Manice - Chapter 5
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 NOAA AVHRR 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 CIS. 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 m;
- RADARSAT ScanSAR Wide - pixel resolution is 100 m;
- ScanSAR Narrow - pixel resolution is 50 m;
- NOAA resolution is approximately 1 km 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 m for 100 m resolution imagery.
5.3.2 Method of Production
This chart is a visual interpretation of the SAR imagery by an experienced analyst using a digital
image display and vector-drawing tools. The analysis of the ice regime seen on the SAR 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. SAR 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 CIS.
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:
Figure 5.13: The Egg Code
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 CIS Web site 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
| Light |
up to 1/10 |
L |
 |
| Medium |
2/10 - 3/10 |
M |
| Heavy |
4/10 - 10/10 |
H |
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
| Fast Ice |
 |
Open Water
(less than 1/10 sea ice, no ice of land origin) |
 |
Bergy Water
(less than 1/10 sea ice may be present and
total ice concentration is less than 1/10)
|
 |
Crack
(symbol indicating presence of crack
at a specific location)
|
 |
| Strips |
 |
| Ice Island |
 |
| Ice-free (no ice present) |
 |
Symbols for Defining Limits
| Limit of radar observation |
 |
| Limit of undercast for AVHRR |
 |
| Limit of bergy water |
 |
| Estimated ice edge |
 |
| Ice edge boundary |
 |
