·shall normally appear on the Canadian Ice Service's daily ice analysis charts from 01 October to 31 December.
  4. Brash ice (-), when present, will always appear as Sa(see Example 11).
Form of Ice (F)

Floe Size corresponding to SaSbSc

Diagram of the egg code indicating the location of forms of ice. See description below for details.

Table 5.3: Coding for Form of Ice (FaFbFc)

DescriptionWidthCode
Small ice cake, brash ice< 2 metres1
Ice cake2 - 20 metres2
Small floe20-100 metres3
Medium floe100-500 metres4
Big floe500-2,000 metres5
Vast floe2 - 10 kilometres6
Giant floe> 10 kilometres7
Fast ice 8
Icebergs 9
No form X
Notes for Table 5.3:
  1. Width refers to the maximum horizontal extent.
  2. At least one code 8 must be used for fast or consolidated ice. When significant ice types are present and it is important to maintain their floe size, the younger ice type will be coded as fast ice (see Example 5).
  3. Occasionally the stage of development of fast ice cannot be determined. The area shall be blackened-in to denote fast ice. Also when the area in question is very small or difficult to place a label, it can be blackened-in. For areas with a trace of old, second or multi-year ice embedded in fast ice, the area will be shaded-in in grey with an attached label or egg.
  4. New sea ice does not have a definite form, therefore, when this stage of development occurs as SaSbor Sc the symbol X shall be used to designate floe size (See Example 1).
  5. When an area of ice has one particular ice type but varying floe sizes, the basic rule will be to represent the ice type that has the predominant concentration and use the corresponding floe size (see Example 6). An exception would be when there are a few giant old floes in a field of medium old floes (see Example 7).
  6. Pancake floe size (code 0) will not appear on the Canadian Ice Service charts. Since pancake ice floes implies new ice, the standard floe size when dealing with new ice at the Canadian Ice Service is always X.
Coding and Symbology for Strips and Patches

The symbol Strips and Patches Symbol, placed at the bottom of the egg in Form of Ice section, indicates that the ice is in strips and patches and that the concentration within the strips and patches is represented by C (see Example 8).

In an area in which the ice is arranged in strips and patches and the ice floes are medium (code 4) or greater, the floe size shall be indicated by using two eggs. The floe sizes are indicated as normal in the first egg with the Strips and Patches Symbol symbol placed between the first and second eggs. The Strips and Patches Symbol symbol is repeated in the second egg beside the total concentration of the strips and patches (see Example 9).

In an area of ice in which some first-year or thicker ice type(s) is/are embedded as strips and patches, the strips and patches shall be indicated by the use of two eggs. The overall partial concentrations of the ice types are indicated in the first egg and the concentration within the strips and patches are indicated in the second egg. The Strips and Patches Symbol symbol shall be placed between the two eggs and along with the total concentration in the second egg (see Example 10). Double eggs will be indicted with a leader line to the polygon in question.

Where there are isolated strips and patches of ice, of less than 1/10 concentration, located outside the main ice areas, the strip (Strips and Patches Symbol) symbol will be placed in the area of these strips. Usually these symbols are used to indicate ice in the final stage of melt.

5.1.2.1 Defining Polygons

The parsing of ice areas can be done in one of two ways:

  1. By various ice types;
  2. By concentration.

Note that only solid lines will be used to separate areas of different ice type/concentration (no dash lines).

Ice Type

Mandatory boundaries are required between new, grey, grey-white, first-year and old ice.

Please note that ice codes 2 (nilas ice, ice rind), 3 (young ice), 8 (first stage thin first-year ice) and 9 (second stage thin first-year ice) and X (undetermined or unknown) will not appear on any daily ice analysis charts from the Canadian Ice Service.

For old ice, (7·, 8· and 9·) boundaries are required between areas with concentrations of:

  • No old ice
  • Trace of old ice
  • 1 - 3/10
  • 4 - 6/10
  • 7 - 8/10
  • 9 - 9+/10

old ice (7 · , 8 · and 9· ) with a concentration of 4 tenths or more will be considered predominant.

When two ice types are present in equal concentration, the older/thicker type is considered predominant.

When three or more types are present in equal concentrations, the second oldest is considered predominant.

Total Concentration

In the case of total concentration, mandatory boundaries, shown as solid lines are required between areas of:

  • Open water/bergy water: < 1 tenth
  • Very open drift: 1 to 3 tenths
  • Open drift: 4 to 6 tenths
  • Close pack: 7 to 8 tenths
  • Very close pack: 9 to 9+ tenths
  • Compact or consolidated: 10 tenths

The total concentration is the first determining factor in defining ice boundaries. Partial concentrations of new ice are ignored when first-year or thicker ice is present.

5.1.2.2 Floe Size

Mandatory boundaries must also be placed between areas of predominantly medium floes or larger (code 4) and areas of predominantly small floes or smaller (code 3) when 6 tenths of thin first-year or thicker/older ice are present.

5.1.2.3 Discretionary boundary

In addition to the guidelines for mandatory boundaries, discretionary boundaries can also be used when sufficient data or knowledge of the ice regime has been verified by up-to-date reconnaissance flight, reports or satellite information. These boundaries are to be maintained on subsequent charts only if there is sufficient knowledge of the location, as provided by these data sources.

Discretionary boundaries should only be used in operationally sensitive areas, namely:

  • Great Lakes: shipping routes
  • Gulf of St. Lawrence: shipping routes
  • Newfoundland: coastal waterway to Botwood
  • Arctic: shipping routes
Ice type to consider:

When considering the use of a discretionary boundary, only first-year and old ice are considered, provided there is sufficient knowledge to supply this additional detail. The exception would be in the Great Lakes, where thick or very thick lake ice and areas of ridging should be considered for discretionary boundaries.

