Joss-Waldvogel Disdrometer (JWD) Observations
Collected During the GPM-Front Range Pilot Study


General Description
The Rd-69 Distromet disdrometer (also known as the Joss-Waldvogel disdrometer) was manufactured by Distromet ltd. and three disdrometers were used in the GPM-Front Range Pilot Study.  One was at the Boulder Atmospheric Observatory (BAO) and two were located at the Platteville Atmospheric Observatory (PLT). 

The disdrometer electronics estimates the rain drop sizes using 127 different diameter sizes.  The Distromet software accumulates the number of rain drops detected in 20 different diameter sizes over 1 minute intervals.  The disdrometer at BAO used the manufacture's software.  At PLT, software developed at the NOAA Aeronomy Laboratory was used to read and store the full 127 different diameter sizes at a 10 second resolution.  The recorded 127 bin resolution data was filtered to produce the 20 bin and 1 minute resolution data that many researchers use in their work.  The 20 diameter and 127 diameter data sets for PLT are provided below.  Caution must be used when using the 127 bin resolution data.  The Joss-Waldvogel disdrometer was not designed to used with this resolution.  Thus, the 127 bin data is considered a research data product without the endorsement of the manufacture.

There were two JWDs located at Platteville.  One unit is owned by the NOAA Aeronomy Laboratory (AL) and the other unit is owned by the University of Colorado (CU).  The two sensor heads were located 0.5 m apart.  The AL unit was re-reburbished and re-calibrated by the manufacture in April 2004.

Altitude Adjustment

The JWD is designed to estimate the raindrop size by converting the 'momentum' of the raindrops impacting the sensor into a diameter size assuming that the raindrops are falling at their sea level terminal velocities.  An adjustment was made to the diameter sizes recorded by the disdrometer to account for the observations being made at 1600 m above sea level.  The details of the altitude adjustment are provided in this PDF document.

 PLT Observations
The PLT disdrometer observations are available in three different data formats:
These three data sets are available in the 20 and 127 diameter resolutions.  The 20 diameter resolution integrated moments are slightly larger than the 127 diameter resolution estimates because the 20 diameter resolution estimates are derived from the 127 diameter observations and uses the average diameter while the observed number of raindrops usually decreases with increasing diameter size.  Thus, the diameter size is weighted uniformly and the number of raindrops is weighted toward the smaller drops.

 PLT Integrated Moments: Z, R, LWC, Do, Dm
The integrated moments were estimated from the 20 diameter sizes and 1 minute accumulation.  The format of the integrated moment data is:
Column Number Description
1 year
2 day of year
3
 month
4
 day of month
5
 hour of day
6
 minute of hour
7
 number of drops detected in minute
8
 reflectivity, dBZ
9
 rain rate, mm/hour
10
 liquid water content, g/m^3
11 median diameter, Do, mm
12 mean diameter, Dm, mm, (Fourth Moment / Third Moment)
When the number of drops detected is zero (as reported in column 7), then all of the calculated values in columns 8 through 12 are set to -99.99.
The integrated moments are in ASCII format and have been zipped to reduce the file size.  This file names are:
plt_jwd_al_mom20.dat          (AL unit, 20 diameter resolution)
plt_jwd_cu_mom20.dat         (CU unit, 20 diameter resolution)
plt_jwd_mom20.zip               (zipped version of both AL and CU 20 diameter resolution data files)

The integrated moments were estimated from the 127 diameter sizes and 1 minute accumulation.  The format of the integrated moment data is:
Column Number Description
1 year
2 day of year
3
 month
4
 day of month
5
 hour of day
6
 minute of hour
7
 number of drops detected in minute
8
 reflectivity, dBZ
9
 rain rate, mm/hour
10
 liquid water content, g/m^3
11 median diameter, Do, mm
12 mean diameter, Dm, mm, (Fourth Moment / Third Moment)
When the number of drops detected is zero (as reported in column 7), then all of the calculated values in columns 8 through 12 are set to -99.99.
The integrated moments are in ASCII format and have been zipped to reduce the file size.  This file names are:
plt_jwd_al_mom127.dat           (AL unit, 127 diameter resolution)
plt_jwd_cu_mom127.dat          (CU unit, 127 diameter resolution)
plt_jwd_mom127.zip                (zipped version of both AL and CU 127 diameter resolution data files)

