NASA Ocean Color

ocssw V2022

 import sys
 import numpy as np
 import datetime
  
 TAI58_OFFSET = datetime.datetime(1970, 1, 1) - datetime.datetime(1958, 1, 1)
 LEAPSEC = 37  # TODO: look up by year
  
 def decode_timestamp(seconds,subseconds):
     return float(seconds) + float(subseconds) / pow(2,8*subseconds.itemsize)
  
 CCSDS_timestamp = np.dtype([
     ('seconds',   '>u4'),   # Time since start of epoch in seconds (TAI58)
     ('subsecs',   '>u2'),   # fractional seconds
 ])                          # total length = 6 bytes
  
 def parse_CCSDS_timestamp(timestr):
     return decode_timestamp(timestr['seconds'], timestr['subsecs'])
  
 def readTimestamp(data):
     tmp = np.frombuffer(data, dtype=CCSDS_timestamp, count=1)
     ts = parse_CCSDS_timestamp(tmp[0])
     return ts
  
 def tai58_as_datetime(tai58):
     # convert tai58 (seconds since 1958, including leapsecs) to datetime object
     dt = datetime.datetime.utcfromtimestamp(tai58 - LEAPSEC) - TAI58_OFFSET
     return dt  # seconds since Jan 1, 1970
  
 def seconds_since(tai58, basetime=None):
     # translate TAI58 to seconds since a baseline time (defaults to start of day)
     dt = tai58_as_datetime(tai58)
     if not basetime:
         basetime = dt.replace(hour=0, minute=0, second=0, microsecond=0)
     return (dt - basetime).total_seconds()
  
 def datetime_repr(dt):
     return dt.strftime('%Y-%m-%dT%H:%M:%S.%fZ')
  
 #-------------------------------------------------------------------------------
  
 def getDict(structured_array):
     '''
     convert numpy structured array to dict of scalars and numpy arrays
     '''
     myDict = {}
  
     for key in structured_array.dtype.names:
         if ( key.upper().startswith('PADDING') or
              key.upper().startswith('SPARE') ):
             continue  # skip meaningless fields
         myDict[key] = structured_array[key][0]
  
     return myDict
  
 def pad_packet(data, length):
     # pad or truncate bytearray to expected length
     packet = bytearray(length)
     if len(data) > length:
         packet[:] = data[0:length]
     else:
         packet[0:len(data)] = data
     return packet
  
 #-------------------------------------------------------------------------------
  
 cfeHeaderFields = np.dtype([
     ('filetype', 'S4'),              # "type of file = "cFE1"
     ('subtype', '>u4'),              # 101d = downloaded PACE DS files
     ('length', '>u4'),               # length of CFE file header = 64 bytes
     ('SCID', 'S4'),                  # Spacecraft ID
     ('APID', '>u4'),                 # Application ID
     ('processorid', '>u4'),          # 1=Spacecraft, 2=OCI  (30 in ETE files)
     ('fileopen_seconds', '>u4'),     # Time when file created
     ('fileopen_subseconds', '>u4'),  # Time when file created (fractional seconds)
     ('description', 'S32'),          # = "DS data storage file"
 ])                                   # total length = 64 bytes
  
 dsfHeaderFields = np.dtype([         # CFE/S Data Storage header
     ('fileclose_seconds', '>u4'),    # Time when file closed
     ('fileclose_subseconds', '>u4'), # Time when file closed (fractional seconds)
     ('filetable_index', '>u2'),      # 0=events, 1=housekeeping
     ('filename_type', '>u2'),        # 1=count, 2=time (PACE uses count)
     ('filename', 'S64'),             # fully qualified file path
 ])                                   # total length = 76 bytes
  
 def readFileHeader(filehandle):
  
     # is a CFE header present?
     pos = filehandle.tell()
     fourchars = filehandle.read(4)
     filehandle.seek(pos) # rewind to original position
     if fourchars != b'cFE1':
         return None
  
     # read CFE header
     data = filehandle.read(cfeHeaderFields.itemsize)
     tmp = np.frombuffer(data, dtype=cfeHeaderFields, count=1)
     myDict = getDict(tmp)
     myDict['fileopen_ts'] = decode_timestamp(myDict['fileopen_seconds'],
                                              myDict['fileopen_subseconds'])
     myDict['fileopen'] = datetime_repr(tai58_as_datetime(myDict['fileopen_ts']))
  
     # append DS header, if it's there.
     if myDict['description'].startswith(b'DS'):
         data = filehandle.read(dsfHeaderFields.itemsize)
         tmp = np.frombuffer(data, dtype=dsfHeaderFields, count=1)
         myDict.update(getDict(tmp))
         myDict['fileclose_ts'] = decode_timestamp(myDict['fileclose_seconds'],
                                                   myDict['fileclose_subseconds'])
         myDict['fileclose'] = datetime_repr(tai58_as_datetime(myDict['fileclose_ts']))
  
     return myDict
  
 #-------------------------------------------------------------------------------