Ice Concentration of ice to consider:

Total ice concentration must be at least "close pack" (7 or 8 tenths of ice). New ice, as usual, is ignored when evaluating the total concentration.

Variance of the concentration to consider:

A discretionary boundary may be used if the partial concentration of the first-year or thicker (thick or very thick lake ice) ice varies by at least 3 tenths in a definable area within a mandatory polygon (see Examples 13 and 14).

5.1.2.4 Valid Time

Normally every daily analysis chart generated at the Canadian Ice Service has a valid time of 1800 UTC. The chart thus represents ice conditions at 1800 UTC.

5.1.2.5 Corrections and Amendments

When a correction or amendment is made to the chart, the abbreviation CCA or AAA will appear next to "ICE ANALYSIS/ANALYSE DE GLACES" at the top of the legend.

  • A correction is required if an error appears on a chart (examples: Ct indicated 5/10, but should have read 8/10; the ice drift is missing; wrong date for an image in the legend).
  • An amendment is warranted when a significant change in ice conditions in a certain area occurs (examples: Ct was put as 5/10 but a report indicated that the concentration was 9+/10; ice is reported in an area shown as open water).

5.1.2.6 Chart Legend

Example of a chart legend for North East Newfoundland waters
Example of Chart Legend

The legend is used on the daily ice analysis charts to describe the region, the valid time and date, what information the chart is based on and any warnings in effect.

The information on the source data is to give the client an idea of what was used to prepare the chart, to give a general level of confidence. Only sources that made a significant contribution to the analysis will be indicated. Where possible, the time and the area covered by that source will be given.

5.1.2.7 Deadlines

Deadlines may vary from chart to chart, and from season to season.

  • Transmission

As a general rule, at least one chart should be made ready for transmission from the Canadian Ice Service at 1600 Eastern Standard Time (or Daylight Saving Time). However, in consultation with the Canadian Coast Guard Ice Operations Centre(s), priorities regarding which chart to send out first will be determined on a daily basis, to ensure that the most operationally sensitive chart is first selected for transmission.

  • Data reception and integration

For information received from outside sources (CFR charts, Canadian Coast Guard ship reports, etc.), a minimum of 2.5 hours before the transmission deadline is required to integrate it into the daily ice analysis chart. In most cases when the information arrives late, the forecaster will endeavour to integrate the information, especially if it is operationally sensitive. However, this may cause a delay in the delivery of the chart. The decision to process the information or not, for use in the chart, will be at the discretion of the forecaster in consultation with the Canadian Coast Guard ice operations office.

5.1.3 Dissemination of Charts

Upon completion of the analyses, daily ice analysis ice charts are disseminated electronically via a product delivery system. Clients will receive products via e-mail, fax or the internet. The Ice Service Specialist and Canadian Coast Guard clients have a special customised delivery system set up.

5.1.4 Symbols Used on Daily Ice Analysis Charts

Symbols for Dynamic Process

Symbol indicating direction and drift speed
Indicates the direction and drift speed (in nautical miles per day) in the general area for the next 24 hours from the valid time of the daily ice analysis chart

Note: The drift arrow gives the direction and the number of nautical miles that ice, within 10 nautical miles of the centre of the arrow, is expected to travel over the next 24 hours. Due to the influence of currents and winds, there can be large differences in the direction and speed of the ice even over areas within close proximity. This drift does not take into account the effect of land on the drift. When the arrow points towards land, there may be an increase in ice concentration and ice pressure along the coast.

Symbols for Defining Limits

DescriptionSymbol
Analysed edge or boundary edge or boundary symbol
Bergy water boundary Bergy water boundary symbol

 

Other Symbols Used

ConditionsSymbolDescription
Ship reportsCGTF I5ZUsed to indicate the latest position and time of a Coast Guard ship (during last 24 hrs).
Bergy water Bergy water symbolSymbol used to indicate bergy water conditions.
Ice-free Ice-free symbolSymbol used to indicate ice-free conditions.
Ice island or Ice island fragment Ice island or Ice island fragment symbolSymbol used to indicate ice island or fragments
Open water Open water symbolStipple pattern used to indicate open water areas (less than 1/10).
Fast ice Fast ice symbolBlackened area representing fast ice.
Strips and patches Strips and patches symbolSymbol used to indicate strips and patches of ice outside the ice edge.

Note: Some symbols may be displaced and have a leader line pointing to its actual location.

5.2 Regional Ice Charts

5.2.1 Description

The Canadian Ice Service (CIS) is responsible for maintaining the historical sea ice record for Canada.  The regional sea ice analyses and charts serve as this record and become part of the national archive.  They are used for a wide variety of purposes; as a strategic marine navigation and transportation planning tool, for climate research, for weather models and input to the Global Digital Sea Ice Data Bank The ice charts are created through the manual analysis of in situ, satellite, and aerial reconnaissance data incorporating meteorological, and ice climatology  parameters as required.

Regional ice charts are produced for the following 5 regions:

  • Eastern Arctic
  • Western Arctic
  • Hudson Bay
  • Great Lakes
  • East Coast of Canada.

A high standard of excellence in the production of the regional analyses must be maintained. In order to maintain the quality and consistency between the analyses, the following guidelines shall be followed.

Frequency

Regional ice analyses and charts represent ice conditions on a specific date. Usually they are prepared weekly, but sometimes biweekly or monthly, depending on the season and the region.

The regional charts are scheduled so they align with the historical climate dates, (+ or – 3 days). The historical dates are weekly starting the first of January each year.

To maintain a consistent record of the start and end of the ice season, the regional analyses for the East Coast and Great Lakes have a fixed start and end date. The dates are chosen based on climatology as the week before first ice and the week after last ice. Regional analyses are produced during these dates, even if the region is Open Water or Ice Free. Arctic charts are produced year-round.

