Global Hydrology Resource Center(GHRC) is one of NASA's Earth Science Data Centers and is a collaboration between MSFC and University of Alabama in Huntsville.

GPM Ground Validation Environment Canada (EC) Visibility Sensor FD12P and Present Weather Detector GCPEx

Table of Contents

Instrument Description
File Naming Convention
Data Format
Contact Information


The GPM Ground Validation Environment Canada (EC) Visibility Sensor FD12P and Present Weather Detector GCPEx data was collected January 15 through March 1, 2012 in Huronia, Canada for the GPM Cold-season Precipitation Experiment (GCPEx). The Vaisala FD12P combines the functions of a forward scatter visibility meter and a present weather detector. It also measures the intensity and the amount of both liquid and solid precipitation. The FD12P data is available in browse(.png) and ASCII format.


The GPM Cold-season Precipitation Experiment (GCPEx) occurred in Ontario, Canada during the winter season of 2011-2012. GCPEx addressed shortcomings in the GPM snowfall retrieval algorithm by collecting microphysical properties, associated remote sensing observations, and coordinated model simulations of precipitating snow. These data sets were collected to aid in the achievement of the over arching goal of GCPEx which is to characterize the ability of multi-frequency active and passive microwave sensors to detect and estimate falling snow.

The GPM Ground Validation Environment Canada (EC) Visibility Sensor FD12P and Present Weather Detector data was collected at the Huronia, Canada site. Huronia's location is

Lat: 44 degrees 41'10.25"N; Lon: 79 degrees 55'40.60"W

Further details on GCPEx are available at Information on the Global Precipitation Measurement (GPM) mission is available at

Instrument Description

The Vaisala FD12P Weather Sensor is made up of three sensing elements: a forward scatter visibility meter, a rain detector, and a temperature sensor. The visibility meter is comprised of a transmitter that pulses near-infrared light and a receiver that measures the scattered part of the light from the transmitter. The visibility meter can measure optical range, optical precipitation intensity and optical precipitation amounts. The rain detector measures capacitance changes in two sensing elements to calculate precipitation amounts. The output of the rain detector is proportional to the amount of water on the capacitive sensors. The ratio of rain detector intensities and optical precipitation intensities can be used to determine basic precipitation types.

More information on the Vaisala FD12P can be found at


David Hudak
Resesarch Scientist, Cloud Physics and Severe Weather Research Section
Environment Canada
King City, Ontario

File Naming Convention

The FD12P browse and data files are named with the following convention:



gcpex = GPM Cold-season Precipitation Experiment
vis = Visibility Meter
YYYYMMDD = the year, month and day of the data
EC = Environment Canada
HURONIA = site location of the instrument
png = raster graphics file format

Data Format

The FD12P browse files are daily .png files. The browse files include visibility, precipitation rate, cumulative water, and cumulative snow graphs. The browse files also include two graphs that illustrate weather codes and FD12P warning codes.

The FD12P data set consists of ASCII text files. The columns of the text files are formatted as shown below:



HH:MM:SS = hours, minutes, seconds in UTC time
FD = instrument name (Vaisala FD12P)
ALM = unit ID number and alarm message numbers
VIS1 = visibility, one minute average, max 50000 m
VIS10 = visibility ten minute average, max 50000 m
PWC = instant present weather, NWS codes
W# = instant present weather, WMO codes
15W# = fifteen minute present weather, WMO codes
1HW# = one hour present weather, WMO codes
PI = precipitation intensity (mm/h)
CW = cumulative water (mm)
CS = cumulative snow (mm)

The ALM number is a three digit number (i.e. 100). The first number signifies the unit ID number which has defaulted to "1" for the FD12P data set. The second number in the sequence signals a hardware issue. This number "0" indicates no issues, "1" indicates a hardware error, and "2" indicates a hardware warning. The third number in the sequence signals an alarm. The number " 0" indicates no problems, "1" indicates visibility alarm 1, and "2" indicates visibility alarm 2.

More information on the NWS and the WMO codes can be found on pages 143 - 145 in the Vaisala FD12P User's Guide.


Our data sets are provided through the NASA Earth Science Data and Information System (ESDIS) Project and the Global Hydrology Resource Center (GHRC) Distributed Active Archive Center (DAAC). GHRC DAAC is one of NASA's Earth Observing System Data and Information System (EOSDIS) data centers that are part of the ESDIS project. ESDIS data are not copyrighted; however, in the event that you publish our data or results derived by using our data, we request that you include an acknowledgment within the text of the article and a citation on your reference list. Examples for general acknowledgments, data set citation in a reference listing, and crediting online web images and information can be found at:

Contact Information

To order these data or for further information, please contact:

Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932