GPM Ground Validation Autonomous Parsivel Unit (APU) at the National Space Science and Technology Center (NSSTC)
Huntsville, AL.

Table of Contents

Introduction

The Autonomous Parsivel Unit (APU) provides a means for measuring the particle size and fall velocity of all liquid and solid precipitation. It consists of a Parsivel, which is an optical disdrometer developed by OTT Messtechnik in Germany, and its support systems, which were designed and built by the University of Alabama in Huntsville.

Note: This collection will be updated periodically as data is received.

Campaign

The Global Precipitation Measurement (GPM) mission Ground Validation (GV) campaign will use a variety of methods for validation of GPM satellite constellation measurements prior to launch of the GPM Core Satellite, which is currently scheduled for July 2013. The validation effort will entail numerous GPM-specific and joint-agency/international external field campaigns, using state of the art cloud and precipitation observational infrastructure (polarimetric radars, profilers, rain gauges, disdrometers). Surface rainfall will be measured by very dense rain gauge and disdrometer networks at various field campaign sites. These field campaigns will account for the majority of the effort and resources expended by Global Precipitation Measurement (GPM) mission Ground Validation (GV).

Instrument Description

The primary instrument is the parsivel disdrometer, produced by OTT Messtechnik, Germany. The OTT parsivel disdrometer is a modern, laser-based optical system for measuring all types of precipitation. The transmitter unit of the sensor generates a flat, horizontal beam of light, which the receiver converts into an electrical signal. The signal changes whenever a hydrometeor falls through the beam anywhere within the measurement area. The degree of dimming is a measure of the size of the hydrometeor, and together with the duration of the signal, the fall velocity can be derived.

File Naming Convention

The NSSTC Parsivel dataset has two different file naming conventions:

parsivel1_nsstc_brm_yyyymmdd_dsd.dat
apuxx_nsstc_yyyymmdd.tar - daily tar files

The tar files contain hourly data files of the form:

apuxx_nsstc_apuxx_yyyymmddhh.dat

where

parsivel1 = nume of apu
apu =  Autonomous Parsivel Unit
xx =   A unique notation, to further identify the instrument
nsstc, nsstc_brm =   the location site of the instrument (National Space Science and Technology Center (NSSTC), Huntsville, AL)
yyyymmdd =   Is the year, month and day of the data
hh = hour
dsd = drop size distribution
dat = ASCII data file
tar =   Unix "tape archive" format

Data Format

The "parsivel1_*" and the "apuxx" tar file data files have different formats.

The parsivel1_* files have additional data fields compared to the "apuxx" files. The format of one line of the "parsivel1_* files" is

DD,mm,YYYY,HHMM,SS,Intensity(mm/hr),Number of Particles, NWS Weather Code, Radar Reflectivity (dBz), MOR Visibility (m), N(d), v(d), RAW_DATA, Rain Accumulation (mm)
(the fields N(d) and v(d) contain the 32 bin counts of measured drop diameter and velocity)

The "apuxx" parsivel data is recorded every 10 seconds and time stamped by the APU software. : Two formats exists: one prior to Feb 25, 2011 and a newer format starting Feb 25, 2011 listed below. A PDF version of the PI document detailing the Pasivel Raw Data Format is provided for downloading.

Information detailing APU Parsivel operating instructions can be found in the OTT Operating instructions,Present Weather Sensor Parsivel; this document also provides information on the characterization of precipitation codes.

The format prior to Feb. 25, 2011 is :

YYYYmmDDHHMMSS;APUXX,ST,TEMP,RAW_DATA

where

YYYY = 4-digit year
mm = 2-digit month
DD = 2-digit day
HH = 2-digit hour
MM = 2-digit minute
SS = 2-digit second
APUXX = station name (xx == 2-digit APU number)
ST = Parsivel sensor status ranging from 0-3

0 = Everything OK;
1 = Laser protective glass is dirty, but measurements still possible
2 = Laser protective glass is dirty, partially covered. No further measurements are possible
3 = Laser damaged
TEMP = 3-digit Sensor temperature in °C
RAW_DATA = particle counts in each bin of the 32 x 32 (diameter x velocity) matrix (consult OTT Present Weather Sensor manual for classification of bins)

New format as of Feb 25, 2011 adds 6 new fields before the raw data:

YYYYmmDDHHMMSS;APUXX,ST,TEMP,N,R,Z,VIS,WX4680,WX4677,RAW_DATA

where

N = Number of detected particles
R = Rain intensity (32bit, mm/hr)
Z = Reflectivity factor (16bit, dBZ)
VIS = MOR Visibility in the precipitation (m)
WX4680 = 2-digit weather code according to SYNOP wawa Tbl 4680
WX4677 = 2-digit weather code according to SYNOP w.w. Tbl 4677

Contact Information

The data producers are:

Walter A.Petersen
NASA Wallops Flight Facility
Wallops Island, VA 233375

Larry Carey
Earth Systems Science Center
UAHuntsville
Huntsville, AL 35805

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
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/