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Plotting the Laptev Sea#Extent

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Let us assume you have installed the open-source Generic Mapping Tools (GMT) on your computer. Let us further assume, you downloaded the (freely available) topographic Netcdf-file of ETOPO1 available from the NOAA National Geophysical Data Center. Then, the follow bash-script generates a postscript file with the bathymetry of Laptev Sea: 

#!/bin/bash
OUT=BrnBld_LaptevTopo.ps  # output file name
ORO=BrnBld_Oro.cpt        # file with Color PaleTte (CPT)
REG=-R109/70/165/80.8r    # plot region
PRJ=-JS128/70/12c         # map projection and size in cm
ANN=-B20g10/5g5/sENw      # grid lines and annotations
TOP=etopo1_laptev.nc      # ETOPO1-input data

# initializing settings
gmtset VERBOSE TRUE ANNOT_FONT_SIZE_PRIMARY=8p ANNOT_FONT_SIZE_SECONDARY=8p--

# creating color map only for negative heights above -70m
makecpt -Cgray -N -T -I -T-70/40/10 | grep "^-" > $ORO

# write postscript header using nothing (/dev/null) as input
psxy -R0/1/0/1 -P -JX1 -K /dev/null > $OUT

# shading the different depths
grdimage $TOP -Sb/1 $REG $PRJ -C$ORO -E100i \
 --COLOR_FOREGROUND=169/181/9 --COLOR_BACKGROUND=white -V -O -K >> $OUT

# place legend for the color palette
psscale -D2.5c/0.5c/4c/0.3ch -A -C$ORO -B10/:'m': -O -K >> $OUT

# not sure, whether that's really necessary
psbasemap $REG $PRJ $ANN -V -O -K >> $OUT

# Plotting squares and triangles for settlements.
echo "128.5 71.6" | psxy -G212/45/18 -Ss0.4c ${REG} ${PRJ} -O -K >> $OUT
cat <<EOF | psxy -G212/45/18 -St0.3c $REG $PRJ -O -K >> $OUT
136.167 71.3
119.8167 73.0333
126.5 72.37
113.2304 72.8116
126.992 72.0038
EOF

# Plotting the Laptev-Sea boundaries
cat <<EOF | psxy -m -W1p,black,- $REG $PRJ -O -K >> $OUT
141.2000 72.7000 # Svyatoy Nos on main land (East)
139.8333 73.4333 # Cape Vagina
140.5833 74.0833 # Lyakhovsky Island
138.8333 76.1667 # Northernmost cape of Kotelny
95.2500 81.2166 # Arctic Cape
100.3561 79.6602 # Cape Anuchin
102.5166 79.4269 # Cape Unslicht
104.8333 78.2833 # Cape Yevgenov
105.9011 77.5491 # Cape Pronchishchev at main land (West)
EOF

# Labeling everything else in black
cat <<EOF | pstext -N ${REG} ${PRJ} -G0/0/0 -O -K >> $OUT
128.5 71.6 12 0 1 TR TIKSI
103 75.3 9 0 1 BL Taymyr
100 78.2 9 0 1 BL Bolshevik
95 79.3 9 0 1 BL October Revolution
92 80 9 0 1 BL Komsomolets
141 73.5 9 0 1 BL Lyakhovsky
138 75.3 9 0 1 BL Kotelny
EOF

# write postscript footer
psxy -R0/1/0/1 -JX1 -O /dev/null >> $OUT;

Calculating the Laptev Sea area

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Using the open-source tool-kit de:Climate Data Operators (CDO), it is possible to evaluate the Laptev Sea area with only a few lines of code: 

#!/bin/bash

# cut out a box around Laptev Sea to speed up computation
cdo sellonlatbox,85,165,70,83 ETOPO1_Ice_g_gmt4.grd laptev_cut.nc

# cut out polygon laptev_lim.text, take only depths (not heights), remove NANs
cdo setmisstoc,0.0 -lec,0 -maskregion,laptev_lim.txt laptev_cut.nc laptev_mask.nc

# calculate area per box in m^2 first, then convert to km^2
cdo divc,1000000 -gridarea laptev_mask.nc laptev_weight.nc

# multiply weights with mask, afterwards sum over the field
cdo fldsum -mul laptev_weight.nc laptev_mask.nc laptev_sum.nc

# display result, the file should contain only a single value
cdo info laptev_sum.nc

(Brn-Bld (talk) 11:53, 27 September 2012 (UTC)).[reply]

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