East Coast :

Charts are produced beginning on the Monday that falls between the 9 and the 15 of November, corresponding to the historical date of November 12.  

End charts on the Monday which falls between the 24 and the 30 of August for the historical date of  August 27.

Great Lakes :

Charts are produced beginning on the Monday falling between the 2 and the 8 of November for the historical date of November 5.

End charts on the Monday falling between the 1 and the 7 of June for historical date of  June 4.

5.2.2 Method of Production

These charts show generalized ice conditions; they incorporate all available data, usually within three days of the valid date. The main data sources are satellite images. The daily ice analyses can be referenced; however, too much detail clutters the chart and is not useful.  Areas of ice can be combined based on the predominant ice type.

5.2.2.1 The Egg Code

Diagram of the components of the egg code: total and partial concentration, stage of development and forms of ice. See description below for details.

The Egg Code is an international code that describes the ice concentration, stage of development and form. There are specific standards that are used in the Regional charts compared to the image analysis and the daily ice charts.

Concentration (C)

Diagram of the egg code indicating the location of concentration of ice.  See description below for details.

The total concentration (Ct) of ice in the area, and partial concentrations of thickest (Ca), second thickest (Cb) and third thickest (Cc) are indicated in tenths.

Notes:
  1. When only one ice type is present, the partial concentrations, (Ca, Cb Cc), shall not be indicated.
  2. Using 0 (zero), for Ct is not allowed
  3. Only single values allowed for Ct, no ranges.
  4. Cd will not be used.
  5. Double eggs are not allowed.
Stage of Development (S)

Diagram of the egg code indicating the location of stage of development. See description below for details.

Table 5.4: Coding for Sea-Ice Stages of Development (So Sa Sb ScSd)

DescriptionThicknessCode
New ice< 10 centimetres1
Grey ice10 - 15 centimetres4
Grey-white ice15 - 30 centimetres5
First-Year ice> 30 centimetres6
Thin first-year ice30 - 70 centimetres7
Medium first-year ice70 - 120 centimetres1•
Thick first-year ice> 120 centimetres4•
Old ice 7•
Second-year ice 8•
Multi-year ice 9•

Table 5.5: Coding for Lake Ice Stages of Development (So Sa Sb ScSd)

DescriptionThicknessCode
New lake ice< 5 centimetres1
Thin lake ice5 - 15 centimetres4
Medium lake ice15 - 30 centimetres5
Thick lake ice30 - 70 centimetres7
Very thick lake ice> 70 centimetres1•

Reporting the stage of development (SOD) should generally be restricted to three significant classes (SaSbSc) and each ice type or Stage of Development will only be used once for each egg.

Notes:
  1. In exceptional cases further classes may be reported as follows:
    • So - used only when the trace of ice is first-year or thicker.
    • Sd  -used when remaining ice type has a concentration of 1/10 or more.
  2. Se - this stage of development will not be used.
  3. ICE / GLACE will not be used.
  4. NO DATA will not be used.
  5. Nilas (code 2) will not be used.
  6. Young Ice (code 3) will not be used.
  7. Generic First-Year Ice (code 6) will not be used.
  8. Brash Ice (“- “ ) will not be reported as a Stage of Development.
  9. Second Year and Multi-Year (8• and 9•)  can be used  between Oct 1 and Dec 31.
  10. Symbol for ice of land origin  (Ice of land Origin) will not be used.
  11.  Ice Islands ( < ) will only be plotted as a non topological point symbol. (see symbols section) i.e. do not outline an Ice Island as a polygon.
Form of Ice (F)

Diagram of the egg code indicating the location of forms of ice. See description below for details.

Table 5.6: Coding for Form of Ice (FaFb Fc)

DescriptionWidthCode
Small ice cake, brash ice< 2 metres1
Small floe20 - 100 metres3
Medium floe100 - 500 metres4
Big floe500 - 2,000 metres5
Vast floe2 - 10 kilometres6
Giant floe> 10 kilometres7
Fast ice 8
No form X

Reporting of Form of Ice or Floe Size will be restricted to a maximum of three classes (FaFbFc ) which corresponds to (Sa SbSc).

Floe sizes are not used in climate statistics so there is no need to analyze areas based on floe size alone. Fast Ice (8) is the only floe size information used for climate analysis and products.

Notes:
  1. New Ice is always coded with floe size X (no form).
  2. Pancake ice (code 0) and Ice cakes (code 2), will not be used.
  3. Brash ice (code 1) should only be used when it can be confirmed by visual observations or high resolution imagery.
  4. Ice of Land Origin (code 9) will not be used.

5.2.2.2 Symbols Represented on Regional Ice Charts

*Hatching on colour charts can vary.

Symbols for Defining Limits

DescriptionSymbol
Analysed Ice Edge or Boundary Symbol for analysed ice edge or boundary
Bergy Water Boundary Symbol for bergy water boundary

 

Area Symbols

DescriptionSymbol
Bergy Water Symbol for bergy water
Ice-Free Symbol for ice-free
Ice islands Symbol of ice islands
Open WaterSymbol for open water
Stipple pattern used to indicate open water areas.
Fast Ice Symbol for fast ice
Ice Shelves Symbol for ice shelves
Notes:
  1. Strips and patches symbol (Symbol for Strips and patches) will not be used outside of the eggs.
  2. Ice Islands will be represented using the ice island point symbol and only where their position is known either by beacon positioning or where they are visible on imagery and have length greater than 5 kilometres.

5.2.2.3 Defining Ice Area Polygons

Areas of ice are analysed using standards based on ice concentration, ice type and if the ice is fast or mobile.

