year=$1
month=$2
inst=$3

for sat in f15 f16 f17 f18
do
    for what in $inst
    do
        wget -e robots=off --wait 0.5 --no-host-directories --no-parent --cut-dirs=2 -r --level=1 -A ".gz,.cdf" --timestamping http://satdat.ngdc.noaa.gov/dmsp/data/$sat/$what/$year/$month
    done
done