This script will produce two new files: *.land and *.water where:
*.land=the part of the input file underlain by land.
*.water=the part of th input file underlain by water.
The script is below between the horizontal rules.
echo making land mask
emath expr_vars="lsmask" \
expression="x1>0" \
var_name="land" \
var_units="" \
var_type="fl" \
Master land.mask
echo making water mask
emath expr_vars="lsmask" \
expression="x1<1" \
var_name="water" \
var_units="" \
var_type="fl" \
Master water.mask
echo assembling mask file
assemble include_vars="land water" \
extend_names="no" \
instantiate="yes" \
land.mask water.mask mask.file
\rm land.mask water.mask
for I in `ls $1*.reg | cut -c1-14 | sort | uniq`
do
echo masking $I.reg
emath2 file1_vars="avhrr_ch4" \
file2_vars="land" \
expression="x1/x2" \
var_name="avhrr_ch4" \
var_type="fl" \
var_units="" \
$I.reg mask.file land4
emath2 file1_vars="avhrr_ch5" \
file2_vars="land" \
expression="x1/x2" \
var_name="avhrr_ch5" \
var_type="fl" \
var_units="" \
$I.reg mask.file land5
emath2 file1_vars="avhrr_ch4" \
file2_vars="water" \
expression="x1/x2" \
var_name="avhrr_ch4" \
var_type="fl" \
var_units="" \
$I.reg mask.file water4
emath2 file1_vars="avhrr_ch5" \
file2_vars="water" \
expression="x1/x2" \
var_name="avhrr_ch5" \
var_type="fl" \
var_units="" \
$I.reg mask.file water5
assemble include_vars="avhrr_ch4 avhrr_ch5" \
extend_names="no" \
instantiate="yes" \
land4 land5 $I.land
assemble include_vars="avhrr_ch4 avhrr_ch5" \
extend_names="no" \
instantiate="yes" \
water4 water5 $I.water
\rm land4 land5 water4 water5
done