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Indoor User Terminal |
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Indoor User Terminal |
Figure 1:The 2D-Video-Distrometer
The 2D-Video-Distrometer is a precipitation
gauge, working on the basis of video cameras.
It has been developed by
JOANNEUM RESEARCH
in cooperation with
ESA/ESTEC
(European Space Agency / European Space and Technology Centre)
for research purposes. Students of the
Graz University of Technology
/ Austria have also contributed to the work presented.
This homepage presents information on the instrument and on measurement results.
What does the 2D-Video-Distrometer do?
Originated in the area of weather radar and propagation research, the 2D-Video-Distrometer is now suited for all kinds of applications where details on precipitation are of interest.
In the left part of Figure 1 the outdoor part, consisting of the Sensor Unit (SU) with the Outdoor Electronics Unit (OEU) closeby is shown.
The new design shown in the middle of Figure 1 only consists of a Sensor Unit (SU) equipped with intelligent cameras doing the data processing and compression.
The Indoor User Terminal (IUT) is actually a standard PC / Laptop, the right part of Figure 1 shows screen, mouse and keyboard.
Figure 2 presents the IUT main screen of the Indoor User Terminal, summarizing the features of the 2D-Video-Distrometer.
Of each single hydrometeor reaching the measuring area the front- and the side view and the vertical fall velocity are measured and recorded. Online as well as offline the following displays are available:
rainrate vs. time, dropsize distribution, vertical velocity vs. equivolumetric diameter, horizontal velocity, oblateness vs. diameter.
These five displays, an oblateness distribution diagram and the single hydrometeor display may be selected for full screen representation with additional information and further menu choices. A top view of the measuring area is drawn in the middle of the main screen.
What are the specifications of the instrument (Compact version)?
Performance Specifications
- horizontal resolution better than 0.19 mm
- vertical resolution better than 0.19 mm (vert. vel. < 10 m/s)
- vertical velocity accuracy better than 4% (vert. vel. < 10 m/s)
- sampling area approx. 100 x 100 mm²
- integration time 15 sec. to 12 hours (for display)
- mains voltage 100 - 240 V at 50/60 Hz
- power consumption appr. 300 W
- operating temperature 0°C .. +35°C
- survival temperature -20°C .. +50°C
Dimensions and weights (compact 2DVD)
- Outdoor Unit (housing):
length appr. 850 mm
width appr. 850 mm
height appr. 200 mm
weigth appr. 80 kg
Advantages of the measurement principle:
About data rate and precision of alignment:
The raw data rate of each of the two high-speed line scan cameras is 40 MByte per second, resulting 80 MByte of data per second processed.
Alignment precision requirement: in the order of 1 foot per 1 mile.
Here are some selected samples of data:
First of all a series of 9 water drops with approx. 1 mm diameter steps is given.
Then four different precipitation situations are presented: widespread rain, storm, melting snow and snowfall. The shapes of hydrometeors, their fall velocity and size distribution indicate quite clearly the kind of precipitation.
Figure 3 represents a widespread rain event, confirming very well the relationships v(D) taken from literature. Figure 4 presents the measurements of an even smaller number of drops than in Figure 3, being widely spread around the mean values expected. A thunderstorm is recognized. Drop shapes in storms differ quite significantly from the Figures given in the literature. In Figure 5 the influence of heavy horizontal wind forces is clearly recognized. The drop passes the side view camera (blue shape) from the right to the left side at an angle to the vertical of around 45 degree, obviously being accelerated by the wind or by turbulences near to the ground and therefore flattened at the right side. The front view camera (red shape) records the drop moving downwards at an angle of around 45 degree directly into its face with a shape differing not much from the expected figure. In this case the front view is not as oblate as it would be expected in situations without any horizontal forces. For comparison in Figure 6 the views of a drop in stagnant air are shown.