Concentration:

Mandatory boundaries are drawn where the total concentration varies from the following categories:

  • Ice Free
  • Open Water or Bergy Water
  • 1 to 3 tenths: very open drift
  • 4 to 6 tenths : open drift
  • 7 to 8 tenths : close pack
  • 9 to 9+ tenths : very close pack
  • 10/10 : compact/consolidated/fast

Other rules:

Example of two similar egg codes. See description below for details.

Similar areas that contain at least one tenth or more of first-year ice or thicker can be combined if only the new ice is different.

  • Open Water does not require a Stage of Development value.
  • The Iceberg limit will separate Bergy Water from Open Water or Ice Free.  The Iceberg limit will not cross over sea ice polygons/areas.

Boundaries are discretionary if the partial concentration of the First-year or thicker ice types vary by at least 3 tenths. For the Great Lakes use Thick or Very Thick Lake Ice.

Examples: Great Lakes use Thick or Very Thick Lake Ice

Example of egg codes with a partial concentration of first-year or thicker ice types varying by at least 3 tenths.

Example of egg codes with a partial concentration of first-year or thicker ice types varying by at least 3 tenths.

Example of egg codes with a partial concentration of first-year or thicker ice types varying by at least 3 tenths.

Example of egg codes with a partial concentration of first-year or thicker ice types varying by at least 3 tenths.
(lake ice)

Boundaries are discretionary if New Ice of various concentrations are adjacent.

Example of two similar egg codes which could be grouped into one polygon.

These two eggs could be grouped into one polygon.

Stage of development:

Boundaries are mandatory between areas of old ice in the following categories: 

  • no Old Ice
  • trace of Old Ice
  • 1 to 3 tenths
  • 4 to 6 tenths
  • 7 to 8 tenths
  • 9 to 9+ tenths
  • 10/10 or consolidated

Boundaries are mandatory where the stage of development of the predominant ice type varies from New, Grey, Grey-White, Thin First-Year,  Medium First-Year, Thick First-Year and Old ice. Or in the case of lake ice, between New, Thin, Medium, Thick and Very Thick Lake ice.  The stage of development is restricted to 4 significant types (Sa,Sb,Sc,Sd) that have a concentration of one tenth or more. (i.e. no trace amounts are allowed in the Sd position)

  • when two ice types are present in equal concentration, the older/thicker type is considered predominant.
  • when three or more types are present in equal concentrations, the second oldest/thickest is considered predominant.

Other rules:

  • Open Water does not require a Stage of Development value.
  • Old ice should be carefully monitored. A trace of Old ice, with  a floe size of 3 or smaller cannot be detected using satellite imagery.  Therefore care should be taken when drifting traces of Old ice, to ensure that the trace amounts do not unrealistically spread to cover large geographic areas. A trace of Old ice will be reported when it is confirmed by visual observation.
Form of Ice:

Boundaries are mandatory between areas of mobile ice and Fast Ice.  

Other rules:

  • Fast Ice –
    • If the area is too small to be seen on a 8 ½ X 11 paper chart, it does not need to be analysed.
    • Small Areas (< 800 - 1,000 kilometres2) should be shaded black. Thepredominant ice type should be identified using the point symbol (e.g.# 7).  As the ice grows in aerial extent the shaded area will be replaced with an egg.
    • Only one type of First-Year ice, Thick First-Year (4.), Medium First-Year (1.) or Thin First-Year (7) will be used in a Fast Ice area. Other Ice types can be included in the egg.
  • The strips and patches symbols “~”  may be used within the egg when the total concentration of ice is less than 7 tenths.

5.2.2.4 Polygon Sizes

The size of a polygon can become problematic if they are too small. The scale of a regional chart is roughly half that of a daily chart. An area should be large enough to be clearly visible on a letter size (8 ½ x 11) paper and allow the placement of a remote egg letter within the polygon. A general rule to follow is that if the polygon is < 1,000 kilometres2 (size of a label letter) it is should be combined with another region.

To determine if an area is large enough, in an IMAGINE viewer, select  VIEW/SCALE and set to 1:4,000,000. If the polygon is not discernable then it is too small and should be amalgamated with the adjacent area.

Examples of minimal polygon sizes for guidance:

Example of a chart with minimal polygon sizes.  See above for description.

Example of a chart with minimal polygon sizes.  See above for description.

Example of a chart with minimal polygon sizes.  See above for description.

5.2.3 Quality Control

The regional analyses and charts are quality controlled for data consistency and for international standard reporting practices.

The regional analyses and charts will be amended or corrected after the issue date if significant additional information is made available or if errors are found within the analyses.

The amended or corrected version will be distributed through the Canadian Ice Service normal channels when the amendment or correction is made prior to the next issued regional.  If amendments or corrections are made after the next issued regional the amended or corrected analyses and charts will only be available through the Canadian Ice Service archives and not through the normal distribution channels. 

5.3 Image Analysis Charts

5.3.1 Description

Image analysis charts are tailored products that provide a visual interpretation of the ice conditions primarily from radar imagery that may come from a variety of platforms such as on the ERS, RADARSAT or ENVISAT satellites. The Canadian Ice Service (CIS) receives approximately 3,600 RADARSAT images and 12,000 National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer images per year. Operationally significant images are analyzed and the image analysis chart is issued in near-real time (within 4 hours) of data reception at the Canadian Ice Service. The international standard for coding ice information, the Egg Code, is used with some minor modifications. The modifications will be dealt with in the method of production section below, a complete description of the Egg Code can be found in Chapter 3.

This product is primarily intended for the Canadian Coast Guard ice offices and icebreakers to assist them with decision making on ship routings and escorts. The product is used as well by Ice Forecasters to supplement the daily ice analysis and regional analysis charts. Grid-point ice data from the analysis is provided to the Canadian Meteorological Centre weather models, and to ice models at the Canadian Ice Service (CIS) and the Maurice Lamontagne Institute.