PLT Number Concentration: N(D)

The number concentration, N(D), was estimated from the 20 diameter sizes and 1 minute accumulation observations.  The format of the N(D) data is:

Column Number Description
1 year
2 day of year
3
 month
4
 day of month
5
 hour of day
6
 minute of hour
7-27
 number concentration, N(D)
The number concentration file has been zipped to reduce the file size.  The diameters, the dD, and velocities of the 20 diameter sizes are also provided in ASCII format.  This file names are:
plt_jwd_al_ND20.dat         (AL unit, 20 diameter resolution)
plt_jwd_cu_ND20.dat        (CU unit, 20 diameter resolution)
plt_jwd_diameter20.dat
plt_jwd_delta_diameter20.dat
plt_jwd_velocities20.dat
plt_jwd_ND20.zip              (zipped version of the five ASCII files)

The number conctration, N(D), was estimated from the 127 diameter sizes and 1 minute accumulation observations.  The format of the N(D) data is:

Column Number Description
1 year
2 day of year
3
 month
4
 day of month
5
 hour of day
6
 minute of hour
7-27
 number concentration, N(D)
The number concentration file has been zipped to reduce the file size.  The diameters, the dD, and velocities of the 20 diameter sizes are also provided in ASCII format.  This file names are:
plt_jwd_al_ND127.dat         (AL unit, 127 diameter resolution)
plt_jwd_cu_ND127.dat        (CU unit, 127 diameter resolution)
plt_jwd_diameter127.dat
plt_jwd_delta_diameter127.dat
plt_jwd_velocities127.dat
plt_jwd_ND127.zip              (zipped version of the five ASCII files)


PLT Number of Raindrops Detected at each Diameter Size

The number of raindrops detected at each of the 20 diameter sizes during the 1 minute accumulation is presented in ASCII format:

Column Number Description
1 year
2 day of year
3
 month
4
 day of month
5
 hour of day
6
 minute of hour
7-27
 number of drops detected in the minute, m(D)
The file containing the number of raindrops has been zipped to reduce the file size.  The diameters, the dD, and velocities of the 20 diameter sizes are also provided in ASCII format.  This file names are:
plt_jwd_al_cnt20.dat         (AL unit, 20 diameter resolution)
plt_jwd_cu_cnt20.dat        (CU unit, 20 diameter resolution)
plt_jwd_diameter20.dat
plt_jwd_delta_diameter20.dat
plt_jwd_velocities20.dat
plt_jwd_cnt20.zip              (zipped version of the five ASCII files)

The number of raindrops detected at each of the 127 diameter sizes during the 1 minute accumulation is presented in ASCII format:

Column Number Description
1 year
2 day of year
3
 month
4
 day of month
5
 hour of day
6
 minute of hour
7-27
 number of drops detected in the minute, m(D)
The file containing the number of raindrops has been zipped to reduce the file size.  The diameters, the dD, and velocities of the 20 diameter sizes are also provided in ASCII format.  This file names are:
plt_jwd_al_cnt127.dat         (AL unit, 127 diameter resolution)
plt_jwd_cu_cnt127.dat        (CU unit, 127 diameter resolution)
plt_jwd_diameter127.dat
plt_jwd_delta_diameter127.dat
plt_jwd_velocities127.dat
plt_jwd_cnt127.zip              (zipped version of the five ASCII files)


Updated: 22 September 2004, C.R. Williams, Christopher.R.Williams@noaa.gov