Figure 7 and Figure 8 identify melting snow. In the vertical velocity versus diameter diagram (Fig. 7) it is recognized that small particles are completely melted yet, they follow the theoretical values closely. The bigger particles are still mixtures of ice and water, they have not reached the terminal fall velocity of raindrops and they show quite irregular shapes. Figure 8 gives an example.
Finally snow data shall be presented. Figure 9 clearly indicates, that snowflakes of any size are hardly faster than 2 m/s in fall velocity.
Snowflakes present totally irregular shapes to the camera, Figure 10 give an example. Such data provide detailed information and allow unprecedented investigations on snowfall, [e.g. Hanesch et al., 1998; Barthazy et al., 1998; Vaxevanakis, 1999], its interaction with electromagnetic waves and also of growth and structure of the snow cover.
Figure 11 shows a Rainrate vs. Time
diagram for a short convective event on June 18, 1997, 17:00 - 19:00 in Graz
/ Austria with rather moderate rainrates (not exceeding 30 mm/hr). The DSD for the most intense period of
this event (17:54 - 18:00) clearly indicates drops of more than 7 mm in equivolumetric
sphere diameter. Distrometer-derived reflectivities
show considerable differences, based either on the rainrate or on DSDs.
Tropical DSDs frequently
present a contrary behaviour in comparison with moderate climate storms.
Canting angles of axially symmetrical particles may be determined. Before however
distortions of horizontally moving particles, introduced by the line scan camera
measurments, have to be corrected. Figure
16 shows a distorted image, the approximate and the precise correction.
Further samples of canted
raindrops are shown.
A mobile employment in a hail chase van has been done!
One 2D-Video-Distrometer has been mounted in a hail chase van for the Field Campaigns 1995 and 1996 of Colorado State University (CSU). The campaigns were managed by Prof. V.N. Bringi. The CSU Chill Radar was employed, one electricity and two hail chase vans and the T28 aircraft of the South Dakota School of Mines and Technology (contact person: Dr. Andrew Detwiler). Several storm events have been recorded, allowing detailed comparisons of radar reflectivities with in-situ measurements. As examples the front- and side view of two hailstones are presented in Figures 17 and 18.
Avalanche Research in the Alps
For enhanced avalanche warning systems research activities were carried out in the Alpine Mountain range not far from Graz / Austria. The 2D-Video-Distrometer data used for detailed investigations of the structure of the snow cover. Installation took place in November 1999.
Drop oscillation and canting angle experiments
At an 80 meter railroad bridge (Jauntalbrücke) near the village of Ruden in Carinthia / Austria an experiment to study drop shapes, their oscillations and canting angles was carried out. The experiment was initiated by Prof. Bringi, Colorado State University. For several days a fire brigade water hose was used under calm wind conditions to create significant artificial rainrates.
Special thanks to Jauntal Bungy Adventure ( http://www.bungy.at/en/ ) and to the Fire Brigade Untermitterdorf (http://www.ff-untermitterdorf.at/) making possible the experiment with their voluntary and generous support !
A tool for meteorologists only?
The excellent possibilities of the 2D-Video-Distrometer do not only address meteorologists and persons interested in precipitation, but also scientists working in different fields.
Contact us and we will be pleased promptly to send you our proposal solving your measurement tasks.
A commercial product, used all over the world
Cf. end of table of customers / partners
Here is a list of our customers/partners:
References (including some downloadable documents in PDF format)
Links to other sites dealing with the 2D-Video-Distrometer
Remark: Clicking on certain links within distrometer.at or any of JOANNEUM RESEARCH's hosted sites will take you to other Web sites for which JOANNEUM RESEARCH takes no responsibility.
For more information please contact:
JOANNEUM RESEARCH
DIGITAL - Institute of Communication and Information Technologies
SPA - Space Technology and Acoustics
Schieszstattgasse 14b
A-8010 GRAZ
Austria (Europe)
| Tel: | ++43 - 316 - 876 - 2511 |
| Fax: | ++43 - 316 - 876 92511 |
Last update of this homepage: 2012-03-05
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