The accuracy of an analysis is affected by the spatial resolution of the source data and the processing quality. Here are a few examples:

  • ERS2 - pixel resolution is 25 metres;
  • RADARSAT ScanSAR Wide - pixel resolution is 100 metres;
  • ScanSAR Narrow - pixel resolution is 50 metres;
  • National Oceanic and Atmospheric Administration resolution is approximately 1 kilometre at nadir.

In addition to being able to resolve different ice features, the absolute positional accuracy of the data (geo-coding) will be affected by the accuracy of the satellite orbit information. The Canadian Space Agency estimates that the geometric accuracy of a feature such as an ice edge will be within 630 metres for 100 metres resolution imagery.

5.3.2 Method of Production

This chart is a visual interpretation of the Synthetic Aperture Radar imagery by an experienced analyst using a digital image display and vector-drawing tools. The analysis of the ice regime seen on the Synthetic Aperture Radar image is actually a composite of ice signature recognition and support data. Support data sources include the prevailing environmental conditions, ice climatology and coincident ice reconnaissance charts from ships, aircraft or helicopters. Synthetic Aperture Radar analysis charts are tailored to meet the user's requirements. The scale of the chart is not fixed. It will be tailored to the client's geographic area of interest, constrained by the footprint and resolution of the sensor and the need to ensure that the information presented using the egg code is clear, and readable and is issued in a timely fashion. Image analysis charts are issued and archived in digital format, in near-real time, usually within 4 hours of data reception at the Canadian Ice Service.

Defining Polygons

Analysts extract ice concentration, ice type and ice topography from the images, based on tone, texture and spatial context of the ice features (resolution). The extraction of accurate information requires an understanding of ice forms and remote-sensing signatures, as well as access to the meteorological conditions and historic patterns of ice in a specific region. Accuracy may be diminished by poorly processed imagery, artifacts within the imagery or by the effects of moisture on/in the ice.

Areas of different ice conditions are described using elements of the Egg Code on a variable scaled chart. Principally, this code describes the ice in terms of:

  • Ct the total ice concentration expressed to the nearest tenth
  • Ca, Cb, Cc the partial concentrations of up to four main ice types present, to the nearest tenth plus a trace amount.Cd is not used but its value is apparent from the total concentration values.
  • So, Sa, Sb, Sc, Sd the stage of development of sea ice and lake ice. See Table 3.1 and 3.2

Note: Seis not used. X may be coded when ice type is undeterminable.

  • Fa, Fb, Fc the form of the three main ice types present (pancake, brash, small, medium, big, vast, giant floes, strips and patches, or X- indeterminable) depending on the image resolution. See Table 3.3.

Note: Fd and Fe are not used.

  • Brash ice is not coded using the observed VKMT standard. Brash is coded only when there are coincident visual reports to support the signature analysis. If brash is present it will always be Ca. If present Sawill always be a dash (-) and Fa=1.

Diagram of the components of the egg code: total and partial concentration, stage of development and forms of ice. See description below for details.

Mandatory boundaries (solid lines) are drawn:

  • Concentration:
    where the total concentration varies from the following categories:
    • open water or bergy water
    • 1 to 3 tenths
    • 4 to 6 tenths
    • 7 to 8 tenths
    • 9 to 9+ tenths
    • 10/10 or consolidated
  • Stage of Development:
    • the stage of development of the predominant ice type present changes in any way;
    • mandatory boundaries are required between 6/10 and 7/10ths and between 8/10ths and 9/10ths of old ice.
  • Form of ice:
    • the form of the predominant type of ice present changes in any way

Discretionary Boundary lines are drawn for any changes within the Egg Code which could impact on tactical ice operations. For example an area of heavily ridged ice may be separated from level ice.

Estimated Ice Edge Boundaries are used when the analyst may be in doubt about the positional accuracy of the edge because of poor image quality or signature ambiguity.

5.3.3 Dissemination of Charts

The image analysis chart product is available for distribution in near-real time or from the archive in raster or grid point format. Delivery methods include the Internet at the Canadian Ice Service website and by subscription service via ftp, email or fax.

5.3.4 Symbols Used

Topographical Features

The resolution and imaging mode of the sensor directly affects the analyst's ability to detect surface features. Not all topographical features are analyzed. Below is an accounting of the topographical symbology presently in use.

Relative Roughness

Lightup to 1/10L
Medium2/10 - 3/10M
Heavy4/10 - 10/10H

Symbol for Relative Roughness

In operational areas, relative roughness will be indicated when there are coincident visual reports to support the signature analysis.

Symbols In Use On Image Analysis Charts

DescriptionSymbol
Fast Ice Symbol for Fast Ice
Open Water
(less than 1/10 sea ice, no ice of land origin)
 Symbol for Open Water
Bergy Water
(less than 1/10 sea ice may be present and total ice concentration is less than 1/10)
 Symbol for Bergy Water
Crack
(symbol indicating presence of crack
at a specific location)
 Symbol for Crack
Strips Symbol for Strips
Ice Island Symbol for Ice Island
Ice-free (no ice present) Symbol for Ice-free

 

Symbols for Defining Limits

DescriptionSymbol
Limit of radar observation Symbol for Limit of radar observation
Limit of undercast for AVHRR Symbol for Limit of undercast for AVHRR
Limit of bergy water Symbol for Limit of bergy water
Estimated ice edge Symbol for Estimated ice edge
Ice edge boundary Symbol for Ice edge boundary

5.4 Daily Iceberg Analysis Chart

5.4.1 Description

These charts are important to shipping and fishing vessels as well as the tourism industry. They assist them in determining the limit of all known icebergs on Canada's east coast.

