GPM Ground Validation Two-Dimensional Video Disdrometer (2DVD) at the NSSTC
Table of Contents
A disdrometer is an instrument that measures the size of rain drops. The Two-Dimensional Video Disdrometer (2DVD), developed by Joanneum Research (Graz, Austria), is unique in that it records two, side view optical images of each raindrop. Used for in situ measurements of precipitation drop size distribution, This instrument records orthogonal image projections of raindrops as they cross its sensing area, and can provide a wealth of information, including velocity and shape, of individual raindrops. An interesting article showing how the 2DVD can be used to analyze the microstructure of individual raindrops can be found here.
This disdrometer dataset gathers data at the National Space Science and Technology Center (NSSTC), Huntsville, AL. when the 2DVDs are not deplyed to other mission sites for the Global Precipitation Measurement (GPM) misson Ground Validation campaigns.
Note: This collection will be updated periodically as data is received.
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 and Location
The Two-Dimensional Video Disdrometer (2DVD) uses two high speed line scan cameras which provide continuous measurements of size distribution, shape and fall velocities of all precipitation particles and types. Two orthogonal light planes, provided by two internal lamps, transect the approximate 10x10 cm virtual measurement area and are projected onto two high speed line-scan cameras. Precipitation particles (hydrometeors) that fall through the light planes cast a shadow that is recorded by the two cameras nested within the instrument (this is analogous to flat-bed scanners, except here the scan head is stationary and the scanned object moves). Detailed shape and size information for each individual hydrometeor is available via the two "side image shadows" that are recorded by the cameras. The light planes are separated by a precisely calibrated distance (nominally 6 mm) from which the vertical fall velocity can be measured. The line scan cameras sample each plane at a rate of ~18 microseconds and a horizontal resolution of ~200 microns. Therefore, as a raindrop falls through the measurement area, several line scans of each image are recorded from two sides and two different heights, from which precise measurements can be made.
File Naming Convention
These data files are archived in a daily tar format, with the following naming convention:
2dvdcp = Two-Dimensional Video Disdrometer
snxx = A unique system number
site = Represents the location of the instrument (NSSTC, LPVEx, MC3E, and others)
yyyymmdd = Is the year, month and day of the data
tar = "tar archive" a method of bundling multiple files into one file
The following files are contained within the tar archive:
These files are created daily and their filename format begins with “Vyyddd”, where "yy" is the last two digits of the year and "ddd" is the day of the year.
Vyyddd.hyd = compressed binary files preprocessed from the raw camera data
- contain information on individual hydrometeors
- can be viewed graphically with VIEW_HYD software available from Joanneum Research, the instrument manufacturer
- decompression and data read possible with HYD2ASC program
Vyyddd[_1].hd = header file associated with V*.hyd file used by HYD programs
Vyyddd_[1.]drops.txt = ASCII file containing information on individual hydrometeors
Vyyddd_[1.]dsd.txt = ASCII file containing drop size distribution each minute hydrometeors were detected and binned by 0.2 mm
Vyyddd_[1.]rainrate.txt = ASCII file containing the precipitation rate for each minute hydrometeors were detected
The Two-Dimensional Video Disdrometer dataset consists of both binary preprocessed hydrometer files created by the instrument manufacturer’s software (.hyd files), as well as ASCII (.txt) files containing rain rate, drop size distribution and information on individual hydrometeors. More detailed information on the Data Format and Data Levels can be found here.
The data producers are:
NASA Marshall Space Flight Center
Huntsville, Alabama, 35805
Earth Systems Science Center
Huntsville, AL 35805
To order these data or for further information, please contact:
Global Hydrology Resource Center
320 Sparkman Drive
Huntsville, AL 35805