Lufft CHM 15k Nimbus, Manual

Page: 48 / 101

Communication RS485 & Ethernet
48 Revision R09, November 2016
8.4 NetCDF Format Structure
8.4.1 General
The Cloud Height Meter saves all measured backscatter profiles in a day file of
NetCDF format (
Net work C ommon D ata F ile). Its storage capacity allows the
files to be kept on record for approximately one month. In a “Communication
interrupted” service case, affected data can be inspected and traced back. The
raw data of a single measurement can be called up as a raw data telegram via
the RS485 interface. Standard operation does not include the transmission of a
day file, since this would negatively influence the time sequencing in this mode.
Because the transmission rate depends on the time resolution of the measured
data and the RS485 interface settings, this transmission would take too long. An
one day NetCDF file with dt(s)=30s measurement time intervals will be approxi-
mately 11 MB in size. Switching to 15s time resolution 22 MB file sizes are gen-
erated. In service cases, a transmission of the NetCDF file is possible (direct con-
nection to Cloud Height Meter via RS485 or Ethernet) (refer to Service Manual).
8.4.2 Fundamentals
NetCDF provides a computer-platform-independent interface for the saving and
reading of scientific data. It was developed under Unidata, a project funded by
the National Science Foundation (
http://www.unidata.ucar.edu) . Each data set
contains an explanation of its storage content.
The ceilometer saves all data from a single day in a file, using UTC as the time
base. In serial mode (RS485) the CHM 15k transmits a raw data telegram with a
single backscatter profile and any related descriptive variables and attributes in
NetCDF format. The raw data daily telegrams may, in turn, be summarised in a
day file.The “JO-DataClient” software will generate the day files automatically.
8.4.3 File Names
NOTE
For fail-safe transmission of files, ISO standard requirements must be
observed in their extended version, i.e. the length of a file name must not
exceed 31 characters. In terms of the setup of a day file with
[Date]_[location]_[Device-ID]_[Index].nc (8_5_9_3.2=31 characters) this
implies that the “location” name must not be longer than 5 characters.
Daily NetCDF file:
YYYYMMDD_[location]_[Device]_[Index].nc
Raw data in
RS485 telegram:
YYYYMMDDhhmmss_[location]_[Device].nc
Raw data with 5 minute
time resolution for ftp
mode (AFD):
YYYYMMDD_[location]_[Device]_
[hhmm]_[Index].nc