5.4.2 Method of Production

Iceberg analysis charts are generated with the use of mapping software (Geographic information system). The system allows the forecaster to model the position of icebergs and targets that were visually or remotely sited up to 40 days prior. The forecaster can use reports from ships, land stations, and radar satellites, but mostly relies on dedicated iceberg flights using fixed wing aircraft. The individual iceberg information is entered into the modelling database, where currents, wind and water temperature and other factors are applied to estimate the iceberg position and size at the time of the chart valid time.

5.4.2.1 Valid Time

The Iceberg Analysis charts have a valid time of 1200 UTC. The chart represents the iceberg conditions at 1200 UTC on the date that it is issued.

5.4.2.2 Corrections and Amendments

If a correction is warranted, then the chart is re-issued but with the same valid time as the original. There would be nothing on the chart to indicate that it is a correction. Amendments are not issued. If an iceberg is sited outside the iceberg limit, then a bulletin is issued to notify mariners. The chart will not be re-issued.

5.4.2.3 Chart Legend

A legend is used on the daily iceberg analysis charts to detail the valid date and time of the chart. When the International Ice Patrol (IIP) is in operation, there is a note that the iceberg limit and the distribution of icebergs in the vicinity of the limit south of 52 North is estimated by theInternational Ice Patrol. The initials of the forecaster who produced the chart will be in the bottom right corner of the legend.

5.4.2.4 Deadlines

The transmission deadline is 1700 UTC.

5.4.3 Dissemination of Charts

Daily iceberg analysis charts are disseminated electronically via a product delivery system. Clients may receive the chart via e-mail, fax or the internet.

5.4.4 Symbols used on the Daily Iceberg Analysis Charts

Symbols used on the Daily Iceberg Analysis Charts

DescriptionSymbol
Iceberg Limit:
Known icebergs in the Atlantic located landward (north and west) of the iceberg limit.
 Symbol for Iceberg Limit
Iceberg Limit in the Gulf of St Lawrence:
Known icebergs in the Gulf of St Lawrence are located east of this line.
 Symbol for Iceberg Limit in the Gulf of St Lawrence
Sea Ice Limit:
Landward of this line is the location of sea ice of any concentration. Exception: Sea ice in the Gulf of St Lawrence is not usually depicted on the iceberg chart.
 Symbol for Sea Ice Limit
Known Data Limit:
This line depicts the iceberg coverage of the most recent dedicated iceberg flight. This limit is moved southward with the icebergs as they drift. South of this line there is more confidence in the position and number of icebergs than to the north.
 Symbol for Known Data Limit
This number represents the number of icebergs within that degree square. Growlers and/or bergy bits are not included in the count but may be present anywhere within the limit. Symbol for the number of icebergs within that degree square

5.4.5 Area of Coverage

The iceberg analysis chart covers icebergs located in waters east and southeast of Newfoundland and Labrador, as well as in the Gulf of St Lawrence. There are two chart extents. The northern extent is used most of the year and shows icebergs between about 45 North and 61 North. The southern extent is used when the International Ice Patrol (IIP) is in operation. It shows icebergs that are between about 40 North and 57 North. On rare occasions when the iceberg limit is south of 40 North, then a text message on the chart will describe the latitude and longitude of the points not seen on the chart.

5.4.6 Notes on the Role of the International Ice Patrol (IIP)

The International Ice Patrol was established after the sinking of the Titanic to monitor and report icebergs for Atlantic shipping. While the Canadian Ice Service monitors icebergs year-round, International Ice Patrol usually begins operations when icebergs cross 48º North latitude. This is usually in the late spring. When the International Ice Patrol is in operation they are responsible for determining the iceberg limit south of 52 North. At this time the Canadian Ice Service uses the same iceberg limit as International Ice Patrol for the daily iceberg chart and maintains the limit north of 52 North.

5.5 Colour Coding Ice Charts

Colours are used to enhance ice charts for presentations and briefings. The codes allow users to make a quick assessment of the general ice conditions and to visually follow trends. It is important to remember that the colours alone cannot be used for navigation decisions and that more detailed ice information is contained within the Egg Code. There are four colour codes in use at the Canadian Ice Service, since each code displays the ice in different ways.

5.5.1 Standard Canadian Ice Service Colour Code or Ice Services Specialist Colour Code

The Standard Canadian Ice Service Colour code is intended to assist navigation decisions in ice infested waters. It represents the severity of the ice conditions and is somewhat similar to a traffic light. Colours are used to identify ice concentrations of significant ice.

  • Blue and Green represent relatively easy conditions
  • Yellow and Orange indicate caution is needed
  • Red and Purple indicate the more dangerous ice conditions

5.5.1.1 Colours used in Standard Canadian Ice Service Colour Code

Total amount of ice thicker than 15 centimetres (grey-white ice or thicker)

Colours used in Standard Canadian Ice Service Colour Code for total amount of ice thicker than 15 centimetres

ColourDescription
 Whiteless than 1/10 of ice >15 centimetres but at least 1 tenth of thinner ice types present
 Green1 to 3 tenths of ice >15 centimetres
 Yellow4 to 6 tenths of ice >15 centimetres
 Orange7 to 8 tenths of ice >15 centimetres
 Red9 to 10 tenths of ice >15 centimetres
 Purple5 to 10 tenths old ice (takes precedence over the other colours)

If there are other ice types present, the following symbols would be added to the above colours:

Symbols added to the Standard Canadian Ice Service Colour Code for total amount of ice thicker than 15 centimetres

SymbolsDescription
 Blue star1/10 or more of new ice (less than 10 centimetres). Would not be visible if equal or greater amount of grey ice is present.
 Red star1/10 or more of grey ice (10 to 15 centimetres). Would not be visible if there was also 9 tenths of ice grey-white or thicker.
 Diagonal lines1 to 4 tenths old ice. Would be visible in addition to blue or red stars.

