aggregate_modis.sh

set -eu

# Get input files from the command line
INPUTS=$*

add_time() {
    INPUT=$1

    OUTPUT=${INPUT}.nc

    # Get the time from the filename
    TIME=$(python modis_time.py $INPUT)

    echo "${INPUT} has time ${TIME}"

    # Create a new UNLIMITED dimension 'time', with the value from the file's timestamp
    ncap2 -s 'defdim("time",-1);time[time]='$TIME';time@units="days since 1980-01-01 00:00"' -O $INPUT $OUTPUT
}
export -f add_time

# Add the time record to each file in parallel
parallel add_time ::: $INPUTS

# Join all the files along the UNLIMITED dimension
ncrcat  $(sed 's/\(\S*\)/\1.nc/g' <<< $INPUTS) MOD06_L2.nc

modis_time.py

from datetime import datetime
import re
import sys

epoch = datetime(1980,1,1,0,0,0,0,None)

# MOD06_L2.A2002059.0525.006.2014311051339.hdf
date_re = re.compile(r'MOD06_L2.A(?P<datestamp>\d{7}\.\d{4})\.006.*\.hdf')

def calculate_date(filename):
    """
    Calculate the days since the epoch from a MODIS file's name
    """
    datestamp = date_re.match(filename).group('datestamp')
    date = datetime.strptime(datestamp,'%Y%j.%H%M')
    days_since_epoch = (date - epoch).total_seconds() / 60.0 / 60.0 / 24.0
    return days_since_epoch

print(calculate_date(sys.argv[1]))