Generalised characteristics of discontinuities in the ice cover of the seas of
the Russian Arctic
This description below is based on the original one from AARI (See Expl.doc).
The source tables referred to are included in the
\INSROP_GIS\Sourcedata\AARI-FNI 1996\DiscontinuitiesInIce folder.
A brief description of the initial data
As initial data, "Meteor" and "NOAA" low resolution TV and IR images received
in the direct transmission mode, were used. These images indicate large
discontinuities and zones of more densely spaced discontinuities 300 to 500 m wide and
more. There are gaps in the initial data. This is related to the influence of
clouds, which prevent the discontinuities on the images to be distinguished.
A method for data processing/analysis
Based on satellite images, the charts of discontinuities (with a scale of
1:10000000 and in the stereographic projection) for the periods 1 to 5 days were
compiled. Each discontinuity plotted on the chart was divided into comparatively
rectilinear segments within which the changes in direction did not exceed 10°
According to the co-ordinates of the ends of these segments, their length and
orientation by the regular grid squares were calculated.
For presentation of data on discontinuities in the ice cover the grids of
squares constructed on a uniform basis were employed. For the Chukchi, the
East-Siberian and the Laptev Seas in both cases a regular grid with a spacing of 100 km
constructed at reference meridian 130° was used. The beginning of the grid
co-ordinates is in 700 km from the North Pole along the X-axis and in 600 km along
the Y-axis. In the Kara Sea for presenting data on discontinuities in the ice
cover, a grid with a 50-km spacing constructed at reference meridian 130° is
used with the beginning of co-ordinates in 350 km from the North Pole along the
X-axis and in 2300 km along the Y-axis. Data on currents in the Kara Sea are
presented using a grid with a 100 km spacing, like in the other seas. The grid
squares have uniform numbering. The numbers 1 to 53 refer to the Chukchi Sea, 54
to 134 - to the East-Siberian, 135 to 200 to the Laptev Sea, 201 to 865 - to the
Kara Sea.
For each of the grid squares (if the initial data were available) the
following characteristics of discontinuities generalised for the monthly periods, were
calculated:
1. The specific length (q) is mean length of discontinuities per unit area.
This characteristic is a measure of density of discontinuities and is expressed
in m/km2. The length of discontinuities is averaged using the number of
observations in the square q=L/nS, where L is the total length of all segments of
discontinuities in the square for a month, n is the number of observations, S is
the square area.
2. Modal orientation of discontinuities (ALFAm) is the direction (read from
the positive direction of the X-axis) to which the largest probability density
corresponds. For determining ALFAm the total length of the segments of
discontinuities whose orientation in the given square is within the range ALFAi ±dALFA
("running range") is calculated. The direction ALFAi successively changes by 1°
passing the entire range from 0° to 180°. dALFA is assumed to be equal to ±20°.
The direction ALFAi at which the total length of the segments of
discontinuities in the "running range" has the largest value is assumed to be modal. Along
with the first mode, the second mode next by significance, is identified.
3. The occurrence frequency of the modal range (pm) is a ratio of the total
length of the segments of discontinuities Lm whose direction is within the ALFAi
±dALFA range, to the total length of all segments in the square: pm= Lm / L
A brief description of the data transferred
The co-ordinates of the grid points (centres of the squares) are presented in
the form of the ASCII files (tbl_01.txt), containing Table 1. The results of
calculations of the characteristics of discontinuities are presented in the form
of the ASCII file (tbl_35.txt), containing Table 5. The record of Table 5
includes the following fields: No. of the square; year; month; the specific length
(m/km2); the first mode of orientation of discontinuities (degrees); the
occurrence frequency of the first modal range (%); the second mode of orientation of
discontinuities (degrees); the occurrence frequency of the second modal range
(%). In case the second mode is absent, the two latter fields remain empty.
Path: <NSR_DATA>\icesnow\aari_dis
GeoDataset type: Shapefile with Point features.
Coordinate system: Latitude/longitude in decimal degrees
* Discontinuities in ice - data points
865 Points, 1 descriptive field.
Fields: [<Name>] -- <Alias> (type of field)
[Point__] -- "Point #" (Numeric, no decimals)
Point #
Discontinuities in ice - data points