In addition, the following colours are used:

Colours used in Standard Canadian Ice Service Colour Code for total amount of ice thicker than 15 centimetres

ColourDescription
 Light blueopen or bergy water (less than 1/10 total ice of any thickness)
 Greyareas of land fast ice of any thickness

5.5.2 Internal Quality Assurance Colour Code

The Quality Assurance colour code is used internally to help identify total concentration and thickest ice types within the polygons. Colour is used to identify the stages of ice development and patterns are used to identify ice concentration.

5.5.2.1 Colours used in Internal Quality Assurance Colour Code

The pattern of the predominant ice colour is determined by the total concentration of the ice. Total concentration is calculated by adding the partial concentrations. The exception is when first year ice or older is present, any new ice is not included in the calculation of the total concentration.

Patterns used in Internal Quality Assurance Colour Code

PatternIce concentration
 Horizontal lines1 to 3 tenths total concentration
 Vertical lines4 to 6 tenths total concentration
 Diagonal lines 7 to 8 tenths
 Solid black9 to 9+ tenths
 Hatched white background10 tenth compacted ice
 Hatcehed grey background10 tenths land fast ice that is coded with an egg

The colour of the predominant ice displays the most common type of ice present. Again, new ice is ignored if first year ice or greater (or older or thicker) is present. The other exception is that old ice is considered predominant if there are 4 tenths or more present.

Colours used in Internal Quality Assurance Colour Code

ColourDescription
 YellowNew ice
 OrangeGrey ice
 BlueGrey-white ice
 PinkThin first-year ice
 RedMedium first-year ice or combined all stages of first-year ice
 PurpleThick first-year ice
 BrownOld ice

The second pattern and colour will be the determined by the partial concentration of the second most common ice type. The rules for determining this ice type are:

  • New ice is ignored if first year or thicker ice is present
  • When any old ice is present, it will be used as the second ice type.
  • When 2 ice types have the same concentration, the oldest will be used.
  • When 3 ice types have the same concentration, the middle will be used.

The patterns and colours used for the second ice type are:

Colours and Patterns used in Internal Quality Assurance Colour Code

Colour/
Pattern
Description
 Starless than 1 tenth concentration
 Horizontal lines - 1 to 3 tenths concentration1 to 3 tenths concentration
 Vertical lines - 4 or 5 or 6 tenths concentration4 or 5 or 6 tenths concentration
 YellowNew ice
 OrangeGrey ice
 BlueGrey-white ice
 PinkThin first-year ice
 RedMedium first-year ice or combined all stages of first-year ice
 PurpleThick first-year ice
 GreenOld ice (colour changes from what it is as a predominant colour so that it is more visible)

In addition, other colours that may be seen on the charts are:

Colours used in Internal Quality Assurance Colour Code

ColourDescription
 Light blueopen water (less than 1/10 sea ice, no ice of land origin)
 BlueBergy water (less than 1/10 sea ice, and less than 1/10 iceberg concentration).
 Whiteless than 1/10 of ice >15 cm but at least 1 tenth of thinner ice types present
 BlackSmall areas of land fast ice or any thickness.

5.5.3 World Meteorological Organization's Colour Code for Concentration

The World Meteorological Organization's colour code for total concentration is an international code that is intended for use when the stage of development is relatively uniform, but concentrations are highly variable (e.g. arctic summer). The legend for the use of the colour code is included on the chart. No colours are used to indicate differences in the ice stage of development.

Table 5.7: World Meteorological Organization's Total Concentration Colour Code

Colour/
Pattern
Total concentration
 BlueIce free
 WhiteIce free (Used at CIS)
 Light blueLess than one tenth (open water)
 Light green1/10 - 3/10 (very open ice)
 Yellow4/10 - 6/10 (open ice)
 Orange7/10 - 8/10 (close ice)
 Red9/10 - 10/10 (very close ice)
 GreyFast ice
? ? ? ?
Undefined ice

Table 5.7.1: Optional World Meteorological Organization's Total Concentration Colour Code

ColourTotal concentration
 Light pink7/10-10/10 new ice
 Pink9/10-10/10 nilas, grey ice (mainly on leads)

*Areas of "No Information" are annotated accordingly

Table 5.8: World Meteorological Organization's Total Concentration Colour Code for Lake Ice

Colour/
Pattern
Description
 WhiteIce Free
 Light blueLess than one tenth (open water)
 Light green1/10 - 3/10 (very open ice)
 Yellow4/10 - 6/10 (open ice)
 Orange7/10 - 8/10 (close ice)
 Red9/10 - 10/10 (very close ice)
 GreyFast Ice of Unspecified Stage of Development
? ? ? ?
Undefined Ice

*Areas of "No Information" are annotated accordingly

5.5.4 World Meteorological Organization's Colour Code for Stage of Development

The World Meteorological Organization's colour code for stage of development is an international code that is intended for use when the concentration is relatively uniform, but the stage of development is highly variable (e.g. Atlantic winter). The legend for the use of the colour code is included on the chart. No colours are used to indicate differences in the concentration of the ice.

