Geology Reference
In-Depth Information
Table 11.1
World Meteorological Organization (WMO) thickness‐based ice types and their conventional codes.
Ice Type
Symbol
Code
Thick. (cm)
Description
New
NI
1
< 10
Recently formed, weakly frozen
Nilas
NS
2
< 10
Thin elastic crust of ice
Gray
GI
4
10-15
Less elastic than Nilas but breaks on swell
Gray‐white
GWI
5
15-30
More likely to ridge than to raft under pressure
First year thin
FY thin
7
30-70
Ice of not more than one winter growth
First year medium
FY medium
1.
70-120
Ice of not more than one winter growth
First year thick
FY thick
4.
> 120
Ice of not more than one winter growth
Second year
SY
8
Ice that have survived only one summer melt
Multi Year
MY
9
Ice that has survived at least two summer melts
Note
: The table is not inclusive.
Table 11.2
Egg coding for forms of ice and floe size.
why aircrafts that are equipped with SAR and have to fly
at a high altitude are not used for visual observations.
Some ice types may look virtually identical when observed
from a distance. Therefore, ice observers should be famil-
iar with the ice climatology when aerial reconnaissance is
performed. Detailed ice charts can be generated through
observations from a helicopter. These charts provide best
information for tactical ice information. The Canadian
Coast Guard provides ship‐based helicopters for that
purpose. An example of an ice chart generated by an ISS
on a helicopter is shown in Figure 11.7.
Shipboard observations provide details that cannot be
acquired by aerial reconnaissance, such as snow depth,
ice thickness, number of ridges per unit length, state of sur-
face melt, iceberg counts, etc. It is possible for the ISS to
disembark from the ship to the ice in order to conduct the
measurements. Moreover, accurate ice thickness can be
made by observing upturned ice blocks along the ship's hull.
A disadvantage of shipboard observations is the low observ-
ing angle, which does not allow easy identification of dis-
tances between ice floes. This can result in an overestimation
of floe size or ice concentration. A daily chart of observed
ice conditions are produced for the entire area, while the
ship is on route and the ISS is on duty. Ice charts generated
from shipboard observation may augment information
from helicopter observations. Shipboard observations are
used as ancillary data to interpret remote sensing data and
produce image analysis charts and daily ice analysis charts.
Description
Width (m)
Code
Pancake ice
0
Small ice cake; brash ice
<2
1
Ice cake
2-20
2
Small floe
20-100
3
Medium floe
100-500
4
Big floe
500-2000
5
Vast floe
2000-10000
6
Giant floe
>10000
7
Fast floe, growlers, or floeberg
8
Icebergs
9
Undetermined or unknown
X
total ice concentration (the ratio of ice to water area) in
tenths. The third line is a numerical code for the ice types
as shown in Table 11.1. Ice types are formally called stages
of development (hence denoted
S
). The number of ice
types is generally restricted to a maximum of three signifi-
cant classes. In exceptional cases more classes are added
outside the egg (e.g.,
S
o
,
S
d
, and
S
e
shown in the figure).
S
o
indicated an ice type thicker than
S
a
but has a concentra-
tion less than 1/10.
S
d
is the stage of development of the
thickest remaining ice type, and
S
e
does not usually appear
in the charts. The second line includes the partial concen-
tration of each ice type, and the fourth line is a code for the
form of ice, namely the floe size corresponding to each ice
type
S
. Table 11.2 provides the codes for 11 floe size cate-
gories but only codes 3 or larger (20-100 m) floes are
reported on the charts. More symbols that are employed in
the egg code are presented in
MANICE
[2005].
11.2.3. Image Analysis Charts
These charts are produced from satellite imagery data
that come from a variety of platforms. Currently, about
90% of the satellite images analyzed in the CIS are from
Radarsat. The CIS receives about 4000 Radarsat scenes
and 12,000 NOAA AVHRR scenes per year. However,
most of the AVHRR images are not used because of the
cloud cover. Image analysis charts are generated within
4 h from data reception at CIS. This product is intended
for the use of the CCG icebreakers to assist their tasks of
11.2.2. Ice Reconnaissance Charts
Ice reconnaissance charts can be generated through
visual observations of the ice field from aerial (aircraft or
helicopter) or surface‐based (ship or coastal station) plat-
forms. There is a limit on the altitude of the aircraft
beyond which ice surface detection is not possible. That is