Table 5.9: World Meteorological Organization's Stage of Development Colour Code

Colour/
Pattern
Stage of DevelopmentThickness
 BlueIce Free 
 WhiteIce free (Used at CIS) 
 Light blue< 1/10 Ice (Open Water) 
 Light purpleNew Ice< 10 centimetres
 PurpleGrey Ice10 - 15 centimetres
 PinkGrey-white Ice15 - 30 centimetres
 YellowFirst-year Ice>= 30 centimetres
 Light greenThin First-year Ice30 - 70 centimetres
 GreenMedium First-year Ice70 - 120 centimetres
 Dark GreenThick First-year Ice> 120 centimetres
 Dark orangeOld Ice 
 OrangeSecond-year Ice 
 RedMulti-year Ice 
 GreyFast Ice of Unspecified Stage of Development 
? ? ? ?
Undefined Ice 
White with red triangle fill
Drifting Ice of Land Origin (icebergs) 

Table 5.10: World Meteorological Organization's Stage of Development Colour Code for Lake Ice

Colour/
Pattern
Stage of DevelopmentThickness
 WhiteIce Free 
 Light blueIce of Unspecified Stage of Development (open water) 
 Light purpleNew Lake Ice< 5 centimetres
 PurpleThin Lake Ice5 - 15 centimetres
 PinkMedium Lake Ice15 - 30 centimetres
 Light greenThick Lake Ice30 - 70 centimetres
 GreenVery Thick Lake Ice> 70 centimetres
 GreyFast Ice of Unspecified Stage of Development 
? ? ? ?
Undefined Ice 

5.6 Examples of the Use of the Egg Code

Example 1

Image of an egg with 6/10 of new ice with no form. See description below for details.

Description:

6/10 of new ice with no form. Note that there is no partial concentration when only one ice type is represented in the egg.

Example 2

Image of an egg with 4/10 of old ice in medium floes; new ice with a concentration of less than 1/10. See description below for details.

Description:

4/10 of old ice in medium floes. New ice is also present with a concentration of less than 1/10.

Example 3

Image of an egg with 6/10 total ice concentration; 2/10 thin first-year ice; 4/10 grey-white ice in medium floes. See description below for details.

Description:

6/10 total ice concentration. 2/10 thin first-year ice and 4/10 grey-white ice in medium floes. If more than one ice type is present, the partial concentration of each ice type must be indicated.

Example 4

Image of an egg with 7/10 total ice concentration; 3/10 thick first-year ice; 2/10 medium first-year ice; 1/10 thin first-year ice, all in small floes; <1/10 of old ice; 1/10 of grey-white ice. See description below for details.

Description:

7/10 total ice concentration. 3/10 thick first-year ice, 2/10 medium first-year ice and 1/10 thin first-year ice, all in small floes. Note also the presence of old ice with a concentration of less than 1/10, and 1/10 of grey-white ice.

Example 5

Image of an egg with fast ice composed of grey ice with 3/10 of embedded multi-year ice in small floes. See description below for details.

Description:

Fast ice composed of grey ice with 3/10 of embedded multi-year ice in small floes.

Example 6

Image of an egg with 9+/10 total ice concentration; 2/10 thick first-year ice in vast floes; 2/10 thick first-year ice in big floes; 6/10 thick first-year ice in medium floes. See description below for details.

Description:

9+/10 total ice concentration. 2/10 thick first-year ice in vast floes, 2/10 thick first-year ice in big floes, and 6/10 thick first-year ice in medium floes. Since 6/10 of the thick first-year ice is in medium floes it becomes the representative floe size.

Example 7

Image of an egg with 9+/10 total ice concentration; 3/10 old ice of giant floes; 7/10 old ice of medium floes. See description below for details.

Description:

9+/10 total ice concentration. 3/10 old ice of giant floes and 7/10 old ice of medium floes.

5.6.1 Strips and Patches

Example 8

Image of an egg with 3/10 total ice concentration;  2/10 old ice; 1/10 thick first-year ice. All ice is concentrated in strips and patches of 9+/10. See description below for details.

Description:

3/10 total ice concentration. 2/10 old ice and 1/10 thick first-year ice. All ice is concentrated in strips and patches of 9+/10. Floe sizes are code 3 or less.

Example 9

Image of an egg with 3/10 total ice concentration in strips and patches of 9+/10; 6/10 old ice in vast floes; 4/10 thick first-year ice in big floes. See description below for details.

Description:

3/10 total ice concentration in strips and patches of 9+/10. 6/10 old ice in vast floes and 4/10 thick first-year ice in big floes. These floe sizes are significant and warrant the use of two ovals.

Example 10

Image of an egg with 9+/10 total ice concentration; 1/10 thick first-year ice; 1/10 medium first-year ice; 8/10 new ice; <1/10 old ice. See description below for details.

Description:

9+/10 total ice concentration comprised of 1/10 thick first-year ice, 1/10 medium first-year ice, 8/10 new ice and old ice with a concentration of less than 1/10. The old and thick first-year ice are distributed throughout the area in strips and patches made up of 3/10 old and 7/10 thick first-year ice. All ice types in the second oval must be included in the first oval.

Example 11

Image of an egg with 6/10 total ice concentration; 4/10 brash ice; 2/10 new ice with no form. See description below for details.

Description:

6/10 total ice concentration. 4/10 brash and 2/10 new ice with no form.

Example 12

Image of an egg with 9+/10 total ice concentration; 1/10 of ice of land origin with floe size of 9 (icebergs); 5/10 thin first-year ice in big floes; 4/10 grey-white ice in medium floes. See description below for details.

Description:

9+/10 total ice concentration. 1/10 of ice of land origin with floe size of 9 (icebergs). 5/10 thin first-year ice in big floes and 4/10 grey-white ice in medium floes.

Example 13

Image of two eggs with a discretionary boundary due to the varied concentration of at least 3/10 of thin first-year ice. See description below for details.

Description:

A discretionary boundary could be placed between these two eggs since the concentration of thin first-year ice varies by at least 3 tenths.

Example 14

Image of two eggs with a discretionary boundary due to the varied partial concentration of at least 3/10 of thick and medium first-year ice. See description below for details.

Description:

A discretionary boundary could be placed between these two eggs since the partial concentrations of thick and medium first-year ice varies by at least 3 tenths.

5.7 Examples of Ice Charts